Marine Distributions 9781442654020

Table of contents :
Preface
Contents
Contributions
The Purpose and Significance of the Serial Atlas of the Marine Environment
Seasonal Temperature Structure in the Eastern Subarctic Pacific Ocean
Distribution of Attached Marine Algae in Relation to Oceanographic Conditions in the Northeast Pacific
Distributions of Atlantic Pelagic Organisms in Relation to Surface Water Bodies
Copepods of the Genus Calanus as Indicators of Eastern Canadian Waters
Salinity, Osmoregulation, and Distribution in Macroscopic Crustacea
Summary and Comment

Citation preview

MARINE DISTRIBUTIONS

A symposium of the Royal Society of Canada was held in June of 1962 to outline what is being done in Canadian oceanography to map the salinity, temperature, and plankton in the waters around Canada and in the Norht Atlantic across to Europe. This volume, based on the symposium, emphasizes the interdisciplinary nature of research in marine biogeography and in the distribution of environmental factors in the sea. The book is intended to show the breadth of biogeographic work in the sea, and the relation between biogeiography and the physics and chemistry of the marine environment. It serves also to introduce to the scientific public the new serial Atlas of the Marine Environment, a scientific journal of a new kind sponsored jointly by the Royal Society of Canada and the U.S. National Academy of Sciences. Contributors j . D U N B A R (editor), Department of Zoology, McGill University, Montreal, P . Q .

M.

B. MCK. B A R Y ,

ver,

Institute of Oceanography, University of British Columbia, Vancou­

B.C.

L. F . G I O V A N D O ,

Fisheries Research Board of Canada, Pacific Oceanographic Group,

Nanaimo, B . C . E. H . G R A I N G E R ,

OTTO KINNE,

Fisheries Research Board of Canada, Arctic Unit, Montreal, P . Q .

Biologische Anstalt Helgoland, Hamburg-Altona, Germany.

ROBERT F. SCAGEL,

Institute of Oceanography, University of British Columbia, Van­

couver, B . C . j . P . T U L L Y , Fisheries Research Board of Canada, Pacific Oceanographic Group, Nanaimo, B . C . LIONEL

A. WALFORD,

Highlands, N . J .

u.s. Fish and Wildlife Service, Atlantic Marine Laboratory,

THE ROYAL SOCIETY OF C A N A D A Special Publications 1. The Grenville Problem. Edited by J A M E S E .

THOMSON

2. The Proterozoic in Canada. Edited by J A M E S E . G I L L

3. Soils in Canada. Edited by R O B E R T E .

LEGGET

4. The Tectonics of the Canadian Shield. Edited by 5. Marine Distributions. Edited by M .

J . DUNBAR

J O H N S. S T E V E N S O N

MARINE DISTRIBUTIONS

THE ROYAL SOCIETY OF C A N A D A SPECIAL PUBLICATIONS, NO. 5 Edited by M. J. Dunbar, F.R.S.C.

P U B L I S H E D B Y T H E U N I V E R S I T Y O F T O R O N T O PRESS IN CO-OPERATION WITH T H E R O Y A L SOCIETY OF CANADA 1963

C O P Y R I G H T ,C A N A D A , 1 9 6 3 ,B YU N I V E R S I YO FT O R O N T OP R E S PRINTED IN CANADA

PREFACE

was organized with the general intention of focusing attention upon the growing study of marine biogeography and the distribu– tion of environmental factors in the sea, and in particular to introduce the new Serial Atlas of the Marine Environment sponsored by the U.S. National Academy of Sciences and the Royal Society of Canada and published by the American Geographical Society of New York. It emphasizes the inter– disciplinary nature of research in marine distributions, and of all oceanographic research. The paper by J . P. Tully and L . F. Giovando was given at a different session of the same meeting of the Society, and is included here, with the co-operation and permission of the authors, because of its close relevance to the matter in hand. M.J.D. THIS SYMPOSIUM

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CONTENTS

Preface

v

The Purpose and Significance of the Serial Atlas of the Marine Environment

M.

J.

DUNBAR

3

Seasonal Temperature Structure in the Eastern Subarctic Pacific j . p. T U L L Y A N D L . F . GIOVANDO Ocean

10

Distribution of Attached Marine Algae in Relation to Oceanographic Conditions in the Northeast Pacific ROBERT F . SCAGEL

37

Distributions of Atlantic Pelagic Organisms in Relation to Surface Water Bodies B . M C K . BARY Copepods of the Genus Calanus as Indicators of Eastern Canadian Waters E . H . GRAINGER

51

68

Salinity, Osmoregulation, and Distribution in Macroscopic Crustacea

Summary and Comment

OTTO K I N N E

95

LIONEL WALFORD

106

CONTRIBUTORS

B. M C K . BARY, Institute of Oceanography, University of British Columbia, Vancouver, B . C . M . j . DUNBAR, Department of Zoology, McGill University, Montreal, Que. L . F . GIOVANDO, Fisheries Research Board of Canada, Pacific Oceanographic Group, Nanaimo, B.C. E. H . GRAINGER, Fisheries Research Board of Canada, Arctic Unit, Montreal, Que. OTTO KINNE, Biologische Anstalt Helgoland, Hamburg-Altona, Germany. Institute of Oceanography, University of British Colum­ bia, Vancouver, B . C .

ROBERT F . SCAGEL,

j . p. T U L L Y , Fisheries Research Board of Canada, Pacific Oceanographic Group, Nanaimo, B.C. y . S . Fish and Wildlife Service, Atlantic Marine Labo­ ratory, Highlands, N . J .

L I O N E L A . WALFORD,

MARINE DISTRIBUTIONS

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THE PURPOSE A N D SIGNIFICANCE OF T H E SERIAL ATLAS OF THE MARINE ENVIRONMENT M. J. Dunbar, F.R.S.C.

and even many ecologists, would take exception to the claim that ecology is essentially the study of the distribution of animals and plants. Distribution, or biogeography, is a static matter, entirely a descriptive business and without any connotation other than the drawing of maps; this still appears to be a common view. History is about chaps, geography is about maps. And yet the presentation of distributions as the core and essence of ecology has a long history, from the time of Alfred Russell Wallace at the latest (1855). Elton (1927) in his classical book, Animal Ecology, empha– sized the importance of zoogeography, and has underlined it several times since, notably in his most recent study of the Ecology of Invasions (1958). Biogeography is the ground theme or burden of Hesse's Tiergeographie auf oekologischer Grundlage (1924); also of Andrewartha and Birch's Distribu– tion and Abundance of Animals (1954). Perhaps most impressive of all, the study of distribution has become the focus of the investigation into the mechanism of speciation, from Wallace to the present day, as in Mayr (1942). This is not simply a matter of the relevance of present distribution to past dispersal history; a sort of contemporary projection of paleoecology. The distribution of living things, in all scales from the global to the microecological, expresses and manifests the relation between organisms and their living and non-living environment, the accepted material and content of ecology. Therefore all ecological study can ultimately be reduced to bio– geography. I would go further than this. In a very real sense, the whole of natural science, physical as well as biological, reduces to the study of distributions. Distributions of qualities, properties, measured quantitatively, in time and in space, make up most of what scientists concern themselves with, and results are expressed in terms of the distribution of one variable upon another; of the way in which distributions change. Our starting point is a paper of Wallace's, printed in 1855, which has not yet been acknowledged its true importance. This paper, printed three years before the appearance of the famous joint paper with Darwin in the Linnaean Society in 1858, examines the distribution of organisms in space and in time. It shows that the same rules of the relationship of species in M A N Y BIOLOGISTS,

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adjacent and distant parts apply in both geographical and geological (fossil) patterns, and concludes with the generalization that "every species has come into existence coincident both in time and space with a pre-existing closely allied species." This was good circumstantial evidence for the mutability of species, and it is the first published indication we have of the direction in which Wallace's field work was taking him. This 1855 paper was buried and attracted little notice, and in spite of the emphasis laid on biogeography in the Origin of Species, biological research in the half century following, with certain important individual exceptions, went back to the laboratory and focused especially upon the working out of phylogenies from the study of the fossil record, the evolutionary implications of embryological study, and, more lately, the mechanism of heredity. Indeed, this research was essential for the realization of the full value of biogeographical work. It was not until the publication by Ernst Mayr, in 1942, of his Systematics and the Origin of Species that the study of the distribution of organisms became once more a purposeful and directed affair. We are concerned here particularly with marine distributions, and with the distribution not only of organisms but also of physical and chemical parameters of the environment. Before moving on to specifically marine matters, I wish only to make the point that evolution is a practical matter as well as one of great intrinsic interest. We live in a dynamic system, that is to say a changing or evolving system, and organic evolution is an important part of that dynamic. Upon evolution depends, for one thing, the ordinary down-to-earth matter of systematics, of taxonomic botany and zoology; and hence the understanding of the patterns of fish stocks, to take a practical example, or of plankton systematics, is based upon an understanding of the mechanism of evolution. The history of the study of the sea with a view to exploiting its resources has been one of an ever widening approach from somewhat narrow begin­ nings. Fish, according to the early view, were where you found them, and if they disappeared it was probably because they had migrated elsewhere for reasons unknown. Much myth, superstition, and prejudice had to be cleared away as the scientific attack moved in. Fisheries have long histories and fishermen are conservative people; it is perhaps as a legacy of this that we have so often, in fishery science, built up correlations between pairs of vari­ ables and allowed their implications to be put into practice in commercial fishing, only to have them break down quite soon because of the involvement of other variables whose existence had not been suspected or explored. It must be admitted, however, that this is a characteristic of method not by any means confined to the science of the sea. At all events, understanding of the sea became rapidly more broadly defined, largely as a matter of economic necessity or with a view to economic advantage. At the beginning of this century, for instance, the fishery for the plaice (Pleuronectes platessa) in the North Sea had declined somewhat since its beginnings in the middle of the century before (Wimpenny, 1953). This

PURPOSE A N D SIGNIFICANCE OF T H E SERIAL A T L A S

5

stimulated research on the biology of the plaice from several lines of attack and in several countries, especially Norway, Denmark, Holland, Germany, and the United Kingdom. Gradually the pattern of migration, breeding cycle, mortality, water movement, emerged as a series of interrelated dis­ tributions, until there exists today one of the best regulated and most pro­ ductive fisheries in the Atlantic area, indeed in the world. The work began rather tentatively, with the beginnings of fish-tagging experiments and the study of feeding habits, grew to include the biology of the planktonic eggs and larvae, which in turn became closely tied in with the physical oceanographic research. This is a good example of expansion in method; and it was essentially a study of the distribution of the species concerned, in all stages, and of the physical properties of the water and the atmosphere responsible for the North Sea currents. The study of the physics and chemistry of the sea, to the marine biologist, is the study of the environment, and it has been progres­ sing steadily, with the introduction of new techniques and methods all of which are developed either to measure or to interpret the basic empirical information of the distribution of the properties of sea water in space and in time. The development of the plankton indicator technique, of which up-to-theminute examples are presented here by Dr. Bary and Dr. Grainger, can be looked upon as a return in kind, from the biologists to the physicists, of help received in the past by the biologists from the physicists. It has been greatly accelerated by Sir Alister Hardy's invention and development of the con­ tinuous plankton recorder. This instrument is now being used in all the oceans of the world, and the accumulation of data is such as to be an open invitation to some new and standardized means of publication of the biogeographic results. The Bulletins of Marine Ecology have already begun the publication of the North Sea results, where the Recorder was first used. The extension of its use across the North Atlantic (Henderson, 1961), together with Danish work using the two-metre stramin net (Hansen and Andersen, 1961), has led to the opening up of possibilities of the harvesting of a vast stock of redfish (Sebastes) whose existence was unsuspected until a few years ago. Finally, I C N A F , the International Commission for the Northwest Atlantic Fisheries, has recently set up an Environmental Working Party to plan and develop an intensive study of the environment of the commercially impor­ tant or exploitable biological resources of the sea, aimed at discovering what are the factors determining their presence, absence, and abundance. This is in fact the latest step in the increase of the geographic and conceptual scale of marine biology as applied to the development of marine food resources. Its realization will require the plotting of the distribution of very many physical and chemical parameters, at different times and at different depths, and of living organisms. Considerations of this sort have been behind the launching of the Serial

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M . J . DUNBAR

Atlas of the Marine Environment. It can, I think, truly be called the brain­ child of Dr. L . A . Walford, and owes its existence principally to the interest shown in it by Dr. Charles Hitchcock of the American Geographical Society of New York. A brief description of it has already been published (Webster, 1961). It is sponsored in the United States by the National Academy of Sciences—National Research Council, but the panel which has organized and planned its format and its proposed content is made up of Canadians as well as United States citizens, and in 1959 the Royal Society of Canada undertook to sponsor the atlas in Canada, on the recommendation of the Society's Committee on Oceanography. There are two members of the panel in Europe, one representing the International Council for the Exploration of the Sea, the other the Food and Agricultural Organization of the United Nations. It is prepared and published by the American Geographical Society. It has been very difficult to communicate precisely what the Serial Atlas is supposed to do. The word "atlas" seems to get caught in the narrows of the brain-stream and is sometimes impossible to dislodge; perhaps it was the wrong word to use in the first place. The important word in the title is "serial"; this is a new sort of journal, not a one-time compendium. It is not an atlas in the sense of the Oxford Advanced Atlas or the Bartholomew Atlas of Zoogeography. It is to be published in folios, each one dealing with one subject only, each with its own author, analogous to a paper in a scientific journal. These folios will appear at more or less irregular intervals according to the availability of suitable manuscripts and of the money to cover the costs. As the years go by the folios will accumulate, and form a collection of individual studies not only useful in themselves, but, more importantly, comparable between themselves. In this way anomalies of distribution will be brought into sharp focus, such anomalies becoming at once, we hope, the targets for further research. Each folio will be produced in a double-spread format, 25 / X 16 inches, and will be available on transparent paper as well as on durable opaque paper. Each will consist of the distribution charts together with text giving details of method, materials and references. The first folio, recently published, is a study by Robert L . Pyle, U.S. Bureau of Commercial Fisheries, of the sea surface temperature in the western North Atlantic during 1953 and 1954, done in considerable detail on over fifty maps. The second folio, in preparation, is a study of the distribution of Spisula polynyma, a clam, by Dr. J . L . Chamberlin, which shows not only where Spisula is found and is not found, but also why it lives where it does, in terms of limiting environmental factors. Other projected folios include the bathymetry of the North Atlantic in great detail, the distribution of temperature at 200 metres, (which is below the depth of seasonal temperature change), the circulation of surface waters on the continental shelf from Cape Breton Island to Cape Hatteras, and a study of the distribution of certain pelagic Crustacea related to water masses. Bottom sediments are also under consideration. Finally, and most important in 1

2

PURPOSE A N D SIGNIFICANCE OF T H E SERIAL A T L A S

F I G U R E 1. Chart areas for the Serial Atlas of the Marine

7

Environment.

demonstrating the international nature of the enterprise, the Food and Agri­ cultural Organization proposes to submit for publication in the Atlas the Oceanographic Synopses, at present being compiled, designed to summarize what is known of the physical and chemical environment of important fish stocks. This is being done in collaboration with the World Meteorological Organization (Webster, 1961). The Serial Atlas is infinitely adaptable, and is to be looked upon as a new facility for publication. In order to simplify and standardize the mechanism of preparing material, the American Geographical Society has prepared a number of worksheets or outline charts, nineteen in all, built upon a special projection of the North Atlantic and Arctic Oceans, as shown in Figure 1. Although we hope, ultimately, to be able to serve all the oceans of the world in this way, space and time, and above all, money, force us to limit our attentions at present to the North Atlantic area. The projection chosen, after much discussion, is a single oblique stereographic conformal projection centred at 54° N , 38° W, which was specially computed for the purpose.

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M . J . DUNBAR

The lines of latitude and longitude cross everywhere at right angles on this projection, which is a great advantage in plotting flow lines and in transpos­ ing from Mercator charts, and the slight distortion in area is of no conse­ quence. The sheets are quite large, for ease of working. Sheets 1 to 14 are on a scale of 1:2,500,000; sheets 15 and 16 on a scale of 1:5,000,000; sheet 17, 1:10,000,000; and sheet 18, 1:20,000,000. Sheet 19 is the whole area including the Arctic Ocean and part of the North Pacific. The pattern of coverage of sheets 7 to 14, in the northern and eastern parts of the Atlantic, was arranged in consultation with European biologists of the I C N A F organization. The sheets are provided at nominal cost, and have already been shipped in large numbers to fill well over a hundred orders from Europe and North and Central America. Early in the planning of the Serial Atlas, it was realized that large and valuable deposits of recorded oceanographic observations, and of biological collections, lay forgotten, unworked and unpublished, in laboratories and institutions on both sides of the Atlantic. Funds were accordingly found, with hard work and from good friends, to prepare an inventory of all this material on the United States and Canadian side. This considerable task has been proceeding for more than two years and should be completed next year, ably done by Rear Admiral Charles W . Thomas (U.S. Coast Guard, retired). I hope I have avoided giving the impression that the Serial Atlas is of use only or mainly in the applications of marine science, including the exploita­ tion of living populations. It is in fact a basic tool, and its greatest value will undoubtedly lie in the widening of our understanding of the sea in general. There has for long been a need for a standardized method of pub­ lication and comparison of the distributions of the properties of the sea, both physical and biological. Perhaps it should be emphasized that this is an oceanographic undertak­ ing. There seems to be a retrograde tendency at present, in Canada and particularly in Ottawa, to limit the term "oceanography" to the study of the physics of the sea; whereas originally, and in most other countries the word is accepted as meaning the study of "the seas and all that in them is," to use the phrase of the catechism. The study of the life of the oceans is an important part of the total study of the oceans, and marine biologists should tenaciously insist on the comprehensive, not the limited, definition of their science. Oceanography is a meeting place of many sciences, or parts of them, and this is an asset to be guarded jealously against all who would have us go back to our little cubicles of isolated specialization. It is in this spirit of interdisciplinary enterprise that the Serial Atlas of the Marine Environment has been conceived and brought to birth. REFERENCES ANDREWARTHA,

H . G . and B I R C H ,

animals. Chicago:

L . C. (1954).

T h e distribution and abundance

University of Chicago Press.

of

P U R P O S E A N D SIGNIFICANCE O F T H E SERIAL A T L A S

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E L T O N , C . S. (1927). Animal ecology. London: Sidgwick and Jackson. (1958). The ecology of invasions by animals and plants. London: Methuen & Go. H A N S E N , V A G N K R . and A N D E R S E N , K . P. (1961). Recent Danish investigations on the

distribution of larvae of Sebastes marinus in the North Atlantic. Cons. Perm. Internat. Expl. Mer., Rapp. et Proc.-Verb., 150: 201-15. H E N D E R S O N , G . T . D . (1961). Continuous plankton records across the Atlantic: the distribution of young redfish. Challenger Society, A n n . Rep. 3, no. X I I I : 42. H E S S E , R . (1924). Tiergeographie auf oekologischer Grundlage. Jena: G . Fischer. M A Y R , E . (1942). Systematics and the origin of species. New York: Columbia University Press. W A L L A C E , A . R . (1855). O n the law which has regulated the introduction of species. Ann. & Mag. Nat. Hist., 2nd Ser., 16: 184-9. W E B S T E R , W . (1961). The American Geographical Society's Serial Atlas of the Marine Environment. Geogr. Review, L I (4) : 570-4. W I M P E N N Y , R. S. (1953). The Plaice. London: Edward Arnold & Co.

SEASONAL TEMPERATURE STRUCTURE IN THE EASTERN SUBARCTIC PACIFIC O C E A N J. P. Tully and L. F. Giovando

ABSTRACT

The growth and decay of the seasonal thermocline in the eastern Subarctic Pacific Ocean is discussed in terms of surface heating, wind mixing, cooling, and convection. During the heating season (mid-April to mid-September) diurnal heat gains exceed the heat loss by continuous cooling. The heat gains and associated transient (negative) thermoclines are mixed downward through an otherwise isothermal layer (potential layer) to the limit of wind mixing. There the thermoclines accumulate, forming a seasonal thermocline whose magnitude ( A T ) increases during the heating season. Due to internal waves its vertical limits oscillate. Convection occurs during the cooling season, due to surface radiative cooling and to evaporation. The potential layer becomes truly isothermal, and the seasonal thermocline is eroded and sinks. It reaches the halocline (100 m) about February. During the remainder of the cooling season the waters above the halocline continue to cool. No surface effects penetrate the seasonal thermocline; hence, the remnants of the winter-cooled waters are preserved under it while it exists (April through November). The study is summarized in a model defining the seasonal temperature structures and behaviour. The model is applied to show how existing ocean temperature data can be exploited to the maximum to provide an oceanographic informa­ tion and forecasting service.

INTRODUCTION

On the basis of recent major oceanographic research programs (Dodime^d et al., 1963), it is possible to define a rational model of the occurrence and of the behaviour of the seasonal thermocline in the Subarctic Pacific Region (Fig. 1). Salinity Structure The physical structure in the ocean depends both on salinity and on temperature. These factors usually limit or influence each other. Therefore, before the temperature structure can be discussed in any detail, a brief review of the basic salinity structure is in order. Dodimead (1961) and Tabata (1961) have described the salinity structure at Ocean Station " P " (Lat 50° N , Long 145° W ) . This is idealized in Figure 2. The principal feature is a marked halocline in which the salinity increases by about \%o between about 100 and 200 m depth. This halocline is permanent throughout the year. Below it, there is a lower zone in which the salinity increases very gradually with depth to the bottom. Above it, there is a near-isohaline, low-salinity upper zone maintained by the excess of

S E A S O N A L T E M P E R A T U R E S IN T H E SUBARCTIC PACIFIC

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F I G U R E 1. The Subarctic Pacific Region.

precipitation over evaporation (Jacobs, 1951). In this upper zone, a small halocline (0.2%o) develops during the summer. This is coincident with a seasonal thermocline. Dodimead (1961) showed that the basic features of this structure occur throughout the Subarctic Region, but that the ver­ tical dimensions of the features vary with locality. It may be noted that south of the Subarctic Boundary, in the Subtropic Region, the halocline does not exist. Rather, the salinity decreases with depth to a minimum between 200 and 800 m. The stability above this minimum depends solely on the temperature structure.

F I G U R E 2. Structures in the eastern Subarctic Pacific.

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Currents and Weather Effects In the central and eastern Subarctic Pacific Ocean, the prevailing currents are slow (2 to 4 miles per day) and are not visibly turbulent. Hence the weather conditions waters experience during a season's transport (less than 400 miles) are similar, within the present limits of assessment of oceanic weather, to the conditions they would experience if they remained stationary. With this proviso, the interaction between sea and atmosphere can be regarded as the dominant process determining temperature structure, to the limiting depth of local effects. Below this depth, which varies during the year, temperature is essentially a retained property, and the structure is determined by internal processes, such as transport and mixing. Temperature Structure Figure 3 illustrates the annual cycle of heating and cooling, and its relation to sea-surface temperature, at Ocean Station " P " during 1957. While the details may vary somewhat, the cycle is generally similar from year to year throughout the entire Subarctic region (Von Arx, 1962; p. 142). Figure 4 shows idealized sequences of temperature structure illustrating the growth and decay of the seasonal thermocline. Dodimead (1961) has observed that in March, at the end of the cooling season, the waters are virtually isothermal to the top of the halocline (a depth of about 100 m). With the advent of the heating season in April, a marked negative (sea­ sonal) thermocline is formed. The overlying waters continue to warm throughout the heating season, which lasts until mid-September. Below this thermocline there is an unwarmed layer, which has been shown to be the remnant of the (cold) isothermal structure formed during the previous

F I G U R E 3. Annual cycles of heating and cooling, and sea-surface temperature, at Ocean Station "P".

SEASONAL T E M P E R A T U R E S IN T H E SUBARCTIC PACIFIC

F I G U R E 4. Growth and decay of the thermocline at Ocean Station " P " .

13

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J . P . T U L L Y A N D L . F . GIOVANDO

winter. During the cooling season the surface layer cools and deepens. The seasonal thermocline decays. It is eroded, becomes abrupt, and sinks until it reaches the halocline. Examination of the data shows that in the open oceanic regions, i.e., those not influenced by coastal effects, four dominant processes are involved in the growth and decay of the thermocline: heating and wind mixing, cooling and convection. These processes have been discussed by Sverdrup et al (1942). G R O W T H O F T H E SEASONAL T H E R M O C L I N E

The Heating-Wind-mixing Process Heating is due mainly to solar radiation which is absorbed in the upper few metres of the ocean. Such heating occurs only during day time (after­ noon effect) and varies both with the sun's altitude (date) and with cloud cover. Cooling is due to evaporation, back radiation and conduction of heat from the sea surface, and its continuous day and night. Hence, when heating exceeds cooling during the day time there is a diurnal cycle of heating and cooling. There is a frictional transfer of wind energy to the sea which results in mixing. The downward transfer of this energy is opposed by internal friction (viscosity) in the water. Hence, the turbulence (mixing) decreases with depth and there is a lower limit of wind mixing which varies primarily with the wind force.

FIGURE

5. Sequence of structures illustrating the heating-wind mixing process.

SEASONAL T E M P E R A T U R E S IN T H E SUBARCTIC PACIFIC

15

In this background, the heating and mixing process in the sea may be explained with the aid of the sequence of structures illustrated in Figure 5. If there is no wind, only the surface of the water is warmed, as indicated by structure Number 0. Usually, however, there is some wind, so that heating and mixing occur simultaneously. As indicated by structure Number 1, a near-surface isothermal layer of warmed water is formed. It is separated from the underlying water by a negative thermocline (usually of magnitude less than 2° C ) . The heat will be lost, and the small thermocline will vanish, if the night­ time cooling equals or exceeds the day-time heating. If all the heat is not lost, and the wind continues or increases, the remaining heat will continue to be mixed downward. The limiting depth of the mixing is determined by the wind force, and is marked by the small thermocline—as indicated in the successive structures (7 through 5) in Figure 5. This downward mixing process is irreversible. The thermocline cannot ascend toward the surface. This would require the "unmixing" of the warmed and unwarmed waters; this cannot be accomplished by any mechanical means. However, the mixed layer can deepen in the presence of any process which will increase the mixing or remove the heat. It follows that heat cannot be transferred downward through a thermo­ cline. Such a transfer requires mixing which must lower or destroy the struc­ ture. Hence, a thermocline forms a "cover," protecting the waters below it against further heating from the surface. (Thus the uppermost of a series of thermoclines marks the limit of existing surface influence. In and below this uppermost thermocline, the temperature and structure can only be changed by internal processes.) If the wind is light, only a small amount of mixing will take place, and the small thermocline will rest at a shallow depth. Eventually, strong winds must occur, and if the heat is retained, it and the associated thermocline will be mixed downward to some limiting depth. Hence, the successive retained heat gains accumulate in a layer whose temperature increases during the heating season and whose depth is determined by the strongest seasonal winds. This warmed layer is bounded by the seasonal thermocline, whose magnitude (AT) increases through the heating season. Any thermoclines in the layer above the seasonal thermoclines are tran­ sient because they may be destroyed at any time by cooling, or may be mixed further downward by increasing winds (and eventually must lose their identity by being driven into the seasonal thermocline). It follows that the structure in this layer is potentially isothermal. Hence, it is called the potential layer. The depth from the surface to the top of the seasonal thermocline is the potential layer depth. 1

*If the surface waters diverge, underlying waters must rise. In such cases, the thermocline will rise and may intercept the surface. Such situations, termed "upwelling," occur at the boundary between opposing currents, and in coastal regions. However, marked divergences do not occur in the oceanic regions of the Subarctic Pacific Ocean (Dodimead et al, 1963).

F I G U R E 6. Features of the thermocline at Ocean Station "P" during the heating season.

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J . P. T U L L Y A N D L . F . GIOVANDO

It is important to distinguish between a mixed (isothermal) layer and the potential layer as defined here. In keeping with the definition by Rossby and Montgomery (1935), a mixed layer is truly isothermal from the surface to the first thermocline, whether or not that thermocline is transient. The potential layer extends from the surface to the seasonal thermocline. It may be identical with the mixed layer, it may contain a shallow mixed layer with one or more underlying transients, or it may contain a series of transients forming a more or less continuous temperature decrease with depth. The variety of structures and their behaviour that develop from these processes at Ocean Station " P " are illustrated in Figure 6, which was constructed from twice-daily bathythermograms. The position of the sea­ sonal thermocline is shown by dark shading. The positions of transient thermoclines are shown by lighter shading. This example illustrates the case of two stable thermoclines. This case has occurred only twice (1956 and 1960) since 1955; it is presented here to emphasize some of the features of the processes. Similar diagrams, illustrating the semi-daily data collected during the four years 1956 through 1959, are shown by Tabata and Giovando (1963)! Internal Waves Figure 6 shows that the depths of the upper and the lower limits of transient and of seasonal thermoclines fluctuate considerably. Tabata exam­ ined these fluctuations statistically as part of another study (private com­ munication ). He fitted a linear regression line to the twice-daily observations of mixed-layer depth through each of the four months, May through August, 1956. Then he evaluated the extent of the non-systematic fluctua­ tions as the standard error of estimate. These limits of deviation, between which are contained about two-thirds of the data, varied between ± 4 and ± 6 metres, as shown in Table I. He made corresponding examinations for several series of eight or more bathythermograms observed at 15, 60 and 120 minute intervals. The mean mixed-layer depths and the standard deviations (limits enclosing two-thirds of the data) were computed as shown in the examples in Table I. Comparison of these analyses shows that the limits of fluctuation are generally similar for all the time intervals from 15 minutes to a month. Evidently the fluctuations are frequent and random. Internal waves of semi-diurnal and diurnal periods have long been recognized (Defant, 1961). At the depth of the seasonal thermocline (about 30 m) in the open ocean, Ufford (1947) observed internal waves having periods of about 10 minutes and amplitudes of about 3 m. At 10 to 20 m depth in the coastal waters off California, Lee (1961) observed internal waves having periods of 5 to 15 minutes and amplitudes to 3 m. LaFond (private communication), using a towed thermister chain, obtained continuous records of the isotherms between the surface and 240 m depth from California to Hawaii, during the summer of 1961. Power-

SEASONAL T E M P E R A T U R E S IN T H E SUBARCTIC PACIFIC

19

TABLE I E X A M P L E S OF STATISTICAL A N A L Y S E S OF T H E F L U C T U A T I O N S OF T H E D E P T H OF T H E M I X E D L A Y E R AT O C E A N STATION " P "

(Lat. 50° N , Long. 145° W) (Tabata, private communication)

Date

Mixed layer Mean depth Fluctuation (m)

1-31 May, 1956 1-30 June, 1956 11-31 July, 1956 1-31 Aug., 1956 28-29 M a y , 1957 29-30 July, 1957 18-19 Aug., 1957 16-17 June, 1958 16-17 July, 1958 15-16 Aug., 1958 1 June, 1961 4 June, 1961 8 June, 1961 12 June, 1961 15 June, 1961 18 June, 1961 22 June, 1961 24 June, 1961 27 June, 1961 2 July, 1961

39.2 45.4 19.9 45.2 19.3 45.1 21.9 11.3 3.1 19.1 11.6 30.0 31.6 25.0 31.4 39.5 40.8 14.5 14.6 17.2 24.5 15.0

(±m) Error of Estimate Standard 6.2 4.9 3.7 4.4 4.5 4.2 Standard Deviation 6.9 7.2 3.5 6.0 2.8 3.0 6.5 2.4 5.5 3.2 2.3 1.7 4.1 7.0 3.0 3.2

Observations Number Frequency

56 48 60 60 57 57

Semi-daily

10 10 10 10 10 10 8 8 8 8 8 8 8 8 8 8

120 minutes

} ff

60 minutes }}

15 minutes }}

}} } }}

»

spectrum analyses of these data showed that the periods were random from about 5 minutes to at least half a day, and the amplitudes were found to be quite variable and subject to sudden changes. Representative values near the top of the thermocline were of the order of 4 to 8 m ( ± 2 to ± 4 m) and increased with depth to about 16 to 20 m ( ± 8 to ± 1 0 m) at 200 m depth. He observed that the frequencies and amplitudes were independent both of the speed and of the direction of the towed sensors. Vaisala (1925) derived a formula defining the maximum frequency (shortest period) at which internal waves can be created and be propagated in a density-stratified fluid. Application of this formula to the density gradient at the level of the summer thermocline at Ocean Station " P " indi­ cates that internal waves with periods as short as 5 minutes can form and persist. It is therefore concluded that the observed fluctuations in the depths of the thermocline limits result generally from the superposition of a large number of internal wave trains. Each train can be moving in a different direction in the (effectively) horizontal plane. Periods involved range from a few minutes to at least half a day. It is therefore apparent that the position of a thermocline is best described by the mean depth of each of its limits and the standard deviations from the means. Statistical analysis of considerable data at Ocean Station " P "

20

J . P . T U L L Y A N D L . F . GIOVANDO

(e.g., Table I) and in the eastern Subarctic Region (Oceanographic Services for Defence, 1961) has shown that the standard deviation of the depth of each limit is between 3 and 5 m, and that extreme deviations may be as great as 20 m from the mean. Transients During the period shown in Figure 6, transients due to surface heating first occurred in April and a seasonal thermocline was formed, at the end of the month, at about 20 m depth. Thereafter, in the presence of increasing winds, it descended to a depth of more than 40 m by late June. During this two-month period its magnitude was increased by occasional heat additions, some of which were revealed by the occurrence of observable transients. During intervals of light winds, these transients rested temporarily at intermediate depths in the potential layer. During periods of stronger winds, they descended to the seasonal thermocline within one day. Doubt­ less, there were transients which were not recognized in the twice-daily data. A period of lighter winds commenced in late June. Transient thermoclines formed, rested, accumulated, and stabilized in mean positions at an inter­ mediate depth, thus forming a second seasonal thermocline overlying the first one. Such an occurrence is most easily recognized in retrospect because, initially, the magnitude (AT) of the second thermocline is small and cannot be distinguished from a resting transient. However, in the vicinity of Ocean Station " P " , the usual depth of the seasonal thermocline is 20 to 30 m. If, as on this occasion, the potential layer depth much exceeds 30 m, it may be concluded that the winds have been unusually strong and will probably relax. When this occurs, a second thermocline will be formed at the usual depth. It is evident from these observations that seasonal warming of the sea is an intermittent process. It cannot occur at night, and will only occur during day time if the rate of heating is greater than that of cooling. Effective heating periods are revealed by the occurrence of transients in the potential layer. Periods of cooling or strong winds are indicated by the absence of transients. At present, there is no sure means of assessing the horizontal extent of the transients. However, some useful speculations can be made from the data presented in Figure 7. During the summer of 1934, surface temperatures were observed off Vancouver Island, British Columbia every 4 minutes ?????? ???????? ???? ?? ??? ????? ?????? ???????? ????? ???????????? ??? quired most of a day in each area shown, they were plotted as being synoptic. It is evident that there was considerable small-scale variability in surface temperature. There were warm and cold areas, the temperature difference between them being as great as 1.5° C. The exact nature and causes of this "patchiness" have not been thoroughly investigated. However, it is reasoned that the warm patches are associated with the occurrence of transient structures in the potential layer, and that

SEASONAL TEMPERATURES IN THE SUBARCTIC PACIFIC

21

F I G U R E 7. Sea surface temperatures observed with bucket and thermometer at 4-minute intervals, during the heating season, 1 9 3 4 (after Tully, 1 9 3 7 ) .

the over-all structure in the potential layer is more nearly isothermal in the cool patches. It is concluded that the horizontal extent of each area containing transient thermoclines is limited. This condition may result from any process which causes local variations of heating or cooling at the sea surface. For example, cooling is partly due to evaporation, which varies with wind force (Tabata, 1961). Surface winds occur as gusts which progress slowly. It is reasoned that cooling is more rapid in the areas of strong gusts than between them. In such cases there would be cool (isothermal) patches in a general area of heating (transient structures). It is interesting to speculate on the effect of scattered clouds. Recalling that as much as 70 per cent of the incident energy from the sun may be intercepted by heavy clouds (Sverdrup et ai, 1942), it is evident that the heating process will be drastically reduced in the area of a "cloud shadow." However, there is no reason to expect the cooling process to be materially altered. It may be reasoned that cooling can occur during daylight hours in areas of cloud shadow. In such areas transients would not form, and any

22

J . P . T U L L Y A N D L . F . GIOVANDO

transients originally present would be reduced or destroyed. However, heat­ ing could occur in adjacent sunny areas, causing the formation and growth of transients. Hence, a variable pattern of surface temperature, and the occurrence of transient structures, could be anticipated in the presence of scattered clouds during the heating season. The Seasonal Thermocline The data (Fig. 6) show that heat additions and transient thermoclines become more frequent as the heating season advances. These increase the temperature in the potential layer and contribute to the growth (AT) of the (uppermost) seasonal thermocline. However, it is seen that the tempera­ ture at the lower boundary of this thermocline, and at both boundaries of the underlying thermocline, remained constant. Within small limits, these boundaries were isotherms. This confirms the deduction that there is no appreciable transfer of surface-induced influence through the uppermost thermocline at any time. It is also notable that the mean depth of the upper and lower boundaries of both seasonal thermoclines remained constant throughout the heating season. Hence, the mean thickness (AZ) of each thermocline remained constant. Such a high degree of conservation of the principal features of structure can occur only if the internal mixing is very small and the inherent stability of the structure is very great. It is evident that, as the magnitude (AT) of a thermocline increases, so does the associated density difference through it. Hence, the stability of the seasonal thermocline must increase with time. This has been confirmed by the data. The mean potential layer depth usually becomes stable when the magnitude (AT) of the thermocline reaches 3° C. This usually occurs about the end of June. Thereafter, the mean potential layer depth remains nearly constant until the beginning of the cooling season in mid-September (Tabata and Giovando, 1963). Jacobs (1951) showed that there is an excess of precipitation over evaporation throughout the Subarctic Region. The behaviour of this fresh water is similar to that of the "surface" heat. It is mixed downward through the potential layer and forms a small halocline (0.2%o), which is coincident with the seasonal thermocline (Dodimead, 1961) and contributes materially to the stability of the structure. Evidently the seasonal thermocline is a very stable entity which can only be destroyed by a long-continued process such as winter cooling. It is shown by the data that there is, below the seasonal thermocline, a good deal of fine structure superimposed upon the principal structure. This fine structure undergoes considerable ambient variation. This is illustrated in Figure 8, which shows a series of bathythermograms typical of those observed at intervals of 5 to 60 minutes at Ocean Station " P . " It is concluded that the (relatively) small-scale irregularities are "vagrant" structures whose vari­ ability is due to internal mechanisms.

SEASONAL T E M P E R A T U R E S I N T H E SUBARCTIC PACIFIC

FIGURE

23

8. A series of bathythermograms observed at 15-minute intervals during the heating season at Station " P " .

It may be reasoned that such mechanisms must displace parcels of water vertically relative to each other. Internal waves which have been shown to give rise to orbital motion and differential displacement throughout the body of a fluid (Defant, 1961) provide one possible mechanism. D E C A Y OF T H E SEASONAL T H E R M O C L I N E

The Cooling—Convection Process During the cooling season, from about mid-September to mid-April (Fig. 3), the heat input is reduced and a net daily heat loss results. Also evapora­ tion increases (Tabata, 1961) and sporadic increases in salinity result. Convection currents therefore occur. The potential layer becomes isothermal and deepens, as shown in Figures 4 and 9. In the first stage only the upper most seasonal thermocline is affected (if more than one is present). It sinks, and merges with the underlying thermocline. Thereafter, the residue con­ tinues to be eroded, and sinks until it reaches the permanent halocline. The erosion process is clearly attributable to cooling and convection, but why the residue of the thermocline should sink, rather than be eroded in its

FIGURE

9. Features of the thermocline at Ocean Station " P " during the cooling season.

26

J . P. T U L L Y A N D L . F . GIOVANDO

stable position, is not understood at this time. Part of this sinking process might be attributed to increased wind mixing due to autumnal and winter gales. If this were the case, the residue of the thermocline would sink during gale periods and rest at an effectively constant mean level during fairweather periods. The data (Fig. 9, and Tabata and Giovando, 1963) show that such behaviour does not occur. Rather, the thermocline sinks at a rela­ tively constant rate until it reaches the halocline (about 100 m depth). Also, it has been shown (Fig. 6) that simple wind mixing is not likely to be effective below about 60 m depth at Ocean Station " P , " even when the stability of the thermocline is least, i.e., during its formation period in spring. Late Winter Cooling If the winter is severe, the residue of the decaying thermocline descends to the halocline early in the cooling season. In this case the overlying waters (upper zone, Fig. 2) continue to cool during the remainder of the season and become colder than die waters in the halocline. This results in a positive temperature gradient with depth and an attendant temperature maximum (mesothermal temperature) in the upper part of the halocline. This struc­ ture is possible and stable because of the inherent positive density gradient. Later, when the surface waters are warmed again during the following heat­ ing season, the residue of these winter-cooled waters are preserved under the seasonal thermocline. This residue provides a temperature minimum (dichothermal temperature; Fig. 2) in the sub-thermocline duct between the seasonal thermocline and the halocline. These processes, structures and their distribution have been discussed by Uda (1963) and by Dodimead et al. (1963), who also show that under such conditions the upper part of the halocline is eroded. These phenomena occur regularly in the northern part of the Gulf of Alaska and along the Aleutian Islands. Extreme examples are found in the Bering and Okhotsk Seas where the difference betwen the mesoand dicho-thermal temperatures often exceeds 3° C. The structure can endure for several years as the waters are carried from the Oyashio across the ocean in the West Wind Drift. The structure is eroded by internal mix­ ing en route; it usually does not reach Ocean Station " P . " If the winter is mild, the residue of the sinking thermocline may not reach the halocline until the end of the cooling season, or even until some time after the beginning of the heating season. In this case the halocline is not eroded. In the vicinity of Ocean Station " P , " the upper waters usually cool to about the same temperature as the waters in the halocline, and the temperature structure has been observed to be isothermal to 140 m depth (Tabata, 1961). Deep positive gradients are rare and usually vagrant. 2

T h e salinity difference from top to bottom of the halocline is about \% . The associated density difference is approximately equal to that associated with a temperature difference of 5° C at temperatures between 4° and 9° C (cf. Sverdrup et al. 1942). 2

0

SEASONAL T E M P E R A T U R E S I N T H E SUBARCTIC PACIFIC

27

Further south, towards the Subarctic boundary (Fig. 1), the upper zone seldom cools to the temperature of the halocline waters. Here, there is usually a small residual negative temperature gradient at the end of winter. In the Subtropic Region, where there is no halocline, the erosion and sinking of the residual thermocline continues through the following summer, after the new seasonal thermocline has been formed. The ultimate limit at which such structures can be recognized is not known. However, it must be somewhere in the zone of the temperature minimum, between 200 and 800 m depth. Reference Surface In the Subarctic Region, the convective "erosion" process is stopped by the permanent halocline. Depending on the severity of the winter, the upper part of the halocline may be eroded, but the process does not continue long enough to erase the halocline anywhere in the region. Hence, wherever it occurs, the top of the permanent halocline is the reference surface to which all seasonal temperature structures are referred. At Ocean Station " P " and in the Central Subarctic Region (Fig. 1) the mean depth of the top of the halocline is about 100 m. The ambient fluctua­ tions there are about 20 m in depth and about 0.5° C in temperature (Dodimead, private communication). Undoubtedly these fluctuations are due to internal waves. The reference surface is shallower (about 80 m) in the Alaska Gyre, and deepens to about 140 m at the Subarctic boundary (Dodimead, 1961). Since there is no halocline in the Subtropic Region, the reference surface is assumed to be at a depth where the annual cycle of temperature is obscured by ambient fluctuations. This depth appears to be about 140 m (Robinson, 1957). T H E SUB-THERMOCLINE DUCT

Since both the seasonal ("summer") thermocline and the permanent halocline (Fig. 2) are structures having inherent stability, the zone between them must be regarded as a distinct feature of the structure. Figure 10 shows semi-daily temperature data at the surface and at 100 m depth. These latter values may be considered as definitive of the values at the top of the halocline and in the sub-thermocline duct where the tempera­ ture/depth gradient is small (Tabata, 1961; Dodimead, 1961). Figure 10 reveals the heating and cooling seasons to be the periods when the surface temperatures were increasing or decreasing, respectively. A seasonal thermocline and a sub-thermocline duct existed when the tempera­ tures at the two levels were different. The waters were isothermal (no thermocline) when these temperatures were the same. Examination shows that the sub-thermocline waters (100 m) cooled

28

FIGURE

J . P . T U L L Y A N D L . F . GIOVANDO

10.

Temperature at the surface and at (1956,

1957,

1958,

100

m depth at Ocean Station "P"

1959).

SEASONAL T E M P E R A T U R E S I N T H E SUBARCTIC PACIFIC

29

30

J . P. T U L L Y A N D L . F . GIOVANDO

during the thermocline seasons of 1956 and 1958, warmed during 1957, and remained constant during 1959. This behaviour can be explained by the entrainment process. Entrainment Fleming (1958) and Tully and Barber (1960) showed that there is a net upward transfer (entrainment) of water through the permanent halocline, and that the salinity structure is maintained by refreshment of the upper zone from the excess of precipitation over evaporation in the Subarctic Region. However, as has been shown here, such refreshment is retained in the potential layer and cannot reach the sub-thermocline duct while the seasonal thermocline and the associated seasonal halocline exist. Evidently, during this period the sub-halocline duct must be invaded by waters from below carrying the properties of the halocline. Hence its properties must change during the season. Dodimead (1961) observed that the salinity in this duct invariably increased during the summer. Since one property cannot be transported independently of another, it is evident that the seasonal trend of temperature structure in this sub-thermocline duct depends on the temperature structure in the halocline. The temperature in the duct will increase if the waters in the halocline are warmer, and will progressively decrease if they are cooler. SUMMARY: T H E THERMOCLINE

MODEL

The previous discussions are summarized in Figure 11. It indicates, in idealized form, the sequence of structures occurring throughout the year in the upper 140 m of depth. There are four zones: the potential layer, the seasonal thermocline, the sub-thermocline duct, and the permanent halo­ cline. The potential layer extends from the surface to the (shallowest) seasonal thermocline. It is shallowest, and will contain transient thermoclines spora­ dically, throughout the heating season. It becomes isothermal and deepens throughout the cooling season. Late in the cooling season, when the residue of the thermocline sinks to the halocline, the potential layer becomes identi­ cal with the upper zone defined by salinity structure. Transient thermoclines can only occur, during a heating situation, in the presence of light winds (less than 12 knots). During strong winds the heat gain is mixed downward so rapidly that it becomes a heat flow, and the transient structures are too small to be apparent on bathythermograms. During the cooling season, transient structures may be formed, on occasion, during day time, but they are invariably destroyed by night-time cooling. The seasonal thermocline is (or thermoclines are) formed by surface heating and wind mixing early in the heating season. Through the heating season its position is determined by the most recent strong winds. During the cooling season it is eroded and sinks primarily because of radiative cooling,

SEASONAL T E M P E R A T U R E S I N T H E SUBARCTIC PACIFIC

FIGURE

31

11. The thermocline model.

evaporation, and convective mixing. No surface effects can penetrate this structure; they can only lower or destroy it. The seasonal thermocline, while it exists, marks the limit of influence of surface mixing processes. The magnitude of the thermocline is a measure of the cumulative heating and cooling since the beginning of the heating season. The sub-thermocline duct is created anew each year, at the end of the cooling season. Its properties are protected by the overlying seasonal thermo­ cline from any change by surface-induced effects, as long as a vestige of that thermocline remains. Vagrant structure fluctuations in this zone are due to internal waves; systematic temperature changes are due to entrainment. The mean depth of the top of the halocline is established by convective mixing at the end of the cooling season. Thereafter, under the "shelter" of the seasonal thermocline, there is a slow upward transfer of water by entrainment. This only affects the temperature structure in the subthermocline duct if the temperature in the halocline is materially warmer or cooler. The structure in the halocline zone is not affected by the local surface processes. It is subject only to internal processes (Tully and Barber, I960). Throughout most of the Subarctic Pacific (exceptions being the coastal and 3

T u l l y and Barber (1960) showed that the halocline is a transition zone between the upper (seasonal) zone and the deep (non-seasonal) zone. However, the exchange is so slow that local and short-term fluctuations are integrated over one or more years, while the water is transported horizontally over long distances. Hence the halocline structure in any locality may be considered constant for practical purposes. 3

32

J . P. T U L L Y A N D L . F . GIOVANDO

the western boundary regimes (Fig. 1)), these processes are steady and slow so that changes during a year are considerably less than at the upper limit of the halocline. S O M E APPLICATIONS OF T H E M O D E L

The Canadian Oceanographic Information Service A n oceanographic information service has been founded in the Naval Weather Service at Esquimalt, British Columbia (Tully, 1961), to provide frequent assessments and forecasts of the oceanographic conditions in the eastern Subarctic Region. It is based on the O C E A N system of observation, assessment and forecasting which were developed from this model (Fig. 11) of temperature structure and behaviour (Giovando, 1962). Some ships make regular bathythermograph observations; others observe surface temperature only. A l l these data are radioed, together with the weather data, to the Information Centre at Esquimalt where they are collated, assessed and plotted to provide weekly charts showing: (1) surface tem­ perature, (2) potential layer depth, and occurrence and intensity of transients, (3) magnitude of the thermocline, (4) depth of the bottom of the thermocline and (5) temperature at the reference surface (100 m, 330 ft). The following sections explain some of the techniques and procedures developed from this model and employed in the Information Service. Assessment of Temperature Structure A knowledge of temperature structure is a prerequisite for the assessment of sound-ranging conditions and for the studies of fisheries ecology, heat budget, and evaporation. In all these, it is necessary to analyse considerable data to define representative conditions throughout a considerable area or during an appreciable period of time. Hence the assessment of temperature structure must be reduced to the minimum information that will define the significant features, within acceptable limits of error. This may be accomplished by specifying the temperatures at, and the depths of, the limits of the principal zones (Fig. 12) by mean values and standard deviations. The dimensions of the zones (thicknesses and tempera­ ture differences) are the differences of successive values. This assessment defines the total effect, but not the detail, of multiple thermoclines, and of the small structures such as transients in the potential layer or vagrant structures in and below the thermocline. It is argued that the enumeration of the fine structures is properly ignored because they are transient, variable, and small with respect to the principal structure. The assessment implies that there are sufficient observations to provide a valid statistical sample. From the study of the series of observations at Ocean Station " P " (Table I), it was concluded that eight observations would be sufficient. Preliminary considerations indicated that they should be taken,

SEASONAL T E M P E R A T U R E S IN T H E SUBARCTIC PACIFIC

33

F I G U R E 12. The O C E A N model of temperature structure.

from a stopped ship, at 15-minute or longer intervals. However, recalling that the variability in the dimensions of the zones is due primarily to internal waves, it was later reasoned that the eight observations could be made, with equal significance, at intervals as short as 5 minutes, from a ship proceeding at 6 knots or faster. Such a sequence of observations distin­ guishes the transient and stable features of the structure.

34

J . P . T U L L Y A N D L . F . GIOVANDO

This definition of temperature structure by the mean values of the depths and temperatures at the zone boundaries and by the standard deviations associated with these values, derived from multiple observations, is the basis of the O C E A N system of assessment (Giovando, 1962). Obviously this concept is applicable in any situation. These ambient variabilities have an important consequence. The charac­ ter of the seasonal thermocline is usually defined by its temperature gradient. This definition cannot be maintained in the presence of the observed vari­ ability of the depths of both limits (Fig. 6). It appears that a definition based on temperature differences associated with the principal features of structure, rather than with a depth interval, would be more representative. Magnitude of the Thermocline For various purposes it is of interest to monitor the magnitude of the thermocline throughout the year in all parts of the Subarctic Region. Continuous data are available only from fixed positions, such as Ocean Station " P , " where semi-daily bathythermograms are taken. Elsewhere, such data are too sparse and infrequent. However, two existing groups of data can be combined in terms of the model to fulfil the requirements within acceptable limits of accuracy. In most of the region, the temperature structure in the potential layer and in the sub-thermocline zone is usually near-isothermal (Figs. 6, 8, and 9). Hence the difference of temperature between the surface and the top of the halocline (0 and 100 m depth) is a measure of the magnitude (AT) of the seasonal thermocline. Such data are shown in Fig. 10, which also shows the ambient variation due to internal waves ( ± 0 . 2 ° C ) . When the seasonal thermocline is small, transient structures are rare (Figs. 6 and 9) and the structures in the poten­ tial layer and the sub-thermocline duct are most nearly isothermal. Hence the error of estimate is small. Transient structures are common when the magnitude of the thermocline is large. However, the total magnitude of such transients is usually less than 0.5° C. Hence the total error of estimate of the magnitude of the seasonal thermocline by this means rarely exceeds 10 per cent. Recalling that the sub-thermocline temperatures remain nearly constant while the thermocline exists, it is evident that the temperature data at 100 m depth may be accumulated on a single "Reference Level" temperature chart from April through November each year. Obviously this chart can be continuously revised as data become available. Assessment of Winter Cooling It is a feature of the model (Fig. 11) that the seasonal zone above the halocline becomes isothermal (hence isohaline) at the end of the cooling season; this characteristic temperature is preserved under the seasonal thermocline until the following winter. Hence the extreme of winter condi-

SEASONAL T E M P E R A T U R E S I N T H E SUBARCTIC PACIFIC

35

tions can be recognized in retrospect in observations made during the follow­ ing summer. Dodimead (1961) first applied this principle. Agencies from Canada, Japan, and United States, working together, have carried out comprehensive surveys throughout the Subarctic Region during each summer since 1955. Winter data were only available in the eastern part of the region during three winters. Dodimead showed that, in this part of the region, the tempera­ ture distribution observed during summer at the top of the halocline (in the sub-thermocline duct) was the same, within ± 0 . 5 ° C, as the temperature of the isothermal upper zone during the previous winter (Fig. 10). He then applied this conclusion to the extensive summer data to define and compare the severity of the several winters. Since the same data also revealed the summer conditions, he was able to assess the extremes of heating and cooling in the seasonal zone, and distinguish the trends in the non-seasonal zones (halocline and lower zone), from the summer data alone. It was evident that winter surveys were unnecessary in this region, and none have been made since 1959. Forecasting It has been shown that in this region, where surface heating and wind mixing, and cooling and convective mixing, are the dominant processes in the growth and decay of the thermocline, the temperature structure in the upper zone can be related to the atmospheric conditions and sea-surface temperature. These parameters are regularly observed by the Weather Services. Hence, in such regions it is feasible to forecast the depth of the potential layer, the occurrence of transients, and the magnitude of the thermocline, at any time throughout the region, on the basis of currently available data. REFERENCES

D E F A N T , A . (1961). Physical oceanography. V o l . II. London: Pergamon Press. D O D I M E A D , A . J . (1961). Some features of the upper zone of the Subarctic Pacific Ocean. Int. North Pac. Fish. Com. Bull., no. 3, 11-24. F A V O R I T E F . , and H I R A N O T . , (1963). Review of oceanography in the Subarctic Pacific Region. Int. North Pac. Fish. Com. Bull. In press. F L E M I N G , R. H . (1958). Notes concerning the halocline in the northeastern Pacific Ocean. J . Mar. Res. 17: 158-73. G I O V A N D O , L . F . (1962). The O C E A N system of assessment of bathythermograms. Fish. Res. Bd. Can., M S Rept. Series (Oceanogr. and Limnol.) no. 105. J A C O B S , W O O D R O W C . (1951). The energy exchange between sea and atmosphere and some of its consequences. Bull. Scripps Inst, of Oceanogr., U . of Calif., 6(2). L E E , O W E N S. (1961). Internal waves in shallow water. Limnol. and Oceanogr. 6(3): 312-21. Oceanographic Services for Defence (West Coast Canada) (1961). Data Record. "Ocean" reports from R C N ships—1961. Oceanographic Information Centre, H . M . C . Dockyard, Esquimalt, B . C . R O B I N S O N , M . K . (1957). Sea temperatures in the Gulf of Alaska and in the Northeast Pacific Ocean, 1941-1952. Bull. Scripps Inst, of Oceanogr., U . of Calif., 7(1): 1-98.

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R O S S B Y , C . G . and M O N T G O M E R Y , R. B. ( 1 9 3 5 ) . T h e layer of frictional influence in wind

and ocean currents. Papers in Physical Oceanogr. and Meteorol., vol. 3 , no. 3. SVERDRUP, H . U . , J O H N S O N ,

M . W . , and F L E M I N G , R . H . ( 1 9 4 2 ) . T h e oceans, their

physics, chemistry and general biology. New York: Prentice-Hall. T A B A T A , S. ( 1 9 6 1 ) . Temporal changes of salinity, temperature and dissolved oxygen content of the water at Station "P" in the Northeast Pacific Ocean, and some of their determining factors. J . Fish. Res. Bd. Can., 18(6): 1 0 7 3 - 1 2 4 . and G I O V A N D O , L . F . ( 1 9 6 3 ) . Diagrams of the seasonal thermocline at Ocean Station "P" during 1 9 5 6 through 1 9 5 9 . Fish. Res. B d . Canada, M S Rept. Series (Oceanogr. and Limnol.). In preparation. T U L L Y , J . P. ( 1 9 3 7 ) . A procedure for increasing the accuracy of surface current charts based on hydrodynamic observations. J . Biol. Bd. Can., 5 ( 2 ) : 9 3 - 9 . ( 1 9 6 1 ) . Assessment of temperature structure in the eastern Subarctic Pacific Ocean. Fish. Res. Bd. Can., M S Rept. Series (Oceanogr. and Limnol.) no. 1 0 3 . and Barber, F . G . ( 1 9 6 0 ) . A n estuarine analogy in the Subarctic Pacific Ocean. J.

Fish. Res. B d . C a n . 7 7 ( 1 ) :

91-112.

U D A , M . ( 1 9 6 3 ) . Oceanography of the Subarctic Pacific Ocean. J . Fish. Res. Bd. Can. 20(1):

119-79.

U F F O R D , C . W . ( 1 9 4 7 ) . Internal waves in the ocean. Trans. A m . Geophys. Union, 25(1):

79-86.

V A I S A L A , V I L H O . 1 9 2 5 . Ueber die Wirkung der Windschwankungen auf die Pilotbeobachtungen. Soc. Sci. Fennica, Commentationes Phys.-Math. II, 19. V O N A R X , W . S. ( 1 9 6 2 ) . Introduction to physical oceanography. Reading, Mass: Addison-Wesley.

DISTRIBUTION OF A T T A C H E D MARINE A L G A E IN RELATION T O OCEANOGRAPHIC CONDITIONS IN T H E NORTHEAST PACIFIC Robert F. Scagel

FOR SEVERAL YEARS the distributions of marine benthonic or attached organisms have been studied in relation to the oceanographic conditions prevailing along the coast of British Columbia. Attention has been directed especially toward the conspicuous, larger, non-planktonic algae. In an effort to determine the natural occurrence of marine benthonic algae in this area and the factors responsible for the observed patterns of distribution, it has become apparent that the provincial boundaries of British Columbia are quite artificial oceanographically and biologically. Attention has been turned, therefore, at first southward into Washington, Oregon and northern California, and more recently northward into the Gulf of Alaska and the Aleutian Islands. As our knowledge of the algal flora and the oceanographic conditions of the Pacific coast of North America expands, it becomes increas­ ingly apparent that a more careful comparison with the northwest Pacific, particularly in the northern part of Japan (Okamura, 1926 and 1932; Nagai, 1940; Tokida, 1954), will also be necessary before many of the distributional and taxonomic problems encountered can be completely resolved. It is 175 years ago that Archibald Menzies collected the first marine alga on the coast of British Columbia (Newcombe, 1923) and 100 years since David Lyall made the first comprehensive collection of marine algae (com­ prising about a hundred species) in the vicinity of Esquimalt (Harvey, 1862). Even this first comprehensive collection was quite limited in scope; by 1913, in the same general area, there were over two hundred and fifty known to occur (Collins, 1913); and at the present time more than five hundred species of marine algae have been recorded (Scagel, 1957). It has only been in the past sixty years that our knowledge of the systematics of the various groups of marine algae has taken significant strides. But even now some of the more common and conspicuous species still present difficult taxonomic problems. It should be pointed out therefore, that there is still a great need for monographic studies of many of the algal genera on the Pacific coast using all of the modern tools and concepts now available to the algal taxonomist. Despite the pressing need for taxonomic clarification of

38

ROBERT F . SCAGEL

much of the flora, our knowledge of distributions and systematics has now reached a point where the marine algal ecologist can use some of the existing data with confidence. However, our knowledge of the subtidal regions, except where more intensive dredging has been done in northern Washing­ ton and southern British Columbia, is still only fragmentary. A great deal more effort by dredging and with underwater diving methods is needed, especially along the exposed region of the coast from California to Alaska. This is essential to extend our knowledge of the oceanography of the inshore environment to the limit of depth of the flora and thus broaden the algal ecologist's horizon from the two-dimensional to the three-dimensional para­ meters of the marine environment. We know from physiological evidence that organisms differ in their need for a certain complex of environmental factors. Therefore, one expects that certain of them, especially if they are somewhat narrow in their physical or chemical requirements with respect to one or more of these factors, should be useful indicators of water characteristics and movements in the sea. This has been the philosophy behind much of the research effort in biological oceanography, using plankton organisms to trace ocean current systems and characterize water masses. In dealing with free-swimming or free-floating organisms, one of the greatest problems is to determine whether the plant or animal collected in a given area is really indicative of the conditions common to that area in time or whether it is only an ad hoc indicator. This problem is further compli­ cated by the relatively short life span of many of the planktonic organisms. In other words, an organism may be indicative of the characteristics of the water mass which brought it to an area at one particular phase of its life history; but it may not be indicative of the conditions of the water in the same place an hour, a day, a week or a month hence; or at another phase of its life history. Interpretation of causal relationships is especially difficult in the shallower, coastal regions where, from an instrumentation standpoint, some of the most complex oceanographic conditions exist. By virtue of their sedentary habit, and because most of them live for a longer period of time in this condition, the benthonic organisms have certain potential advantages over the plankton as indicators of oceanographic condi­ tions. Most benthonic organisms have planktonic phases or stages in their life history. But the fact that they spend the greater part of their life history —and especially their mature stages—firmly attached to the substratum makes them particularly useful. These attached organisms must live and reproduce, or die, in situ on the basis of the physical, chemical, and bio­ logical conditions to which they are exposed. Such organisms, especially where they have a life span of months or years, should thus provide a measure of the oceanographic conditions in time as well as in space. As a result of field studies and experimental evidence from the laboratory, it has become apparent that field observations in small local regions in this area are not particularly fruitful as a beginning in testing hypotheses relating

FIGURE

1.

Coastline of British Columbia and adjacent regions.

40

ROBERT F . SCAGEL

to the observed patterns of distribution. Just as in many physical oceanographic studies, it is not easy to detect small but significant changes in the distribution of properties unless one looks at the environment over a very large area (also seasonally) and over a broad spectrum of conditions. Thus in this study the whole coast was first subjected to a preliminary survey from Juan de Fuca Strait to Dixon Entrance. Later, as already indicated, observa­ tions were extended both southward and northward, in an attempt to estab­ lish the patterns of distribution of as many benthonic algae as possible. To the extent feasible, concurrent physical and chemical data were also col­ lected. These distributional data were then correlated with the general data available on the oceanographic conditions as they are known for the North Pacific. Secondly, more detailed hydrographic and botanical observations were made at three points where transitional conditions between exposed and protected coastal regions exist: these are Dixon Entrance, Queen Charlotte Strait, and Juan de Fuca Strait. Thirdly, a more intensive study of one of these, Queen Charlotte Strait, was carried out (Scagel, 1948 and 1961). In addition, experimental studies on a number of species under con­ trolled laboratory conditions have also been undertaken. As a result of this broad survey, it is apparent that the flora from northern Washington to northern British Columbia is exceedingly uniform. Except for some local anomalies, this uniformity in the algal flora can be related directly to the relative uniformity in temperature conditions encountered along this part of the Pacific coast (Fig. 4). In other words, under approxi­ mately the same conditions of substratum and exposure, with few exceptions, one finds the same species at Cape Flattery and Port Renfrew at the entrance to Juan de Fuca Strait in the south as at Langara Island in Dixon Entrance in the north and throughout the intervening area. A n extension of these observations further south indicates that the same flora, with little change, extends southward to the vicinity of the Columbia River at the WashingtonOregon boundary. South of the Columbia River one finds elements more typical of the northern California region, such as Cystoseira osmundacea. From the scanty literature (Setchell, 1893, 1917, 1932 and 1935; Okamura, 1933; Setchell and Gardner, 1925), it appeared that a similar transition was most likely in the vicinity of Sitka, Alaska. Here some of the colder water elements, such as Thalassiophyllum clathrus, typical of the Bering Sea, were encountered. In the summer of 1960 an expedition was undertaken to collect marine algae at thirty-five points in the Gulf of Alaska. Collections were made chiefly in the Aleutians, extending out as far as Attu Island, but also including the mainland coast to a point south of Sitka, Alaska. The distance involved in this survey (about two thousand miles) is of such magnitude that the points selected may still not be fully representative of the marine algal flora of this area. However, this survey has appreciably clarified the picture of algal distributions in the northeast Pacific. But more extensive observations are still needed throughout the Gulf of Alaska and into the Aleutian Islands. The evidence from this survey confirms the earlier assump-

F I G U R E 2.

FIGURE

Circulation pattern in the North Pacific (after Rakestraw

et

3. Salinity (%e) distribution in the North Pacific (after Rakestraw

al.,

1955).

et al.,

1955).

F I G U R E 4. Temperature ( ° G) distribution in the North Pacific (after Rakestraw et al., 1955).

42

ROBERT F . SCAGEL

tions and indicates that there is a transitional region in the vicinity of Sitka, Alaska, In the far Aleutian area, there are certain affinities, such as Arthrothamnus biftdus, with the northwestern Pacific flora (particularly of northern Japan). The summer temperatures of the waters in the vicinity of the Aleutian Islands (Fig. 5) are generally almost as low as those which occur along the greater part of the coast of British Columbia in winter (Figs. 6 and 10). Of some 182 species of marine algae reported to occur in southern Sakhalin (Tokida, 1954) 64 are found on the Pacific coast of North America; 67 are found in the Aleutian Islands and Alaska; 141 in northern Japan (Hok­ kaido). Of 864 species recorded from Japan (Okamura, 1932) 53 occur in the eastern Pacific area. The larger number of species recorded from Japan obscures to some extent the degree of affinity. This is because of the extreme variations in oceanographic conditions that occur (Fig. 4) from the southern to the northern extremities of Japan; in fact, only the northern part of Japan is at all comparable oceanographically with the northeast Pacific area. Certain affinities with the North Atlantic floras are also apparent; some of the species involved, such as Chorda filum and probably certain species of Laminaria, occur only as far south as the northern part of the Gulf of Alaska; whereas over a hundred species recorded in British Columbia, such as Agarum cribrosum, also occur in the North Atlantic.

5. Temperature (° C ) distribution in the Aleutian Islands, July-August, 1958 (after Dodimead, 1958).

FIGURE

However, there is one striking exception to the pattern of uniformity in British Columbia. In the vicinity of Cape Cook, on the west coast of Vancouver Island, a number of anomalies have appeared; for example, Gigartina canaliculata, known in Oregon and southward, occurs in this region; also Eisenia arborea, otherwise not known northward of the Channel Islands (south of Point Conception) occurs in the same region; and there are other algae typical of the warmer waters to the south that are restricted to this local region in British Columbia.

A T T A C H E D M A R I N E A L G A E I N T H E N O R T H E A S T PACIFIC

43

Although the oceanographic data that the ecologist has available for studies in coastal areas are still far short of what is desirable, with the effort devoted to oceanography in the North Pacific during the past few years the broad picture of circulation (Fig. 2), salinity (Fig. 3), and temperature (Fig. 4) distributions on a three-dimensional basis has now become apparent (Rakestraw et al., 1955). In trying to relate distributions of organisms to

6. Temperature ( ° G) distribution in the Northeast Pacific, January-February, 1959 (after Dodimead, 1959).

FIGURE

7. Temperature ( ° C ) distribution off the coast of British Columbia, March-April, 1959 (after Herlinveaux, 1959a).

FIGURE

44

ROBERT F . S C A G E L

8. Temperature ( ° C ) distribution off the coast of British Columbia, June-July, 1959 (after Herlinveaux, 1959b).

FIGURE

oceanographic conditions temperature is usually the first to be selected and, again on a large scale, there are certain distributions which can be fitted closely to the pattern of temperature distributions. The genus Macrocystis, for example, has been shown to follow the temperature distributions in both northern and southern hemispheres (Setchell, 1935; Womersley, 1954). It now appears, from the available data, that the anomalous situation in the vicinity of Cape Cook may also be a reflection of temperature distribution. This is apparent, however, only from the seasonal fluctuations in tempera­ ture (Figs. 6 to 10). In this area, during summer, an extensive tongue of warmer water (Fig. 8) moves inshore and northward along the southern portion of the coast of British Columbia. Its effect is particularly apparent (Fig. 9) along the west coast of Vancouver Island. The Eisenia population occurs just south of Cape Cook. Cape Cook is almost at the westernmost extremity of Vancouver Island. It seems most likely that the coastal region in this area, which is still poorly known, at times comes under the influence of this warmer water, resulting in a restricted distribution of certain marine algae that are representative of the flora typical of an area much farther south. Furthermore, it may be a sporadic rather than a regular annual temperature change that permits the restricted distribution of Eisenia and a number of other species in this area. On the other hand, in the local situation in British Columbia the distribu­ tion of Macrocystis integrifolia is not reflected by a temperature distribution,

A T T A C H E D MARINE A L G A E IN T H E N O R T H E A S T PACIFIC

45

F I G U R E 9. Temperature ( ° G ) distribution in the Northeast Pacific, August, 1959 (after Dodimead and Fofonoff, 1 9 5 9 ) .

as it is on a larger geographic basis. Macrocystis occurs throughout the length of the coast of British Columbia, as well as southward into California and northward into Alaska. However, it appears to follow more closely the salinity pattern as one proceeds from the open coast to the inner, estuarial regions of the Coast. This is indicated not only in Juan de Fuca Strait and Dixon Entrance, but also in Queen Charlotte Strait, where a more detailed study of its distribution has been made (Scagel, 1948 and 1961). A comparison of the distributional patterns of many of the more con­ spicuous species with some of the physico-chemical conditions has been undertaken in Queen Charlotte Strait (Scagel, 1961). Neither temperature, oxygen, nor inorganic phosphate distributions appear significant. But a great number of species do follow closely the salinity distribution in this area. As one proceeds from regions of high salinity on the open coast to the estuarial conditions of protected coastal areas, the species composition changes markedly, chiefly by a process of elimination (Scagel, 1961). This

46

ROBERT F . SCAGEL

FIGURE

10. Temperature ( ° G) distribution off the coast of British Columbia, November-December, 1959 (after Herlinveaux, 1959c).

is not to say that salinity per se acts as the causal agent. In some instances it may, but in other instances experimental evidence refutes it. It may be nothing more than a mechanical effect related to greater mixing and replenishment of nutrients on the open coast, as far as some of the species are concerned. There is one species which occurs in British Columbia which does appear to have its local and geographic distribution on the Pacific coast controlled largely by temperature. This is Sargassum muticum (Yendo) Fensholt, an alga which was apparently unintentionally introduced from the warmer waters of the Pacific side of Honshu Island, Japan. It occurs throughout the southern portion of British Columbia in protected embayments where temperatures during the summer may be higher than those prevailing along the open coast. This species also occurs in similar areas as far south as central Oregon. Coming back now to the broad picture in the North Pacific: it would appear that nowhere in the northeastern Pacific north of Point Conception is there a sharp boundary of floristic change; but rather there is a more gradual transition or continuum, with now one element and now another dropping out or appearing. This is what one would expect in the absence

A T T A C H E D MARINE ALGAE IN T H E N O R T H E A S T PACIFIC

47

of any sharp and consistently maintained change in physical and chemical conditions within a short distance, as occurs in the vicinity of Point Concep­ tion in California and in central Japan (Fig. 4). The range in fluctuation of salinity along the open coast is especially narrow (Fig. 3). Similarly, there is no region of sharp temperature gradient in this area, as occurs else­ where in the Pacific (Fig. 4). There does seem to be some significance, however, in the degree of seasonal change of the order of about 5° to 8° C from the Columbia River to Sitka (Figs. 6 to 10), which demarcates this transitional floristic region. That is to say, the typical composition of the flora is maintained throughout the area from about the Columbia River to Sitka, Alaska, except for a few anomalies; but the composition does not change rapidly at either extreme. This uniformity in composition of the flora is reflected by the relative uniformity in temperature conditions that exists along the open coast. The annual temperature range along the open coast (at 10 m depth) in the vicinity of Sitka is approximately 6° to 12° C ; and near the Columbia River it is approximately 9° to 14° C. Thus, the temperature range for this flora at the extremes appears to be approximately 5 ° to 6° C, and through the whole range about 8° C. The limits of tolerance for the flora are also confirmed from observations in Queen Charlotte Strait (Scagel, 1961), where the annual temperature during a ten-year period at the surface occasionally reached a maximum of about 12° C and a minimum of about 5 ° C ; but over the same period (1942-52), there was an annual mean minimum seawater temperature of about 6° C, and an annual mean maximum temperature of about 11 ° C ; in other words, an annual mean range of about 5° C. In striving to obtain a knowledge of functional ecology, it is at the point where individual species drop out or appear that one must look for the fundamental factors that control the individual distributions. To point out some of the more conspicuous possibilities, one has only to look at the northern and southern limits of the following (Fig. 11): Macrocystis integrifolia Bory, Postelsia palmaeformis Ruprecht, Lessoniopsis littoralis (Farlow et Setchell) Reinke, Cystoseira osmundacea (Menzies) C. Agardh, Nereocystis luetkeana (Mertens) Postels et Ruprecht, Thalassiophyllum clathrus (Gmelin) Postels et Ruprecht, Chorda filum (Linnaeus) Lamouroux, Egregia menziesii (Turner) Areschoug, Pleurophycus gardneri Setchell et Saunders, Sargassum muticum (Yendo) Fensholt, Dictyoneurum californicum Ruprecht, Agarum cribrosum Bory, and Alaria ftstulosa Postels et Ruprecht. In contrast to these there are others (Fig. 11) which have an extremely broad range of north-south distribution, as follows: Codium fragile (Suringar) Hariot, Enteromorpha compressa (Linnaeus) Greville, Colpomenia sinuosa (Roth) Derbes et Solier, Porphyra perforata J. Agardh, Endocladia muricata (Harvey) J . Agardh, Ahnfeltia plicata (Hudson) Fries, Halosaccion glandiforme (Gmelin) Ruprecht, Pterosiphonia bipinnata (Postels et Ruprecht) Falkenberg, Rhodomela larix (Turner) C. Agardh, Spongomorpha coalita (Ruprecht) Collins, Soranthera ulvoidea

48

ROBERT F . S C A G E L

MACROCYSTIS INTEGRIFOLIA POSTELSIA PALMAEFORMIS LESSONIOPSIS LITTORALIS CYSTOSEIRA OSMUNDACEA NEREOCYSTIS LUETKEANA THALASSIOPHYLLUM CLATHRUS CHORDA FILUM EGREGIA MENZIESII PLEUROPHYCUS GARDNERI ALARIA FISTULOSA LAMINARIA SETCHELLII CYMATHERE TRIPLICATA EISENIA ARBOREA ARTHROTHAMNUS BIFIOUS DLCTYONEURUM CALIFORNICUM AGARUM CRIBROSUM SARGASSUM MUTICUM CODIUM FRAGILE ENTEROMORPHA COMPRESSA COLPOMENIA SINUOSA PORPHYRA PERFORATA ENDOCLADIA MURICATA AHNFELTIA PLICATA HALOSACCION GLANDI FORME PTEROSIPHONIA BIPINNATA RHODOMELA LARIX SPONGOMORPHA COALITA SORANTHERA ULVOIDEA CRYPTOSIPHONIA WOODII SCHIZYMENIA PACIFICA LAURENCIA SPECTABILIS F I G U R E 11. Distribution of certain species of marine algae along the west coast of North America.

Postels et Ruprecht, Cryptosiphonia woodii J. Agardh, Schizymenia pacifica Kylin, and Laurencia spectabilis Postels et Ruprecht. On examining these two groups of species another conclusion can be drawn. It is the species in the lower intertidal and subtidal regions (Group I) that are most useful as indicators; for the most part these are the forms that appear to have least flexibility, and thus tolerate a narrower range of conditions. The upper and middle intertidal forms (Group II), in general extend over a much wider range. These are the forms which, in any one locality, can and must tolerate greater extremes; and therefore one would expect an equal degree of flexibility in their horizontal distributions.

A T T A C H E D MARINE ALGAE I N T H E N O R T H E A S T PACIFIC

49

In summary, there are a number of clear-cut and conspicuous species that can be used with some confidence as indicators of oceanographic conditions; but aside from these clear-cut entities the algal ecologist must, for the present, be exceedingly cautious. There is still a great need for monographic studies and clarification of the taxonomic and genetic status of many of the entities. One has only to look at the common plastic genera Ulva, Laminaria, Fucus, and Alaria to be critically aware of the magnitude of this problem. These taxonomic problems cannot be studied exclusively in the herbarium; they can only be solved by more intensive seasonal and genetic studies of populations in the field as well as under experimental laboratory conditions. There are inherent difficulties because of the fundamental biological nature of the problems involved. The size of many of the larger algae poses special culture problems. But just as the thermometer is an essential tool of the physical oceanographer, taxonomy is the tool of the biological oceanographer. In both fields, the degree of reliability of the data obtained is a function of the accuracy of the tool. Unfortunately, the analogy breaks down at this point because of the different nature of the units used. The physicist's units of temperature (degrees) are static; the temperature may change, but the units do not. The ecologist's units are species; as the environment changes, so does the species composition of an area, in direct relation to the environmental changes. But at the same time there may be more subtle, but fundamental changes in the units themselves as a result of their genetic flexibility. Species of sexually reproducing organisms merge and diverge because of this potential genetic flexibility. If this were not so, the problem would be much simpler; the biologist's units would be static and lend themselves to the precision and prediction usually possible in the physical sciences. Thus one is faced with dynamic biological as well as physical, chemical, and geological changes in the marine environment. The benthonic plants (Scagel, 1959) undoubtedly form a significant part of the complex coastal segment of the marine environment. Many of them are potentially useful as indicators of the conditions in this unique habitat. But in order to solve the dynamic problems intrinsic to the area we must tackle them with all of the modern techniques at our disposal. Financial support from the Defence Research Board of Canada ( D R B 9520-14) which contributed to this study is gratefully acknowledged. REFERENCES

C O L L I N S , F . S. (1913). T h e marine algae of Vancouver Island. Victoria Memorial Museum Bull., no. 1, X I I I : 99-137. D O D I M E A D , A . J . (1958). Oceanographic observations in the vicinity of the Aleutian Islands. Fish. Res. Bd. Can., Pac. Oceanog. Gp., Bull. 5808. (1959). Northeast Pacific oceanographic cruise in G . N . A . V . "Oshawa," January 19 to February 16, 1959. Fish. Res. Bd. Can., Pac. Oceanog. G p . , circular 1959-6. and F O F O N O F F , N . P. (1959). Northeast Pacific oceanographic survey, August 3 to September 1, 1959. Fish. Res. Bd. Can., Pac. Oceanog. Gp., circular 1959-23.

50

ROBERT F . SCAGEL

W. H . (1862). Notice of a collection of algae made on the north-west coast of North America, chiefly at Vancouver's Island, by David Lyall, Esq., M . D . , R . N . , in the years 1859-61. J. Proc. Linn. Soc, 6: 157-76. H E R L I N V E A U X , R. H . (1959a). Coastal seaways cruise in C . N . A . V . "Oshawa" CS 59-1, March 31-April 22, 1959. Fish. Res. Bd. Can., Pac. Oceanog. Gp., circular 1959-13. (1959b). Coastal seaways cruise in C . N . A . V . "Oshawa" CS 59-2, June 8-July 1, 1959. Fish. Res. Bd. Can., Pac. Oceanog. Gp., circular 1959-18. (1959c). Coastal seaways cruise in C . N . A . V . "Oshawa" CS 59-3, November 16-December 13, 1959. Fish. Res. Bd. Can., Pac. Oceanog. Gp., circular 1959-29. N A G A L , M . (1940). Marine algae of the Kurile Islands, I. J . Fac. A g r i c , Hokkaido Imp. HARVEY,

Univ.,

46(1).

C. F. (1923). Menzies' journal of Vancouver's voyage, April to October, 1792. Archiv. Brit. Col., mem. no. 5. O K A M U R A , K . (1926). O n the distribution of marine algae in Japan. Proc. Third Pacific Sci. Congr., 1: 958-63. (1932). O n the nature of the marine algae of Japan and the origin of the Japan Sea. Bot. Mag. Tokyo, 41: 588-92. (1933). O n the algae from Alaska collected by Y . Kobayashi. Rec. Oceanog. Works Japan, 5(1) : 85-97. RAKESTRAW, N . W., et al. eds. (1955). Oceanic observations of the Pacific. The N O R P A C Atlas (Prepared by the N O R P A C Committee). Berkeley: University of California Press; Tokyo: University of Tokyo Press. S C A G E L , R. F. (1948). A n investigation on marine plants near Hardy Bay, B. C. Prov. Dept. Fish., 1. (1956). Introduction of a Japanese alga, Sargassum muticum, into the northeast Pacific. Fish. Res. Papers, Wash. Dept. Fish., 7 ( 4 ) : 1-10. • (1957). A n annotated list of the marine algae of British Columbia and northern Washington. Bull. Nat. Mus. Can., no. 152. (1959). The role of plants in relation to animals in the marine environment. In Twentieth Annual Biology Colloquium, Marine Biology, Oregon State College, 9-29. (1961). The distribution of certain benthonic algae in Queen Charlotte Strait, British Columbia, in relation to some environmental factors. Pac. Sci., 75(4) : 494-539. S E T G H E L L , W. A . (1893). O n the classification and geographical distribution of the Laminariaceae. Trans. Conn. Acad. Arts Sci., 9: 333-75. (1917). Geographical distribution of the marine algae. Science, 45: 197-204. (1932). Macrocystis and its holdfasts. Univ. Calif. Publ. Bot., 16: 445-92. (1935). Geographical elements of the marine flora of the North Pacific Ocean. Amer. Nat., 69: 560-77. and G A R D N E R , N . L . (1925). The marine algae of the Pacific Coast of North America: pt. I l l , Melanophyceae. Univ. Calif. Publ. Bot., 5 ( 3 ) : 383-898. TOKIDA, J . (1954). The marine algae of southern Saghalien. Mem. Fac. Fish., Hokkaido Imp. Univ., 2(1) : 1-264. W O M E R S L E Y , H . B. S. (1954). The species of Macrocystis with special reference to those on Southern Australian coasts. Univ. Calif. Publ. Bot., 27: 109-32. NEWCOMBE,

3

DISTRIBUTIONS OF A T L A N T I C PELAGIC ORGANISMS IN RELATION T O SURFACE W A T E R BODIES B. McK. Bary

INTRODUCTION

A n increasing body of published information suggests that the distribu­ tions of planktonic species can be interpreted in terms of their relationships to discrete bodies of water. Most often the body of water used as a reference is the water mass, which is characterized by plotting temperature against salinity in a T-S diagram. Sverdrup, Johnson, and Fleming (1942) depict the major water masses of the oceans. If a relationship is to be demonstrated between species and such water masses, organisms and hydrographic observa­ tions are required from deeper than about 100 m. Data from nearer the surface are less reliably related since shallow waters may be rapidly modified. On the other hand, the permanence of oceanic water masses below 100 m enables hydrographic and planktonic data, collected over many years and even at different times, to be brought together and relationships demon­ strated. In surface or near-surface waters, relatively rapid fluctuations in temperature, and variations in salinity, occur. Bodies of water can still be characterized by temperature and salinity using a modified T-S diagram (Miller, 1950; Rochford, 1957; Bary, 1959), constructed from observations made during a brief period of a few days or weeks. In order to demonstrate the relationships between species and the water bodies so characterized, concurrent observations of hydrography and occurrences of species are necessary. The presence and relative abundance of each species collected is entered on the T-S diagram in the intercept of the temperature and salinity obtaining at the position, and for the time, the species were collected. The technique directly relates occurrences of organisms and the conditions in which they are living (Bary, 1959). The correlation diagrams so constructed are the Temperature-SalinityPlankton (T-S-P) diagrams (Bary, 1959). Each diagram is concerned with a brief period; short-term changes resulting on shifts of "fronts" or mixing patterns, and their effects on occurrences of species, may be detected by comparing series of diagrams. Likewise gradual changes such as seasonal fluctuations in the measured properties, which have relatively small effects in any single diagram, also are apparent from a series.

FIGURE

1. Composite diagram showing either the location of, or actual routes over which, Continuous Plankton Recorder samples were collected during 1957.

FIGURE 2 . Typical T - S diagram of oceanic and coastal near-surface waters of the eastern North Atlantic and coastal areas of Britain.

54

B . M C K . BARY

Knowledge of the species' relationships to the waters in a region, and the effects that seasonal fluctuations, or variations of other physical causes exert on occurrences of the species, are necessary to understanding the basis of the distributions of planktonic organisms. This paper presents a demon­ stration of species' relationships to near-surface water bodies of the eastern North Atlantic and coastal areas of Britain, discusses the distribution of the species in terms of the relationships, and outlines a means whereby water bodies may exercise a regulatory function on species' occurrences. MATERIALS AND M E T H O D S

The present discussion is a summary of the relevant results of an investigation of twelve months of observations, from near-surface oceanic and coastal waters about Britain, made during 1957. A full account is to be published elsewhere (Bary, in press, Parts I to I V ) . Plankton was collected by the Continuous Plankton Recorder (Hardy, 1939) from a depth of approximately 10 m, along more or less regularly run routes, during routine plankton surveys of the Oceanographic Labora­ tory of the Scottish Marine Biological Association. Figure 1 is a composite diagram showing most of the routes along which samples applicable to the present study were collected (for a full record of all routes run, month by month, see John and Brown, 1958). Temperatures and salinities were collected concurrently with the towing of the Recorder, from a depth approximating 5 m. Figure 2 illustrates the typical T-S diagram for the area (discussed later). The technique of analysing the plankton collected on the band of silk of the recorder is detailed by Hardy (1939), Rae and Fraser (1941), and Colebrook (1960). The method of collecting the samples and the subsequent analysis procedure "smooth" the data (Rae and Fraser, 1941). The result is that only major faunal changes are detected. T-S and T-S-P diagrams were prepared for each month of 1957. It is not feasible to present all these data. In order that a reasonably repre­ sentative picture is provided, winter and summer conditions are illustrated and discussed (Figs. 6a to 11 a). In the geographic charts (Figs. 6b to 116) the areas occupied by the water bodies characterized in the T-S diagrams are shown. Occurrences of species are included as appropriate. This part of the procedure requires that each plotted point in T-S and T-S-P diagrams is identified with the corresponding position on the chart. The "water boundaries" shown between water bodies are the geographic representation of narrow zones between the water bodies in the T-S diagram. The zones have been arbitrarily determined. One occurs at each of the two angles in the oceanic water envelope (Fig. 2), at the position where the water body of intermediate properties meets the warm-water and cold-water bodies. There is another such boundary zone between oceanic waters and mixed oceanic-coastal

F I G U R E 3. Winter and summer T - S diagrams for surface waters of the eastern North Atlantic, compared with diagrams for waters up to 500 m deep drawn after Helland-Hansen and Nansen (1926) and Sverdrup et al. (1942).

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waters. In the charts the boundaries as drawn are neither isohalines nor isotherms; they are "T-S isolines" and their "T-S values" fluctuate with seasonal warming and cooling of the waters. The T-S isolines on the charts enclose the areas occupied by the water bodies. T H E T-S D I A G R A M S A N D T H E W A T E R BODIES

There are three parts to the oceanic water envelope (Fig. 2). Each part is identified with a water body. The warm water is the Southern water body and the cold water the Northern water body, so called from their geographic locations (Fig. 1). Between them is a water body of inter­ mediate properties, named Transitional water. Coastal water is the diluted water lying to the left of the envelope of oceanic waters. In Figure 3, the T-S diagrams of the surface waters can be compared with diagrams for North Atlantic Central Water of the upper 500 m, drawn after HellandHansen and Nansen (1926) and Sverdrup et al. (1942). The effect of seasonal warming at the surface in the oceanic waters is shown in Figure 3 where winter and summer T-S diagrams are illustrated together. There was a considerable summer increase in temperatures of all water bodies, but it can be shown from mean values that no significant change of salinity occurred in any of the water bodies. The T-S diagram retained its form at the higher and lower temperatures. Coastal waters are illustrated in Figure 2, but not in Figure 3. For the most part the annual range of temperature in coastal water was greater than in the oceanic waters; see Figures 6a to 11 A . The diagrams illustrate that the Transitional water is intermediate in properties between Northern and Southern waters; it is considered a mixture of these. Coastal waters are also composed of a typical or indigenous coastal water and a mixed oceanic-coastal water. It is generally recognized for European coastal areas (Harvey, 1925; Carruthers, 1927; Russell, 1935; Tait 1937) that salinities greater than 35%c indicate a mixture of oceanic with coastal waters; water at the lesser salinities is mostly "indi­ genous coastal water" (Fraser, 1952). Mixing was from oceanic towards coastal water, for the depth sampled, which agrees with evidence from drift bottles (Tulloch and Tait, 1959) and drift envelopes (Lawford, 1956). In Figure 1 the general areas occupied by the oceanic waters are indicated. Figures 6b to lib illustrate these areas in more detail, during winter and summer. Transitional water occurred west and north of Eire, with Northern and Southern waters lying respectively to north and south of it. In winter, Southern water penetrated northward along the Irish coast, but in summer, it retreated southward and was replaced by Transitional water. The move­ ments are indicated by the positions of the boundaries. These indicate the inner limits of unmixed Northern and Southern waters relative to Transi­ tional water, and the shoreward limit of oceanic waters unmixed with

ATLANTIC PELAGIC ORGANISM A N D W A T E R BODIES

57

coastal water. The boundary is shown as a more or less narrow zone which is regarded as representing a "zone of immediate mixing" (Bary, in press Part 1). It may be noted that oceanic waters commence to mix with coastal water in a position fairly closely approximating the position of the edge of the continental shelf. These boundary zones are important when considering the distributions of the zooplankton. T H E T-S-P D I A G R A M S A N D DISTRIBUTIONS OF SPECIES

The T-S-P diagrams are a means of demonstrating whether occurrences of species of zooplankton, as collected during a survey, are in fact related in some way to the water bodies as characterized by the T-S diagrams. In other words, if the occurrence of a species in the sea is the result of some sort of relationship between itself and the water body, the T-S-P diagram should illustrate this relationship. The present section reports on some of the results of entering seventeen species of zooplankton (one gastropod, three chaetognaths, and thirteen copepods) on T-S diagrams (Bary, in press, Parts II and III). The occurrences of each species show a characteristic relationship to the water bodies and the distribution of the species can be interpreted in terms of these relationships. Species have been grouped together according to similarities in their TABLE I S E V E N T E E N SPECIES O F ZOOPLANKTON A N D THEIR FROM T H ET-S-P

GROUPINGS

DIAGRAMS

Grouping and species Warm (Southern) group Centropages bradyi Wheeler Euchaeta tonsa Giesebrecht Euchaeta acuta Giesebrecht Nannocalanus minor Claus

Warm-Transitional group Pleuromamma robusta (Dahl) Pleuromamma gracilis (Claus) Sagitta serratodentata Krohn

Cold (Northern)-Transitional group Pareuchaeta norvegica Boeck

Warm-Transitional-Neritic group Euchaeta hebes Giesebrecht Candacia armata Boeck Centropages typicus Kroyer Spiratella retroversa Fleming

General-Neritic group Metridia lucens Boeck Acartia clausi Giesebrecht

Coastal (Neritic) group Temora longicornis 0 . F r . Muller Sagitta elegans Verrill Sagitta setosa J . Muller

Animal group Copepod Copepod Copepod Copepod Copepod Copepod Chaetognath Copepod Copepod Copepod Copepod Mollusc Copepod Copepod Copepod Chaetognath Chaetognath

FIGURE

4. Diagrammatic presentation of T - S - P relationships of three oceanic groups of species: for list of species, see Table I.

FIGURE

5. Diagrammatic presentation of T - S - P relationships of two oceanic-neritic groups of species and the Coastal (Neritic) species: for lists of species, see Table I.

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occurrences in the T-S-P diagrams. Six groups have been determined (Table I and Figs. 4 and 5). The Warm (Southern) group was restricted to the Southern water body; the Warm-Transitional group probably dis­ persed from Southern into Transitional water; the Cold (Northern) group dispersed from Northern into Transitional water. These three groups were almost entirely oceanic in their occurrences. One group, the Coastal (Neritic) group was collected almost only from coastal or oceanic-coastal water. The remaining two groups are considered to disperse from oceanic into oceanic-coastal and on occasion into coastal waters; they differ chiefly in degree and often are referred to collectively as the "oceanic-neritic" groups. In Figures 6a to 11a detailed relationships are demonstrated in T-S-P diagrams for winter and summer conditions. The species' distributions and the areas occupied by the water bodies are shown in Figures 6 b to lib. Figure 6a shows the relationships to the water bodies of the Warm (Southern) group of four species (see Table I ) . It is apparent that the species are closely associated with the Southern water body at both its winter and summer temperatures. Specimens were collected from Transi­ tional water but rarely, and only from the warmest of this water, that is, from near the Southern water body in the diagrams. None of these species was present during 1957 in oceanic-coastal or coastal waters. In Figure 64> it is seen that the species occurred in the south of the area surveyed. They are restricted in their distribution to Southern water by the boundaries between this water and Transitional and oceanic-coastal waters. Such restriction to the Southern water body probably accounts for the southern distributions accorded these species by previous investigators (Ostenfeld, 1931; Russell, 1935; Colebrook, John, and Brown, 1961). Figure 7a illustrates the relationships of two of three Warm-Transitional species (Table I ) . Sagitta serratodentata was not represented in the parti­ cular months chosen in Figure 7. As a whole, the group occurred, winter and summer, in Southern and Transitional water bodies. Occasionally one species from the group was present in Northern and Coastal waters, but apart from these, the species did not regularly occur across the boundaries between Transitional and Northern waters, or between oceanic and oceaniccoastal waters. They are warm-water, oceanic species; and to judge from higher numbers and more numerous samples present in Southern water, they probably originated in this water and dispersed into Transitional water. The two species illustrated, Pleuromamma robusta and P. gracilis, showed differing relationships to the waters. Pleuromamma robusta extended throughout Southern and Transitional waters and into Northern water at times; P. gracilis extended into Transitional water only up to about the "50% level of mixing" between Southern and Northern waters. Sagitta serratodentata, over the twelve months, appeared to parallel the occurrences of P. gracilis. It may be noted that the different relationships of P. robusta and P. gracilis are evident in winter and in summer. Figure lb demonstrates that, geographically, the species extend north­ wards from Southern water into the area occupied by Transitional water.

FIGURE 6. T-S-P diagrams (a] and geographic occurrences ( b ) , of the Warm (Southern) group, March and August, 1957.

FIGURE 7. T-S-P diagrams (a) and geographic occurrences ( & ) , of the Warm-Transitional group, February and August, 1957.

FIGURE 8. T-S-P diagrams (a) and geographic occurrences ( b ) , of Pareuchaeta norvegica (Cold (Northern) -Transitional species) for May and September, 1957.

FIOURE 9. T-S-P diagrams ( « ) . and geographic occurrences ( b ) , of the Coastal (Ncritic) species, April and August, 1957.

A T L A N T I C PELAGIC ORGANISM AND W A T E R BODIES

61

They did not occur shorewards of the boundary between oceanic and oceanic-coastal water. The few occurrences of P. robusta northwards of the boundary between Transitional and Northern water were in close proximity to this boundary. The distributions of the species as recorded in the litera­ ture (Ostenfeld, 1931; Wilson, 1932; Farran, 1948; Golebrook, John, and Brown, 1961) and as shown in Fig. lb, agree; in addition, P. robusta has been recorded, usually in low numbers, from the Norwegian Sea (Wiborg, 1955; Hansen, 1960). The distributions appear to result from the fact that the species are restricted in their occurrences (on the whole) to the Southern and Transitional water bodies. The relationship of P. robusta suggests it could extend into more northern areas than illustrated in Figure lb. To do so, however, it would seem that Transitional water would have to be present. O n the other hand, P. gracilis probably could neither extend as far north as P. robusta nor into an area in which Southern or Transitional waters were in low proportion. Figure 8a illustrates the occurrences of one species of copepod, Pareuchaeta norvegica. Its relationship is to the Northern and Transitional water bodies. The occurrences of this species are complicated by seasonal vertical migration (Wiborg, 1955; Hansen 1960). In the present study its absence from the surface during winter and early spring may have been due to this. It first appeared in numbers in Northern water; subsequently it also occur­ red in Transitional water. Again, it was restricted to the oceanic waters. Pareuchaeta norvegica has been recorded previously as an arctic and temperate species (Sars, 1903; Ostenfeld, 1931; Golebrook, et al, 1961). Its distribution in 1957 (Fig. 8b) accords with this. Its occurrences in Northern and Transitional waters and its absence from oceanic-coastal and coastal waters can be interpreted as due to the relationship to the northern oceanic waters demonstrated in the T-S-P diagrams. The species of the above three groups are restricted to oceanic waters. In contrast, a fourth group, the Coastal (Neritic) group, occurs in coastal and not in oceanic waters (Fig. 9a). There is differentiation in relationships of the three species in the coastal group. Sagitta setosa occurred in water of salinities up to approximately 35%o; S. elegans was dominant at salinities above 35%o, that is, in oceanic-coastal mixed waters. Temora longicornis, however, was present throughout coastal and oceanic-coastal waters, al­ though this is not apparent in Fig. 9a. Again, the relationships were main­ tained during winter and summer. In Fig. 9b, the species' distributions reflect these relationships. Temora longicornis was widespread; S. elegans occurred where mixed oceanic and coastal waters could be expected, in and near the mouth of the English Channel, whereas S. setosa was present within more typically coastal waters such as in the English Channel. It was rare for T. longicornis or S. elegans to occur beyond the boundary between oceanic-coastal and oceanic water. These distributions agree with those in the literature (Meek, 1928; Osten­ feld, 1931; Russell, 1935; Rae and Fraser, 1941; Fraser, 1952; Colebrook, John, and Brown, 1961). There seems little doubt that the species are

62

B. MCK. BARY

distributed in the same way as the waters with which they are associated in the T-S-P diagram. The two remaining groups occurred in both oceanic and coastal waters. They are the Warm-Transitional-Neritic and the General-Neritic groups; species in the latter group differ from the former in being usually more numerous and occurring over a wider range of conditions. These groups are difficult to present since interpretation of their occurrences has depended more on trends shown from the year's T-S-P diagrams and charts, than on information demonstrated from the winter-summer relationships as shown in Figures 10a and 11a. It is apparent that the relationships of the species of both groups to the water bodies are broad. The Warm-Transitional-Neritic species (Table I) are considered as pro­ bably dispersing from Southern water into oceanic-coastal and Transi­ tional waters. Geographically, the species are widespread, (Fig. 10b) as their relationships in the T-S-P diagrams would suggest. The species crossed the boundary zones, not only between oceanic water bodies, but also be­ tween oceanic and oceanic-coastal waters and even into coastal water. Although considered to originate in warmer oceanic water (in which they might be sparse) and to disperse shorewards, most species of the group occurred in higher numbers in the mixed oceanic-coastal than in the oceanic water. This feature appears to have confused the distributional picture recorded in the literature, but several investigators have registered the species as oceanic ones, which extend into coastal areas (Gough, 1905; Ostenfeld, 1931; Wilson, 1932). The General-Neritic group (Fig. 11 a) occurred frequently and some­ times in high numbers. In oceanic waters Metridia lucens appeared to originate in Southern water and to extend throughout Transitional and into Northern water. It also was present in oceanic-coastal or coastal waters. The other species, Acartia clausi, appeared to associate principally with cool Transitional water; it was able to occur in warmer Northern water and also in oceanic-coastal and coastal waters. The present study suggests these species were oceanic in origin, dispersing thence into inshore waters. The species have broad relationships and these are apparent in their widespread geographic occurrences (Fig. lib). Differences between the species in their distributions, such as M. lucens being commoner in the south, but occurring as far north as samples were collected, and A. clausi extending from the northern Transitional water southwards into warmer water, are clearly an expression of the different relationships between the species and the oceanic waters. The species cross some or all the boundaries in oceanic waters, and they also cross into oceanic-coastal water and coastal waters. Reasons for the widespread distributions in the north Atlantic area accorded these species in the literature (Gough, 1905; Farran, 1910, 1911; Ostenfeld, 1931; Rae and Rees, 1947; Colebrook, John, and Brown, 1961) and for the confusion as to whether they are oceanic, neritic, or both, can be found in these broad relationships to the waters and ability to cross freely from one water body to another. These points apply especially to M. lucens.

I ; it;URK 10. T-S-P diagrams (fi}. and -geographic occurrences ( 6 ) . of tht: Wann-Tran,sition;d-\eritic group, March and September, 1957.

FIGURK 11. T-S-P diagrams ( a ) . and geographic occurrences ( f e ) , of the Gcncral-Neritic group). March and August, 1957.

F I G U R E 12. Diagram illustrating courses of mixing of the "unique properties" of Northern and Southern waters (a), and of oceanic and coastal waters (b) : and see text.

64

B. M C K . BARY DISCUSSION

The brief analysis of the several groups above show that species can be related in the T-S-P diagram to near-surface water bodies that have been characterized in the T-S diagram. These demonstrated relationships are then "turned about" as it were, and used to interpret the occurrences and distributions of the species. In other words, occurrences of species in field collections are shown to be regulated or controlled, and this information is then used to explain features of the geographic distribution. The species were associated with particular environmental conditions in the T-S-P diagrams, winter or summer; geographically they were dis­ tributed according as these particular conditions were distributed. The factors regulating occurrences must be other than temperature and salinity themselves since species remained associated with the particular conditions throughout the seasonal fluctuations of temperature and variations of sali­ nity. However, such factors must need be an integral part of the water body as characterized by temperature and salinity. Another part of the same problem concerns the different reactions of species at the boundary zones between water bodies. Some species were able to cross one of more boun­ daries, but other species of similar origin, and presumably with similar (oceanographic) opportunities to cross, did not do so. These features raise the problem that if temperature and salinity are not effective in determining the species' distributions in the area surveyed, what is the effective factor? There would appear to be two aspects to the question: firstly, an oceano­ graphic one which includes the nature of the factors regulating the species' occurrences; and secondly, the species itself and the manner in which the "regulatory factor" operates. These two features are obviously interrelated; they require assumptions to be made to provide a basis by which they might be explained. Let it be assumed, firstly, that each of the three "primary" water bodies, Southern, Northern, and coastal, contain factors that are in some sense unique to it: the "unique properties." Where there is mixing between water bodies there would be mixing of the unique properties and this would commence at the boundary zones separating the Northern, Southern, and coastal water bodies from the mixed Transitional and oceanic-coastal waters. In Figure 12 the course of mixing of the unique properties between the oceanic waters (12a) and between oceanic and coastal waters (126) is diagrammatically illustrated. A second assumption requires that each species reacts to the unique properties in an individual manner. Thus, there is an oceanographic factor—the unique properties—and a biological factor— the reaction of species to these properties. It is suggested that this is the basis of the relationships demonstrated in the T-S-P diagrams, and hence, the basis of the distribution of species. The nature of a species reaction to the unique properties is regarded as being dependent on its tolerance towards the properties. The effect of the

ATLANTIC PELAGIC ORGANISM A N D W A T E R BODIES

65

species tolerance would become evident at some "point" along gradients of concentrations of the properties, usually in mixed waters. This "point" may be, and frequently is, at the boundary zone between the primary water body and the mixed water; or it may be at some other concentration, within the body of mixing waters. In view of the fact that relationships to the water bodies are maintained during winter and summer it must be presumed that over the range of temperature and salinity experienced, the reactions of the species are not appreciably affected. In this connection it is pertinent to note that the changes of temperature are gradual ones—the species are not confronted with large or sudden gradients within a water body. In the context of the above comments, species tolerant only of the property in Southern water (property " A " in Fig. 12a) would occur only in Southern water; these are the Warm (Southern) species. Species originat­ ing in Southern water, but tolerant towards some dilution in Transitional (mixed) water of the property of Northern water (property " B " ) , would occur in the mixture according to the degree of their tolerance. These are the Warm-Transitional species. Species which dispersed from oceanic into oceanic-coastal or coastal water would be able to do so because of their tolerance towards the unique property of coastal water (property " C " in Fig. 12b); those species which were confined to oceanic water would be intolerant of " C . " Species, therefore, might be intolerant of properties from other water bodies, such as, for instance, the Warm (Southern) and the Coastal (Neritic) species (Figs. 4a; 5c), and not be able to cross the boundary between, respectively, the Southern and the other waters, or coastal and oceanic waters; other species may tolerate some admixture of the properties of the two oceanic waters e.g., the Warm-Transitional or Cold-Transitional species (Fig. 4, b, c), and be able to cross from Southern or Northern into Transi­ tional water; still others may tolerate mixed oceanic and coastal properties (the oceanic-neritic groups; Fig. 5, a, b) and therefore be able to cross boundary zones between oceanic water bodies and between oceanic and coastal waters. In the above examples, distributional discontinuities would be manifest at the boundary zones. However, Pleuromamma gracilis (Fig. 7a) is a species which crosses the boundary zone between Southern and Transi­ tional water, but its tolerance apparently limits it to about a "50% mixture" of Southern and Northern waters and the unique properties of these waters. Its occurrences, geographically, comply with this limitation and it is found much less further northward in Transitional water than P. robusta (which is tolerant of both properties " A " and " B " in Transitional water). Thus a distributional discontinuity may not always be associated with a boundary zone, but, as in this instance, occur at some point within a mixture of waters. In the present study the occurrences of species from field collections are

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shown to be related, by means of one pair of oceanographic properties (temperature and salinity), to a water body, or its influence in a mixture. The relationship does not appear to depend on the temperature or salinity and therefore it has been postulated that other properties are present which determine the relationship. In turn the relationship probably is a reflection of the reactions of the species to the properties, the reaction depending on tolerances of species towards the properties. The situation that develops is one in which species occur as a regular feature only where conditions are favourable, that is, in conditions against which the species did not react adversely. Thus species will be distributed according as the waters with which they are associated in the T-S-P diagram. Species may be carried by water movements into another area, but they will continue to be present only so long as the same water body is present; should this water mix with another, the species may or may not remain, depending on their reactions to the properties in the mixture. Again, species which migrate vertically would appear in a water body (for example, at the surface) only if the conditions were tolerable. Such conjectures are included in the concept of indicator species. It is important that they be stated in the present context since the T-S-P tech­ nique enables the relationships on which they are based to be demonstrated and their effectiveness in regulating the occurrences and distributions of species to be evaluated. From the present study, it would appear that the relationships of the species to the water bodies in an area are more important in the study of distribution than the geographic location of a sample. ACKNOWLEDGMENTS

The writer is grateful to M r . R. S. Glover, Officer-in-Charge, and to members of the staff of the Oceanographic Laboratory, Edinburgh, for mak­ ing available, and assisting with, data. He is indebted also to the Fisheries Laboratory, Lowestoft, of the Ministry of Agriculture, Fisheries and Food, U . K . , and to the Netherlands Meteorological Office for providing tem­ perature and salinity data, and to the officers and men of the weather ships and those commercial vessels of Britain, the Netherlands, Norway, and France who made the hydrographic observations and assisted with towing the continuous plankton recorder. REFERENCES

B A R Y , B. M . (1959). Species of zooplankton as a means of identifying different surface waters and demonstrating their movements and mixing. Pac. Sci., 13(1): 14-34. (In Press) Temperature, salinity and plankton in the eastern North Atlantic and coastal waters of Britain, 1957. Part I: The characterization and distribution of surface waters; Part II: The relationships between species and water bodies; Part III: The distribution of zooplankton in relation to water bodies; Part I V : Some aspects of relationships of species to water bodies. J . Fish. Res. Bd. Can. C A R R U T H E R S , J . N . (1927). Investigations upon the water movements in the English Channel, summer, 1924. J . Mar. Biol. Assoc., 74(3): 635-722.

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C O L E B R O O K , J . M . (1960). Continuous plankton records: methods of analysis, 1950-59. Bull. Mar. Ecol., 5(41): 51-64. , JOHN,

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contributions towards a plankton atlas of the north-eastern Atlantic and the North Sea. Part I I : Copepoda. Bull. M a r . Ecol., 5(42) : 90-7. F A R R A N , C . P. (1910). Resume des observations des mers explorees par le conseil pendant les annees 1902-1908. Copepoda (in part). Bull, trim., Cons. perm. int. Explor. Mer, 1910: 60-79. (1911). Resume des observations des mers explorees par le conseil pendant les annees 1902-1908. Copepoda (in part). Bull, trim., Cons. perm. int. Explor. Mer, 1911: 81-105. (1948). Copepoda. Cons. perm. int. Explor. Mer, Fiches d'Ident. Zooplankton. Copenhagen: Andr. Fr. Hest. F R A S E R , J . H . (1952). T h e Chaetognatha and other zooplankton of the Scottish area and their value as biological indicators of hydrographical conditions. Scottish Home Dept., Mar. Res., 1952, no. 2: 1-52. G O U G H , L . N . (1905). Report on the plankton in the English Channel in 1903. Mar. Biol. Assoc., Internat. Fish. Invest. First Rep. (Southern Area), 1902-1903: 325-77. H A N S E N , V . K . (1960). Investigations on the quantitative and qualitative distribution of zooplankton in the southern part of the Norwegian Sea. Medd. Komm. Havundersog., K b h . , Ny. Ser., 2(23): 1-53. H A R D Y , A . C . (1939). Ecological investigations with the continuous plankton recorder: object, plan and methods. Hull Bull. Mar. Ecol., 7 ( 1 ) : 1-57. H A R V E Y , H . W . (1925). Hydrography of the English Channel. Cons. perm. int. Explor. Mer, Rapp. Proc.-Verb., 37: 58-89. H E L L A N D - H A N S E N , B. and N A N S E N , F . (1926). The eastern North Atlantic. Geofysiske Publikasjoner, 4(2): 1-75. J O H N , D O R A E . and B R O W N , W . W . (1958). Continuous plankton records: list of records, 1955-57. Bull. M a r . Ecol., 5 ( 4 ) : 44-50. L A W F O R D , A . L . (1956). The effect of wind upon the surface drift in the northeastern Atlantic and the North Sea. Weather, 11(5): 155-61. M E E K , A . (1928). O n Sagitta elegans and Sagitta setosa from the Northumbrian plank­ ton, with a note on a trematode parasite. Proc. Zool. Soc, London, 1928: 743-76. M I L L E R , A . R . (1950). A study of mixing processes over the edge of the continental shelf. J . Mar. Res., 9 ( 2 ) : 145 60. O S T E N F E L D , C . H . (1931). Resume des observations sur le plancton des mers explorees par le Conseil pendant les annees 1902—1908. Bull, trim., Cons. perm. int. Explor. Mer, 1931, pt. 4: 601-72. R A E , K . M . and F R A S E R , J . H . (1941). Continuous plankton records: the Copepoda of the southern North Sea, 1932-37. Hull Bull. M a r . Ecol., 7(4) : 171-238. and R E E S , C . B. (1947). Continuous plankton records: The Copepoda of the southern North Sea, 1938-1939. Hull Bull. Mar. Ecol., 2(11), 95-132. R O G H F O R D , D . J . (1957). T h e identification and nomenclature of the surface water masses in the Tasman Sea (data to the end of 1954). Austral. J . Mar. Freshw. Res., 5(4): 369-413. R U S S E L L , F. S. (1935). O n the value of certain plankton animals as indicators of water movements in the English Channel and North Sea. J . Mar. Biol. Assoc., 20(2): 309-32. SARS, G . O . (1903). Copepoda: Calanoida. In Crustacea of Norway, Bergen, 4: 1-167. r

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R . H . (1942). T h e oceans, their

physics, chemistry and general biology. New York: Prentice Hall. T A I T , J . B. (1937). T h e surface water drift in the northern and middle areas of the North Sea and in the Faroe-Shetland Channel. Pt. 11, sec. 3, Fisheries, Scotland, Sci. Invest., no. 1. T U L L O C H , D . S. and T A I T , J . B. (1959). Hydrography in the north-western approaches to the British Isles. Scottish Home Dept., Mar. Res., 1959, 7: 1-32. WIBORG, K . F . (1955). Zooplankton in relation to hydrography in the Norwegian Sea. Rep. Norweg. Fish. Mar. Invest., 77(4): 1-66. W I L S O N , C . B. (1932). Copepoda of the Woods Hole region. U . S . Nat. Mus., Bull. 755: 1-623.

COPEPODS OF T H E GENUS CALAMUS AS INDICATORS OF EASTERN C A N A D I A N WATERS E. H. Grainger

ABSTRACT The distributions of three species of the copepod genus Calanus occurring in arctic and subarctic waters of eastern North America, C. finmarchicus, C. glacialis, and C. hyperboreus, are considered in all copepodite stages. C. finmarchicus is shown to be an Atlantic boreal species, C. glacialis and C. hyperboreus arctic species in all stages. Arctic water is indicated by the presence of C. glacialis without C. finmarchicus, boreal water by C. finmarchicus without C. glacialis, and subarctic (mixed arctic and Atlantic) water by the presence of both species. Variations in breeding times and in development rates of populations may be used to indicate water movements.

is CONCERNED with three species of the copepod genus Calanus, C. finmarchicus (Gunnerus), C. glacialis Jaschnov, and C. hyperboreus Kr0yer, and in particular with features of their distribution in northeast North America. The material available for the study was collected mainly by the Atlantic Oceanographic Group and the Department of Mines and Technical Surveys during oceanographic cruises between 1954 and 1961 in the vessels Labrador, Theta, Sackville, and Vema. Use was made also of plankton collections taken on M . V . Calanus of the Fisheries Research Board of Canada. To all who participated in these cruises, and especially to Dr. N . J. Campbell, M r . A . E . Collin, M r . F. G . Barber, and M r . A . Holler, the writer extends his thanks. Plankton collections were made vertically between a maximum of 150 metres and the surface. Frequently two hauls were made at single stations, the deep one from 100 or 150 metres to the surface and the shallow one from between 25 and 50 metres and the surface. Nets of no. 5 mesh were used in the first year and of no. 6 mesh in all subsequent years. As a result of relatively shallow sampling only the upper layers of Baffin Bay, which is as deep as 2,000 metres in its central part, Davis Strait, about 600 metres deep, and the north Labrador Sea, more than 2,000 metres deep, can be considered here. Hudson Strait, more than 300 metres in depth in only a small proportion of its total area, was more completely sampled, and Hudson Bay, very little of which is deeper than 200 metres, was generally sampled from near the bottom to the surface. The deepest parts of Foxe Channel, and of the region of confluence of Foxe Channel, Hudson Strait, and THIS PAPER

F I G U R E 1. North America and surrounding waters. Arrows show general water movements.

70

E . H . GRAINGER

Hudson Bay, respectively exceeding 300 and 400 metres, were not sampled. Roes Welcome Sound, on the west side of Southampton Island, was sampled from bottom to surface. It is emphasized therefore that it is the plankton of the upper waters only which is discussed here and that total vertical coverage is considered in only a few areas. Individual collections used con­ tained from thirty to several hundred specimens. Measurements were made on all specimens from the smaller samples, from subsamples of up to three hundred from the larger samples. HYDROGRAPHY

Figure 1 shows general water movements in the seas surrounding northern North America, from data of Dunbar (1951), Hachey, Herman, and Bailey (1954), Campbell and Collin (1956), Bailey (1957), Dunbar (1958), U.S. Navy Hydrographic Office (1958), and Campbell (1958, 1959). Arctic surface water is shown to flow from the Arctic Ocean in a generally southeasterly direction among the islands of the Canadian arctic archipelago and between Canada and Greenland. Northward-moving mixed water is present along most of the coast of west Greenland, and elements of it can be traced to northernmost Baffin Bay. A flow, consisting in part of this same water, enters Hudson Strait from the east and, it is suggested, reaches at least to southern Foxe Basin and northeast Hudson Bay. Mixed water moves southward along the Labrador coast and rounds southeast Newfoundland. Atlantic water, without discernible arctic elements, exists between southwest Greenland and Labrador-Newfoundland and to the south of the cold water off southern Newfoundland and Nova Scotia. T H E SPECIES O F C A L A N U S

Each of the three species of Calanus, C. finmarchicus, C. glacialis, and C. hyperboreus, inhabiting the waters between the Arctic Ocean and south­ eastern Canada can be shown to occupy a specific zoogeographical area and to occur in a very definite relationship to physically identifiable water masses. Calanus finmarchicus (Fig. 2) is an Atlantic species found in our region only in Baffin Bay, Davis Strait, Hudson Strait, south Foxe Basin, the northeasternmost corner of Hudson Bay, and in subarctic and boreal waters off southeast Canada and the eastern United States. Its northern limit appears to be controlled by the northernmost extent of Atlantic water, and it evidently is unable to exist under pure arctic conditions. It is therefore classed as a boreal Atlantic species, and in the northern part of its range, in company with C. glacialis, as an indicator of subarctic, that is of mixed arctic and Atlantic, water. C. finmarchicus, once considered as being almost world-wide in distribution, has comparatively recently been allotted a sub­ stantially reduced range following reappraisal of members of the genus

FIGURE

2. The North American distribution of Calanus finmarchicus.

FIGURE

3. The North American distribution of Calanus glacialis.

F I G U R E 4. T h e North American distribution of Calanus hyperboreus.

74

E . H . GRAINGER

Calanus. North Pacific representatives previously designated as C. fin­ marchicus (and as C. helgolandicus) were referred to C. pacificus by Brodsky (1948, 1959). Jaschnov (1955) separated the so-called "large form" of C. finmarchicus, found in waters north of the Atlantic, from the "small form" and called the former C. glacialis. He (Jaschnov, 1958) showed C. glacialis rather than C. finmarchicus occurring over all of the Arctic Ocean and extending to the Sea of Okhotsk. Grainger (1961) traced C. glacialis, with C. finmarchicus excluded, through the Canadian arctic archipelago, and recorded C. glacialis south to the Gulf of Maine, and in the same year Jaschnov (1961) elaborated on the occurrence of the species in the North Atlantic. C. finmarchicus was thus reduced to a boreal species of the Atlantic Ocean only. Calanus glacialis (Fig. 3) is an arctic species, found over most of the Arctic Ocean and adjacent waters, and southward along the eastern coast of North America to about 40° N . Everywhere it is seen to occur either in pure arctic or mixed (subarctic) waters and it appears to be excluded from unmixed Atlantic water. It is therefore classed as an indicator species of arctic water, and in the absence of C. finmarchicus of unmixed arctic water. Calanus hyperboreus (Fig. 4), primarily an arctic species, is distributed in much the same way as C. glacialis. It is a surface-water species of the Arctic Ocean and occurs besides throughout archipelago waters, Baffin Bay, Davis Strait, the north and west Labrador Sea, and off southeast Canada and the northeast United States. Perhaps the most abundant Calanus species in the Arctic Ocean and throughout much of the archipelago, it is by far the least abundant of the three species considered here in waters south of Baffin Bay and in Foxe Basin, Hudson Bay, and Hudson Strait. In these areas it appears generally to exist in deeper waters than either C. finmarchicus or C. glacialis. COMPARISON OF C. G L A C I A L I S A N D C. F I N M A R C H I C U S

Jaschnov's (1955) description of C. glacialis distinguished it from C. finmarchicus primarily on the basis of fifth leg structure of adult females and stage V copepodites. Other anatomical features, also stressing stages V and V I , were discussed by Jaschnov (1957). Length differences were also shown, and these too were limited to stages V and V I . Anatomical differences between the two species were considered by Grainger (1961) who was concerned with stage V I only. Consequently there has been no detailed attention yet paid to the younger copepodite stages. Part of the purpose of the present study is to consider the two species in all copepodite stages from the point of view of distribution in space and time. In the course of this investigation cephalothoracic length measurements were made on several thousand Calanus copepodites of stages I to V I . Clear bimodality within all stages was evident at many stations, and especially at

GOPEPODS AS INDICATORS O F E A S T E R N CANADIAN WATERS T A B L E

75

I

C. glacialis C. finmarchicus, G I V E N I N M E A S U R I N G U N I T S (1 U N I T = 0.063 M M ) , F O R T H E A R E A F R O M

CEPHALOTHORACIC LENGTH RANGES OF

A ND

NEWFOUNDLAND TO NORTH BAFFIN BAY AND W E S T TO H U D S O N B A Y A N D F O X E

Cephalothoracic length (1 unit = 0.063 mm) C. finmarchicus C. glacialis

Stage I II III IV V VI

CHANNEL

12-17 16-24 22-34 30-45 42-63 51-70

9-14 12-19 17-27 21-38 31-52 37-54

9

those where the presence of both species was demonstrated by morphological features in stages V and V I . Table I shows length ranges of all stages throughout the entire region considered here and over the time period of June until October. It is obvious from Table I that there is considerable overlapping in length between the two species in all stages, and therefore that such data, covering a wide range of space and time, will not suffice to allow specific separation of many of the individuals in each stage. It is well known, however, that Calanus undergoes considerable seasonal length variation at any one loca­ tion (Adler and Jespersen, 1920; Marshall, Nichols and Orr, 1934; Clarke and Zinn, 1937; Ussing, 1938; etc.). It has been suggested too that Calanus varies in size geographically, although most works on the subject have con­ sidered the small C. finmarchicus and the large C. glacialis as a single species. In fact, C. finmarchicus does vary in size over its geographical range, T A B L E

II

CEPHALOTHORACIC LENGTH RANGES OF G I V E N IN M E A S U R I N G UNITS

(1

C. glacialis A N D C. finmarchicus, U N I T = 0.063 M M ) , F O R

SELECTED LOCALITIES AND DATES

Stage VI

9

IV V I II III IV V VI III IV V

III IV V

Area

Date

Woods Hole,* Gulf of Maine S. E.Nfld.

early/1

N . Labrador Sea

mid/8 mid/6 11

M

11

11 11

9

11

E . Davis Str.

M

late/7 11

11

S.E. Baffin Bay

11

late/9

11 a

*from Clarke and Zinn (1937)

11

C. finmarchicus

C. glacialis

c 35-c 46 25-31 32-43 9-13 14-18 21-27 31-37 41-52 40-54 17-23 25-30 36-42 (21) 24-30 33-40

52-57 33-42 45-52 13-17 19-23 27-34 37-43 52-59 (55) 24-27 35-41 44-49 23-29 32-40 43-62

76

E . H . GRAINGER

as shown by Grainger (1961) for adults and in this paper, below, for younger stages as well. Examination of length data from single collections containing both species or from separate stations closely placed in both space and time shows an almost total absence of overlapping size. The examples given in Table II demonstrate this. From the large series of measurements made on all stages of both C. finmarchicus and C. glacialis it is concluded that with knowledge of size variation in both time and place nearly all individuals can be assigned with reasonable certainty to the correct species on the basis of cephalothoracic length alone. This comparison has been extended to the third species, C. hyperboreus below, and it is similarly concluded that stages I and II of C. hyperboreus can almost always be separated from the same stages of C. glacialis, between which there are no demonstrated morphological differences, on length alone. C A L A N U S FINMARCHICUS

Occurrence of all stages of C. finmarchicus in collections reported here is shown in figures 5 to 7 by black and stippled circles which give the ratio of all copepodite stages of C. finmarchicus (black areas) to all copepodite stages of C. glacialis (stippled areas). In Smith, Jones, and Lancaster Sounds, most of northwest Baffin Bay, along the east coast of Baffin Island (Fig. 5), in south Foxe Basin, most of northeast Hudson Bay, and west and central Hudson Strait (Fig. 6), the ratio of C. finmarchicus to C. glacialis was less than 1 : 100 individuals. A slightly larger number, about 5 per cent, was found at three stations off Lancaster Sound and south of the east end of Hudson Strait (Fig. 5) and in northeast Hudson Bay (Fig. 6). In southeast Baffin Bay C. finmarchicus represented about 15 to 30 per cent of individuals, in the north Labrador Sea about 60 to 100 per cent (Fig. 5), in northeast Hudson Strait about 30 to 70 per cent, at a single station in northeast Hudson Bay about 25 per cent (Fig. 6) and at stations south of northern Labrador from about 60 to 100 per cent. (Fig. 7). These collections show numerical dominance of C. finmarchicus over C. glacialis throughout most of the region south of Hudson Strait, especially in offshore (central Labrador Sea) locations. Greater numbers are evident in east than in west Davis Strait and Baffin Bay and smallest numbers are seen along the Baffin Island coast and at the northern limits of the distribution of the species. A fairly large population evidently enters Hudson Strait from the east, but it appears to be limited to the east end of the strait, west of which generally only few specimens are found. This occurrence can be clearly associated with water movements shown by arrows in Figs. 5 to 7. Non-arctic central Labrador Sea water supports a population consisting almost exclusively of C. finmarchicus, while mixed waters on both the Canadian and southwest Greenland sides show a greater proportion of C. glacialis. The mixed, relatively warm waters of east Davis Strait and at least

FIGURE 5. Baffin Bay and Davis Strait. White circles show stations where C. glacialis occurred without C. finmarchicus, stippled and black circles relative occurrence of all copepodite stages of C. glacialis (stippled) and C. finmarchicus (black) at stations where both species occurred. Numbers of a few stations are shown.

F I G U R E 6. Hudson Bay and Hudson Strait. Symbols as in Fig. 5.

F I G U R E 7.

Labrador Sea and southeast Canadian waters. Symbols as in Fig.

5.

80

E . H . GRAINGER

southeast Baffin Bay support noticeably greater numbers of C. finmarchicus than the more arctic, colder waters of the Baffin Island coast. Pure arctic areas to the north of Smith Sound and to the west of Jones and Lancaster Sounds appear to support no C. finmarchicus. The apparent minor inflow of water from the east which passes the eastern end of Hudson Strait evidently carries only few C. finmarchicus to west Hudson Strait, Foxe Basin, and northeast Hudson Bay. The occurrence of the species so far west provides direct evidence of water movement from east of Hudson Strait. Failure of the species to extend farther north in Foxe Basin appears, at least in part, to be the result of the depth at which it is found in Foxe Channel. C. finmarchicus was absent from 50-metre plankton hauls in Foxe Channel and was found only in 100-metre and deeper collections. Thus its occurrence only below 50 metres is indicated, and it is from about 50 metres and deeper that northward movement of water is described in Foxe Channel by Camp­ bell (1959). Continued northward movement of this water into Foxe Basin is inhibited by shallow depths, and on the west side of the basin by a strong southward moving arctic current. The primarily arctic flow through Frozen Strait and into Roes Welcome Sound, where depths of little more than 60 metres appear to limit exchange via this route between Foxe Basin and Hudson Bay to the upper arctic water of west Foxe Basin, also evidently excludes C. finmarchicus from this area. Water exchange between Foxe Channel, Hudson Strait, and Hudson Bay appears to be complicated and may vary considerably on a seasonal basis. While the main features of flow are given as being northward and eastward through all the channels leading from Hudson Bay to Hudson Strait, there is evidence, according to Dunbar (1958) and Campbell (1959), of southward movement at various depths at certain times of the year. The occurrence of a few C. finmarchicus in a very restricted part of northeast Hudson Bay implies at least some southerly flow. Apparent failure of the species to survive in the main body of Hudson Bay, it is suggested, is because of the primarily arctic nature of Hudson Bay water which supports the arctic C. glacialis at all depths. It suggests too that Atlantic influence in Hudson Bay is slight if present at all. Length variation in C. finmarchicus in time and place is Illustrated by Figure 8. North Labrador Sea specimens in mid-June, soon after the begin­ ning of spring copepodite production when copepodite stages would be expected to be at about their maximum length for the year (Marshall and Orr, 1955), were the largest collected. Slightly smaller size is shown from off east Newfoundland in late August where the presence of large numbers of young stages suggests occurrence here of a second generation of the season. Specimens of a similar size from the north Labrador Sea, in early September, appear too possibly to be of a second summer generation, the first in this region being produced as early as the first part of June. By early October the youngest stages (I and II) had disappeared from southeast Davis Strait. A sample of adult females taken in mid-April in the Gulf of Maine appeared conspicuously smaller than the near-maximum size group

cepholothorocic

length

( I unit * 0-063 mm).

,0 OJ

N.Labrador 14/6 J Sea E.Hudson 12/7 Str.

E.Newfoundand 21/8 J

N.Labrador 6/9 Sea S.E. Davis Str. 2/10

G.of Maine 15/4 J

Woods Hole late/4 Woods Hole early/6 Woods Hole late/8 Woods Hole late/9

S. Nova Scotia 14/8 J

E.Davis Str.28/7

NE. Davis Str. 28/9

S.E.Baffin Bay 27/9 J

FIGURE 8. Length frequencies of copepodite stages of C. finmarchicus, giving various locations and dates. Stippled areas show overlap of stages V and VI.

82

E . H . GRAINGER

from the Labrador Sea. Sizes taken from Clarke and Zinn (1937) from the Woods Hole region show that the Gulf of Maine sample was at about its maximum annual size, compared to the annual range given for nearby Woods Hole. A south Nova Scotia sample shows smaller sizes than one from east of Newfoundland collected at about the same time, and an east Davis Strait sample from late July consists of much smaller individuals than east Hudson Strait material taken at about the same time. Continued size reduc­ tion is shown in northeast Davis Strait and in southeast Baffin Bay. Individuals of the species appear to achieve their greatest length in the area between the offshore Newfoundland stations and southeast Davis Strait, that is, in more or less unmixed Atlantic waters. To the south, towards the Gulf of Maine and Woods Hole, reduction in size occurs, and to the north there is also clear evidence of reduced maximum lengths of various stages. These length reductions towards both the north and south from the area of greatest length may be associated with the presence towards both extremes of greater mixture of arctic and Atlantic waters than was found in the central part of this species' distribution here. In addition to length variation, data on breeding time may be related to the general distribution pattern of the species and may be used to differen­ tiate populations in different water masses. From known breeding times of C. finmarchicus in various parts of its North American range (Willey, 1919; Pinhey, 1926, 1927; Fish, 1936; Clarke and Zinn, 1937; Filteau and Tremblay, 1953; Fontaine, 1955) and from copepodite stage occurrence in the present collections, the general breeding regime over the region under consideration here may be assessed. At least two generations per year are described from Woods Hole, the Gulf of Maine, and Chaleur Bay. Occur­ rence of copepodites in the Gulf of St. Lawrence suggests the possibility of a second generation being produced there during the summer. In the Strait of Belle Isle a significant difference between the north and south sides is shown by Pinhey's (1927) data. In the cold northern part, cooled by arctic water from the Labrador coast, stage II was the most numerous in the middle of August, and stage III in early September. In the warmer southern part, influenced by water from the Gulf of St. Lawrence, stage V was the dominant stage at this time, as it was elsewhere in the Gulf. Off northeast Newfoundland, in the present collections, stages II and III were dominant offshore, stage V inshore in late August, indicating arctic conditions in the first instance and Gulf of St. Lawrence conditions in the second. The copepods therefore indicated that inshore waters of northeast Newfoundland, at the time of sampling, were primarily influenced by the Gulf of St. Lawrence, while stations farther offshore more nearly resembled the subarctic condi­ tion of the Labrador coast. Similar conclusions, on other grounds, are found in Pinhey (1926) and Huntsman, Bailey, and Hachey (1954). In the north Labrador Sea June collections point to production of what was probably the first generation of the year around late May, and in the

GOPEPODS AS INDICATORS OF E A S T E R N CANADIAN WATERS

83

same area stage III dominance in early September suggests a possible second generation, probably the same one found to the south in north Strait of Belle Isle and offshore from east Newfoundland. The condition of east Hudson Strait copepods in July suggests June production of the first stages. The same time was proposed by Fontaine (1955) for the major breeding period in Ungava Bay, and a possible second generation was suggested for August. In east Davis Strait late July dominance of stage III and presence of stages I to V I indicate June generation production, and the presence of stage I in northeast Davis Strait in late September the pos­ sibility of a second summer generation. No copepodites younger than stage I V occurred among the very few members of the species taken between July and October in all of Baffin Bay and waters to the north and west or in western Davis Strait. Also none younger than stage III was found west of the east end of Hudson Strait where the great majority of the small total number were of stages V and V I 9It is concluded that breeding of C. finmarchicus does not generally occur north of Davis Strait in the east or north of Hudson Strait in the west of the waters between Canada and Greenland, and that it does not normally occur west of the eastern end of Hudson Strait. It appears therefore to be a phenomenon of the Atlantic and of the southernmost part of the subarctic area only. At the northern extremities of its range the species is represented only by old individuals which evidently are able to survive but not to breed. C A L A N U S GLACIALIS

Occurrence of all stages of C. glacialis reported here is shown in Figures 5 to 7 by white and stippled circles which give the ratio of C. glacialis (white and stippled areas) to C. finmarchicus (black areas). Exclusive occurrence of C. glacialis is indicated (Fig. 5) in parts of Smith, Jones, and Lancaster Sounds, as well as along much of the east coast of Baffin Island. Also in all but south Foxe Basin, all of Roes Welcome Sound and all but northeast Hudson Bay (Fig. 6) C. glacialis occurred without C. finmarchicus. Scattered occurrence of small numbers of the species is shown (Fig. 7) to south of Newfoundland. Exclusive occurrence of C. glacialis coincides with the distribution of unmixed arctic water. Dominance over C. finmarchicus at localities where both species occurred was evident throughout Baffin Bay, west Davis Strait and at nearly all the Hudson Strait, Foxe Basin, and Hudson Bay locations. The occurrence of C. glacialis rather than C. finmarchicus throughout the main body of Hudson Bay implies clearly entry of Foxe Basin water to Hudson Bay. The species obviously enters through Roes Welcome Sound where, it was pointed out above, water from approximately the upper 60 metres of Foxe Basin flows into Hudson Bay. Whether or not the species also enters Hudson Bay directly from Foxe Channel cannot be demonstrated

cepholothoracic

Itngth

(I unit * 0-063mm).

4/8

Loncosttr Sound

15/9 Loncosttr Sound

17/9 N.E.Boffin Boy

1/10 W.DOVÍS Str.

13-14/6 N.E. Labrador SM J 28/7 E.DovitStr.

28/9 E.DOVÍS Str.

24/7 N.Hudson Boy

27/8 N. Hudson R.

2/10 N. Hudson Boy 21-25/8 S.E. of Nfld. 19/8 E. Nfld. 10/1 G. of Main*

FIGURE 9. Length frequencies of copepodite stages of C. glacialis, giving various locations and dates. Stippled areas show overlap of stages V and VI.

COPEPODS AS INDICATORS OF E A S T E R N CANADIAN WATERS

85

at present, although the apparent introduction of C. hyperboreus by this route (see below) would tend to suggest that C. glacialis may accompany it. Length variations in time and place are shown in Figure 9. Change in copepodite stage length between early August and mid-September in Lan­ caster Sound shows slight reduction in most stages between the two dates. Lengths near mid-September in northeast Baffin Bay were similar to Lancaster Sound, as were those from early October in west Davis Strait. North Labrador Sea specimens, at the time of sampling (mid-June) prob­ ably close to their maximum size, were similar in length to those from early August from Lancaster Sound, which too were probably near their maxi­ mum length at the time of sampling. Davis Strait material, smaller than that above, may reflect size decrease subsequent to early copepodite produc­ tion. Generally larger individuals occurred in north Hudson Bay soon after the onset of copepodite production in late July than later in the summer. Others, from off Newfoundland and the Gulf of Maine, were taken well past the season of production. They are smaller, however, than those taken at comparable periods of the annual cycle in northern waters (Grainger, 1959). Apart from the possibility of smaller specimens occurring in the southernmost part of its range there is no clear indication of geographical length variation in the region being considered here. Breeding periods vary and may be associated with hydrographic features. The earliest breeding appeared in the east Labrador Sea where stage I probably developed in early June. This is about the same time as reported by Digby (1954) from east Greenland for C. finmarchicus (which in the light of subsequent investigations was probably in reality C. glacialis). This population, it is suggested, may have originated in east Greenland. Evidence of this stock is seen in east Hudson Strait in July. Stage I development appears to begin in north Hudson Bay in early July and in Lancaster Sound, north Baffin Bay and Foxe Channel in the second half of July. There is evidence of extremely late production (or possibly delayed develop­ ment) along the west side of Baffin Bay and Davis Strait, where stage I was still dominant at the end of September. There appear to be two major sources of C. glacialis in the region con­ sidered here. One is the early breeding population with east Greenland affinities which occupies the north Labrador Sea area and the other is associated with the Canadian arctic region and appears to breed latest in the northernmost or "most arctic" part of its range and somewhat earlier farther south. Data on breeding and development are not yet available from the region south of northern Labrador. Throughout at least the Baffin Bay, Davis Strait, Foxe Basin, and Hudson Strait regions, C. glacialis is a surface-dwelling species. Data given by Jaschnov (1961) show that it inhabits the upper 100 metres within the Labrador Current at least as far south as southeast of Newfoundland. Along the continental shelf of Nova Scotia and the northeast United States how­ ever it is generally found at a depth of about 500 metres and greater.

86

E . H . GRAINGER CALANUS HYPERBOREUS

Occurrence of all stages of C. hyperboreus in collections reported here is shown in figures 10 and 11 which give copepodites present and dates of collections. The species extends over the entire area of discussion. Evidently a common near-surface form in nearly all stages in the Arctic Ocean (Brodsky and Nitikin, 1955), in at least parts of the Canadian archipelago waters (author's unpublished data), in northern Baffin Bay and western Davis Strait, it appears, in its late stages, to seek subsurface depths in Foxe Basin, east Davis Strait and in waters to the south (Willey, 1919; Pirihey, 1926, 1927; Bigelow, 1926; Jespersen, 1934; Hansen, 1960; Grainger, 1962). Within Foxe Channel, Hudson Bay, and at least western Hudson Strait it was found in the present collections as a subsurface form in all stages collected. Early investigations in Hudson Bay (Willey, 1931) which had been based on near-surface collections only failed to show the presence of any C. hyperboreus in Hudson Bay. The first record of its occurrence in the bay is given here, and it is clear that the species extends widely over Hudson Bay, although it appears to be excluded from the upper 30 to 50 metres everywhere within the bay as well as in adjacent waters to the northeast. This includes most of Foxe Basin where in maximum depths of little more than 50 metres in the west central part specimens were found to be very rare (Grainger, 1962). More numerous in deeper Foxe Basin water, the species does not appear to enter Hudson Bay via Roes Welcome Sound, presumably being limited by shallow depths in the sound. Entry to Hudson Bay would seem therefore inevitably to be via Foxe Channel, by subsurface currents between the islands in northeast Hudson Bay. Numbers collected were very small over the entire region shown in Figure 10 except for the east end of Hudson Strait. No stage I was identified between June and October and stage II was taken only twice (on 24 and 26 July). A few more stage III were found but the great majority were older copepodites. Breeding evidently occurred at or near Igloolik in northwest Foxe Basin (Grainger, 1959). At Igloolik stage II was the most numerous stage col­ lected through most of July and August, and first nauplius production was reported as being in late May. It is possible that the Hudson Bay collections were not made early enough in the season to show stage I development. However, the almost total absence of stages II and III, the extremely small total number of individuals, and the apparent total absence of all stages from the surface waters suggest at most an exceedingly early and small production of the species and in fact give good reason to doubt that breed­ ing occurs at all in south Foxe Basin, Foxe Channel, west Hudson Strait, and Hudson Bay. The population of C. hyperboreus in these areas resembles closely that of C. finmarchicus in parts of the same region and in north Baffin Bay, and may be accounted for simply by passive drift of predomi­ nantly old individuals from the nearest breeding area in the north. Elsewhere in the area representatives of the earliest copepodite stages

F I G U R E 10. Baffin Bay and Davis Strait. Circles indicate occurrence of C. hyperboreus, darkened segments showing copepodite stages present. Dates (as day/month) of collec­ tions are given.

FIGURE 11. Hudson Bay and Hudson Strait. Symbols as in Fig. 10.

F I G U R E 12. Length frequencies of copepodite stages of C. hyperboreus.

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E . H . GRAINGER

were found in central Baffin Bay at the end of July, in Smith, Jones, and Lancaster Sounds during the first half of August and in southwest Baffin Bay in late September. Except for the northern areas and the east Labrador Sea, stages II and III were fairly rare at all locations, stages I V to V I comprising the total stock at most stations. Apparent development to the degree of dominance of at least stage II of the new generation (and possibly to stage III although these may represent spring rising of the previous year's stock) had occurred in the north Labrador Sea by mid-June. This timing is roughly in phase with east Greenland development reported by Digby (1954) and, as with C. glacialis in the same location, may indicate east Greenland as the origin of the population. Elsewhere no clear variation in development could be seen from the Canadian arctic cycle described by Grainger (1959) in which stage II dominated during August and stage I V , with fewer stage III, outnumbered the others during September. The presence of a few stage II individuals in the Gulf of St. Lawrence and off south Nova Scotia in summer (Willey, 1919) indicates spring breeding at least near the areas of collecting, and according to Bigelow (1926) breeding occurs in the Gulf of Maine. No evidence of length range variation was noted in this species, either seasonally or geographically. The majority of collections included too few specimens in most stages however to give strict confirmation of this. Other studies on the species also have shown no sign of seasonal length change (Ussing, 1938; Digby, 1954) although many of the collections used by both authors were also too small to be conclusive. Figure 12 shows combined collections from representative stations and dates in a single histogram. The following length ranges are recorded for the copepodite stages, in measuring units of 0.063 mm: stage I, 16-21; stage II, 23-31; stage III, 34^15; stage I V , 47-64; stage V , 65-99; stage V I 2 , 90-118. CONCLUSION

The distribution of C. glacialis and C. finmarchicus described here is for the most part in close agreement with arctic and Atlantic water distribution as shown by physical oceanographic studies. The arctic species, C. glacialis, occurs in all copepodite stages in the absence of all copepodite stages of C. finmarchicus in arctic water. It is present in far larger number than C. finmarchicus in the northern part of the mixed water zone, and becomes gradually less numerous than C. finmarchicus towards the southern part of the mixed water. The Atlantic species, C. finmarchicus, present in all cope­ podite stages in the absence of all copepodite stages of C. glacialis in the Atlantic region, becomes gradually less numerous towards the north of the mixed water region. The Hudson Bay region may provide the principal point of difference here between interpretations of biological indicators and physical oceanogra­ phic studies. The possible entry of Atlantic water into Hudson Bay has

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previously been suggested, although apparently not decisively demonstrated, by physical methods. While data given here do not permit firm conclusions on the identity of Hudson Bay waters, the apparent limiting of C. finmarchicus to the northeast portion of the bay and the presence of C. glacialis and C. hyperboreus, both indicating arctic water, over the remainder of the area of the bay, points strongly to the dominance of arctic water there and gives no indication of Atlantic intrusion into the main part of Hudson Bay. C. finmarchicus in Foxe Basin, west Hudson Strait, and the northeasternmost corner of Hudson Bay, although present in small numbers only, indicates Atlantic influence reaching westward only as far as those areas. The three Calanus species discussed here show noticeable differences in the matter of length variation, differences which may be associated with the peculiarities of the waters inhabited by the three species. C. finmarchicus appears to vary considerably in length (up to 25 per cent at least in mean length in some stages) seasonally at single locations and in different parts of its range. C. glacialis shows length variation with time at single locations but little evidence of geographical length variation within the area studied here. C. hyperboreus shows no clear evidence of any significant mean length variation, either seasonally or in different parts of its range. It is possibly of significance that C. finmarchicus lives under the widest range of temperature conditions, individuals being found from near 0° to about 22° C, breeds over the greatest time period, and in general is subject to the widest fluctuations in environmental conditions. Largest sizes, season­ ally, are found during the phytoplankton maximum and thus appear to be a result, at least in part, of available food supply. C. glacialis, restricted to much lower temperatures, from near —2° to about 8° to 10° C, breeds probably only once per year at close to the same time everywhere in its range and under generally much more stable environmental conditions than C. finmarchicus. As with C. finmarchicus, the largest individuals of the year are found during the phytoplankton maximum which occurs soon after breeding. C. hyperboreus lives under conditions similar to those of C. glacialis. It differs however in that breeding evidently occurs at least a month earlier than in C. glacialis, as shown by Ussing (1938) and Digby (1954) in east Greenland and by Grainger (1959) in the Canadian arctic. It is suggested from these works that while the earliest nauplii of C. hyperboreus may be developed before high summer phytoplankton levels have been reached, late nauplii and the first three copepodite stages are passed through almost in their entirety during the period of maximum phyto­ plankton food availability. In contrast to this, C. glacialis reaches the peak of copepodite stage I only, during high phytoplankton abundance, and subsequent copepodite stages moult to maximum numbers only after the phytoplankton food supply has dropped to a small fraction of the summer maximum. Thus there appears to be a far greater range of food supply, from plenty to relative scarcity, available for the first three copepodite stages

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of C. glacialis, while the corresponding stages of C. hyperboreus appear, from the examples above, to have maximum food available during develop­ ment of almost all members of the same three stages. A possible consequence of this is availability not only of a more plentiful but also of a more uniform food supply for young C. hyperboreus than for young C. glacialis. This, if so, would tend to reduce the effect on growth of C. hyperboreus which a more variable food supply appears to exert on C. glacialis and on C. finmarchicuc, and to promote a less variable rate of development than is found in the other species. C. glacialis, evidently more influenced in its earliest stages by variable food supply, appears to develop a seasonal size range by the young copepodites growing more quickly during food abundance than when food is scarce. C. finmarchicus, with the greatest range of environmental conditions, also illustrates the effect of food supply upon young copepodites. In addition to this the greater temperature range of the species may be expected, as was shown by Deevey (1960) for other copepod species, further to influence size variation in C. finmarchicus to a greater degree than it affects either the cold-water C. glacialis or C. hyperboreus. SUMMARY

Three species of the copepod genus Calanus, C. finmarchicus, C. glacialis and C. hyperboreus, occur in arctic-subarctic waters of eastern Canada. The largest species, C. hyperboreus, easily distinguishable morphologically from the others in all but its youngest copepodites, may be readily separated from the other species by size alone in its youngest stages. The other two species, morphologically distinguishable only in copepodite stages V and V I , may be separated satisfactorily in their younger copepodite stages by size. Calanus finmarchicus is an Atlantic boreal species in all copepodite stages, C. glacialis and C. hyperboreus arctic species in all stages. Subarctic (mixed arctic and Atlantic) water may be indicated by the combined presence of C. glacialis and C. finmarchicus in all copepodite stages. C. finmarchicus appears to breed at least twice a year, in the southern part of its range only, and not to breed at all in the northern or "most arctic" parts of its range where only advanced copepodite stages are found. C. glacialis, breeding at least over the arctic part of its range, appears to breed only once in a single year. Variations in breeding times and in development rates reveal differences in populations, inhabiting adjacent areas and thus may be used to show water movements from various sources. Analysis of length range within copepodite stages of the three species shows that C. finmarchicus varies in length both seasonally and geographic­ ally, C. glacialis seasonally but little if at all geographically, and C. hyperboreus little if at all seasonally or geographically. These differences are related to differing effects of temperature and food supply on the developing copepodites of the three species in different parts of their ranges.

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REFERENCES

A D L E R , G . and J E S P E R S E N , P. (1920). Variations saisonnieres chez quelques copepodes planctoniques marins. Medd. Komm. Havunders., Ser. Plankton 2 ( 1 ) . B A I L E Y , W . B. (1957). Oceanographic features of the Canadian Archipelago. J . Fish. Res. Bd. Can. 14(5): 731-69. B I G E L O W , H . B. (1926). Plankton of the offshore waters of the Gulf of Maine. Bull. U . S . Bur. Fish. 40(2). B R O D S K Y , K . A . (1948). [Free-living copepods of the Sea of Japan.] Izv. Tikhook. inst. rybn. khoz. i okeanogr. 26. (1959). [On the phylogenetic relationship of certain species of Calanus (Copepoda) from the northern and southern hemispheres.] Zoologicheskii Zhurnal 55(10): 1537-53. and N I T I K I N , M . N . (1955). [Hydrobiological work.] Materially nabliudenii nauchno-issledovatel'skoi dreifuiushchei stantsii 1950/51 goda, ed. M . M . Somov, Izd. "Morskoi transport," 1: 401-10. C A M P B E L L , N . J . (1958). T h e oceanography of Hudson Strait. Fish. Res. Bd. Can., M S Rep. Ser. (Oceanogr. and Limnol.) 12. • (1959). Some oceanographic features of northern Hudson Bay, Foxe Channel, and Hudson Strait. Ibid. 46. and C O L L I N , A . E . (1956). A preliminary report on some of the oceanographic features of Foxe Basin. Fish. Res. Bd. Can., M S Rep. Biol. Stations 613. C L A R K E , G . L . and Z I N N , D . J . (1937). Seasonal production of zooplankton off Woods Hole with special reference to Calanus finmarchicus. Biol. Bull. 75(3): 464—87. D E E V E Y , G E O R G I A N A B. (1960). Relative effects of temperature and food on seasonal variations in length of marine copepods in some eastern American and western European waters. Bull. Bingham Oceanogr. Coll., 17(2) : 54-86. D U N B A R , M . J . (1951). Eastern arctic waters. Fish. Res. Bd. Can. Bull. 88. (1958). Physical oceanographic results of the "Calanus" expeditions in Ungava Bay, Frobisher Bay, Cumberland Sound, Hudson Strait and northern Hudson Bay, 1949-1955. J . Fish. Res. Bd. Can. 15(2): 155-201. F I L T E A U , G . and T R E M B L A Y , J . - L . (1953). Ecologie de Calanus finmarchicus dans la Baie-des-Chaleurs. Nat. Can. 80(1-2). F I S H , C . J . (1936). The biology of Calanus finmarchicus in the Gulf of Maine and Bay of Fundy. Biol. Bull. 70: 118-41. F O N T A I N E , M A R I O N (1955). The planktonic copepods (Calanoida, Cyclopoida, Monstrilloida) of Ungava Bay, with special reference to the biology of Pseudocalanus minutus and Calanus finmarchicus. J . Fish. Res. Bd. Can. 12(6) : 858-98. GRAINGER, E . H . (1959). T h e annual oceanographic cycle at Igloolik in the Canadian arctic. 1. The zooplankton and physical and chemical observations. J . Fish. Res. Bd. Can. 76(4) : 453-501. (1961). T h e copepods Calanus glacialis Jaschnov and Calanus finmarchicus (Gunnerus) in Canadian arctic-subarctic waters. Ibid. 18(5) : 663-78. (1962). Zooplankton of Foxe Basin in the Canadian arctic. Ibid. 19(3). H A C H E Y , H . B., H E R M A N N ,

F . , and B A I L E Y ,

W . B. (1954). T h e waters of the

ICNAF

Convention Area. A n n . Proc. Internat. Comm. Northwest Atlantic Fisheries 4: 67-102. H A N S E N , V . K . (1960). Investigations on the quantitative and qualitative distribution of zooplankton in the southern part of the Norwegian Sea. Medd. fra Danmarks Fiskeri- og Havunders, N . S. 2(23): 1-53. H U N T S M A N , A . G . , B A I L E Y , W . B., and H A C H E Y , H . B. (1954). T h e general oceanography

of the Strait of Belle Isle. J . Fish. Res. Bd. Can. 11(3): 198-260. J A S C H N O V , V . A . (1955). [Morphology, distribution and systematics of Calanus fin­ marchicus s.l.] Zoologicheskii Zhurnal 34(6) : 1210-23. (1957). [Comparative morphology of the species of Calanus finmarchicus s.l.] Ibid. 36(2): 191-8. (1958). [Origin of the species Calanus finmarchicus s.l.] Ibid. 37(6): 838-44. (1961). [Water masses and plankton. 1. Species of Calanus finmarchicus s.l. as indicators of definite water masses.] Ibid. 40(9): 1314-34. J E S P E R S E N , P. (1934). T h e Godthaab Expedition 1928. Copepoda. Medd. om Gronland 79(10).

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M A R S H A L L , S. M . , N I G H O L L S , A . G . , and O R R , A . P. (1934). O n the biology of Calanus finmarchicus. V : Seasonal distribution, size, weight and chemical composition in Loch Striven in 1933 and their relation to the phytoplankton. J . M a r . Biol. Ass 19: 793-828. M A R S H A L L , S. M . and O R R , A . P. (1955). The biology of a marine copepod. Edinburgh and London: Oliver and Boyd. P I N H E Y , K A T H L E E N F . (1926). Entomostraca of the Belle Isle Strait Expedition, 1923, with notes on other plankton species. Contr. Can. Biol. Fish. 5 ( 6 ) : 179-234. (1927). Entomostraca of the Belle Isle Strait Expedition, 1923, with notes on other planktonic species: pt. II; and a record of other collections in the region. Ibid. 5(13): 331-46. R U S S E L L , F . S. (1939). Hydrographical and biological conditions in the North Sea as indicated by plankton organisms. J . Conseil 14(2) : 171-92. U . S . N A V Y H Y D R O G R A P H I G O F F I C E (1958). Oceanographic atlas of the polar seas. Part II. Arctic. Washington, D . C . U S S I N G , H . H . (1938). T h e history of some important plankton animals in the fjords of East Greenland. Medd. om Gronland 100(7). W I L L E Y , A . (1919). Report on the Copepoda obtained in the Gulf of St. Lawrence and adjacent waters, 1915. Canadian Fisheries Expedition 1914-15: 173-220. (1931). Biological and oceanographic conditions in Hudson Bay. 4. Hudson Bay copepod plankton. Contr. Can. Biol. Fish. 6(10) : 483-93.

SALINITY, OSMOREGULATION, A N D DISTRIBUTION IN MACROSCOPIC CRUSTACEA Otto Kinne

MARINE DISTRIBUTIONS can be considered under two principal aspects: the historical aspect and the ecological, present-day aspect. I have chosen here the ecological aspect and shall restrict myself to a special portion of this aspect, paying particular attention to salinity. Other important physical factors such as temperature and depth, differences between benthic and pelagic regions, topographic factors, different bottom types such as mud, sand, gravel or rock, and the effects of still or moved water will not be considered here. Biotic factors will also be neglected. It is my intention to illustrate relationships between salinity, osmoregula­ tion, and distribution in some well-known macroscopic crustaceans. O n the basis of their occurrence in waters of different salinities, I shall consider their ability to osmoregulate and the osmoregulative mechanisms employed. The average salinity of sea water is roughly the same in the various oceans. Average surface salinity amounts to 35.3%c, for example, in the North Atlantic Ocean and to 33.7%c in the North Pacific; it is 34.5%o in the South Atlantic and 34.6%o in the South Pacific (Wiist, 1936). Con­ siderable variations of salinity, however, are found in secondary seas which are more or less isolated from the ocean (Sverdrup et al. 1942), for example the European Mediterranean Sea (37-39%o), the Red Sea (up to 41%c), the Baltic Sea (1-16%^), and in coastal waters, bays and estuaries subjected to dilution by fresh water, or bodies of salt water subjected to extensive evaporation. The different degrees to which crustaceans are capable of osmoregulating largely determine their distribution in waters of normal or of modified salinity. In an attempt to classify the different degrees of their osmoregula­ tive capacities, four groups of crustaceans may be distinguished: (1) Polystenohaline osmoconformers which inhabit the free ocean with its unmodified salinity of 34 to 35%©; (2) euryhaline osmoregulators which inhabit coastal waters, bays, estuaries or brines, characterized by reduced, fluctuating, or extremely high salinities; (3) oligostenohaline osmoregulators which inhabit fresh water; and (4) holeuryhaline osmoregulators which inhabit water of salt concentrations ranging from that of fresh water to full strength sea water. The first three groups represent more than 95 per cent of the macrocrustaceans; holeuryhaline forms comprise only a few specialized species. 9

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Let us now examine representative species that belong to the above mentioned four groups and briefly discuss their osmoregulative mechanisms. (All species names are used in accordance with The Physiology of Crustacea, [New York: Academic Press, 1960-61] regardless of the names used origi­ nally by the authors of cited articles). 1) . Polystenohaline osmoconformers exhibition and volume regulation but no or negligible osmoregulation. This group comprises the decapods Macropipus puber, Maja verrucosa, Hyas araneus, Cancer antennarius, Emerita talpoida, Speocarcinus calif or niensis, Lophopanopeus heathii, Pagurus longicarpus, Palinurus elephas, and various species of Callianassa, Upogebia, ^ndPugettia (e.g. Duval, 1925; Schlieper, 1929; Schwabe, 1933; Robertson, 1949, 1960; Gross, 1957a) and presumably most other oceanic Crustacea. They swell rapidly in diluted sea water and gain salt in concen­ trated sea water. Their blood osmoconcentration is isosmotic to the sur­ rounding sea water, that is, it has a freezing point depression of A — —1.9° C ; it conforms readily to any salinity changes (e.g., Krogh, 1939). Much the same is apparently true for the marine prawns Pandalus montagui and Pandalina brevirostris (Panikkar, 1950). Maja verrucosa survives only a few hours if its natural sea water environment is diluted by more than 20 per cent, exhibiting decreased rates of respiration due to osmotic damage in its tissues (Schwabe, 1933). 2) . Euryhaline osmoregulators are characterized by reduced surface permeability to salt and water, high tissue tolerance to deviations in blood osmoconcentration, and by improved mechanisms for differential absorp­ tion and excretions of ions. O n the basis of their osmoregulative capacity and the osmoregulatory mechanisms employed, two groups of euryhaline osmoregulators can be distinguished: (a) the hyperosmotic regulators, and (b) the hyper-hypo-osmotic regulators (Fig. 1). The hyperosmotic regulators are hyperosmotic in diluted sea water but more or less isosmotic in higher salinities. In other words, they are osmoregu­ lators in low salinities, but osmoconformers in high salinities. Examples are the marine-brackish water decapods Carcinus maenas (Duval, 1925; Schlie­ per, 1929; Nagel, 1934), Rhithropanopeus harrisii tridentatus (Kinne and Rotthauwe, 1952), and the marine-brackish water amphipods Gammarus locusta, G. obtusatm (Beadle and Cragg, 1940), G. duebeni (Beadle and Cragg, 1940; Kinne, 1952), G. oceanicus, Marino gammarus finmarchicus (Werntz, in Prosser and Brown, 1961), Marino gammarus marinus ( Widmann, 1935), and the brackish-freshwater amphipods Gammarus tigrinis and G. fasciatus (Werntz, in Prosser and Brown, 1961). The mechanism of hyperosmotic regulation appears to be based on an antagonism between loss of salt from external surfaces and antennal glands, and active salt uptake from the medium. Beadle and Cragg (1940) have shown, that in Gammarus duebeni, G. locusta, and G. obtusatus changes in blood osmoconcentration are due to salt movements rather than to water movements. Gammarus duebeni can reduce the rate of salt loss in low

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F I G U R E 1. Blood-osmoconcentration as function of salinity in euryhaline Crustacea. Hyperosmotic regulators: amphipod Gammarus (from Kinne, 1952) and decapod crab Rhithropanopeus (Kinne and Rotthauwe, 1952). Hyper-hypo-osmotic regulators: deca­ pod land crab Uca (Jones, 1941), shore shrimp Crangon (Flugel, 1959), and anostracan brine shrimp Artemia (Croghan, 1958b). (From Kinne, 1962).

salinities by producing urine which is hypo-osmotic to the blood but hyper­ osmotic to the external medium and possibly also by changes in surface permeability (Shaw and Sutcliffe, 1961; Lockwood, 1961). As salinity decreases below 17%c, Gammarus duebeni increases the rate of urine flow until, in fresh water, the equivalent of 70 per cent total body water/day is reached, and simultaneously decreases the osmoconcentration of its urine. Such adjustments may be achieved within two hours—a fact that appears quite important in view of the rapid salinity fluctuations to which G. duebeni may be exposed in its natural habitat. Blood-hypo-osmotic urine

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is presumably also produced by Gammarus zaddachi and G. salinus in dilute media (Lockwood, 1961). In Carcinus maenas, the most important osmo­ regulatory organ seems to be the gill. In sea and brackish water, its antennal glands produce approximately blood-isosmotic urine; consequently, they play no significant part in osmoregulation. The rate of urine output increases with decreasing salinity, and it is assumed that the gills replace such pro­ gressive salt loss by a reciprocal increase in active salt absorption (Nagel, 1934). The hyper-hypo-osmotic regulators are hyperosmotic in diluted sea water and hypo-osmotic in salinities higher than that of sea water. In other words, they are osmoregulators both in reduced and increased salinities. Hyperhypo-osmotic regulation is characteristic of shore and estuarine shrimps, brine shrimps, and land crabs. Examples are the shrimps Palaemonetes varians, Palaemon serratus, Palaemon squilla, Penaeus indicus, Penaeus carinatus, Metapenaeus dobsoni (Panikkar, 1939, 1940a, 1941a, 1950), Metapenaeus monoceros (Panikkar and Viswanathan, 1948) and Crangon crangon (Broekema, 1941; Flugel, 1959); the brine shrimp Artemia salina (Croghan, 1958b); the land crabs Pachygrapsus crassipes, Uca crenulata (Jones, 1941; Prosser et al., 1955; Gross, 1955, 1957a and b, Uca minax, U. pugilator, U. pugnax (Green et ai, 1959), Ocypode quadrata (Flemister and Flemister, 1951), Hemigrapsus oregonensis (Gross, 1957a, 1961), Heloecius cordiformis, Leptograpsus variegatus (Dakin and Edmonds, 1931; Edmonds 1935), and Birgus latro (Gross, 1955, 1957a). Hyporegulation is apparently always correlated with hyperregulation, sug­ gesting that hyper-hypo-regulation is indicative of an advanced stage of adaptation to fluctuating or extreme salinities. This very effective mechan­ ism is also found in some marine insects. It represents the most elaborate osmoregulative mechanism known within the Invertebrata. The mechanism employed in hypo-osmotic regulation is not yet suf­ ficiently investigated to allow for generalizations. The most thoroughly analysed species is the famous brine shrimp, Artemia salina (Croghan, 1958a, b, c, d, e). Artemia swallows continuously its ambient medium and takes up water from its gut lumen. The osmoconcentration of the gut fluid is appreciably higher than that of its blood, but in more concentrated brine is considerably below that of the medium. Regulation occurs in gills (salt balance) and gut (water balance). The low osmoconcentration of body fluids, the type of ionic regulation and the low internal magnesium concen­ tration resemble conditions found in freshwater organisms and have been interpreted as evidence for the freshwater ancestry of the brine shrimp (e.g., Robertson, 1960). Artemia can actively excrete (first ten pairs of gills) and absorb (probably first ten pairs of gills and gut) sodium chloride. Its mechanisms are similar to those employed by marine teleosts. Artemia can exist in salt lakes and brines with salinities higher than 220%o and has been successfully kept in the laboratory in salinities as low as 3%o. However, in spite of its great osmoregulatory capacity, the brine shrimp is restricted

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in nature to waters of high salinities. The reason for this restriction is presumably its poor ability to compete and to escape from predators, under more normal conditions required by other brackish water and marine animals. Salinities above 200%c represent ecologically a near-vacuum with little or no competition. Palaemonetes varians and Palaemon longirostris produce rather large amounts of blood-isosmotic urine over a wide range of salinities (Panikkar, 1939; Parry, 1955, 1957); there must consequently be an intensive absorp­ tion of water or excretion of salt, especially in high salinities. Pachigrapsus crassipes produces slightly blood-hypo-osmotic urine when exposed to reduced salinities, and blood-isosmotic urine when in salinities above 31%o (Prosser et aL, 1955). The muscle tissue of P. crassipes swells if the crab is immersed in water of reduced salinity and shrinks if it is immersed in salinities above that of sea water. These volume changes of muscles take place at the expense of the blood space; the crab does not change weight (Gross and Marshall, 1960). In Uca pugnax and Uca pugilator kept in 34.5%o and 60.4%o salinity, urine osmotic and electrolyte concentrations are significantly blood-hyperosmotic. The chief sites of entrance of water and salt are the stomach and the gills, and the chief sites of regulation are the antennal glands and the gills with some regulation by the stomach and possibly the mid-gut gland (Green et aL, 1959). Ocypode quadrata re­ absorbs water in its antennal glands when in air or in blood-hyperosmotic salinities. It excretes water in its antennal glands when in blood-hypo-osmotic salinities (Flemister and Flemister, 1951). Reabsorption of water in antennal glands has also been demonstrated in another land crab, namely Gecarcinus lateralis (Flemister, 1958). As has been shown above, the antennal glands are of little or no impor­ tance as an osmoregulative mechanism in Palaemonetes, Palaemon, and Pachygrapsus, but they may assist in ionic regulation as is the case in Pachygrapsus. In the land crabs Uca, Ocypode, and Gecarcinus, however, antennal glands have become increasingly important as sites for water reabsorption and salt excretion against gradients and constitute effective osmoregulative mechanisms. 3). Oligostenohaline osmoregulators inhabit fresh water and are charac­ terized by hyperosmotic regulation which is extremely efficient even in very dilute media (Fig. 2). Two groups of oligostenohaline osmoregulators can be distinguished: (a) the producers of more or less blood-isosmotic urine, and (b) the producers of blood-hypo-osmotic urine. The producers of blood-isosmotic urine comprise such forms as the river crabs Potamon edulis (Shlieper and Herrmann, 1930) and Potamon niloticus (Shaw, 1959), and the shrimp Palaemonetes antennarius (Parry, 1957). They are rather poorly equipped for life in fresh water. Potamon exhibits a high blood osmoconcentration (A = — 1 . 1 ° to — 1 . 2 ° C in P . edulis) and is more permeable to water and salt than most other freshwater living animals. However, if compared to the shore crab Carcinus or the

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fresh

F I G U R E 2. Blood-osmoconcentration as function of salinity in oligostenohaline and holeuryhaline Crustacea. Oligostenohaline inhabitants of freshwater: decapods, river crab Potamon (from Duval, 1925; Schlieper and Herrmann, 1930) and crayfish Astacus (Herrmann, 1931; Beadle, 1943), amphipod Gammarus (Beadle and Cragg, 1940), and diplostracan water flea Daphnia (Fritzsche, 1917). Holeuryhaline inhabitant of sea, brackish, and fresh water: decapod crab Eriocheir (Scholles, 1933). (From Kinne, 1962).

holeuryhaline crab Eriocheir, it shows an all-around reduction in surface permeability, both to water and salt. Potamon produces only small amounts of urine and absorbs ambient sodium and potassium against the gradient (Schlieper and Herrmann, 1930; Shaw, 1959). Palaemonetes antennarius has a lower blood osmoconcentration (A = —0.75° C) than Potamon but loses large amounts of salt via its almost blood-isosmotic urine (A = —0.67° C) which is produced at the rate of about 2 per cent body weight / hr (Parry, 1957). There appears to exist a threshold ambient sodium con­ centration (between 0.125 JJM Na/1 and 0.183 pM Na/1) which seriously

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affects the ion-uptake mechanism. Similar thresholds may exist for other monovalent ions, and may help to account for the prawns' discontinuous geographic distribution (Parry, 1961a). The producers of blood-hypo-osmotic urine comprise members of the crayfish family Astacidae with urine concentrations of only about 10 per cent of the blood osmoconcentration (Robertson, 1960), the amphipods Gammarus pulex and G. lacustris (Lockwood, 1961), and presumably numerous other freshwater living crustaceans. In the Astacidae, blood osmoconcentration varies between A = —0.6° and —0.9° C. In an external medium of A = —0.018° C, the crayfish Astacus astacus maintains a blood osmoconcentration of A = —0.8° to —0.9° C and excretes a very dilute urine of A = —0.09° C ; in fresh water its urine output amounts to 4 per cent of its body weight / 24 hr (Herrmann, 1931) or to 0.175 per cent body weight/hr (Scholles, 1933). Urine output decreases with increasing salinity and approaches zero in a blood-isosmotic medium (Scholles, 1933). Procambarus clarkii compensates for osmotic water inflow in fresh water by excreting blood-hypo-osmotic urine at the rate of 5.2 per cent of its body weight/24 hr (Lienemann, 1938). Gammarus pulex and Asellus sp. have lower blood osmoconcentrations with Arranging from—0.4° to—0.6° C Beadle and Cragg, 1940; Parry, 1953, and the blood of Daphnia magna has A's of —0.2° to —0.3° C (Fritzsche, 1917). The capacity of the euryhaline Gammarus duebeni to vary its urine concentration is lacking in the oligostenohaline G. pulex (Lockwood, 1961). The main osmoregu­ latory mechanisms of G. pulex seem to be active ion uptake and differential surface permeability. Asellus aquaticus is fairly permeable to salt and water, and maintenance of its internal concentration in fresh water must result primarily from replacement of ions from the medium at the same rate as they are lost from the body by diffusion and in urine. Continued main­ tenance of blood osmoconcentration during eight days of starvation shows that lost NaCl can, if necessary, be replaced solely by active uptake from the medium, that is, independent of the food supply (Lockwood, 1959). The oligostenohaline branchiopod Triops cancriformis maintains its blood osmoconcentration by (a) relative impermeability of its body surfaces, and (b) salt uptake from food; its osmoregulation breaks down in slightly bloodhyperosmotic media (Parry, 1961b). Salt uptake from food has also been demonstrated or suggested in other freshwater crustaceans, such as Branchipus (Krogh, 1939) and Chirocephalus (Panikkar, 1941b). 4). Holeuryhaline osmoregulators are rare and poorly investigated. They are able to inhabit all three aquatic media: sea water, brackish water, and fresh water. Important components of their osmoregulatory mechanism appear to be an exceedingly low surface permeability to water and salt, highly advanced absorption and excretion of salt against steep concentrationgradients, and high tissue tolerance to fluctuations in blood osmoconcentra­ tion. The most intensively studied representative, the wool-handed crab, Eriocheir sinensis, exhibits in fresh water a high blood osmoconcentration

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with A's between —1.1° and —1.2° C (Fig. 2), and a low urine output of 3 to 5 ml/day in a 60-gram individual. The urine is isosmotic or slightly hyperosmotic to the blood both in fresh water and sea water (Scholles, 1933; Schlieper 1935). In very low salinities and fresh water, salt (NaCl) is actively absorbed by the gills (Schwabe, 1933; Koch, 1954). There is indication for the existence of a potassium-pump separate from the sodiumabsorbing mechanism, suggesting the presence of a similar osmoregulatory mechanism as has been reported for larvae of some aquatic insects, such as Chironomus and Aedes (Koch and Evans, 1956a, b, c). The antennal glands appear to have little or no osmoregulative function but aid in ionic regulation. Eriocheir resembles the river crab Potamon in that it (a) maintains a high blood osmoconcentration in fresh water, (b) actively absorbs sodium and potassium, and (c) excretes small amounts of more or less blood-isosmotic urine. A similar osmotic behaviour is exhibited by a close Indian relative of Eriocheir, namely Varuna litterata (Panikkar, 1950). The emigration of Crustacea from their oceanic home into waters of different salinity has posed—and still poses—a number of osmotic problems. Emigration into waters of reduced salinity raises such problems as a con­ tinuous osmotic inflow of water which has to be expelled, paucity of ions which have to be actively absorbed from a dilute medium and from food, increased fluctuations of salinity and ionic composition of the medium, and of temperature and water chemistry. Emigration into water of increased salinity poses mainly problems of dehydration, active salt excretion, water reabsorption, and possibly also of respiratory adjustments for the decreased availability of ambient dissolved oxygen. We witness today a diversity of osmoregulative mechanisms which com­ pensate for the ill effects of deviated salinities. Nevertheless, salinity still represents a most potent factor in the distribution of Crustacea. In general, the number of crustacean species tends to decrease in proportion to the TABLE I R E D U C T I O N I N N U M B E R OF C R U S T A C E A N SPECIES IN A N A R E A R E A C H I N G N O R T H S E A N O R T H E A S T W A R D S INTO T H E B A L T I C S E A .

FROM T H E

The reduction in species number is due to various environmental factors of which the salinity appears to be the most effective. The salinities given for the four areas represent rough approximations. (Modified from Remane and Schlieper, 1958).

Groups of Crustacea Phyllopoda Ostracoda Copepoda (Harpacticoida) Cirripedia Mysidacea Amphipoda Isopoda Cumacea Decapoda Total number of species

North Sea (ca 33%p) 6 ca 100 ca 320 10-12 15 147 35 ca 25 ca 50 708-710

Kiel and Mecklenburg Bays (ca 14&) 5 50 126 5 7 55 13 5-6 12 278-279

Southern and Middle Baltic (ca 1%) 5 20 27 5 20 8 1-2 6 93-94

1

Northern Baltic (ca 4 & ) 5 — 20 1 4 9 6 0 2 47

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degree of salinity deviation. From the North Sea north-eastwards into the Baltic Sea, for example, there exists an impressive reduction in the number of species within all taxonomic groups of Crustacea present. This reduction is due to various factors, among which salinity is doubtless of major importance (Table I ) . Within the different groups of osmoregulators distinguished above, the ability to live in salinities that deviate increasingly from the original oceanic condition, increases in the order: polystenohaline forms, euryhaline forms, oligostenohaline forms, holeuryhaline forms. This order appears at the same time often to be indicative of a concomitant reduction in the number of representative species. REFERENCES

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and M A R S H A L L , L . A . (1960). The influence of salinity on the magnesium and water fluxes of a crab. Biol. Bull. 119: 440-53. H E R R M A N N , F . (1931). Ueber den Wasserhaushalt des Flusskrebses (Potamobius astacus Leach). Zeitschr. vergl. Physiol. 14: 479-524. J O N E S , L . L . (1941). Osmotic regulation in several crabs of the Pacific Coast of North America. J . Cell. Comp. Physiol. 18: 79-92. K I N N E , O . (1952). Zur Biologie und Physiologie von Gammarus duebeni Lillj., V : Untersuchungen uber Blutkonzentration, Herzfrequenz und Atmung. Kieler Meeresforsch. 9: 134-50. (1962). Adaptation, a primary mechanism of evolution. (In press). and R O T T H A U W E , H . - W . (1952). Biologische Beobachtungen und Untersuch­ ungen liber die Blutkonzentration an Heteropanope tridentatus Maitland (Decapoda). Kieler Meeresforsch. 8: 212-17. K O C H , H . J . (1954). Cholinesterase and active transport of sodium chloride through the isolated gills of the crab Eriocheir sinensis ( M . Edw.). In Recent Developments in Cell Physiology, ed. J . A . Kitching. New York, Academic Press. 15-27. and E V A N S , J . (1956a). O n the influence of lithium on the uptake of sodium and potassium by the crab Eriocheir sinensis ( M . Edw.). Mededel. K o n . Vlaamse Acad. K l . Wet. 18: 3-10. (1956b). O n the absorption of sodium from dilute solutions by the crab Eriocheir sinensis ( M . Edw.). Mededel. K o n . Vlaamse Acad. K l . Wet. 18: 3-15. (1956c). Influence of a basic dye, thionine, on the absorption of sodium by the crab Eriocheir sinensis ( M . Edw.). Mededel. K o n . Vlaamse Acad. K l . Wet. 18: 3-11. K R O G H , A . (1939). Osmotic regulation in aquatic animals. London, New York: Cam­ bridge University Press. L I E N E M A N N , L . J . (1938). The green glands as a mechanism for osmotic and ionic regulation in the crayfish (Cambarus clarkii Girard). J . Cell. Comp. Physiol. 11: 149-61. L O C K W O O D , A . P. M . (1959). The osmotic and ionic regulation of Asellus aquaticus ( L . ) . J . Exp. Biol. 36: 546-55. (1961). The urine of Gammarus duebeni and G. pulex. J . Exp. Biol. 38: 647-58. N A G E L , H . (1934). Die Aufgaben der Exkretionsorgane und der Kiemen bei der Osmo­ regulation von Carcinus maenas. Ztschr. vergleich. Physiol. 21: 468-91. P A N I K K A R , N . K . (1939). Osmotic behaviour of Palaemonetes varians (Leach). Nature 144: 866-7. (1940). Osmotic properties of the common prawn. Nature 145: 108. (1941a). Osmoregulation in some palaemonid prawns. J . Marine Biol. Assoc. U . K . 25: 317-59. (1941b). Osmotic behaviour of the fairy shrimp Chirocephalus diaphanus Prevost. J . Exp. Biol. 18: 110. (1950). Physiological aspects of adaptation to estuarine conditions. IndoPacific Fisheries Council Proc. (Australia 2nd meet., 168-75. and V I S W A N A T H A N , R. (1948). Active regulation of chloride in Metapenaeus monoceros Fab. Nature 161: 137-8. P A R R Y , G . (1953). Osmotic and ionic regulation in the isopod crustacean Ligia oceanica. J . Exp. Biol. 30: 567-74. (1955). Urine production by the antennal glands of Palaemonetes varians Leach. J . Exp. Biol. 32: 408-22. (1957). Osmoregulation in some freshwater prawns. J . Exp. Biol. 34: 417-23. 1961a). Osmoregulation of the freshwater prawn Palaemonetes antennarius. Mem. 1st. Ital. Idrobiol. 13: 139-49. (1961b). Chloride regulation in Triops. Nature 192: 468-9. P R O S S E R , C . L . , G R E E N , J . W . , and C H O W , T . J . (1955). Ionic and osmotic concentra­ tions in blood and urine of Pachygrapsus crassipes acclimated to different salinities. Biol. Bull. 109: 99-107. and B R O W N , F . A . , J R . (1961). Comparative animal physiology. 2nd ed. Philadel­ phia and London: W. B. Saunders Co. R E M A N E , A . and S C H L I E P E R , C . (1958). Die Biologie des Brackwassers. In Die Binnengewasser, vol. 22, ed. A . Thienemann. Stuttgart: E . Schweizerbart'sche Verlagsbuchhandlung.

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R O B E R T S O N , J D . (1949). Ionic regulation in some marine invertebrates. J . Exp. Biol. 26: 182-200. (1960. Osmotic and ionic regulation. In T h e physiology of Crustacea, ed. T . H . Waterman. New York and London: Academic Press. V o l . I: 317-40. S C H L I E P E R , G . (1929). Ueber die Einwirkung niederer Salzkonzentrationen auf marine Organismen. Ztschr. vergl. Physiol. 9: 478-514. (1935). Neuere Ergebnisse und Probleme aus dem Gebiet der Osmoregulation wasserlebender Tiere. Biol. Rev. 10: 334-60. and H E R M A N N , F . (1930). Beziehungen zwischen Bau und Funktion bei den Exkretionsorganen dekapoder Grustaceen. Zool. Jahrb. (Anat.) 52: 624-30. S C H O L L E S , W . (1933). Ueber die Mineralregulation wasserlebender Evertebraten. Ztschr. vergl. Physiol. 19: 522-54. S C H W A B E , (1933). Ueber die Osmoregulation verschiedener Krebse (Malacostracen). Ztschr. vergl. Physiol. 19: 183-236. S H A W , J . (1959). Salt and water balance in the east African fresh-water crab, Potamon niloticus ( M . Edw.). J . Exp. Biol. 36: 157-76. and S T U C L I F F E , D . W . (1961). Studies on sodium balance in Gammarus duebeni Lilljeborg and G. pulex pulex ( L . ) . J . Exp. Biol. 38: 1-15. SVERDRUP, H . U . , J O H N S O N ,

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SUMMARY A N D COMMENT Lionel Walford

combine impressively to show the unity of biogeography, environmental analysis, systematics, and functional morpho­ logy, and to indicate directions which research in these fields should take to enlarge our understanding of the mechanisms controlling distributions of marine animals and plants. In spite of the grand conceptions of the New Systematics, marine biologists still lean heavily on the classical descriptions of most animals and plants of the sea, which for the most part are based on fairly gross anatomical features observed in a few presumptively typical specimens. And the principal infor­ mation available on the distribution of most marine organisms is still the total range. Thus in spite of the sophistication of modern biology, our ideas of the structure and distribution of the vast majority of marine animals and plants remain at a relatively low level. In order to raise this level, we must contend with some of the most difficult problems in all biology. Think of the elements which must be considered. Species range over very large distances, in the order of hundreds or thou­ sands of miles. They are always spottily distributed. A typical species is composed of a number of more or less separate "populations." Separate though these may be they do not necessarily live apart throughout the year. Often, if not usually, they do not differ strikingly enough or consistently enough to be identifiable with absolute certainty; nevertheless they do differ and in any or all of a variety of morphological details. Their responses to temperature of the water may vary; likewise their growth rates, reproductive seasons, fecundity, longevity, resistance to disease, habits, and body form. Unfortunately the differences are so small and so subtle that they can be detected only by statistical analysis of representative samples. How much do these variations reflect genetic differences and to what extent are they the consequence of variations in environment? It has been suggested repeatedly in this volume that experimental studies must be the best approach to answering this question. However, the technical problem of mimicking natural environments and of maintaining marine organisms in the labora­ tory through several generations must be solved first, and indeed they are being attacked in several marine laboratories in Europe, North America, and Japan. The problems of surveying the distributions of marine species in their natural habitats are also formidable. Motile forms often congregate accordT H E PAPERS I N THIS S Y M P O S I U M

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ing to size. Habits change with age. The sexes may live apart during the non-reproductive season. Many animals migrate, and the distances which they travel may change with age and the migratory routes can vary from year to year. Finally abundance of many species undergoes random fluctua­ tions as well as oscillations of varying period. As we ponder these complications it is all too obvious that sampling must be the first problem to solve in any geographical study of a marine organism. However, it is such a difficult problem that we often pretend it does not exist rather than attempt to solve it. How can samples be quantified? How should they be distributed in space and time and how should they subsequently be combined to construct an accurate complete picture of a species in which we are interested? We know from a few extensive and intensive studies that the ideal sampling plan must be designed to cover and extend beyond the whole range of the species to delineate the shapes of the distribution therein, to determine characteristics of several populations, and to describe as fully as possible the details of their environments. Because all the parameters of our subject change seasonally and vary from year to year, the ideal field program would provide for synoptic and systematic sampling. These requirements are far beyond the capacity of any one scientific institution no matter how lavishly financed, equipped, and staffed it may be. No one has enough research vessels to carry out such a program, enough assistants to go through all the drudgery of sorting and identifying the material and of tabulating the results, or enough scientists to draw the con­ clusions and write the papers. One obvious answer to this problem is co-operation. For among univer­ sities, privately endowed research institutions, and government agencies there is an astonishing number of laboratories devoted to various aspects of the marine sciences. Large-scale studies of species and their environments will become possible as these scientific forces combine in planning and carry­ ing out programs of mutual interest; and in fact the necessity for doing this is becoming increasingly recognized. If each working vessel produced a piece in a complex puzzle it would seem reasonable to expect that the chances of collecting enough pieces to solve the puzzle would improve by increasing the number of vessels. One way of doing this is by co-ordinating the pro­ grams of those that are now working independently; another is by utilizing non-research ships such as passenger liners, freighters, and fishing boats. It was this latter possibility that inspired Sir Alister Hardy to invent the continuous plankton recorder, to which Dunbar has referred in his paper. For more than ten years this ingenious instrument has been the feature of a vast sampling program carried on in the North Atlantic by commercial liners co-operating with the Edinburgh Oceanographic Laboratory. Bary has shown the kind of inferences that can be drawn from the collections of the recorder when supplemented by observations of research vessels. Bary and Grainger working with plankton in different regions of the North Atlantic have analysed distribution patterns in relation to temperature

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and salinity of the water; and in doing so they have extended the use of zooplankton species as oceanographic instruments. The value of these animals as indicators results from the fact that they move only within a small radius and therefore must remain closely associated throughout life with the water in which they originated. They can reproduce only in water having properties that satisfy their specific demands. Their tolerance ranges are generally broader for survival than for reproduction. Thus it is that a water mass can be identified by the plankton fauna which is associated with it; and where it mingles with another water mass having a different fauna, the proportions of the two in the resulting mixture at any point can be measured by the relative numbers of the different types of organisms found there. However, oceanographic indicators are not limited to the plankton com­ munities. Sedentary and sessile benthic organisms might be equally useful in this respect—in some ways even more so. For they offer the supreme advantage of staying in place throughout life once they have settled to the bottom, and therefore obviate the difficulties that plague our studies of migratory species. Although populations of sessile species are usually stable, it often happens that a current deviating from its normal course carries the young during their pelagic stages into an area where the species do not normally occur. If such a colony survives at all, the individuals might live through a normal life span and yet fail to reproduce for want of the neces­ sary combination of environmental conditions. Thus comparison between transient and permanent populations in relation to their respective environ­ ments should give strong leads to finding the factors which are critical to the survival of the species under study. For example, molluscs, which are generally fairly easy to collect, could be used as instruments for large-scale oceanographic studies—the means of a "poor man's oceanography." The patterns of distribution alone would be informative; but even more signifi­ cant is the fact that the annual rings on their shells might provide a fairly accurate estimate of the average ambient temperature where the animals actually live. Here is an opportunity for research which is going begging. Among the most accessible organisms in the sea are the attached algae. They are enormously important in the economy of shore life; for they provide the habitat of many species of animals, including juvenile fishes. Important though this may be, however, they have been rather neglected as subjects of research. Few laboratories make provision in their programs for studying sea weeds. Oceanographic expeditions do not generally include botanists among their scientific parties; and zoologists, sorting through the collections of bottom dredges, usually cast plants overboard along with the other undesired "trash" before preserving their specimens. Consequently progress in the study of systematics, distribution, life histories, and ecology of the attached algae has lagged behind other marine sciences. In studying the distribution of attached algae in relation to oceanographic conditions in the northeast Pacific, Scagel has exposed problems that can be solved only

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by intensive and extensive research in systematics and genetics to be carried on in the field and laboratory as well as in the herbarium. He has shown that the species most useful for oceanographic indicators are those which tolerate the narrowest range of environmental conditions, that is to say, those living in the lower intertidal and subtidal zones. It would be most interesting to investigate how distributions of plants correlate with those of shore-dwelling animals. How can algae be collected simultaneously and at frequent intervals over hundreds of miles of coast? Here the American Littoral Society might be of inestimable help. This is an organization of amateur diver-naturalists, formed last year under the auspices of the Sandy Hook Marine Laboratory of the United States Fish and Wildlife Service. The membership, numbering about 1500 divers distributed along the Atlantic, Gulf, and Pacific coasts, is devoted to observing and recording observations. As the need arises members respond enthusiastically when asked to collect specimens. Scientists who wish to use the service of this organization, should write to the Sandy Hook Marine Laboratory at Highlands, New Jersey. Many marine biologists have long sought to understand distributions of species wholly in terms of the environment. In the final analysis, however, the ways in which organisms respond to the sea around them must be deter­ mined by the peculiarities of their internal mechanisms. Otto Kinne's analysis has illustrated how functional morphology can explain differences in the distribution of closely related species. In examining the osmoregula­ tory mechanisms of crustaceans, he has been able to place over fifty species into four groups according to the means by which they adjust to changes of salinity. These mechanisms for taking in or eliminating water, as required, vary among different genera, and even among different species of a single genus; and of course they determine the type of water in which an animal can live and the range of salinity it can tolerate. The papers in this symposium have dealt only with temperature and salinity. As Bary has pointed out, something more must be involved, some­ thing that can be referred to now only as "unknown factors." The possibili­ ties seem infinite, for environment is composed of many things—"the aggre­ gate of all the external conditions affecting the life and development of an organism," according to Webster's New International Dictionary. As a property of the individual organism, it includes others of its own kind and other species that affect it in various ways—as prey, predators, competitors, commensals, symbionts, and carriers of parasites and diseases; it may include the sediment on the bottom and the attached algae; and of course it includes the water with its regimen of temperature and its organic and inorganic constituents. For any given species as a whole the nature of the environment may differ from one population to another; for any given population it may differ from one age group to another; and everywhere it is subject to continual change. With all these complexities, how can we know what constitutes the whole

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environment of a species? I believe that our best hope of solving this problem lies in systematic mapping of all the many elements of the marine environ­ ment—currents, bathymetry, bottom sediments, salinity and temperature fields and distributions of all species of plants and animals. By mapping all these things on a common projection, and comparing the maps, patterns that now elude us should become evident. This is the idea and plan of the new American Geographical Society's scientific journal called the Serial Atlas of the Marine Environment about which Dunbar has spoken. Certain ideas which have been implied or expressed during the symposium are so important, and yet so often neglected, in designing a biogeographic study of a species that they cannot be repeated too often. I shall attempt to summarize them as follows: 1. If clear-cut relationships between a marine population and its environ­ ment are to be demonstrated, it is absolutely essential that data concerning the two be collected concomitantly. In other words, distribution of a species in one epoch cannot be explained clearly, if at all, by environmental condi­ tions in another. 2. The accuracy with which distributions can be plotted is a function of the closeness of sampling in space and time. 3. For analysis of a species' environment, many factors must be surveyed. 4. The ideal biogeographical study over the entire range of the species being investigated should be covered. The sampling should be carried on systematically and synoptically. This can be accomplished only by the co­ operation of many laboratories in various ways, for example—by co-ordina­ tion of research programs; by standardizing sampling methods; and by recording and publishing distribution data on maps drawn to a common projection, as in the Serial Atlas of the Marine Environment.