The Ecology of Sandy Shores [3rd ed.] 978-0-12-809467-9

Table of contents :
THE ECOLOGY OF SANDY SHORES......Page 1
Copyright......Page 2
Acknowledgments......Page 3
Alexander Claude Brown 1931–2005......Page 4
1 - Introduction......Page 5
2.2 The Littoral Active Zone......Page 8
Particle Size......Page 9
Penetrability......Page 13
Types of Waves......Page 14
Refraction......Page 15
Shoaling and Breaking......Page 16
Bound and Infragravity Waves: Surf Beat......Page 18
Tides......Page 19
Wind......Page 21
2.7 Interactions Among Beach Slope, Waves, Tides, and Sand......Page 23
2.8 Beach Indices......Page 24
Wave-Dominated Beaches......Page 25
Tidal Effects......Page 28
2.10 Circulation Cells and Mixing......Page 31
2.11 Embayments and Headlands......Page 32
2.12 Swash Climate......Page 33
2.14 Latitudinal Effects......Page 36
2.15 Conclusions......Page 37
Mineralogy......Page 39
Porosity......Page 40
Pore Size......Page 41
Moisture Content......Page 42
Thixotropy and Dilatancy......Page 43
Groundwater Discharge......Page 44
Beach Face Wave Run-up......Page 45
Subtidal Wave Pumping......Page 47
Volumes and Residence Times of Tide- and Wave-Driven Inputs......Page 48
Flow Patterns and Interstitial Climate......Page 50
Tidal Effects......Page 54
Influence on Beach Face Erosion/Accretion......Page 55
Zones of Interstitial Moisture......Page 56
Salinity......Page 58
Oxygen Concentrations......Page 59
Nutrients......Page 61
3.7 The Interstitial Environment......Page 62
3.8 Conclusions......Page 64
4.2 Benthic Microflora......Page 65
4.3 Surf-Zone Phytoplankton......Page 67
4.4 Seagrasses......Page 73
4.5 Conclusions......Page 74
Phylum: Cnidaria......Page 76
Phylum: Nemertea......Page 77
Phylum: Kinorhyncha......Page 78
Phylum: Annelida......Page 79
Phylum: Brachiopoda......Page 84
Phylum: Mollusca......Page 85
Phylum: Arthropoda......Page 88
Phylum: Bryozoa......Page 101
5.3 Conclusions......Page 102
6.1 Introduction......Page 103
Burrowing......Page 104
Surfing and Coping With Swash......Page 109
6.3 Rhythms of Activity......Page 111
6.4 Sensory Responses and Orientation......Page 117
6.5 Choice of Habitat......Page 120
6.6 Nutrition......Page 124
6.7 Respiration......Page 126
6.8 Environmental Tolerances......Page 130
6.9 Reproduction......Page 132
6.11 Avoidance of Predators......Page 134
6.12 Phenotypic Plasticity......Page 135
6.13 Conclusions......Page 137
7.1 Introduction......Page 139
Sample Area and Species Accumulation Curves......Page 140
Species–Area Relationships......Page 141
7.3 Taxonomic Composition......Page 143
Species Richness......Page 145
Abundance, Biomass, and Density......Page 147
Latitude......Page 149
Factors Controlling Large-Scale Patterns......Page 158
Deconstructing Diversity......Page 161
Other Trends: Body Size and Density......Page 163
Body Size......Page 164
Beach Length......Page 166
Alongshore Variation......Page 167
Across-Shore Variation......Page 170
Zonation......Page 171
Temporal Changes in Zonation......Page 176
7.6 Microscale: the Forgotten Dimension......Page 178
7.7 Species Interactions......Page 180
Trophic Relations......Page 181
Predation......Page 182
Competition......Page 184
Mutualism and Commensalism......Page 187
Disturbance, Succession, and Colonization......Page 189
7.8 Conclusions......Page 190
Latitude......Page 192
Beach Types, Zones, and Life Histories......Page 194
Metapopulations and Connectivity......Page 197
Long-Term Fluctuations......Page 202
Alongshore......Page 207
Across Shore......Page 210
Temporal Changes......Page 214
8.4 Microscale Patterns......Page 215
8.5 Conclusions......Page 217
9.1 Introduction......Page 218
9.2 Interstitial Climate......Page 219
9.4 Interstitial Biota......Page 220
9.5 Distribution of Interstitial Fauna......Page 223
9.6 Temporal Changes......Page 225
9.7 Meiofaunal Communities......Page 227
9.8 Trophic Relationships......Page 230
9.9 Biological Interactions......Page 231
9.10 Meiofauna and Pollution......Page 232
9.11 Conclusions......Page 233
Composition......Page 236
Sampling......Page 237
Migrations......Page 238
Distribution......Page 239
Food and Feeding Relationships......Page 241
Sampling......Page 242
Larvae, Juveniles, and Nursery Areas......Page 243
Surf-Zone Fish Assemblages......Page 248
Temporal Variability......Page 250
Spatial Variability......Page 253
Trophic Relationships......Page 255
10.4 Other Groups......Page 257
10.5 Conclusions......Page 258
11.2 Turtles......Page 260
Nesting......Page 262
Threats and Conservation......Page 264
Seasonality and Migrations......Page 265
Foraging......Page 266
Human Impacts......Page 269
11.4 Conclusions......Page 270
12.1 Introduction......Page 271
12.2 Food Sources......Page 272
12.3 Macroscopic Food Webs......Page 274
India......Page 278
Western Australia......Page 280
Eastern Cape, South Africa......Page 281
Uruguay......Page 282
Food Web Dynamics and Trophic Niche Shifts......Page 283
Other Spatiotemporal Variations in Organic Inputs......Page 287
12.4 Interstitial Food Webs......Page 288
Western Cape......Page 290
Eastern Cape......Page 291
12.5 The Microbial Loop in Surf Waters......Page 292
12.6 Energy Flow in Beach and Surf-zone Ecosystems......Page 295
12.7 Case Study: Sandy Beaches of the Eastern Cape......Page 296
12.8 Nutrient Cycling......Page 300
12.9 Conclusions......Page 305
13.2 The Physical Environment......Page 307
13.3 Coastal Dune Formation by Vegetation......Page 309
13.4 Dune Types......Page 310
13.5 Edaphic Features......Page 313
13.6 Water......Page 314
13.8 Dune Vegetation......Page 315
13.9 The Fauna......Page 320
13.10 Food Webs......Page 322
13.11 Dune–Beach Exchanges......Page 325
13.12 Conclusions......Page 327
Fishery Types......Page 328
Surf-Zone Fauna......Page 330
Supralittoral and Intertidal Benthic Invertebrates......Page 331
Intertidal Polychaetes and Crustaceans......Page 332
Clams......Page 334
System Structure......Page 337
Main Components......Page 339
Spatial Structure......Page 340
Metapopulations......Page 341
Ecological Effects of Fishing......Page 342
External Drivers......Page 343
14.4 Harvesting Phases and Long-term Trends......Page 345
Harvesting Phases......Page 347
Long-term Bioeconomic Trends......Page 348
Information Requirements for Monitoring Stock Condition......Page 352
Main Concepts......Page 355
Assessing Trends in Reference Points......Page 357
Governance......Page 360
Single Species and the EAF......Page 361
Spatially Explicit Strategies......Page 364
Territorial Use Rights and Privileges......Page 367
Case Study: The Surf Clam in Chile......Page 368
Case Study: Shellfishes in Galicia, Spain......Page 369
14.7 Conclusions......Page 370
15.1 Introduction......Page 372
Off-road Vehicles......Page 373
Trampling and Related Recreational Activities......Page 377
Beach Cleaning......Page 379
Eutrophication: Green and Golden Tides......Page 381
Crude Oil Pollution......Page 382
Plastics and Microplastics......Page 388
Sewage and Organic Enrichment......Page 390
Heavy Metals......Page 391
Effluents......Page 392
15.5 Biological Invasions......Page 394
15.6 Natural Perturbations......Page 395
15.7 Nourishment......Page 396
15.8 Mining......Page 399
The Role of Human Pressure......Page 400
Disrupting Sediment Transport......Page 402
15.10 Human Influence on the Evolution of Beaches......Page 406
Assessment Approaches: Warnings and Perspectives......Page 409
Indicators......Page 410
The Triad Approach in Pollution Assessments......Page 412
Toxicity Studies......Page 414
15.12 Conclusions......Page 415
16.1 Introduction......Page 418
Ocean Warming......Page 420
Sea-level Rise......Page 421
Extreme Events and Winds......Page 422
Life Histories and Differential Responses to Climate Change......Page 424
Distribution, Range Shifts, Mass Mortalities, and Extirpations......Page 427
Demography and Population Dynamics......Page 431
Community and Ecosystem Responses......Page 433
Tipping Points and Regime Shifts......Page 435
16.5 Socioeconomic Effects and Management......Page 436
Managing Climate Change Effects......Page 437
Effects on the Environment......Page 439
Effects on the Biota at Different Organizational Levels......Page 441
16.7 Conclusions......Page 447
17.1 Introduction......Page 448
17.2 The Fragile Littoral Active Zone......Page 449
Manage the LAZ as a Unit......Page 451
Protect the Foredunes as a Buffer......Page 452
Employ Setbacks to Keep the LAZ Intact......Page 453
Assess Shoreline Status and Erosion Risks......Page 456
Determine Pollution, Health, and Safety Levels......Page 458
Undertake Environmental Impact Assessments......Page 459
Objectives, Components, and Phases......Page 460
Restoration, Rehabilitation, and Mitigation......Page 462
Control Access and Estimate Carrying Capacity......Page 463
Mesoscale Zoning......Page 466
Manage Sandy-Beach Services as SESs......Page 468
Address Governance Structure and Processes......Page 469
Identify Relevant External Drivers......Page 473
Core Management Approaches......Page 474
Managing for Recreation, Conservation, and Multipurpose Use......Page 478
Conservation: Sundays River Beach, South Africa......Page 481
Mixed-Use, High Conflict Potential: Mon Repos, Queensland, Australia......Page 483
Limited Use: Maule, South Chile......Page 484
Conservation and the Role of Protected Areas......Page 485
Are Sandy-Beach Ecosystems at Risk......Page 488
17.5 Conclusions......Page 490
17.6 Epilogue......Page 492
The Chemical Environment of Sediments......Page 493
Glossary......Page 495
References......Page 499
B......Page 539
C......Page 541
E......Page 542
F......Page 543
H......Page 544
I......Page 545
L......Page 546
M......Page 547
N......Page 548
P......Page 549
S......Page 551
T......Page 554
X......Page 555
Z......Page 556

Citation preview

THIRD ENGLISH EDITION OF BROWN AND McLACHLAN’S ‘SANDY SHORES’

THE ECOLOGY OF

SANDY SHORES ANTON McLACHLAN

NELSON MANDELA UNIVERSITY SOUTH AFRICA

OMAR DEFEO

FACULTAD DE CIENCIAS UNIVERSIDAD DE LA REPÚBLICA URUGUAY

Academic Press is an imprint of Elsevier 125 London Wall, London EC2Y 5AS, United Kingdom 525 B Street, Suite 1800, San Diego, CA 92101-4495, United States 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom Copyright © 2018 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN: 978-0-12-809467-9 For Information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Candice Janco Acquisition Editor: Louisa Hutchins Editorial Project Manager: Emily Thomson Production Project Manager: Punithavathy Govindaradjane Designer: Greg Harris Typeset by TNQ Books and Journals

Acknowledgments We all stand on the shoulders of those who have gone before. This old saying is equally true of this book, resting as it is on the labors of many who, for almost a century, have been fascinated by sandy beaches and their inhabitants. The contents of the following pages are based on the studies of many ecologists, biologists, geomorphologists, and others who have been lured by the sand at the edge of the sea. We would like to acknowledge them all, too numerous to list, and especially the friends, colleagues, and students with whom we have ventured into the field, discussed beaches over camp fires or glasses of wine, and collaborated in writing proposals and papers. Indeed, this camaraderie has been perhaps the most memorable aspect of our time spent pondering sandy beaches. In particular, we would like to acknowledge the following colleagues and friends for reviewing chapters and giving us permission to use their photographs: Cover—photos by Diego Caballero Sadi, Linda Harris, and Víctor Scarabino. Tribute to AC Brown—photos by Linda Harris and Andrea Plos. Chapter 2—Andy Short for revision and two photos; Anita de Álava for photo. Chapter 3—Olav Giere and Hans Brumsack for reviews. Chapter 4—Clarisse Odebrecht and Debbie du Preez for reviews; Ernesto Arias for seagrass photo. Chapter 5—Fabrizio Scarabino for reviewing “worms” and mollusks sections; Jim Lowry for the talitrid section; Linda Harris and Juan Pablo Lozoya for photos; Coenraad van der Westhuizen for scans of line drawings. Chapter 6—Felicita Scapini for review and added insights and Linda Harris for photo. Chapter 7—Rafael Barboza for review; Carlos AM Barboza for editing some figures. Chapter 8—Linda Harris for review. Chapter 9—Olav Giere and Tatiana Maria for review. Chapter 10—Alan Whitfield for review; Thiebaut Bouveroux for cetacean photo; illustrations of fishes in Fig. 10.8 supplied courtesy of the South African Institute for Aquatic Biodiversity, a Research Facility of the South African National Research Foundation. The illustrations are by Elaine Heemstra from

Coastal Fishes of Southern Africa (2004) by Phil and Elaine Heemstra. Chapter 11—Ronel Nel, Linda Harris, and Paul Martin for reviews; Linda Harris for photos of turtles; and Tris Wooldridge and Diego Caballero Sadi for bird photos. Chapter 12—Diego Lercari for review. Chapter 13—Patrick Hesp for review and photos of foredunes and parabolic dunes; Werner Illenberger for photo of transgressive dunes. Chapter 14—Ignacio Gianelli and Jeremy Pittman for reviews. Greg Ferguson, Sebastián Villasante, Lorenz Hauser, Jenny Dugan, and Dave Hubbard for data and insights for specific fisheries. Jaime Aburto, Leandro Bergamino, the Coastal Education and Research Foundation, Karina Vergara, Sebastián Tapia, Gordon Watson, and Sebastián Horta for photos. Chapter 15—Martin Thiel for providing useful insights for plastics. Linda Harris, Andrew Huckbody, Mariano Lastra, Pete Peterson, Nolwenn Quillien, and Dave Schoeman for photos. Chapter 16—Dave Schoeman for review and photo. Chapter 17—Michael Elliott and Charles Finkl for review; Tatiana Cabrini for photo and Ricardo Cardoso for data. We thank our wives, Hester and Anita, for sharing our enthusiasm, tolerating our many absences, and for their encouragement in so many ways. Anita carefully edited all references. Eleonora Celentano has helped hugely with preparation of many figures. Diego Defeo helped in redrawing some figures. Anita and Eleonora made a thorough revision of the final version of the book. Omar has enjoyed great support, material and moral, from the Faculty of Sciences, the National Direction of Aquatic Resources and CSIC of Uruguay, and Anton from colleagues at Nelson Mandela University. Emily Thomson, Punithavathy Govindaradjane and their colleagues at Elsevier have been an invaluable source of encouragement and assistance. Finally, we remember our friend Alec Brown, the force behind the first edition of this book. We have been very conscious, during our almost 2 years of work on this third edition, of Alec’s presence as we rework chapters, especially those he first wrote. We trust he is pleased with our endeavors.

ix

A Tribute to Alec Brown ALEXANDER CLAUDE BROWN 1931–2005

Bullia at sunrise, photo by Linda Harris; Alec Brown, photo by Andrea Plos.

Alec Brown was a gentle, modest individual who had a passion for the molluskan fauna of sandy beaches. He made huge contributions to our knowledge of sandy beaches over a lifetime of dedicated research. Alec started working on sandy beaches and their faunas in the early 1960s, long before this became a recognized field in coastal ecology. His focus soon fell on sandy beach whelks and, together with Alan Ansell, among others, he laid the foundation for much of what we know about the ecophysiology of sand beach fauna today. Alec joined the CSIR in South Africa after his MSc and moved on to the University of Cape Town (UCT) where he completed a PhD in 1969 and was awarded a DSc in 1979. During a distinguished career in the Zoology Department at UCT, he served terms as Head of Department and simultaneously as acting Dean of Music! He retired as Emeritus Professor in 1996 but continued teaching in the Department till 2002. Between 1954 and 2004, Alec produced 200 publications, including four papers in Nature, and several books. A distinguished musicologist and teacher, he received numerous awards, fellowships, and medals. His research interests included tanaeid taxonomy, marine pollution, and the ecophysiology of sandy beach macrofauna, especially whelks of the genus Bullia. Alec was blessed with a long and happy marriage and close family. His devotion to Ros was obvious during visits to their home in Cape Town. He was always curious and with an enquiring mind, humility, and humor, all these characteristics becoming evident whenever he talked about the mollusks of sandy beaches, which he so loved. He gave a keynote address at the first international symposium on sandy beaches in Port Elizabeth in 1983. Alec’s most important contributions to sandy beach science are probably his insightful reviews and this book on sandy beach ecology. He was the prime mover for the first edition (1990), which was translated into Japanese. Unfortunately, he did not live to see the appearance of the second edition (2006). The chapters on “Sandy Beach Invertebrates” and “Adaptations to Sandy Beach Life” are still largely in the form he wrote them for the first edition. The physiology of macrobenthos was a dominant area of study in the early decades of sandy beach research. Perhaps due to the fact that Alec and others laid such a firm foundation, there is now a perception that most of the basic ecophysiology is well understood. While there will always be more to learn, this says a great deal for the contributions Alec and others made. Those of us who find fascination in sandy shores are fortunate to be able to follow Alec’s deep footprints in the sand.

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C H A P T E R

1

Introduction Ocean sandy beaches are dynamic environments that make up two-thirds of the world’s ice-free coastlines. Here sea meets land, and waves, tides, and wind engage in a battleground where they dissipate their energy in driving sand transport. The alternating turbulence and peace of the beach environment enhance its scenic and aesthetic appeal, while its relative simplicity provides an ideal template for research. This should attract the student of coastal ecology. However, the biological study of sandy beaches has traditionally lagged behind that of rocky shores and other coastal ecosystems (Fairweather, 1990; McLachlan and Defeo, 2013). A few farsighted workers produced seminal papers, for example, Bruce (1928) in England, Stephen (1931) in Scotland, Remane (1933) in the North Sea, and Pearse et al. (1942) in the United States, but for the most part, scientific investigation, as opposed to casual observation and intermittent beachcombing, began only some 50 years after the first intensive studies of rocky shores. The reasons for this early neglect of sandy beach ecosystems are not far to seek. Unlike sandy beaches, rocky shores teem with obvious life. Many of the plants and animals are large and highly colored and, when the tide is out, the life in rock pools may be observed without undue effort. Sessile or slow-moving animals are not only easy to collect, but the biologist may also enclose or exclude species from an area to study biological interactions and recolonization. None of these things is true of any but the most sheltered sandy beaches. To the casual observer, exposed intertidal sands may seem almost devoid of life. There are no attached plants intertidally; the majority of the animals are too small to be seen conveniently with the naked eye, and most macrofaunal invertebrates are cryptic, hiding within the sand and emerging only when necessary to feed or to perform other vital functions, often when covered by the tide. On a sheltered beach, the openings of burrows may give visible evidence of the life within the sand, but on beaches exposed to heavy wave action, the sand is far too unstable to support burrows intertidally. As the sand surface is in constant movement while covered by the tide, so must the animals themselves be highly mobile to maintain their positions on the beach or to regain them if swept out to sea. This mobility, coupled with a semicryptic mode of life, renders the observation of sandy beach animals in situ far more difficult than for other shore types—there simply appears to be little there. Indeed, sandy beaches have been likened to marine deserts. Yet the ocean beach is teeming with life, microscopic and macroscopic. The spectrum of life in the sand includes clams, whelks, worms, sand hoppers, crabs, sea lice, sand dollars, and a host of smaller animals, as well as protozoans, microscopic plants, and bacteria. In addition The Ecology of Sandy Shores, Third Edition http://dx.doi.org/10.1016/B978-0-12-809467-9.00001-1

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1. INTRODUCTION

to these residents of the intertidal beach, a variety of species move up over the beach from the surf zone on the rising tide, while others descend onto the beach from the dunes on the falling tide. All these components interact in a trophic network to create the open ecosystem of the sandy beach, which exchanges materials with sea and land. Increasingly, we have begun to realize that sandy beaches are not marine deserts but are interesting and often productive ecosystems. And so, fortunately, the earlier neglect of sandy beaches by researchers has been quite strongly addressed in the past few decades, providing the material for this book. Although most early work on sandy beach ecology was descriptive, this has changed since the 1970s and 1980s. The complexity of the interactions between the surf-zone fauna and flora, the animals of the intertidal slope and the backshore biota were brought home to workers in this field at the first international symposium on sandy beaches in 1983 (McLachlan and Erasmus, 1983), where sandy beach ecology emerged for the first time as a distinct field of coastal science. In the decade following that symposium, systems energetics was a major theme among sandy beach researchers. Many ideas emerging from that phase of sandy beach research were covered in the first edition of this book (Brown and McLachlan, 1990). In the 16 years after the first edition, international sandy beach symposia (ISBSs) numbers II, III, and IV were held in Chile (1994), Italy (2001), and Spain (2006), respectively; the latter coinciding with the publication of the second edition of this book. During this period emphasis not only shifted to macrobenthic population and community ecology, but also to greater awareness of threats to coastal systems and the need to transfer research results to coastal managers and policy makers. Since the publication of the second edition of this book, three further ISBSs have taken place: number V was held in Morocco in 2009, number VI in South Africa in 2012, and number VII in Brazil in 2015. Over this 10-year period emphasis has shifted to the perception of beaches as social–ecological systems and broader issues of conservation and management in the light of global change. Now held every 3 years, these ISBSs have become a regular part of the sandy beach research landscape. The aim of this third edition of Sandy Shores is to present an integrated account of sandy shore ecology, including the surf zone, the intertidal slope, the back beach, and the dunes. Since the second edition, our appreciation of the problems and pressures facing sandy coasts and the need for research and monitoring to inform strategic planning and coastal conservation and management have increased to a high priority; so this third edition includes major additions to these aspects of beach ecology. As before, we consider beaches as ecosystems: human impacts, climate change, sustainable fisheries, conservation, and management of these social–ecological systems are stressed, and new sections are added based on recent developments. For a full listing of the sandy beach ecological literature before 1990, the reader is referred to McLachlan and Erasmus (1983) and Brown and McLachlan (1990). This book is unashamedly biased in favor of exposed beaches of pure sand. We have omitted consideration of estuarine sand flats, and such sheltered environments are mentioned only in passing; attention being concentrated on the world’s open, oceanic beaches. Because these are dynamic systems, mostly physically controlled, our account begins with two chapters appraising the physical environment of the sandy beach. This is appropriate because it is essential for any beach ecologist to have a sound understanding of the main features and processes of the physical environment of the sandy beach. Following this are chapters on the main components of flora and fauna; thereafter beach and dune systems are considered as a whole.

INTRODUCTION

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FIGURE 1.1  Swash modifies the beach face with every tide—a fresh look always awaits the student. Photo by Anton McLachlan.

Because sandy coastlines, in general, and especially their associated dune systems, are fragile environments facing many threats and because most are eroding, they require conservation and special management frameworks if they are to continue to function ecologically and provide for quality recreation. Appropriate management and successful conservation can only be achieved if the complex ecology of these ecosystems is understood, including humans as keystone species in the system. Indeed, human preference for coastal areas is increasing exponentially, making sandy beaches one of the largest social–ecological systems globally as they extend across different cultures and environmental conditions. Thus, sandy beaches can contribute to a global and fascinating model if we understand how the goods and services they provide will respond to the unprecedented environmental changes that are currently occurring. Furthering this understanding is also the task of this book. Ocean sandy beaches are wonderful venues for recreation for everyone. They are also fascinating and important ecosystems for the student of coastal ecology (Fig. 1.1). They are magnets that draw our attention by their dynamic beauty and their contrasting restlessness and tranquility. And they still hold many secrets awaiting discovery. Willard Bascom’s (1964) epilogue is as true today as it was more than half a century ago: “Fortunately the beaches of the world are cleaned every night by the tide. A fresh look always awaits the student, and every wave is a masterpiece of originality. It will ever be so. Go and see.” We hope the chapters that follow will encourage the reader to do just that.

C H A P T E R

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The Physical Environment 2.1 INTRODUCTION Sandy coastlines are dynamic environments where the physical structure of the habitat is determined by the interaction between sand, waves, and tides. Sandy beaches constitute one of the most resilient types of dynamic coastline because of their ability to absorb wave energy. This wave energy is expended in breaking waves and driving surf zone circulation, which carries sand offshore during storms and moves it back onshore during calms. The beach is characterized not only by wave-driven sand transport but also by aeolian (wind) transport in the backshore and dunes. Most beaches are backed by dunes and interact with them in terms of sediment budgets by either supplying or receiving sand. This sediment transport, in the surf zone by wave action and in the dunes by wind action, has both a shore-normal and a longshore component. On many coasts, longshore transport accounts for vast volumes of sand. The sandy beach is thus an extremely dynamic environment where sand and water are always in motion. After defining the littoral active zone and before considering the overall interactions of these parameters, it is appropriate to examine the characteristics of the defining elements – sand, waves, and tides. Thereafter, we explore the kinds of beaches that result from these interactions and some of their key processes. Two useful general references covering physical processes and features of beaches are Komar (1998) and Short (1999).

2.2  THE LITTORAL ACTIVE ZONE Sandy shores consist of three entities – surf zones, beaches, and dunes – which are linked by the interchange of material, particularly sand (Dyer, 1986; Komar, 1998). Together they comprise a single geomorphic system, termed the littoral active zone (Fig. 2.1) (Tinley, 1985). This is the part of the coast characterized by wave- and wind-driven sand transport and it lies between the outer limit of wave effects on seabed stability (usually between 5 and 20 m depth) and the landward limit of aeolian sand transport (i.e., the landward edge of the active dunes). Although this area constitutes a single geomorphic system, it consists of two distinct ecological systems: a marine beach/surf zone ecosystem populated by marine biota and strongly influenced by wave energy and a terrestrial dune system inhabited by terrestrial plants and animals and strongly influenced by wind energy. In this chapter, we consider The Ecology of Sandy Shores, Third Edition http://dx.doi.org/10.1016/B978-0-12-809467-9.00002-3

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2.  THE PHYSICAL ENVIRONMENT

Break point

Nearshore

Limit of Low tide active mark Storm dunes drift line

Surf zone

Foredunes Backshore Beach

Limit of dunes

Secondary dunes

Forest

Littoral Active Zone

FIGURE 2.1  The littoral active zone (see Chapter 13 for coverage of dunes and Chapter 17 for management and conservation issues).

the physical features of the beach and surf zone and in Chapter 13 we consider the physical features of coastal dunes. In managing sandy coastlines, it is imperative that the contrast between the beach/surf and dune systems is borne in mind, although the two should be managed as a unit (see Chapter 17). The sandy beach and surf zone form the coast’s main wave dissipating apron, and foredunes are only called into play to release their sand during extreme storms. Together, beaches and dunes act as a protective buffer against storms and sea-level rise, and, being interdependent through sediment transport and storage, removal of sand from one compartment affects the others. This zone is resilient as long as it remains free to fluctuate within its natural boundaries, i.e., its sand budget remains intact. The surf zone and beach are malleable and fairly durable. The backshore and dunes are much more sensitive to disturbance because vegetation not only maintains a tenuous foothold here, but they also form an important part of the coastal sand reservoir. Thus, sand, the defining element in these systems, is a good place to start our exploration of the littoral active zone.

2.3 SAND Particle Size Sand originates mainly from erosion of the land and is transported to the sea by rivers. Beaches may, however, also receive sand from biogenic sources in the sea such as animal skeletons and from sea cliff erosion. The two main types of beach material are quartz (or silica) sands of terrestrial origin and carbonate sands of marine origin. Quartz sands have a slightly lower density (2.66 g/cm3) than carbonate sands (2.7–2.95 g/cm3 for calcite and aragonite) and quartz particles tend to be more rounded. Despite their higher density, calcium carbonate particles sink more slowly in water because of their more irregular shapes. Other materials that may contribute to beach sands include heavy minerals, basalt (volcanic rock), and feldspar. The most important feature of sand particles is their size. Particle size is generally classified using the Wentworth scale, in phi units, where φ = −log2 diameter (mm). This classification is summarized in Table 2.1. Analysis of sand particle size can be accomplished using either a settling tube or a nest of sieves. Use of a settling tube is based on Stokes’ law, which defines the rate of sinking of

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2.3 Sand

TABLE 2.1  Wentworth Size Scale for Sediments

Gravel

Sand

Mud

Generic Name

Wentworth Scale Size Range (φ)

Particle Diameter (mm)

Boulder

256

Cobble

−6 to −8

64 to 256

Pebble

−2 to −6

4 to 64

Granule

−1 to −2

2 to 4

Very coarse

0 to −1

1.0 to 2.0

Coarse

1 to 0

0.50 to 1.0

Medium

2 to 1

0.25 to 0.50

Fine

3 to 2

0.125 to 0.25

Very fine

4 to 3

0.0625 to 0.125

Silt

8 to 4

0.0039 to 0.0625

Clay

>8

8 m. The world’s highest tide range is 14 m in the Bay of Fundy. In the deep ocean, tide range tends to be smaller toward the equator (∼18 cm) and larger toward the poles. In general, it is tide range rather than tide type that is most important in sandy beach ecology.

18

2.  THE PHYSICAL ENVIRONMENT

Direction of the sun

Moon

Tide range

Day

1

8

Moon phase Full Tide phase Spring

3rd

15

quarter Neap

New Spring

22 1st

29

quarter Neap

Full Spring

FIGURE 2.10  Weekly tidal variations caused by changes in the relative positions of the earth, moon, and sun. After Sumich, J.L., 1999. An Introduction to the Biology of Marine Life, second ed. McGraw-Hill, Boston.

Diurnal

Tide height (m)

Semidiurnal 3

Mixed semidiurnal

High tides

2

Lower high tide

High tide

1 0 -1

Low tide

Low tides 0

12

24

0

12

24

0

Lower low tide

Higher high tide

Higher low tide 12

24

Time (h)

FIGURE 2.11  Three common types of tides. After Sumich, J.L., 1999. An Introduction to the Biology of Marine Life, second ed. McGraw-Hill, Boston.

Internal Waves Gravity waves occur at the interface between water and air, whereas internal waves occur at the boundary between water layers of different densities. Because the difference in density between two such layers is much less than that between water and air, greater wave heights, up to 30 m or more, can be supported. Internal waves may be caused by tides, underwater avalanches, or wind. They move slowly, with periods of 5–8 min and wavelengths of 0.5– 1 km. Internal waves may cause fluctuations in water level in the surf zone.

Wind The shear stress on the sea surface caused by wind blowing over it induces a water current in the same direction as the wind. This flow decreases rapidly below the surface and is

2.5  Other Drivers of Water Movement

19

FIGURE 2.12  The geographical occurrence of the three types of tides (upper panel, image modified from NOAA Ocean Service Education) and tidal ranges (lower panel, modified from National Tidal Centre, Australian Bureau of Meteorology).

deflected because of Coriolis forces, to the left in the Southern Hemisphere and to the right in the Northern Hemisphere. Generally, surface water movement is at about 2% of wind speed. Winds are important in shaping wave characteristics. Strong onshore winds increase wave height and the tendency for spilling breakers, thereby increasing the size of the surf zone. Offshore winds flatten the surf and increase the tendency for plunging breakers. At the coast, winds can also cause upwelling of cooler bottom water and downwelling of warmer surface water. Winds are also responsible for sediment transport from the beach to the dunes and vice versa (see Chapter 13).

20

2.  THE PHYSICAL ENVIRONMENT

2.6  SAND TRANSPORT Water movement results in shear stress on the sea bed. This may move sand off the bed into the water column, whereupon it can be transported. The coarsest sands occur around the break point and sands generally become finer offshore and onshore, corresponding to the distribution of current velocities. As shear stress on the bed increases with a shoaling wave, a point is reached where the drag on sand particles becomes sufficient to rock them to and fro. Closer inshore, this movement is accentuated. Cyclic water movement leads to the formation of ripples in the sand; in shallow water the size of the ripples increases with increasing particle size and wave height or current speed, up to a maximum current speed of 1 m/s, above which the ripples become washed out until the bed becomes smooth. Sand can be transported in two modes: as bed load and as suspended load. Suspended load is that part transported in the water column above the bed. Oscillating flow over ripples sets up eddies in the lee of the ripples, which explode when the flow is reversed and material is ejected beyond the crest of the ripples. Gravity pulls these particles downward, while turbulence carries them upward. A balance is reached, with an equilibrium profile of material suspended at various levels in the fluid. Sediment may also be suspended by plunging breakers. Bed load is defined as that part of the total volume of material moving close to the bed and not much above ripple height. Coarser material is mainly carried as bed load. This transport may be in a longshore and in an on-offshore direction. During oblique storm wave attack, large amounts of sediment may move alongshore, mostly in the outer surf zone, where turbulence is greatest. Longshore transport is one of the most important processes occurring on exposed beaches and is the focus of much attention by coastal zone managers (Chapter 17). Longshore sand transport along exposed beaches can exceed 100,000 m3/ year, and blocking this with coastal engineering structures can cause accretion and erosion problems of great magnitude. Return flow of water setup in the surf zone by breakers may be in the form of either rip currents or bed return flow. Relative to these conditions, sand movement may be onshore or offshore. The lower the waves and steeper the beach, the greater will be the tendency for accretion. Beaches go through cycles of erosion and accretion coupled to changes in wave energy. During storms, beaches are eroded and flattened, whereas during calm periods sand moves slowly shoreward, causing accretion. These dynamics result in a range of beach states defined in the next section.

2.7 INTERACTIONS AMONG BEACH SLOPE, WAVES, TIDES, AND SAND The slope of a beach face depends on the interaction of the swash and backwash processes planing it. Swash running up the beach carries sand with it and therefore tends to cause accretion and a steep beach face. Backwash has the opposite effect. If a beach consists of very coarse material, such as pebbles, uprunning swashes tend to drain into the beach face, thereby eliminating backwash. Sand or pebbles are thus carried up the beach but not back again, resulting in a steep beach face. Fine-sand beaches, on the other hand, stay waterlogged

21

2.8  Beach Indices 1:100

Beach face slope

Gentle

1:50 1:30 1:20 1:15

Sh elte r ed

1:10

be ac h es

Exp

ose d be ach es

Steep

1:5

Fine

0.2

0.4

0.6

0.8

Sand particle size (mm)

1.0

Coarse

FIGURE 2.13  Conceptual model of the relationship between sand particle size and beach face slope as a function of exposure to wave action.

because of their low permeability, so that each swash is followed by a full backwash, which flattens the beach by removing sand suspended by the swash. Thus, the coarser the sand, the steeper the beach face for a given regime of wave action. If sand particle size is kept constant and wave height increased, the beach will erode and flatten. This is because bigger waves result in larger swashes, which cause a greater amount of waterlogging of the sand and greater erosion in the strong backwash. Beach slope is therefore not merely a function of particle size. This important relationship between beach slope, sand particle size, and wave action is illustrated in Fig. 2.13. Tides also influence slope, in a similar fashion to waves, i.e., beaches become wider and flatter as tide range increases. Storms generally move sand off the beach and expand the surf zone, while calm conditions have the opposite effect. The range of beach morphodynamic states resulting from the relationship between sand, waves, and tides is covered in Section 2.9.

2.8  BEACH INDICES Various indices have been used to characterize beach type. The most useful ones are: DFV (Ω)

Hb 100/W T

RTR

Tide/Hb

BI

log10 (sand·tide/slope)

Slope*

1/beach face slope

Here, DFV, also called Ω, is the dimensionless fall velocity, Hb is significant breaker height (m), W is sand fall velocity (cm/s), T is wave period (s), RTR is Relative Tide Range, tide is maximum spring tide range (m), BI is Beach Index, slope is the beach face slope, sand is mean sand particle size in phi units + 1, and Slope* is the reciprocal of the beach face slope

22

2.  THE PHYSICAL ENVIRONMENT

(McLachlan and Dorvlo, 2005). Tables from Gibbs et al. (1971) are used to calculate settling velocities based on particle size. Most of the above indices are dimensionless. The DFV (Ω, also referred to as Dean’s parameter) is based on a measure of sand transport potential and wave energy and is essentially an index of the ability of waves to move sand. High values (>5) indicate much erosion of the beach by waves and hence a flat or dissipative beach. Conversely, low values (90% of 39 million fishers (Kalikoski and Franz, 2014). The increase in global human fish consumption, which reached a new record high of 20 kg per capita in 2014, could be partially met through aquaculture (mostly in developed nations), but in many of the poorest states it will be met through increased take by artisanal fishers. Therefore, management plans are needed to sustain fisheries over time and to contribute significantly to food security and adequate nutrition for a global population expected to reach 9.7 billion by 2050 (FAO, 2016). In this chapter, we summarize the available information on sandy-beach fisheries, defining some of the main fishery and ecological concepts connected with these resources and pointing out the temporal phases through which they have gone. We also detail the main governance modes and management systems in place and discuss future needs and challenges to be considered if the status of sandy-beach fisheries around the world is to be improved.

14.2  FISHERY TYPES, RESOURCES, AND EXTRACTION PRACTICES Fishery Types Three main types of fisheries are developed on sandy beaches: (1) subsistence, (2) recreational, and (3) commercial, the latter being developed on a small scale or artisanal basis. The Ecology of Sandy Shores, Third Edition http://dx.doi.org/10.1016/B978-0-12-809467-9.00014-X

331

© 2018 Elsevier Inc. All rights reserved.

332

14. FISHERIES

Subsistence fisheries are based on the use of marine resources primarily for food. This covers a spectrum of activities mainly employed in developing countries by intertidal food collectors, including hand gathering, traps, netting, and skin diving (Castilla, 2007). Indigenous communities with age-old knowledge and village-based management regularly exploit intertidal ecosystems (e.g., Schnierer and Egan, 2016). These subsistence activities have occurred on sandy beaches worldwide for millennia, as opposed to more recent commercial fisheries. For example, intertidal shellfish handpicking and digging in the rich upwelled waters of Chile or Peru can be traced back more than 8000 years (Jerardino et al., 1992). In Brazil, clammers have historically harvested trigonal clams (Tivela mactroides), mainly for family consumption (Turra et al., 2016a). However, little is known about subsistence fisheries, and the term subsistence has been considered obscure, because different interpretations of subsistence are used in different circumstances (Schumann and Macinko, 2007). In South Africa, for example, the Marine Living Resources Act of 1998 legally recognized subsistence fishers and made provision for the declaration of coastal areas for their exclusive use (Sowman, 2006). There, sandy-beach invertebrates (particularly crabs and sand mussels) are used for food, bait, local sale, or exchange within fisher communities (Branch et al., 2002). It has been recommended to classify as subsistence fisheries only those in which ultrapoor and vulnerable households are dependent on the activity (see details in Sowman, 2006). A recreational fishery (or “fishing for sport”; sensu Harris et al., 2002) is based on collection for bait and/or food without sale or dependence on the resource. Recreational activities can account for a large portion of the total harvest in some sandy-beach fisheries and can contribute significantly to local economies, particularly by stimulating tourism (McLachlan et al., 1996a; Harris et al., 2002; Solomon and Tremain, 2009). A commercial small-scale or artisanal fishery is based on resource harvesting, mostly for sale, by individuals or groups, using traditional methods with low levels of applied technology (Castilla and Defeo, 2001). These fisheries provide both an important source of employment for rural coastal communities and a key source of quality food, a small percentage of the catch usually being consumed by the fisher community. Most of this chapter deals with this type of fishery. In many cases, subsistence, recreational, and commercial fisheries cooccur (McLachlan et al., 1996a). All beach fisheries include some recreational components, but small-scale fisheries predominate in developing countries. The marked development and expansion of sandy-beach fisheries (see fishery phases in Section 14.4), mainly because of an exponential increase in seafood demand and unemployment in many coastal areas, has intensified extraction rates and encouraged traditional communities to shift from subsistence to commercial fisheries. Although commercial activities play an increasing role in the livelihoods of shore gatherers, there are still some regions where mollusks and crustaceans are collected for direct consumption and/or subsistence. Sandy beaches are scenic and ideal for the development of recreational activities, which can clash with commercial fisheries, especially for intertidal species (e.g., Donax serra, Donax deltoides) where beach recreation is extremely popular (McLachlan et al., 1996a; Schoeman, 1996; Murray-Jones and Steffe, 2000). The exponential growth in the number of recreational harvesters, who are usually opposed to commercial harvest, has led to increased conflict with the commercial sector. In some developed countries, recreational fisheries have tended to replace commercial fisheries (e.g., Tivela stultorum on the west

14.2  Fishery Types, Resources, and Extraction Practices

333

coast of the United States), as beach recreation has become more popular. For subtidal species, this is less of a problem because fishing effort is centered below the intertidal beach.

Harvested Resources and Extraction Practices There are two main categories of harvested resources in sandy beaches: (1) surf-zone fauna (including resident and transient fish and crustaceans), collected mainly through spearing, netting, and hooking; and (2) supralittoral, intertidal, and shallow benthic invertebrates, collected by hand picking, diving, spearing, pot trapping, and artisanal dredging. Surf-Zone Fauna Surf zones are important nursery areas for fish and are home to several resident and seasonal migrant species (see Chapter 10). A wide variety of fishes encountered in surf zones, including adults and juveniles of pelagic and demersal species, support important commercial and recreational fisheries. These fisheries are often developed close to sandy beaches, in coastal lagoons and river mouths, which are nursery grounds for several targeted species. Within these estuarine waters, recruits and juveniles inhabit unvegetated sandy shorelines (like exposed beach habitats), either as the main nursery area or as an interim nursery area (Solomon and Tremain, 2009; Defeo et al., 2011). Typical residents of sandy–beach surf zones exploited recreationally or commercially include members of the genera Trachinotus, Brevoortia, Micropogonias, Cynoscion, Odontesthes, Umbrina, Menticirrhus, Anchoa, Mugil, Trachurus, Pomatomus, Pelsartia, Sillago, various flatfishes and elasmobranchs such as Rhinobatus, Myliobatis, and Squatina. The flatfishes and batoid elasmobranchs (e.g., skates and rays) make up the demersal component (see Chapter 10). A wide variety of fishing gear is employed, including seine nets, trawl nets, trammel nets, push nets, gill nets, dredges, lines, hooks, and traps. Recreational and commercial fishing is conducted directly by individuals and groups of fishers in the shallow subtidal under benign sea conditions (Fig. 14.1). However, in the outer surf zone and the nearshore, artisanal fishers typically employ small vessels with a Gross Registered Tonnage between 3 and 10 and outboard engines 6

44

A&R

Coquina, cadelucha, wedge clam

Donax denticulatus

Caribbean

I

10

1.5

23

A

Beach clam

Donax striatus

Caribbean

I

10

1.5

35

A

Chipi-chipi

Donax cuneatus

Asia

I

12

5

85

A&R

Tuatua

Paphies donacina

New Zealand

I&S

Not known

17

109

A&R

Tuatua, southern tuatua

Siliqua patula

North America

I&S

100

5–19

170

A&R

Pacific razor clam

Tivela stultorum

North America

I&S

25

>20

187

A&R

Pismo clam

Tivela mactroides

Caribbean and South America

I&S

20

1.5–2.5

35

A&R

Guacuco, trigonal clam

Under habitat I, intertidal; S, subtidal. Under fishery type A, artisanal or small-scale; R, recreational; and *, no longer operational. Modified from McLachlan, A., Dugan, J.E., Defeo, O., et al., 1996a. Beach clam fisheries. Oceanogr. Mar. Biol. Annu. Rev. 34, 163–232.

339

Paphies subtriangulata

14.2  Fishery Types, Resources, and Extraction Practices

Mesodesma South America (=Amarilladesma) mactroides

Max Length (mm) Fishery Type

340

14. FISHERIES

FIGURE 14.6  Geographical distribution of 15 species of harvested beach clams. North America: (a) Tivela stultorum and (b) Siliqua patula. Caribbean: (c) Tivela mactroides, (d) Donax denticulatus, and (e) Donax striatus. South America: (f) Mesodesma (=Amarilladesma) mactroides and (g) Mesodesma donacium. Europe: (h) Donax trunculus. Africa: (i) Donax serra. Asia: (j) Donax cuneatus and (k) Donax faba. Australia: (l) Donax (=Plebidonax) deltoides. New Zealand: (m) Paphies ventricosa, (n) Paphies subtriangulata, and (o) Paphies donacina. After McLachlan, A., Dugan, J.E., Defeo, O., et al., 1996a. Beach clam fisheries. Oceanogr. Mar. Biol. Annu. Rev. 34, 163–232.

species at low temperatures. The subtidal shift and absence of tidal migrations in populations in areas of lower water temperature may therefore be a consequence of large size and slower burial rates.

14.3  FISHERIES AS SOCIAL-ECOLOGICAL SYSTEMS System Structure Sustainability in sandy-beach fisheries has been difficult to achieve. Decades of intensive extraction, exacerbated by local (habitat loss and deterioration, pollution, diseases, fishers’ behavior) and global (rise in demand and prices, market globalization, climate change) drivers, have led to a steadily decreasing trend in catch rates and global landings as populations have been reduced (see Section 14.4). Among the multiple reasons that could be invoked to explain this syndrome of overexploitation, some inevitably arise from the inherent characteristics of the fishery system. Undeniably, sandy-beach fisheries constitute complex SES that consist of interactive ecological and human social elements (Berkes and Folke, 1998; Ostrom, 2009). Marine ecosystems and human societies are two interrelated parts of one SES: ecosystem changes have impacts on, and consequences for, the human communities that depend on these

14.3  Fisheries as Social-Ecological Systems

341

FIGURE 14.7  Some harvested beach clam species. Sketch by Dave Hubbard. After McLachlan, A., Dugan, J.E., Defeo, O., et al., 1996a. Beach clam fisheries. Oceanogr. Mar. Biol. Annu. Rev. 34, 163–232.

systems, and vice versa (Perry et al., 2010). Thus, SES are structured by highly connected and interactive biophysical (also called “ecological”) and social (including economic, cultural, ethical, and sociopolitical aspects) subsystems that operate through interdependent feedback relationships (Perry et al., 2010, 2011). This “double exposure” (sensu Leichenko and O’Brien, 2008) has led to collapses of some sandy-beach stocks, with negative implications for numerous coastal communities in developing countries, where poor and vulnerable people draw their livelihoods from this sector (Ortega et al., 2012). Such interactive systems are sensitive to changes in environmental (e.g., temperature), economic (e.g., price shifts, market globalization, labor opportunities), and governance drivers. Thus, these SES are increasingly affected by a series of complex, interdependent, and multifaceted challenges across a wide range of countries (Defeo, 2003; Gutiérrez et al., 2011 and references therein).

342

14. FISHERIES

Governance Centralized or top-down Cogovernance Decentralized or self-governance

High-level goals Long-term policies Management plans

Biological system

Physical environment

Abundance/structure Biodiversity

Management tools Time/space Species/sizes Effort/gear

Fishing process Catch, Effort Processing sector Costs, Revenues

Processes

Stressors

Climate, Poverty, Pollution, Markets

Uncertainty

Ecological, Statistical, Socioeconomic, Governance

FIGURE 14.8  Sandy-beach fisheries as social-ecological systems: a multidimensional framework.

Main Components The fishery system can be decomposed into three interacting subsystems (Seijo et al., 1998; Ostrom, 2009): (1) the resource and its surrounding ecosystem; (2) resource users (notably including fishers), and (3) governance and management (Fig. 14.8). The subsystems have idiosyncrasies that change from fishery to fishery and from place to place (even within a single fishery). The resource subsystem includes: the physical environment affecting the abundance and spatiotemporal distribution of the harvested species; the life cycle, including population dynamics (recruitment, growth, and mortality) and structure, demography and reproductive biology of the exploited species; and ecological interdependencies. The resource users’ subsystem includes the different fishers operating in the fishery, their behavior and spatiotemporal dynamics, main targets (different species or population components in a sequential fishery), the processing sector, and economic functions. The governance and management subsystem captures the dynamics of the first two subsystems, the diverse arrays of governance structures and management tools, and external forces such as high-level governance structures, markets, and societal interests. It considers possible ways of intervention, institutional development, selection criteria for management strategies, enforcement mechanisms, and the way of contending with multiple criteria in the selection of management tools (Defeo et al., 2007). The intrinsic characteristics of the SES vary in response to different life histories, harvesting practices, management options, and governance modes, and thus the subsystems detailed above interact to give the overall system its unique behavior (Castilla and Defeo,

14.3  Fisheries as Social-Ecological Systems

343

2001). In addition, the dynamics of a fishery are influenced by other socioeconomic activities and human-induced stressors that interact and impact not only the fishery but also related ecosystem services (Österblom et al., 2017). These external drivers add dimensionality and complexity to SES (see Section 14.7). Therefore, assessing and managing sandy-beach fisheries as SES requires the integration of the biology and ecology of the resource and its surrounding ecosystem, with socioeconomic and institutional factors that affect the behavior of the system (Seijo et al., 1998; Defeo et al., 2007). Finally, high levels of uncertainty (Fig. 14.8) in ecological (e.g., environmental conditions, stock magnitude, growth, and survival rates), economic (e.g., changes in demand and unit prices), political (long-term behavior of the governance system), and statistical (e.g., availability and reliability) information impose significant barriers for effective management of these SES.

Relevant Ecological Issues for Assessing and Managing the SES Fishing impacts on sandy-beach ecosystems can be significant for various reasons: (1) target species tend to occur in patches (Defeo and Rueda, 2002; Schoeman and Richardson, 2002) and fishers can therefore serially deplete dense aggregations (Caddy and Defeo, 2003; Pérez and Chávez, 2004); (2) several commercial stocks show restricted geographical distributions or are endemic and therefore are prone to local extirpations (McLachlan et al., 1996a; Defeo, 2003); (3) most exploited stocks are also short lived and susceptible to recruitment overfishing in the short term (Defeo, 1996b); and (4) harvesting activities cause incidental mortalities, both directly through physical damage to organisms and indirectly when sediment disturbance lowers habitat quality and suitability (Sims, 1997; Defeo, 1998). Incidental mortality is not only limited to the exploited fraction of the target populations but also affects their unexploited fractions and nontarget species on fished beaches (Defeo, 1996a, 1998). These issues are analyzed in detail in the following sections. Spatial Structure Invertebrate fisheries in sandy beaches may be included in the category of so-called S-fisheries (sensu Orensanz et al., 2005) and can be defined as 6S-fisheries (Small Scale and Spatially Structured fisheries targeting Sedentary resources in Sandy beaches). Indeed, most exploited sandy-beach populations present strong and persistent spatial distribution patterns in response to an environment that is spatially and temporally structured by sharp, smallscale gradients (see Chapter 8). Aggregations may persist in time, but their relative position in the across- and alongshore directions vary according to the susceptibility of each species to variations in environmental conditions (Defeo and Rueda, 2002; Defeo and McLachlan, 2005, see Chapter 8). Thus, assessment and management of these stocks require the identification of meaningful spatial scales to provide unbiased estimates of abundance and population structure and to assess key spatial dimensions (Defeo, 2003; Caddy and Defeo, 2003; Gray, 2016a) namely: (1) population regulation mechanisms and processes and (2) the associated spatial dynamics of the harvesting process. Because of the sedentary nature of sandy-beach stocks, the spatial allocation of fishing effort is not random, but tends to be concentrated on those patches with high abundance and large individual sizes that maximize economic returns (like harvesting a forest). Thus, the relationship between abundance and catch-perunit-of-effort (CPUE) usually departs from proportionality, so CPUE often cannot be used

344

14. FISHERIES

as a reliable index of abundance in 6S-fisheries. Susceptibility to stock depletion owing to the easy removal of clumps of individuals increases the probability of overexploitation. The skill and efficiency of fishers in locating highly profitable patches, especially where larger sizes command a higher unit price, usually means that abundance tends to drop faster than CPUE as the stock is depleted (Caddy and Defeo, 2003). Metapopulations Beach clams are broadcast spawners with external fertilization and high fecundity and usually have complex life cycles defined by planktonic larvae and a benthic adult phase decoupled in time and space (Chapter 8). They are mostly structured as metapopulations. These signature characteristics of sandy-beach species go against the basic tenet of classical fishery science, the unit stock concept, thus implying that the spatial dimension of processes related to both stages of the life cycle (i.e., dispersive larvae and benthic adults) must be considered when assessing and managing these stocks. The open nature of sandy-beach stocks (i.e., metapopulations) imposes additional restrictions on the use of traditional fishery models and should imply different management strategies depending on connectivity patterns (larval replenishment and gene flow) between metapopulation components (“source– sink dynamics”, see Chapter 8 and references therein). Source habitats are considered net exporters of individuals, whereas sinks, where death rates are greater than birth rates, are net importers of individuals. Thus, sink habitats will experience a population decline toward extinction, unless enough individuals are recruited from source habitats. Following a precautionary approach, conservation efforts should be focused on source habitats (which in most sandy-beach populations occur in dissipative beaches, Celentano and Defeo, 2016) to ensure that abundance does not fall below threshold values for successful spawning and recruitment. Information derived from life history traits and stock assessments is needed to clearly define sources or sinks in a metapopulation context. This has been explicitly recognized for managing sandy-beach stocks (Caddy and Defeo, 2003). A direct consequence of the complex life cycle and source–sink process is the high variability in recruitment typically observed in long-term studies (Chapter 8). Variable mortality and dispersion rates of the planktonic phase make predictions of recruitment to the benthic life on sandy shores highly uncertain and difficult to quantify. As most exploited sandy-beach invertebrates are short lived and have rapid growth to maturity (McLachlan et al., 1996a), they are prone to large fluctuations in abundance coupled to variations in recruitment success. This high variability in recruitment makes it difficult to determine the level of parental stock that will maximize recruitment abundance. For this reason, assessing recruit abundance is a particular challenge in a fishery context and indicators of recruitment success need to be monitored periodically to provide information about stock health (see Section 14.5). Until recently, the consensus was that adult stock size was not critical in forecasting recruit abundance, but some recent studies suggest that, even for broadcast spawners, many discrete aggregations at the mesoscale (i.e., within a beach, see Chapter 8) are self-sustaining within the larger metapopulation (see example in Section 14.6). Evidence for this comes from studies conducted on source populations in dissipative beaches (Efford, 1970; Defeo, 1996a,b; Lima et al., 2000). This population typography has advantages for management purposes, because of the possibly reduced importance of larval exchanges. However, dispersal in sandy-beach populations also occurs, and therefore the dynamics of larval dispersal from source (e.g., dissipative beaches)

14.3  Fisheries as Social-Ecological Systems

345

to sink (e.g., reflective beaches) is a critical process that needs to be addressed. A clear match between the scales chosen and the processes being assessed are needed to decipher the extent to which populations within a beach (mesoscale) can be considered connected or not, together with the corresponding management strategies and implications in a fishery context. Density-Dependent and Environmental Factors Sandy-beach populations can undergo large fluctuations because of density-dependent and environmental factors (see Chapter 8). Abundance, population structure, growth, mortality, fecundity, and recruitment can vary markedly spatially and temporally, both within and among beaches. Variations in beach morphodynamics could control the magnitude of the stock available for fishing (McLachlan et al., 1996a) and the strength of potential intraspecific and interspecific interactions (Defeo and de Álava, 1995; Defeo, 1998). In this context, density-dependent recruitment, growth, survival, and fecundity rates have been suggested as key processes in harvested sandy-beach populations (Defeo et al., 1992; Brazeiro and Defeo, 1999; Lima et al., 2000; Turra et al., 2014). Density-dependent processes play a role at high densities through adults filtering out larvae, inhibition of growth, and increased mortality. For instance, overcompensation has been described as a potential regulatory mechanism in sandy-beach populations in which (1) older individuals can suppress subsequent cohorts and (2) the amount of density dependence varies over time (Defeo, 2003 and references therein). Both these intraspecific mechanisms are influenced by the amount of fishing, which regulates the adult component. Thus, density-dependent mechanisms have critical management connotations. The effects of density dependence and habitat quality in mortality estimates can be experimentally assessed (see Section 14.6). Sandy-beach species, including those commercially harvested, are susceptible to rapid environmental changes (see Chapters 8 and 16). Environmental trends may in fact provide useful criteria for a rough forecast of the level of recruitment. Because of their strict association with physical variables, including sediment type and beach slope (Defeo and McLachlan, 2011), many macrofaunal species may be unable to change distribution to compensate for warming sea temperatures and other climate change consequences, such as ocean acidification and sea-level rise (Chapter 16). These drivers could alter demography and life history traits and could also affect critical habitats and biophysical processes, with implications in fishery activities. Ecological Effects of Fishing Fisheries in sandy beaches can be sustainable and provide long-term benefits to humans but, if not properly managed, fishing pressure can have deleterious effects on beach ecosystems, affecting their structure, function, and productivity (Fig. 14.9). Extracting beach macrofauna typically involves digging, the use of suction devices, trampling, and other disturbances. The results of these physical disturbances may be more deleterious to the habitat than the actual removal of target resources (Wynberg and Branch, 1994, 1997). Incidental effects (e.g., shell damage) of fishing pressure can increase mortality rates of harvested and unharvested populations (Defeo and de Álava, 1995; Sims, 1997), so harvesting may constitute a source of incidental mortality. This incidental mortality can also affect clams discarded on the surface, which eventually die. At low fishing pressure, the inherent dynamicism of the habitat and of the intertidal species (e.g., donacid clams) can override pulse perturbations

346

14. FISHERIES

Fishing Extraction

Adults or commercial sizes

Physical damage

Noncommercial sizes: recruits and juveniles

Collateral effects

Changes in biological interactions Nutrient cycling and phytoplankton Sediment disturbance or disruption

Sympatric species

Changes in sandy beach ecosystem structure and function

Red tides

Exogenous environmental stressors

Increasing temperatures, acidification, sea-level rise

Other man-made effects

Pollution, beach mining, recreation

FIGURE 14.9  Ecological effects of fishing and other stressors on sandy-beach ecosystems. Harvesting disturbance can also lead to changes in intraspecific (stock-recruitment) and interspecific relationships (not illustrated).

with ease and populations may recover within a tidal cycle (Schoeman et al., 2000). However, chronic (press) harvesting perturbations can cause large-scale and persistent impacts on the habitat and macrofaunal populations. Detrimental effects of fishing can also be exacerbated when they are superimposed on environmental change, irrespective of whether such change is of anthropogenic origin or not (Defeo, 2003). On a New Zealand beach, clam populations depleted by artisanal fisheries between the mid-1960s and 1990s failed to recover following the closure of the fishery, apparently because continuous erosion of beaches has dramatically reduced the clam habitat (Beentjes et al., 2006). Sediment disturbance during intertidal harvesting activities can cause physical alteration of the habitat and increase macrofaunal mortality rates. Suffocation, perturbation of sediment texture, prolonged air exposure following harvest, and limitation of filtering activities by clogging of the ctenidia and palps in suspension feeders (e.g., bivalves, mole crabs) may be involved in incidental mortality. Incidental damage and the effects of substrate perturbation could be tested through experimental protocols (e.g., mortality of clams right after fishing manipulation vs. control treatment areas) to evaluate the effects of harvesting on population dynamics of the target species and other species within the community (see Section 14.6). External Drivers Sandy-beach fisheries are open SES with permeable boundaries affected by a series of external drivers or stressors (Fig. 14.8) that threaten their resilience. Indeed, small-scale fisheries in sandy beaches around the world are increasingly affected by external drivers acting simultaneously at multiple temporal and spatial scales (Ortega et al., 2012; Defeo et al.,

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TABLE 14.2 Some Distal and Proximate External Drivers Affecting Sandy-Beach Fisheries Driver Type

Driver

Distal

Governance and institutions Economies, international trade, and market connectedness Demographic factors (human migration) Urbanization and coastal development Tourism Cultural and sociopolitical factors Technological factors

Proximate

Fishing Climate change (temperature, sea-level rise, and acidification) and related modifications of the sandy-beach environment Pollution (thermal and chemical) Habitat destruction through human-related stressors (mining, trampling, and nourishment) Eutrophication, pathogens, diseases, and red tides

2013). An external driver is defined as any natural or human-induced factor that indirectly brings about change in the SES (Hall, 2011) and can be categorized as “distal” or “proximate” (Hicks et al., 2016a; Österblom et al., 2017). Distal drivers can include changes in governance structures and policy, new technologies, opening or closures of markets, demographic changes (e.g., human migration to the coast), urbanization, and other sociopolitical factors (Table 14.2). Proximate drivers include climate change issues (see Chapter 16), several sources of pollution, human-induced stressors promoting habitat destruction on sandy shores (e.g., nourishment, beach mining, and recreation, see Chapter 15), eutrophication, diseases, and red tides (Table 14.2). A critical proximate driver threatening the productivity of sandy-beach fisheries and deserving attention is the increasing occurrence of red tides. Exploitation of beach clams is often constrained by the accumulation of toxins, such as those associated with blooms of toxic algae, which can cause mass mortalities or render clams unsafe for human consumption (Fig. 14.9). An increase in the frequency and duration of red tides has been documented as a result of eutrophication and increasing temperatures acting together (proximate drivers, see also Chapter 16). Given that phytoplankton is a key food source for sandy-beach suspension feeders that constitute key fisheries worldwide, the recurrent fishery closures resulting from these events have had important socioeconomic repercussions. This situation is aggravated by the upsurge in blooms of macroalgae, which are expected to increase in intensity and periodicity because of climate change (Smetacek and Zingone, 2013). These events could affect the entire beach food web across several trophic levels (Quillien et al., 2016, see Chapter 12) and could also alter habitat quality and availability for the resident macrofauna. Therefore, the effects of changing physical conditions resulting from unregulated fishing and other human activities on sandy beaches, acting together with climate drivers, could

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have unpredictable impacts on the function of the entire ecosystem and harvested species in particular. Interactions among drivers impact not only the fishery but also the related ecosystem services and could lead to devastating effects on sandy-beach fisheries. Climate-driven changes (proximate drivers) in species distributions and abundance may affect ecosystem services and human well-being, both directly (e.g., diseases and red tides, also proximate drivers) and indirectly (by degrading habitat quality). In Peru, for example, unregulated fishing and weak resource governance (i.e., open access) led to unsustainable harvest levels. The situation was aggravated by the occurrence of a strong warm 1997/98 El Niño that caused mass mortalities. Consequently, the fishery was closed (year 1999) and this management decision is still in place. The lack of response of this and similar sandy-beach stocks to long-term fishery closures suggests that these systems exceeded critical thresholds (i.e., tipping points) and shifted abruptly from one state to another (see also Chapter 16). This highlights the need for early warnings of approaching tipping points to help manage sandy-beach fisheries. Distal drivers, operating on their own or in concert, could affect the magnitude of a proximate driver, with drastic effects on the biophysical (resource) and social (fishery yields and employment) components of the SES. Fishing by itself is a proximate driver affecting the SES and, when uncontrolled, can interact with distal drivers (e.g., market changes) to increase the amount of fishing effort. Changes in fishing technologies (distal driver) that enable more efficient fishing can also result from this interaction among proximate and distal drivers (Defeo, 2003). Thus, the interactions among drivers can have strong effects on the demography and population dynamics of harvested populations (Fig. 14.9). This can lead to local extirpations affecting fishery yields and the livelihood of local fisher communities (see Section 14.4 and Chapter 16). As the number and magnitude of global change drivers increases over time, there is an urgent need to develop a predictive understanding about the behavior of the SES at different spatiotemporal scales. The role of long-term environmental changes, cycles, and patterns in sandy beach fisheries has become a little easier to interpret over recent years because longterm data series are increasingly available. Yet, our ability to discriminate between natural environmental changes, the effects of overfishing, and the impact of other human drivers remains poor (Castrejón and Defeo, 2015). Population fluctuations seem to be produced by the intertwined forces of exogenous factors, environmental and human disturbances, and density-dependent factors operating together at different spatial and temporal scales (see Chapter 8). It has recently been proposed that anthropogenic drivers are rescaling ecological processes and species interactions in such a way that processes that occur at local scales are operating across a much larger spatial extent (Rose et al., 2017, see Chapter 15). Therefore, relevant scales of analysis should be carefully defined when addressing sandy-beach fisheries as SES, acknowledging a physical–biological coupling at different scales in these dynamic environments.

14.4  HARVESTING PHASES AND LONG-TERM TRENDS Because of their socioeconomic significance around the world and the availability of detailed statistical information, harvesting phases and long-term trends are analyzed in this chapter only for beach clam fisheries (Figs. 14.10 and 14.11).

349

Institutionalization

14.4  Harvesting Phases and Long-term Trends

100

1000

100

1 1982

Stabilization

Expansion

10

Closure

10

Landings (ton)

Mass mortalities Fishery closure

Overexploitation

Abundance (ind/m)

1000

1

1986 1990 1994 1998 2002

2006 2010 2014

0

Year

FIGURE 14.10  Long-term variations (1982–2015) in abundance (estimated by stock surveys) and catch of the yellow clam Mesodesma mactroides in Uruguay. The different fishery phases are highlighted. The initial development phase is not shown, as the fishery then had no statistical coverage. Achieving the consolidation phase will require a longer time frame. Note the logarithmic scales on the Y-axes. 

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FIGURE 14.11  Long-term trends in some beach clam fisheries: (A) Mesodesma donacium in Chile and Peru; (B) Donax deltoides in Australia; (C) Siliqua patula in Washington State; and (D) Donax trunculus in Galicia, Spain. Note the different scales on the X and Y axes. (A) Data from Ortega, L., Castilla, J.C., Espino, M., et al., 2012. Large-scale and longterm effects of fishing, market price and climate on two South American sandy beach clam species. Mar. Ecol. Prog. Ser. 469, 71–85; (B) courtesy of Greg Ferguson and PIRSA-SARDI, Australia; (C) data extracted from WDFW, 2016. Summary Report of the 2015 Commercial Fishery for Razor Clams (Siliqua patula). Washington Department of Fish and Wildlife, Ocean Park, WA; and (D) data from Xunta de Galicia, available online at https://www.pescadegalicia.gal/estadisticas/.

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Harvesting Phases The historical trend in landings of clam fisheries are characterized by six temporal phases that typically are passed through before achieving sustainability (sensu Castilla and Defeo, 2001; Defeo, 2003): development, expansion, overexploitation, closures, stabilization/institutionalization, and consolidation. Most of these phases are depicted in Fig. 14.10 for the yellow clam M. mactroides in Uruguay, used here as an illustrative example of a long-term trend in a sandy-beach fishery. Additional details about this targeted species and its fishery are given in Chapters 8 and 16.   

1. The development phase is characterized by relatively low and constant landings. The fishery tends to operate under open access regimes and landings are mostly channeled to domestic markets. Absence of statistical coverage of fishery activity and scientific information is common, but not only restricted to this phase (it prevails in many sandybeach fisheries). 2. The expansion phase includes an exponential upsurge in landings resulting from increasing demand from domestic and, eventually, foreign markets. This phase has been particularly documented in sandy-beach fisheries of developing countries in which fishing intensity and unit prices increased exponentially (Ortega et al., 2012), but has been also observed in developed countries (McLachlan et al., 1996a). Commercial activities by corporate/ collective organizations prevail over individual/family activities (Defeo, 1989). The exponential growth of landings is usually not backed by management regulations founded on solid scientific knowledge of the dynamics of the resource and the fishery, thus leading to inadequate and ineffective management policies. Potential changes in market conditions, defined previously as a distal driver (Table 14.2), could interact with fishing (proximate driver) to increase the amount of fishing effort and the consequent depletion of stocks. 3. The overexploitation phase occurs because of ineffective management systems. Increase in unit prices driven by a demand increase for the product by domestic and foreign markets, together with easy and uncontrolled access to stocks on open coasts, generates an exponential increase in fishery intensity and entry rates. High unemployment rates in rural zones in developing countries accelerate this process because of the relatively easy access, low operating costs, increasing demand, and high unit prices (Castilla and Defeo, 2001). The easy access of fishers to resources and the usually extended spatial scale of operation (in some cases thousands of kilometers) make regulatory efforts expensive and ineffective (Defeo, 1989; Schoeman, 1996; Defeo and Castilla, 2012). This in turn produced the depletion and local extirpations of stocks that have led to fishery collapses (McLachlan et al., 1996a; Ortega et al., 2012). 4. The closure phase occurs because of overfishing and severe depletion of populations, which has led to limited standing stocks and dropping catches and yields. The closure phase varies in intensity and duration according to the fishery and capacity for resilience in the harvested stock and the ecosystem. In some cases, the closure phase was set in sandy-beach fisheries because of the combined effects of fishing and other external drivers (notably climate variability, see Chapter 16) that caused mass mortalities and decimated stocks. We showed that populations of the surf clam M. donacium in Peru were extirpated after the strong warm 1997/98 El Niño event and the fishery based on

14.4  Harvesting Phases and Long-term Trends

351

this species (see Section 16.4) was closed in Peru in 1999. In Uruguay, M. mactroides mass mortality events that occurred in 1994 caused fishery closure until 2008 (Fig. 14.10), and no evidence of recovery of the commercial stock was observed throughout this period (Ortega et al., 2012). Further, the ecological and social components of the SES were not resilient in the face of mass mortalities, which caused loss of incomes and consequent unemployment. 5. The stabilization of harvesting levels and institutionalization phase can occur after the “crisis” period depicted above. Here the scientific information acquired in the long term has been effectively translated into specific management tools, improving the quality of the management measures, which adopt a precautionary approach. This move toward sustainability is characterized by low catch levels defined by global quotas, closures in time and space, and the granting of individual quotas or other strict limits of access, often defined within the general umbrella of access rights (see Section 14.6). Most important, this phase includes the formal development of management plans with clear, long-term policy goals directed to transform the utilization of fisheries resources into sustainable production systems. The institutionalization process includes the formal coordination, cooperation, and communication within and among institutions and stakeholders, which eventually share authority and responsibilities through decentralized fisheries governance. In Uruguay, the reopening of the yellow clam fishery after a 14-year closure was followed by policy goals that included the implementation of an Ecosystem Approach to Fisheries (EAF) and comanagement as the formal governance mode explicitly defined in Uruguayan fishing law (Defeo, 2015; Gianelli et al., 2015). Operational management instruments based on area-specific management plans (minimum legal sizes and total catch levels per fisher and per fishing ground, see Section 14.6) were also implemented. Moreover, an increasing share of the catch was marketed for the gastronomic sector instead of the traditional bait market, this proportion reaching almost 95% of the total catch in 2014. This market shift explains the temporal trend of increasing unit price paid to the fishers at the beach, which reached a maximum of 2.5 US$/kg in 2015 (Fig. 14.12). 6 . The consolidation phase implies the sustainable exploitation over time and the consolidation of institutionalized arrangements. This phase has been difficult to achieve in sandy-beach fisheries around the world. Important limitations precluding long-term stock restoration and sustainable catches have been related to changing sociopolitical scenarios, the absence of communication among critical stakeholders (i.e., fishers and managers), and the poor enforcement of management measures.   

Although extensive and detailed statistics are not available for many small-scale sandybeach invertebrate fisheries, it can be safely stated that the above phases depict the present worldwide situation in general.

Long-term Bioeconomic Trends Most sandy-beach stocks around the world are fully exploited, overexploited, or depleted, particularly in developing countries (McLachlan et al., 1996a; Defeo, 2003). The historical

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catch trends in sandy-beach fisheries show that the number of phases varies among fisheries, mainly as a response to the management options implemented, the life cycle of the harvested species, and the inherent characteristics of each fishery. There are also differences in countryto-country fisher idiosyncrasies and in the increasingly important role of external drivers, which have become major determinants in landings trends worldwide. These drivers include international trade and market globalization (e.g., contractions for products channeled to foreign markets), governance (e.g., political instability and lack of long-term policy goals), and climate change (e.g., temperature and sea-level rise). In the following paragraphs, we show long-term bioeconomic trends from selected case studies around the world. One of the most important harvested sandy-beach resources worldwide during the last century has been the surf clam or “macha” M. donacium from Chile and Peru (Fig. 14.6). M. donacium inhabits intermediate and dissipative beaches (McLachlan et al., 1996a) along the Pacific coast of South America, from Sechura Bay (Peru, 5°S) to southern Chile (43°S) (Fig. 14.7). In Chile, the 40-year data showed a development phase between 1966 and 1982 characterized by annual landings ranging between 1000 and 6000 tons (Fig. 14.11A). The expansion phase extended approximately between 1983 and 1989, when the resource began to be channeled to foreign markets, reaching almost 18,000 tons in 1989, and drastically declined thereafter (1990–2006, overexploitation phase) down to US$ 9 million). However, the combined effects of ocean warming and red tides are increasingly affecting this resource also at the 

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FIGURE 14.12  Long-term trends in unit prices for selected clam fisheries. All data refer to mean prices paid to the fishers at the beach (ex-vessel price), with the exception of Mesodesma donacium (export value). Note the logarithmic scale on the Y-axis. Main sources of data as in Fig. 14.11.

14.4  Harvesting Phases and Long-term Trends

353

leading (poleward) edge of the species distribution. Recently, Chile’s southern coast has been hit by the biggest ever red tide in history caused by toxic microalgae, and this has damaged the local fishing economy. The root cause is likely warming of the Pacific Ocean during El Niño event in 2016 when mass mortalities of beach clams covered miles of shoreline. The Chilean government declared a state of disaster for the southern part of the country and subsidized fishing families to compensate for economic losses. In Peru, the M. donacium fishery showed a development phase characterized by landings ranging between 200 tons in 1970 and 521 tons in 1976. The expansion phase occurred between 1977 and 1980, when catches reached 4000 tons during the period preceding the strongest 1982/83 El Niño event. This latter event caused mass mortalities and no live surf clams were found in shallow waters south of Lima. After another strong warm 1997/98 ENSO event, most local surf clam populations were extirpated. The fishery was closed in 1999 (closure phase) and this management decision is still in place in Peru (Ortega et al., 2012). The fast boom and bust cycle of the fishery in Peru suggests that cumulative impacts of climate and fishing may have precipitated the fishery collapse. The surf clam or “pipi” Donax (=Plebidonax) deltoides (Fig. 14.6) occurs along the south and east coasts of Australia from the Adelaide area up to southeastern Queensland, including Tasmania (Fig. 14.7, McLachlan et al., 1996a). The largest fishery for this clam occurs in South Australia (Fig. 14.11B). The fishery showed a development phase that ran approximately until the late 1980s, characterized by relatively stable landings close to 300 tons. At the very beginning, the fishery tended to operate under open access and the product was mostly channeled to the bait market. The expansion (Phase 2) of the fishery occurred during the second half of the 1980s as landings increased fivefold between 1989 and 2003 (to 1274 tons: historical maximum). This expansion phase was followed by a prolonged period of decline (overexploitation phase), dropping to a minimum in 2010 (284 tons). The fishery is now successfully managed (Phase 5: stabilization and institutionalization) and landings are recovering, having reached 500 tons in 2015. Different management tools have been implemented, including an annual Total Allowable Commercial Catch based on three performance indicators (Ferguson, 2013; Ferguson et al., 2015): (1) biomass; (2) the presence/absence of prerecruits in size frequency distributions from the fishing ground; and (3) an additional economic performance indicator (Fishery Gross Margin) used to assess the ability of the market to absorb the product as the Total Allowable Commercial Catch increases. This economic indicator is given by the total catch multiplied by the net market price averaged across all market segments, less fishery and operator costs that vary with Total Allowable Commercial Catch levels (Ferguson, 2013). Following the same patterns as in the yellow clam M. mactroides and other sandybeach exploited resources around the world, an increasing proportion of the catch is targeted toward the human consumption market (from 23% in 2009 to almost 50% in 2011) instead of the traditional bait market. Moreover, the unit price has increased markedly through time and the total annual value of the catch has increased more than 10-fold in 25 years, i.e., from 4 million clams) to the early 1960s (c. > 14 million clams, McLachlan et al., 1996a), and then declining to very low landing levels between the 1970s and the 2000s (Fig. 14.11C). During this period, the fishery was closed, partly because of low biomass levels but primarily because of the occurrence of epidemic levels of NIX disease and domoic acid that have resulted in significant mortality in S. patula populations. The more recent harvest data from Washington shows an increasing trend in landings during the last 15 years, from 30 tons in 2000 to more than 120 tons in 2014 (Fig. 14.11C). This increase has occurred, although biotoxin events occurred in 2003 and 2015, when the fishery was closed (WDFW, 2016). Following a similar trend as in the fisheries previously analyzed, the unit price of razor clams has increased through time, reaching the highest value in 2013 (ca. 5 US$/kg, Fig. 14.12). Although most of the harvested clams are still sold as bait for the Dungeness crab fishery, this percentage has varied over the past few years as more and more clams are destined to the fresh-food market (WDFW, 2016). D. trunculus (Fig. 14.6) is distributed along the Atlantic coasts of Europe and North Africa, from the Bay of Douarnenez, Brittany France to Senegal, and throughout the Mediterranean and Black seas (Fig. 14.7). In Galicia (Spain), the species (common name: “cadelucha”) is highly valued in the domestic market and subject to a commercial small-scale fishery with very low landing levels (Fig. 14.11D) but extremely high unit prices that topped at more than 40 US$/kg at the end of the time series (Fig. 14.12). Landings peaked close to 20 tons at the beginning of the 21st century but have declined over the past 15 years to 100 mm diameter), macro (>20 mm diameter), meso (5–20 mm), and microplastics (250 times larger than reported for the open ocean. The polymers polypropylene and polyethylene were most abundant, and sandy shorelines more directly exposed to marine currents and tides had higher microplastic abundance and diversity and a higher proportion of denser polymers (e.g., polyester). About 2000 and 500 items/km year of anthropogenic debris strand on North and South Atlantic Ocean beaches (respectively), of which more than half is plastic (Barnes and Milner, 2005). Field surveys conducted in sandy beaches located at the famous Guanabara Bay (Rio de Janeiro, Brazil) showed microplastic concentrations (up to 1300 particles/m2) representing a high percentage of the total debris (de Carvalho and Neto, 2016). Urban areas have also been identified as major sources of marine litter in sandy beaches in central Italy (Poeta et al., 2016). The most frequent litter items in Mediterranean sandy beaches are also plastics and polystyrene, which constitute a threat to dune integrity when cleaning activities are carried out using mechanical equipment (Poeta et al., 2014). Stranded plastic litter persists indefinitely but rapidly becomes buried in beach material or is blown inland and covered with vegetation. The depth profile obtained from sediment cores suggests that microplastic concentrations in sandy beaches reflect the global increase in plastic production (Claessens et al., 2011). The abundance of plastic debris in exposed sandy beaches of Punta del Este (Uruguay) has been found to be positively correlated with both the presence of land-based sources (e.g., storm water drains, beach bars, beach access, car parking, and roads) and dissipative beach conditions (Lozoya et al., 2016), but sheltered beaches can harbor higher litter accumulations than exposed ones. In terms of human health, risk increases when medical plastic wastes reach the shore from coastal dumping sites (Sindermann, 1996). The occurrence of macroplastics associated with wildlife (e.g., in bird nests and stomachs, entangling seals) has increased drastically in the last decades. Major dangers associated with plastic include ingestion by and entanglement of vertebrates, such as seals, seabirds, and turtles (Mascarenhas et al., 2004), which are all prone to microplastic ingestion. This raises toxicity concerns because plastics are known to adsorb hydrophobic pollutants. Monitoring of strandings and effects on birds, which has now commenced on at least a few remote island shores in every ocean, has revealed an increasing amount of plastic accumulation (Barnes et al., 2009). Marine debris (mostly plastics) have been identified as a major impediment for emerging turtle hatchlings in a Mediterranean beach, and two out of three hatchlings had contact with such debris on the way to the sea (Triessnig et al., 2012). Microplastics also affect temperature and sediment permeability (Carson et al., 2011), which can influence sea turtle nest properties and affect hatchling sex ratios and reproductive success (Nelms et al., 2016). These cascading effects could explain long-term declines in nest numbers on some sandy beaches. Microplastics can be ingested by sandy-beach invertebrates, but their fate in the digestive organs and their overall effects on the organism are not well understood. The implications for

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food webs are yet to be elucidated and, without knowledge of retention and egestion rates in field populations, it is difficult to deduce ecological consequences (Lusher, 2015). Adults of the sandhopper Talitrus saltator fed dry fish food mixed with polyethylene microspheres (diameter 10–45 μm) revealed the presence of microspheres in homogenized guts, but these were expelled in 24 h and totally eliminated after 1 week (Ugolini et al., 2013). Therefore, this investigation did not show any consequence of microsphere ingestion on the sandhopper survival capacity in the laboratory. Moreover, feces of freshly collected individuals revealed the presence of polyethylene and polypropylene, suggesting that microplastic debris could be swallowed by T. saltator in natural conditions (Ugolini et al., 2013). Ingestion of microplastics by filter feeders is known to occur, but has not been quantified (Moore, 2008). More research is needed to assess the effects of microplastic ingestion on sandy-beach macrofauna and to which extent this can impair their health and ecological functions under continuous exposure. Sandy beaches are critical sinks for marine litter (including plastics, see, e.g., Rech et al., 2014). However, source–sink patterns could vary among beach types according to local-scale hydrodynamic processes and beach morphopdynamic characteristics (as in macrofaunal populations, see Chapter 8), and this needs to be fully elucidated. Although sandy shores constitute the most easily accessible ecosystems for studying marine debris, irregularity of sampling and considerable variation in methodologies between regions and between investigators have led to few long-term data sets so that more are essential to provide unbiased estimates of this environmental pollutant (Barnes et al., 2009). Standardization of sampling designs and monitoring approaches (Ryan et al., 2009; Hidalgo-Ruz et al., 2012; Galgani et al., 2015) and the implementation of national, regional, and global networks of voluntary beach data gathering and cleaning on sandy shores (as already exist in the United Kingdom, see Nelms et al., 2017) are needed as a basis for efficient management measures. In this vein, Nelms et al. (2017) showed that citizen science projects can give low-cost methods of collecting large volumes of beach debris data with considerable temporal and spatial coverage.

Sewage and Organic Enrichment Sewage is the oldest form of marine pollution of any consequence and the earliest marine antipollution laws were concerned with its disposal. This was mainly on esthetic grounds, but nowadays it is recognized that the discharge of raw sewage to sea may damage sandybeach ecosystems or represent a health hazard to man. The contamination of bathing beaches with sewage is a health problem that cannot be ignored. Intertidal sands (Ulfig et al., 1997; Salvo and Fabiano, 2007) and surf-zone waters (Bonilla et al., 2007) can be contaminated by pathogens, including bacteria and filamentous fungi, which are delivered by sewage systems discharging directly into coastal waters or estuaries near beaches (Araújo and Costa, 2007). Bacterial levels that exceed human health standards in surf-zone waters are a frequent cause of beach closures and public warnings on many developed coasts. The chief effects of sewage are a smothering of organisms near the discharge point by sludge, if this has not previously been removed and an enrichment of the seawater leading to an increase in primary productivity and bacterial biomass. Organic enrichment of the beach itself may lead to a lowering of oxygen tensions and an upward encroachment of the anoxic black layers (see Chapter 3). Dissolved organic matter may be absorbed directly by meiofaunal species and even by some members of the macrofauna.

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Input Organic matter

High organic matter content in sediment Bacterial decomposition Well flushed Oxidized sediment with plentiful food supply High bioturbation

High biomass

Mode rate water renewal

Stagnation

Reduced O2 in water, lower Eh in sediment

Anoxic sediment and overlying layer

Few niches

Poor macrofauna

No macrofauna

FIGURE 15.11  Some pathways and consequences of organic input in relation to water renewal. Eh, redox potential. After Pearson, T.H., Rosenberg, R., 1978. Macrobenthic succession in relation to organic enrichment and the marine environment. Oceanogr. Mar. Biol. Annu. Rev. 16, 229–311.

Unlike crude oil or factory effluents, sewage generally contains few substances that are directly toxic, although in some cases there may be a buildup of metals such as lead. The importance of water movement in determining the effect of organic pollution in macrobenthic succession and gradients of enrichment, species composition, and biomass is illustrated in Fig. 15.11. Washouts (freshwater streams that cross beaches), originating from high water table levels combined with rainwater collected in swamp areas behind the foredunes, can influence beach morphodynamics and macrofaunal diversity (GandaraMartins et al., 2015). Increasing rainfall events because of climate change (Chapter 16) have promoted an increase in freshwater discharges with high human sewage levels and nutrient inputs. Intense urbanization close to the coast seems to be affecting the magnitude of washouts, with consequent deleterious effects on the beach ecosystem. Beach contamination near an outfall is dependent on: (1) the appropriateness of waste water management practices; (2) the timing and intensity of local rainfall events and subsequent runoff; and (3) the strength of mixing and dispersion in the surf zone (Stretch and Mardon, 2005).

Heavy Metals Metal pollution from wastewater and industry accumulates preferentially on finegrained beaches (Ramírez et al., 2005), which usually support relatively high diversity and biomass. This can reduce biodiversity, abundance and affect community composition and structure. Anthropogenic marker elements such as Hg, Cr, Pb, Zn, and Cu can be found, occasionally at potentially toxic levels, on urban beaches. This is perceived as a threat of increasing importance (Cabrini et al., 2017; García-Alonso et al., 2017), especially when accompanied by other pollutants, such as plastic production pellets, which can lead to enrichment of Cd and Pb (Ashton et al., 2010). Trace metals can reduce genetic variability

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in natural populations; for example, some macrofaunal species, like sandhoppers, can accumulate Hg, Cd, and Cu and populations from beaches with high Hg availability have been found to have low genetic diversity (Ungherese et al., 2010), supporting the idea of “genetic erosion”. Further, growth and survival rates can be significantly reduced in impacted sites, as shown in Donax trunculus, suggesting that responses to chemical stress may be reflected at the individual and the population levels (Tlili et al., 2010).

Effluents Factories should ideally be sited where their effluents can enter deep water with strong currents to facilitate dispersal. Yet in practice they tend to be built in estuaries or in shallow, sheltered bays or inlets where sand or mud predominates. Thus, sandy beaches come in for more than their fair share of factory pollution, despite the increasing length of effluent pipes. Small factories and home industries seldom discharge into an effluent pipe at all and too often rely on sewers or on storm water drains, which may open onto the beach above the high water mark. Different countries have varied regulations in this regard, or, in some cases, no control measures at all. Factory pollution is a long-term, continuous process and necessitates the ongoing monitoring of possible damage to the ecosystem. Ideally, one should have a good knowledge of the communities to be monitored before the factory begins discharging and most countries now require impact assessment studies before permission to discharge is given. Assessments imply a prepollution study of the ecosystem, thus facilitating the monitoring of change. Brown (1983b) studied the density of meiofauna along the length of a sandy-beach subject to pollution from a marine oil refinery. This effluent was added to a small stream, which escaped onto the beach through a storm water drain. Meiofaunal numbers were consistently and significantly depressed around the outfall and could be correlated with depressed oxygen tensions, elevated phosphate, and other indices of pollution. After some years, the effluent was rerouted, thus promising a rare opportunity to study the recovery of the sandy-beach system. Meiofaunal densities did not recover, however, and it was eventually shown that the depression in numbers was actually because of reduced salinities attributable to the freshwater stream to which the effluent had previously been added and which continued to run down the beach. It had nothing to do with pollution! Indeed, freshwater effluents arising from human activities can also cause a broader deterioration in the quality of the surrounding sandy-beach marine habitat, with impacts at various levels of ecological organization, ranging from individuals and populations (polychaetes, isopods and bivalves). Species might experience reduced abundance, survival, growth, and fecundity rates (Lozoya and Defeo, 2006; Bergamino et al., 2009, see Chapter 8), feeding through to changes at the community level (reviewed in Defeo and Lercari, 2004). It is difficult to make accurate predictions as to the ecological effects of man-made effluents because so many factors are involved, including the proximity of other discharges, current patterns, and type of shore. For this reason, there has been a move away from legislation governing effluent quality toward regulations aimed at ensuring acceptable sea water quality, and what is acceptable depends on the type of shore and the use to which it is put. The concept of assimilative capacity, originally defined as the amount of material that could be contained within a body of water without producing an unacceptable biological impact, has

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Level of contaminant substance High

Moderate Addition by man or external sources Low

Natural levels

Effect Toxic or reproductive damage to marine animals

Rise in contaminant substances within tolerance (detoxification capacity) of marine animals Wide range of natural contaminant substances in marine animals that are not believed to cause damage

Description Pollution

Threshold damage 100% Assimilative capacity 0% Threshold of manmade contamination Control or reference condition

FIGURE 15.12  The concept of assimilative capacity. Many chemicals that are toxic at high concentrations occur normally in the sea and can be tolerated by the marine fauna over a wide range of lower concentrations. No locations are known where open coastal waters have no contaminants. After Bascom, W., 1984. The Concept of Assimilative Capacity. Southern California Coastal Water Research Project: Biennial Report. pp. 171–177.

gained ground (Fig. 15.12). It is, for example, accepted that all animals have some capacity to withstand contamination; this is to be expected as many pollutants released by man are either naturally present or are similar to naturally occurring compounds. Factory effluents are commonly warmer than the sea water into which they discharge, and therefore potentially add thermal pollution to the chemical pollution they produce. Such thermal pollution is usually small and it is only with the advent of nuclear power stations, which use vast quantities of water for cooling purposes and discharge it back into the sea at temperatures higher by 10°C or more, that the subject has evoked serious study. Infaunal sandy-beach animals may be buffered to some extent against short-term changes in temperature (pulse perturbation) in a way that rocky-shore animals are not, but they are in no way protected against the long-term temperature changes that accompany the continuous operation of generating plants (press perturbation). Subtle ecological changes should be expected in areas affected by heated effluents, including alterations in species composition, population densities, individual sizes, growth rates, and in breeding behavior. At Hunterston, in Scotland, the bivalve Tellina tenuis showed a considerable drop in population density after a power station became operational, although it had a faster growth rate in the warmer water over a 10-year period. Urothoe commenced breeding earlier in the year and juveniles grew for a longer period, attaining a 28% greater size than individuals from unaffected areas (Barnett, 1971). The potential impact of thermal discharge from a coastal power station on wedge clam Donax cuneatus abundance was assessed to determine the impact boundary (Madras Atomic Power Station, India, Hussain et al., 2010). To the north, effects only occurred within 100 m, whereas to the south, effluents had very slight

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effects out to 400 m. Effects on wedge clam population trends could not be shown because of the presence of multiple interacting factors. Similarly, heated water discharged from the San Onofre Nuclear Station in California was found not to be the cause of the abnormal reproduction of sand crabs along nearby beaches (Siegel and Wenner, 1984). Other likely factors that could explain the observed trends included: (1) runoff of agricultural pesticides; (2) release of metals from corroding cooling pipes, and/or (3) increased turbidity of the nearshore waters. Another possible consequence of thermal pollution in some areas is the invasion of warmwater species, to the detriment of the original fauna (see next section). This threat is of increasing importance in view of recent trends of tropicalization of sandy-beach communities (see Chapter 16).

15.5  BIOLOGICAL INVASIONS Human activities that are vectors for species introductions to beaches are not a recent phenomenon. Exchanging large quantities of “dry” ballast sand and gravel onshore during ship maintenance is among the oldest known human agents of species introduction to beaches (Carlton, 1989). Nearshore and intertidal benthic habitats in many regions have been invaded by alien macrophytes that displace native algae and seagrasses, forming large wrack deposits on sandy beaches (Meinesz et al., 2001; Piriz et al., 2003; Chapman et al., 2006). Invasive algae could impact food webs and nutrient cycling (see Chapter 12) because of the preference of wrack consumers (e.g., talitrid amphipods) for macroalgae (Lastra et al., 2008). Colonization of plastic marine debris by sessile organisms provides a vector for transport of alien species and may eventually threaten sandy-beach biodiversity. Few invasive invertebrates have been reported from sandy beaches to date. The semiterrestrial talitrid amphipod Orchestia cavimana, originally from freshwater habitats in the Black Sea and Mediterranean region, has been spreading rapidly on open exposed shores with low salinities in the Baltic Sea (Herkul et al., 2006). The talitrid Platorchestia platensis, which presently inhabits Europe, the Canaries, Japan, India, Hawaii, and other Pacific islands, and which was recently reported in the Baltic, may be an exotic species (Spicer and Janas, 2006). A few widespread polychaetes (e.g., glycerids and spionids) reported from exposed beaches are classified as cryptogenic, implying that their origin is unknown and that they are neither demonstrably native nor introduced (Carlton, 1996). The best known of these are Glycera americana and Scololepis squamata, both of which are reported from beaches and estuaries on several continents (see Chapter 5). The possibility that some cryptogenic forms could represent cryptic species rather than a single widespread invasive species needs to be considered. Invasive terrestrial insects can impact beach ecosystems. Red fire ants (Solenopsis invicta) from Brazil are now found in the United States, Australia, Taiwan and China. They can prey on the eggs and hatchlings of loggerhead and green sea turtles (Allen et al., 2001). The Argentine ant (Linepithema humile, formerly Iridomyrmex humilis), a small, dark ant native to northern Argentina, Uruguay, Paraguay, and southern Brazil, has invaded a variety of habitats, including beaches, in South Africa, New Zealand, Japan, Australia, Europe, and the United States. Finally, sandy beaches of southern Brazil and Uruguay are being affected by massive eruptions of the invasive bryozoan Membraniporopsis tubigera whose leading range edge is expanding at a rate of 190 km/year, possibly as a result of climate change (see Chapter 16).

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The fact that exposed sandy beaches have fewer invasive species than other coastal habitats raises the questions of whether: (1) exposed beaches are more difficult to invade and colonize; and (2) the high frequency and intensity of disturbance on ocean beaches impede the establishment and survival of invasive species. Sandy beaches may serve as a useful model system in which to test general ecological theories about the relationship between physical disturbance regimes and invasion success by alien species (Defeo et al., 2009).

15.6  NATURAL PERTURBATIONS The human activities covered in this chapter pose serious threats to sandy coasts on many scales, but some natural processes can also disrupt beaches. Most are pulse perturbations, but in some circumstances the effects of extreme events are long lasting. Storms are an important part of the natural cycle molding the morphodynamics of sandy beaches and represent an expected hazard faced by sandy-shore animals. Sand and some animals are washed out to sea, whereas others may be stranded upshore, where they die of exposure. Some animals regain the shore if not carried too far out to sea, because the ability to survive storms by behavioral means is a key feature of sandy-shore animals. However, these mechanisms do not always give adequate protection, especially if significant sand erosion occurs. In extreme cases, so much sand may be eroded from the beach that bedrock becomes exposed. This prevents burial and disrupts the laminar flow of the swash, making colonization by swash-riding species impossible. More common are beaches that are simply too inhospitable to accommodate macrofauna for some time during and after storms, this also depending on connectivity patterns and the life cycles of the species involved (see Chapter 8). The most severe natural episodic events, hurricanes and tsunamis, may completely destroy the beach and dune systems, especially where their sediment stores have been reduced by human activities and the littoral active zone is not free to respond naturally. Extreme catastrophic events (e.g., earthquakes, tsunamis, storms) are episodic but often result in mass mortalities and drastic changes in community structure and composition. Therefore, deciphering the ecological effects of these events on sandy beaches is often hampered by a lack of pre-event data. Jaramillo et al. (2012) used results of intertidal surveys conducted shortly before and immediately after Chile’s 2010 earthquake (Mw 8.8) along the entire rupture zone (34–38°S) to assess the effects of the earthquake and tsunami on sandy-beach ecosystems. They showed that beach ecosystems were strongly affected by the magnitude of land-level change. Subsidence along the northern rupture segment, combined with tsunami-associated disturbance, drowned beaches, whereas along the uplifted southern rupture, beaches widened and flattened. On beaches where subsidence occurred, intertidal zones and their associated species disappeared. On some beaches, uplift of rocky subtidal substrate eliminated low intertidal sand-beach habitat required by ecologically important species (Jaramillo et al., 2012). Species responses varied with their mobility and the shore type. Further, interactions between this extreme event and human-altered shorelines (e.g., armored to prevent beach erosion) produced complex responses in beach fauna. Postearthquake human activities affected the colonization process of sandy-beach crustaceans at upper beach levels in front of seawalls

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where the only species found was the lower shore mole crab Emerita analoga (Rodil et al., 2016). Moreover, vegetated dunes at armored sites suffered a slowdown in development and remained impoverished in species richness and cover compared with an unarmored site (Rodil et al., 2015).

15.7 NOURISHMENT More than 70% of the world’s beaches are experiencing erosion (Bird, 1996; Defeo et al., 2009). Hard engineering solutions, such as seawalls, breakwaters, and groins, are often ineffective to the point of causing the loss of the intertidal beach (Pilkey and Wright, 1989; Hsu et al., 2007). In cases where removal of structures and retreat landwards is not possible, beach nourishment has increasingly been used as a soft engineering alternative to the use of hard structures to combat shoreline erosion (Hamm et al., 2002). Nourishment is also preferred on both economic and conservation grounds (Finkl and Walker, 2004), and it is best done as a series of small additions of sand at 1- to 2-year intervals, rather than as a single major episode. The typical scale of nourishment is 1–10 km spatially (Peterson and Bishop, 2005) and temporally from weeks to years (Fig. 15.1). Beach nourishment is used to: (1) protect buildings and infrastructure from wave attack; (2) improve beaches for recreation; (3) create new natural environments; (4) eliminate detrimental effects of shore protection structures by burying them; and (5) retain sediment volumes during sea-level rise. Bypassing operations move sediment from one side of a barrier (e.g., a groin) to the other by pumping sludge in a pipeline or by trucking; such operations usually remove sediment from accreting beaches and deposit it on nearby eroding ones. Beaches can be made more stable by introducing less mobile coarser sediments, such as gravel, which is likely to occur more frequently as suitable sources of sandy-beach fill are exhausted and technologies for transporting gravel improve. Some results are encouraging (Kana et al., 2013): 30 years of monitoring surveys and shoreline erosion studies (1980–2010) along the South Carolina coast show that beach nourishment and the natural process of inlet shoal bypassing have advanced the shoreline along most of the developed beaches and barrier islands; 80% of developed beaches were much healthier in 2010 than in 1980, as evidenced by burial of seawalls, wider berms, and higher dunes. However, the effects of nourishment can often be temporary (Peterson et al., 2014) and could become economically impossible in the future because of raised sea levels (Pilkey and Cooper, 2014, see also Chapter 16). Fill sediments can be deposited in various positions, such as the subaerial beach, the dunes, deep-water offshore, or in the nearshore (Fig. 15.13). Dunes may be nourished directly, often with sediments that come from the same sources as those used to nourish beaches, causing the substrate to resemble the back beach rather than the better sorted, finer-grained sand typical of the dunes (Mendelssohn et al., 1991). Direct fill creates a substrate not found in either natural dunes or dunes created by accretion at sand fences or vegetation plantings. Fill materials borrowed from estuarine environments may contain seeds and rhizomes of salt marsh plants, leading to establishment of salt-tolerant plants such as Phragmites and Spartina in dunes where these species were previously uncommon. Nourishment can provide a source of sand and space that allows well-vegetated dunes to be rapidly established (Freestone and Nordstrom, 2001).

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FIGURE 15.13  Nourishment activities in a North Carolina sandy beach, showing the piping through which sediments from offshore dredging are pumped onto the intertidal beach, where bulldozers redistribute them. There is visual evidence of higher turbidity nearshore where the pipe discharges slurry of salt water and sediments of varying sizes. Gulls are attracted to the slurry. Photo by Charles Peterson.

Beach nourishment has had a positive impact on some dune plant and animal species, including seabeach amaranth (Amaranthus pumilus), piping plover (Charadrius melodus), and several species of sea turtles, by creating habitat (Crain et al., 1995; National Research Council, 1995). A biannual analysis confirmed this perception in Portuguese sand dunes (Silveira et al., 2013) where beneficial effects of nourishment were the following: (1) wider areas for increased dune growth and development, (2) enhancement of potential shorebird nesting areas and habitat, and (3) increased area for recreation purposes. However, beach nourishment operations will not improve dune conditions if active recreational uses take precedence. In other cases, it has been documented that nourishment can disturb the nesting and foraging of birds, destroy dune vegetation, and compact the sand (Speybroeck et al., 2006). Nourishment of the upper beach has been the commonest practice. It can result in a widened and often overly steep beach with a morphology and sediment composition that may be physically different from the original beach in terms of sand compaction, shear resistance, moisture content, and size, sorting, and shape of sediments. It can also increase the likelihood of aeolian transport and decrease the likelihood of marine erosion of the foredune, possibly altering dune growth and vegetation change by increasing beach width. These changes can have negative impacts on the macrobenthos (Rakocinski et al., 1996; Peterson et al., 2000, 2014; Greene, 2002; Peterson and Bishop, 2005). Ecological impacts occur both at the sites from which sediment is extracted and at the receiving environment. Environmental costs may be incurred because of: (1) removal of habitat and death of biota in the borrow area; (2) increased turbidity and sedimentation in both the borrow and nourished areas; (3) disruption of mobile species that use the beach or borrow area for foraging, nesting, nursing, and breeding; (4) increases in undesirable species; (5) changes in wave action and beach morphology (e.g., from dissipative to reflective); (6) changes in grain size characteristics; (7) higher salinity levels in aerosols associated with

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placement by spraying; and (8) change in community structure and evolutionary trajectories resulting from new conditions in the borrow and nourished areas (National Research Council, 1995). Impacts may manifest at the population (demography and dynamics), community (species richness) and ecosystem (functional processes, nutrient flux, and trophic dynamics) levels. Affected biota includes benthic microalgae, vascular plants, terrestrial arthropods, intertidal and subtidal invertebrates, other marine zoobenthos, and avifauna (Bishop et al., 2006; Peterson et al., 2006; Speybroeck et al., 2006; Fanini et al., 2007, 2009). Factors influencing the nature and extent of ecological impacts of nourishment include the mechanical process itself, its timing, and the quality and quantity of the new sediment (Speybroeck et al., 2006). Effects may be direct, such as mortality of organisms when buried, or indirect, such as reduced prey availability for shorebirds (Nelson, 1993; Bishop et al., 2006; Peterson et al., 2006). Most research has targeted the effects of altered sediment quantity and quality on macrofauna (Rakocinski et al., 1996; Peterson et al., 2000; Menn et al., 2003; Bilodeau and Bourgeois, 2004). The immediate impacts are usually large and may be caused either by burial or by emigration (Menn et al., 2003; Peterson et al., 2006). These effects may be compounded by changes in beach morphology, particularly when nourishment creates a steeper beach and reduces the habitat area for some species (Peterson et al., 2006; Fanini et al., 2007, 2009). Compaction affects the interstitial spaces, capillarity, water retention, permeability, and the exchange of gases and nutrients. Nourishment of sandy beaches can act as a short-term pulse disturbance (Peterson and Bishop, 2005), which elicits a pulse ecological response. Thus, recovery probably occurs in months rather than years (Speybroeck et al., 2006; Leewis et al., 2012). However, recent robust long-term analyses have shown that application of unnaturally coarse and shelly sediments acts as a press disturbance to degrade the beach habitat and the resident fauna (Peterson et al., 2014). The longest recovery times are required for invertebrate fauna when there is a poor match between grain size characteristics of the fill material and the original substrate (Nelson, 1993; Peterson et al., 2000, 2006). Thus, if the profile of the nourished beach and the imported sediments do not match the original conditions (e.g., use of unnaturally coarse or fine sediments), severe ecological impacts may occur and recovery is protracted, particularly in the species typifying the community, such as Emerita, Donax, and Ocypode (Peterson et al., 2000, 2006, 2014 and references therein). Under these conditions, a few species dominate, notably opportunistic forms that profit from the nourishment process, such as the spionid polychaete S. squamata (Leewis et al., 2012; Manning et al., 2014), leading to “over-recolonization” (Leewis et al., 2012). Some case studies deserve special consideration, with important methodological implications. A comprehensive study that coupled field monitoring with mesocosm experiments to assess ecological effects of fine sediment disposal on beaches in North Carolina (Manning et al., 2014) showed severe effects including: (1) beach sediments transformed from medium to fine sand; (2) an increase in surf-zone turbidity during and after sediment deposition; (3) a marked negative effect on recruitment of the mole crab Emerita talpoida and the amphipod Parahaustorius longimerus when nourishment occurred before the recruitment season; (4) depressed abundances of the bean clam Donax variabilis and three haustoriid amphipod species; and (5) an increase in abundance of the opportunistic spionid polychaete S. squamata. Mesocosm experiments showed slowed growth of clams and modified habitat choices and feeding by predatory surf fishes like the Florida pompano, Trachinotus carolinus (see also

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Manning et al., 2013). The authors concluded that fine-grained dredge spoils on these sandy beaches maintained depressed abundances of most macroinvertebrates without sustaining elevated volumes of beach sediments for as long as a year. A 4-year monitoring following each of two spatially separated, replicate nourishment projects using unnaturally coarse sediments gave similar results, including: (1) persistence of gravel-sized particles and shell fragments in the low intertidal and swash zones; (2) suppression of densities of infaunal invertebrates over the entire postnourishment period; and (3) multiyear reductions in abundances of their predators, including ghost crabs and foraging shorebirds (Peterson et al., 2014). Thus, monitoring impacts for periods of only a few months is inadequate. It is clear that prediction of the long-term cumulative implications of large-scale projects is needed (Peterson and Lipcius, 2003; Peterson et al., 2014), but conclusions and the implementation of mitigation measures are often constrained by limited data on the life histories of the affected species, recovery rates, and the cumulative effects of repeated nourishment events (Speybroeck et al., 2006). How long impacts persist is unclear because monitoring after nourishment typically only extends for months rather than years (Peterson et al., 2014; Wooldridge et al., 2016). The more robust evidence from recent studies indicates longer recovery times of intertidal invertebrates than previously observed and highlights the importance of conducting long-term studies to aid decision making. This is a critical issue that must become a rule of thumb when performing environmental impact assessments in sandy-beach ecosystems (Defeo et al., 2009). Basic management recommendations for nourishment include: (1) the avoidance of sediment compaction; (2) careful timing of operations to minimize biotic impacts and enhance recovery; (3) the selection of locally appropriate techniques; (4) the implementation of several small projects rather than a single large project, including repeated application of sediment in shallow layers (