AN ABSTRACT OF THE DISSERTATION OF Todd William Miller for the degree of Doctor of Philosophy in Fisheries Science presented on May 9, 2006. Title: Trophic Dynamics of Marine Nekton and Zooplankton in the Northern California Current Pelagic Ecosystem. Abstract approved: Hiram W. Li Richard D. Brodeur The Northern California Current (NCC) ecosystem exhibits extreme seasonal, interannual and interdecadal shifts in the abiotic environment and shifts in primary and higher production. This variability is also apparent in the spatial structure of the ecosystem with nearshore-shelf waters (<150 m isobath) being highly productive and having a different community structure relative to more offshore-slope (>150 m) waters. Very little is known of the trophic relationships between primary consumers and higher trophic levels within this system, and the potential influence of spatial gradients in productivity and community composition on trophic structure. This dissertation research covers several important aspects of trophic dynamics within the NCC ecosystem through the use of conventional dietary analysis and stable isotope analysis of multiple trophic levels. From June and August 2000 and 2002 cruises off the shelf-slope ecosystem from Northern California to central Oregon, I collected and analyzed the diets from 25 species of pelagic nekton (Chapter 2). Trophic groups were formed from agglomerative hierarchical cluster analysis of prey contribution to nekton diet, with cluster groups described by indicator species analysis. Seasonal, interannual and interdecadal comparisons in diet were examined for some nekton species. Results from general description of diets and cluster analysis showed clustering based primarily on prey of copepods, euphausiids, decapod larvae and larval-juvenile fishes, representing lower (copepods), middle (euphausiids and decapod larvae) and upper (larval-juvenile fishes) trophic groups, but that many species exhibited omnivory by feeding on prey several levels down the food web. Results from carbon and nitrogen stable isotope analysis (Chapter 3) support the general trophic structure observed through dietary analysis; that the copepod-euphausiid-larval/juvenile fish structure in the diets were generally observed in relative trophic position using δ15N. Carbon stable isotopes displayed signatures more indicative of onshore-offshore distribution of species (Chapter 4) with nearshore species of nekton and zooplankton being enriched in 13C relative to offshore. This provided an effective trophically-based delineation of the NCC pelagic food web. Although stable isotopes are effective tools for measuring relative trophic position and source production, the duration of time that stable isotopes are a measure of past trophic hsitory is not well known. To examine this, I conducted a laboratory-controlled experiment to examine the tissue-specific response of isotope δ15N to changes in isotopic signature of diet in an adult marine fish (Pacific herring, Clupea pallasi)(Chapter 5). To test which animal tissue was the most accurate measure of isotope shift I examined multiple tissues (eye, heart, liver, blood, and white muscle) and the importance of growth and metabolism in this shift. This study showed that (i) isotopic response of individual tissues following an isotopic shift in diet varied in both rate of change and fractionation level, (ii) most of this isotopic shift is due to growth, and (iii) white muscle and liver tissue appeared the most responsive to isotopic shift in diet, reaching isotopic equilibrium with diet in a matter of months (not years). The culmination of this dissertation in the context of trophic controls on the NCC ecosystem, and how they are different from other EBC systems are discussed in Chapter 6. ©Copyright by Todd William Miller May 9, 2006 All Rights Reserved TROPHIC DYNAMICS OF MARINE NEKTON AND ZOOPLANKTON WITHIN THE NORTHERN CALIFORNIA CURRENT PELAGIC ECOSYSTEM by Todd William Miller A DISSERTATION Submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Presented May 9, 2006 Commencement June 2007 Doctor of Philosophy dissertation of Todd William Miller presented on May 9, 2006. APPROVED: Co-Major Professor, representing Fisheries Science Co-Major Professor, representing Fisheries Science Head of Department of Fisheries and Wildlife Dean of Graduate School I understand that my dissertation will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my dissertation to any reader upon request. Todd William Miller, Author ACKNOWLEDGEMENTS This dissertation could not have been done without the help and support of many people. First, I would like to thank my advisors Richard Brodeur and Hiram Li, and committee members Peter Eldridge, Evelyn Sherr and Lynda Ciuffetti for their guidance and input into my education and research. Their genuine interest in my growth as a person and as a scientist was evident in their openness to meet with me on a personal and professional level. I greatly appreciate the help from many people for providing considerable technical and logistical support: Susan Hinton, Joe Fisher, Paul Bentley, Robert Emmett, Ed Casillas, Cynthia Bucher, Doug Reese, Suzan Pool, Bill Pearcy, Cheryl Morgan, Jesse Lamb, John Chapman, Jack Chapman, Becky Baldwin, Kym Jacobson, Keith Bosley, Margaret Sparrow, Fred Prahl, Susan Sogard, Ian Fleming, Vlada Gertseva, Elizabeth Daly, and Liu Chi-Chang, and Steve MacAvoy. This research was supported by several agencies at the Hatfield Marine Science Center in Newport, and at the Oregon State University campus in Corvallis. Funding and major logistical support was provided through the National Marine Fisheries Service Northwest Fisheries Science Center (NMFS - NWFSC) and the Oregon State University Cooperative Institute of Marine Resources Studies (CIMRS) through the US GLOBEC Northeast Pacific (NEP) program. Additional funds for stable isotope analyses were provided through the Hatfield Marine Science Center Mamie Markham Award and Bill Wick Marine Fisheries Award. Much of the processing of stable isotope material for this work was done through the U.S. Environmental Protection Agency Western Ecology Division Newport Oregon, and at the OSU College of Oceanic and Atmospheric Sciences (COAS). Office and laboratory space on campus was provided through the OSU Fisheries and Wildlife Department. Special thanks to the Hatfield Marine Science Center Marilyn Potts Guin Library and staff for their hard work through the years in providing me unfettered access to the scientific literature. This dissertation is dedicated to my parents, Arthur and Rita Miller, to my brother Bill, and sisters Jennifer and Jane. They have provided love and support that cannot be expressed in writing. I am continually grateful for their being there for me. CONTRIBUTION OF AUTHORS Dr. Richard Brodeur assisted with data collection and analysis, provided laboratory space, supplies and logistical support for the research performed. Dr. Greg Rau provided additional data and use of his laboratory to run additional stable isotopes through his lab. Dr. Hiram Li provided extensive help with the manuscript and interpretation of results and provided laboratory space for research. TABLE OF CONTENTS Page CHAPTER 1 TROPHIC DYNAMICS OF THE NOTHERN CALIFORNIA CURRENT PELAGIC ECOSYSTEM....................................................................................... 1 INTRODUCTION .......................................................................................................... 2 LITERATURE CITED ................................................................................................... 5 CHAPTER 2 TROPHIC RELATIONSHIPS OF MARINE NEKTON WITHIN THE NORTHERN CALIFORNIA CURRENT ECOSYSTEM ..................................... 9 ABSTRACT.................................................................................................................. 10 INTRODUCTION ........................................................................................................ 11 METHODS ................................................................................................................... 13 RESULTS ..................................................................................................................... 17 DISCUSSION............................................................................................................... 37 LITERATURE CITED ................................................................................................. 46 CHAPTER 3 TROPHIC DYNAMICS OF ZOOPLANKTON AND NEKTON IN THE NORTHERN CALIFORNIA CURRENT ECOSYSTEM – AN INTEGRATED APPROACH TO USING DIET AND STABLE ISOTOPE ANALYSES .......... 69 ABSTRACT.................................................................................................................. 70 INTRODUCTION ........................................................................................................ 70 RESULTS ..................................................................................................................... 77 DISCUSSION............................................................................................................... 86 LITERATURE CITED ................................................................................................. 94 TABLE OF CONTENTS (Continued) CHAPTER 4 CARBON STABLE ISOTOPES REVEAL RELATIVE CONTRIBUTION OF SHELF-SLOPE