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260 Pages·1988·10.12 MB·English
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Ecological Studies, Vol. 65 Analysis and Synthesis Edited by W D. Billings, Durham, USA F. Golley, Athens, USA 0. L. Lange, Wiirzburg, FRG J. S. Olson, Oak Ridge, USA H. Remmert, Marburg, FRG Ecological Studies Volume 52 Volume 59 Air Pollution by Photochemical Acid Deposition and the Acidification Oxidants Formation, Transport, Control of Soils and Waters and Effects on Plants By J.O Reuss and D.W. Johnson Edited by Robert Guderian 1986. VIII, 120p., 37 figures. cloth 1985. XI, 346p., 54 figures. cloth ISBN 3-540-96290-5 ISBN 3-540-13966-4 Volume 53 Volume 60 The Gavish Sabkha Amazonian Rain Forests A Model of a Hypersaline Ecosystem Edited by C.F. Jordan Edited by G.M. Friedman and 1987. X, 133p., 55 figures. cloth W.E. Krumbein ISBN 3-540-96397-9 1985. X, 484p., 246 figures. cloth ISBN 3-540-15245-8 Volume 54 Volume 61 Tidal Flat Ecology Potentials and Limitations of An Experimental Approach to Species Ecosystem Analysis Interactions Edited by E.-D. Schulze and H. Zw6lfer By Karsten Reise 1987. XII, 435p., 141 figures. cloth 1985. X, 198p., 69 figures. cloth ISBN 3-540-17138-X ISBN 3-540-15447-7 Volume 55 Volume 62 A Eutrophic Lake Frost Survival of Plants Lake Mendota, Wisconsin By A. Sakai and W. Larcher By Thomas D. Brock 1987. XI, 321 p., 200 figures. cloth 1985. XII, 308p., 82 figures. cloth ISBN 3-540-17332-3 ISBN 3-540-96184-4 Volume 56 Resources and Society Volume 63 A Systems Ecology Study of the Island Long-Term Forest Dynamics of the of Gotland, Sweden Temperate Zone By James J. Zucchetto and By Paul A. Delcourt and Ann-Mari Jansson Hazel R. Delcourt 1985. X, 248p., 70 figures. cloth 1987. XIV, 450 p., 90 figures. ISBN 3-540-96151-8 333 maps. cloth ISBN 3-540-96495-9 Volume 57 Forest Ecosystems in the Alaskan Taiga A Synthesis of Structure and Function Volume 64 Edited by K. Van Cleve, F.S. Chapin Landscape Heterogeneity and Disturbance III, Edited by Monica Goigel Turner L.A. Viereck, C. T. Dyrness and 1987. XI, 241 p., 56 figures. cloth P.W. Flanagan ISBN 3-540-96497-5 1986. X, 240p., 81 figures. cloth ISBN 3-540-96251-4 Volume 58 Volume 65 Ecology of Biological Invasions of North The Community Ecology of Sea Otters America and Hawaii Edited by G.R. VanBlaricom and Edited by H.A. Mooney and J .A. Drake J.A. Estes 1986. X, 320p., 25 figures. cloth 1987. XVI, 247 p., 71 figures. cloth ISBN 3-540-96289-1 ISBN 3-540-18090-7 The Community Ecology of Sea Otters Edited by G.R.VanBlaricom and lA. Estes With 71 Figures Springer-Verlag Berlin Heidelberg New York London Paris Tokyo Professor Dr. GLENN R. VANBLARICOM Professor Dr. JAMES A. ESTES U.S. Department of the Interior Fish and Wildlife Service Institute of Marine Sciences 272 Applied Sciences Building University of California Santa Cruz, CA 95064 USA Legendfor cover motif: A sea otter carries a common prey species, the red sea urchin Strongylocentrotusfranciscanus, to the ocean surface. Illustration by Jenny Wardrip, based on an underwater photograph by Richard Mattison. ISBN-13:978-3-642-72847-1 e-ISBN-13:978-3-642-72845-7 DOl: 10.1007/978-3-642-72845-7 Library of Congress Cataloging in Publication Data. The Community ecology of sea otters. (Ecological studies; v. 65). Bibliography: p. Includes index. 1. Sea otter - California - Pacific Coast - Ecology. 2. Animal populations - California - Pacific Coast. 3. Mammals - California- Pacific Coast- Ecology. 1. VanBlaricom, G. R. (Glenn R.), 1949- . II. Estes, J. A. (James A.), 1945- . III. Series. QL737.C25C66 1987 599.74'47 87-20553. This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. Duplication of this publication or parts thereof is only permitted under the provisions of the German Copyright Law of September 9,1965, in its version of June 24, 1985, and a copyright fee must always be paid. Violations fall under the prosecution act of the German Copyright Law. © Springer-Verlag Berlin Heidelberg 1988. Softcover reprint of the hardcover 1st edition 1988 The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. 2131/3130-543210 Preface The impetus for this volume comes from two sources. The first is scientific: by virtue of a preference for certain large benthic invertebrates as food, sea otters have interesting and significant effects on the structure and dynamics of nearshore communities in the North Pacific. The second is political: be- cause of the precarious status of the sea otter population in coastal California, the U.S. Fish and Wildlife Service (USFWS) announced, in June 1984, a proposal to establish a new population of sea otters at San Nicolas Island, off southern California. The proposal is based on the premise that risks of catastrophic losses of sea otters, due to large oil spills, are greatly reduced by distributing the population among two geographically separate locations. The federal laws of the U.S. require that USFWS publish an Environmental Impact Statement (ElS) regarding the proposed translocation of sea otters to San Nicolas Island. The EIS is intended to be an assessment of likely bio- logical, social, and economic effects of the proposal. In final form, the EIS has an important role in the decision of federal management authority (in this case, the Secretary of the Interior of the U.S.) to accept or reject the proposal. As a result of our positions with USFWS and our experience in the study of sea otter-community interactions, the authors of the draft EIS for the above proposal (USFWS 1986) solicited our views on predicted effects of sea otters on the nearshore benthic communities of San Nicolas Island. Many of our views were incorporated into an early draft of the EIS, which was then made available for review by experts in various relevant disciplines. Several of the reviewers were intensively critical of portions of the early draft ElS. Discussions concerning the relationships of sea otters to kelp forest communities were perceived as particularly contentious, stimulating voci- ferous accusations of bias and even ulterior motives. Our response to the above events was to seek a forum wherein the various views of sea otter-community interactions could be objectively stated, com- pared, and discussed, in an atmosphere free of political overtones. Thus, we organized and moderated a half-day symposium on community effects of foraging by sea otters. The symposium was part of the 66th annual meeting of the Western Society of Naturalists, held in December 1985 at Monterey, California. The gathering included presentations by M. Foster, D. Laur, A. Ebeling, D. Duggins, and S. Levin, in addition to ourselves (see Chaps. 4 through 10, this Vol.). Although the symposium was well attended, well VI Preface presented, and well received, the participants agreed that there was much more to be said, and more topics to be covered. In response to this need, we solicited the manuscripts which comprise this volume. Selection of contribu- tors and subject matter was intended to cover all categories of habitat in which sea otters are known to have biological effects. Thus, Kvitek and Oliver review interactions of sea otters and soft-sediment communities (Chap. 3), VanBlaricom presents data on effects of sea otters in rocky intertidal systems (Chap. 4), and several authors contribute views on relationships of sea otters and kelp forests (Chaps. 5 through 9). We emphasize kelp forests in this Volume because more work has been done with sea otters and kelp forests than with other habitat types influenced by sea otters. In addition (probably as a consequence of the greater research effort), interactions of sea otters and kelp forests are quite controversial, especially in California. Our selec- tion of contributors reflects our desire to have the full range of views in the controversy represented in this Volume. Finally, we sought the views of S.A. Levin as a widely recognized theoretical ecologist and applied mathe- matician, and as one experienced in environmental policy disputes. Dr. Levin's role was to assess available data on sea otter-community interactions, and to determine if existing evidence and lines of inquiry are appropriate for the kinds of answers needed for ecological generalizations and environmental policy decisions. With the exception of Chap. 1, all chapters in this volume were subjected to peer review. We established a panel of 20 scientists to provide the reviews. Panel members are listed below, with the exception of one member, who requested anonymity: Ames, J .A., California Department of Fish and Game, Monterey, Cali- fornia, USA Beddington, J .R., Center for Environmental Technology, Imperial Col- lege of Science and Technology, London, England Cailliet, G.M., Moss Landing Marine Laboratories, Moss Landing, Cali- fornia, USA Dayton, P K., Scripps Institution of Oceanography, University of Cali- fornia, La Jolla, California, USA Gaines, S D., Hopkins Marine Station, Stanford University, Pacific Grove, California, USA Goodman, D., Department of Biology, Montana State University, Boze- man, Montana, USA Hines, A.H., Chesapeake Bay Center for Environmental Studies, Smith- sonian Institution, Edgewater, Maryland, USA Hixon, M.A., Department of Zoology, Oregon State University, Corvallis, Oregon, USA Jackson, G.A., Scripps Institution of Oceanography, University of Cali- fornia, La Jolla, California, USA Jameson, RJ ., US Fish and Wildlife Service, San Simeon, California, USA Johnson, A.M., US Fish and Wildlife Service (retired), Anchorage, Alaska, USA Preface VII Kenyon, K.W., US Fish and Wildlife Service (retired), Seattle, Washington, USA Menge, B.A., Department of Zoology, Oregon State University, Corvallis, Oregon, USA North, WJ ., Kerckhoff Marine Laboratory, California Institute of Tech- nology, Corona del Mar, California, USA Pearse, J .S., Institute of Marine Sciences, University of California, Santa Cruz, California, USA Peterson, C.H., Institute of Marine Sciences, University of North Carolina, Morehead City, North Carolina, USA Simenstad, C.A., Fisheries Research Institute, University of Washington, Seattle, Washington, USA Sousa, W.P., Department of Zoology, University of California, Berkeley, California, USA Suchanek, T .H." Division of Environmental Studies, University of Cali- fornia, Davis, California, USA Chapters 2 through 10 were each reviewed by at least two members of the panel. No panel member reviewed more than one chapter. Chapter 11 (our concluding summary) was reviewed by all of the principal authors of the contributed chapters. In addition, several authors of contributed chapters sought additional review comments from colleagues. These reviewers are acknowledged in the individual chapters as appropriate. Because of our joint roles as editors and contributors to this Volume, we established a procedure to avoid conflict of interest in the review process. For all chapters that we authored or co-authored, Dr. A.W. Ebeling (Uni- versity of California, Santa Barbara, California, USA) assumed the role of editor, and held final authority on any matters of disagreement between us and our reviewers. The review process outlined above was intended to insure that this Volume would be as informative, constructive, and objective as is humanly possible. We believe that the process has been reasonably successful, recognizing that such goals are, in practice, difficult to obtain. We sincerely hope that this Volume will contribute to improved knowledge of the ways in which sea ot- ters influence natural communities. In addition, we hope the Volume will provide a model for the discussion of sea otter ecology in an atmosphere relatively free of the heavy constraints of political intrigue. Santa Cruz, California, USA G.R. VanBlaricom J.A. Estes Acknowledgments We thank the contributors to this Volume for their efforts toward improve- ment of our knowledge of sea otters and natural communities. We are grate- ful for the responsiveness and tolerance of the contributors to the review process, and to deadlines and various other impositions. Likewise, we thank the members of the review panel, whose prompt and constructively critical evaluations led to substantial improvements in the quality, clarity, objectivity, and credibility of the volume. We are particularly grateful to Dr. A.W. Ebeling for his efforts as an editor of manuscripts that we contributed. Dr. Ebeling's time and efforts had a significant positive influence on the quality and objectivity of our chapters. We thank Dr. David Montgomery for his support and assistance in the presentation of our symposium at the 1985 annual meeting of the Western Society of Naturalists, in Monterey, California. The completion of this volume was, to a large degree, a consequence of the successful presentation of our symposium. We thank Dr. Dieter Czeschlik and the editorial staff of Springer-Verlag for their remarkable support, enthusiasm, and tolerance of this project. We also thank the editors of Ecological Studies for supporting the inclusion of this Volume in the Series. We are grateful for the administrative support and patience of the U.S. Fish and Wildlife Service and the University of California, San ta Cruz (UCSC), especially Drs. Robert 1. Brownell, Jr., and William Doyle. The National Ecology Center of the Fish and Wildlife Service was most helpful in the pre- paration of graphics for the volume. The office staff of the Institute of Marine Sciences, UCSC, provided extensive assistance with manuscript preparation, and David Carlson provided valued help with computers. Our own research activities on the community ecology of sea otters probably would not have developed without the support and encouragement of Dr. Clyde Jones during the time he served as Director of the National Fish and Wildlife Laboratory and the Denver Wildlife Research Center. We grate- fully acknowledge his wisdom, friendship and commitment to scientific ex- cellence. It is a particular pleasure to express our thanks to Mrs. Patti Himlan for her contributions to the completion of this volume. In the face of an end- less stream of manuscripts, letters, unreasonable deadlines, and self-destruct- ing hard discs, she has maintained her patience, good humor, and a steady commitment to the completion of this volume. Finally, we thank our families for their continuous support and patience throughout the project. G.R. VanBlaricom and J.A. Estes Contents 1 Introduction G.R. VanBlaricom and J.A. Estes ......................... . 2 A Review of the History, Distribution and Foraging Ecology of Sea Otters M.L. Riedman and J .A. Estes (With 12 Figures) 2.1 Introduction ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4 2.2 Evolution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4 2.3 History, Distribution and Present Status of Populations . . . . . . .. 7 2.4 Diet and Foraging Behavior .......................... 12 2.4.1 Habitat .................................... 12 2.4.2 Diet ...................................... 13 2.4.3 Foraging Behavior. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15 2.4.4 Activity ................................... 16 2.4.5 Class and Individual Variation ..................... 19 2.5 Summary ...................................... 20 3 Sea Otter Foraging Habits and Effects on Prey Populations and Communities in Soft-Bottom Environments R.G. Kvitek and 1.S. Oliver (With 5 Figures) 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 22 3.2 Soft-Bottom Foraging Habits ......................... 23 3.2.1 Epifaunal Prey Communities. . . . . . . . . . . . . . . . . . . . .. 28 3.2.1.1 Prey Populations ....................... 28 3.2.1.2 Prey Communities ...................... 29 3.2.2 Shallow-Burrowing Infaunal Prey. . . . . . . . . . . . . . . . . .. 30 3.2.2.1 Prey Populations ....................... 30 3.2.2.2 Prey Communities ...................... 31 3.2.3 Deep-Burrowing Infaunal Prey .................... 32 3.2.3.1 Prey Populations ....................... 32 3.2.3.2 Prey Communities ...................... 37 3.3 Prey Vulnerability and Patch Dynamics .................. 38 XII Contents 3.3.1 Prey Resistance .............................. 38 3.3.2 Prey Resilience ............................... 41 3.4 Substrate Disturbance .............................. 41 3.5 Rocky and Soft Substrata ........................... 43 3.6 Future Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 45 3.7 Summary ...................................... 45 4 Effects of Foraging by Sea Otters on Mussel-Dominated Intertidal Communities G.R. VanBlaricom (With 19 Figures) 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 48 4.2 Models of Mussel-Dominated Communities ................ 48 4.3 Sea Otters as Predators of Mussels .................... .. 50 4.4 Case 1: Sea Otters and Mussels on the Coast of Central California . 51 4.4.1 Study Location .............................. 52 4.4.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 54 4.4.3 Consumption of Mytilus californumus by Sea Otters: The Basic Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 55 4.4.4 Creation of Gaps in Mussel Cover by Sea Otters: Spatial and Temporal Aggregation. . . . . . . . . . . . . . . . . . . . . . . . .. 57 4.4.5 Size Distribution of Gaps Created by Sea Otters. . . . . . . .. 61 4.4.6 Mussel Size and Vulnerability to Foraging Sea Otters. . . . .. 63 4.5 Case 2: Sea Otters and Mussels in Prince William Sound, Alaska. .. 65 4.5.1 Study Location .............................. 66 4.5.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 69 4.5.3 Consumption of Mytilus edulis by Sea Otters: The Basic Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 70 4.5.4 Size Distribution of Intertidal Mussels and the Population Status of Sea Otters ........................... 73 4.5.5 Mussel Size and Vulnerability to Foraging Sea Otters. . . . .. 82 4.6 Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 84 4.7 Summary ...................................... 88 5 Kelp Communities and Sea Otters: Keystone Species or Just Another Brick in the WaD? M.S. Foster and D.R. Schiel (With 3 Figures) 5.1 Introduction ............. . . . . . . . . . . . . . . . . . . . . . .. 92 5.2 Kelp Community Structure .......................... 94 5.3 The Otter as a Keystone Species in California: Local or General? .. 95 5.3.1 Approach and Methods .... . . . . . . . . . . . . . . . . . . . .. 95 5.3.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 98 5.3.3 Possible Bias ................................ 99 5.4 Otter Effects: Geographic and Historical . . . . . . . . . . . . . . . . . . 102

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