AN ABSTRACT OF THE THESIS OF Jennifer Motley for the degree of Master of Science in Marine Resource Management presented on March 22, 2017. Title: Local and Regional Patterns in Eelgrass (Zostera marina L.) Communities Along an Upwelling-Productivity Gradient in Oregon Estuaries, USA Abstract approved: ______________________________________________________ Fiona Tomas Nash Sally D. Hacker In this thesis, I investigate the organization of eelgrass (Zostera marina L.) and mesograzer communities across local and regional scales in three upwelling- influenced estuaries located along the Oregon coast, USA. Eelgrass ecosystems are an important source of primary production in estuarine systems, providing numerous ecosystem services, including nursery habitat for commercial fish, water quality improvement, and sediment stabilization. Community structure in eelgrass systems, i.e., the diversity, abundance, and composition of primary and secondary consumers, is influenced by a combination of local to regional scale variability in environmental and biotic factors. Thus, an important consideration in the management of these systems is to understand the organization of community structure across spatiotemporal scale and the implications for top-down (consumer) versus bottom-up (resource) control. In upwelling-influenced estuaries of the Pacific Northwest coast of the United States, eelgrass systems are exposed to latitudinal variability in oceanographic inputs, but the degree to which these regional effects versus local effects organize eelgrass community structure is poorly understood. Here I investigate the relationship between primary producers (eelgrass, ulvoid macroalgae, and epiphytes), epifauna mesograzers, and fish predators within and across three estuaries located on the Oregon Coast, USA (Netarts Bay, Yaquina Bay, and Coos Bay). Specifically, I asked: 1) What is the relative importance of local (within estuary) versus regional (across estuaries) scale patterns to eelgrass community structure (i.e., primary producers, epifaunal mesograzers, and fishes) in upwelling-influenced estuaries in Oregon?, 2) What is the potential role of regional oceanography versus trophic interactions in regulating eelgrass community structure, and is this dependent on spatial scale?, and 3) What are the management implications for eelgrass communities when regional and local scales are considered? I found that while local effects were important, regional (estuary) scale patterns strongly influenced community structure in eelgrass communities, providing support that regional oceanographic bottom-up forcing dominates eelgrass communities. Additionally, I found evidence for top-down control by the opisthobranch Phyllaplysia taylori on primary producers at one site within Netarts Bay. I suggest that eelgrass beds in these estuaries are mostly bottom-up systems, and further investigations should focus on quantifying the mechanistic relationship between mesograzers and primary producers at local to regional scales. ©Copyright by Jennifer Motley March 22, 2017 All Rights Reserved Local and Regional Patterns in Eelgrass (Zostera marina L.) Communities Along an Upwelling- Productivity Gradient in Oregon Estuaries, USA by Jennifer Motley A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented March 22, 2017 Commencement June 2018 Master of Science thesis of Jennifer Motley presented on March 22, 2017 APPROVED: Co-Major Professor, representing Marine Resource Management Co-Major Professor, representing Marine Resource Management Dean of the College of Earth, Ocean, and Atmospheric Sciences Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Jennifer Motley, Author ACKNOWLEDGEMENTS I would like to thank my co-advisors, Dr. Fiona Tomas Nash and Dr. Sally Hacker, for providing me with support throughout this process that has helped me develop into an ecologist. In particular, funding from Dr. Tomas Nash has made my experience possible. Additionally, her dedication to this work, creativity, and brilliance as an ecologist has been both an inspiration and an example to me. Dr. Hacker’s clarity of mind has helped me wrap my head around big ecological questions, her input has organized this project, and her help in the writing stages has been invaluable. Thank you also to Dr. Ted DeWitt, who has provided invaluable guidance for me in framing my research. In addition, thank you to Dr. Kelly Riedinger for embracing this project and providing advice and encouragement. In addition, Dr. Margot Hessing-Lewis, Dr. Tony D’Andrea, and C. Kaminksy provided initial insight I was able to run with early on in this project. I am especially grateful to J. Henderson, who provided me with endless local knowledge, logistical help, and assistance in the field throughout the field season. Thank you to R. Klopfenstein, M. Mason, G. Hernan, S. Detwiler, and E. Hayduk for helping me complete fieldwork during those early, early mornings. F. Conway and R. Allan provided unwavering support, encouragement, and perspective – and were there to remind me of life outside of graduate school. Thank you to L. Hartline for her help in tying up the loose ends and making life easier. My MRM cohort and the MRM program was a source of support, fun, and adventure that made graduate school a better experience. Thank you to my housemates for being an excellent support network and all-around great company. Finally, special thanks to my husband, E. Hayduk, for selflessly taking on the additional roles of field technician, life coach, editor, cook, and dishwasher. TABLE OF CONTENTS Page 1 Chapter 1: General Introduction.…………..……………………………………… 1 2 Chapter 2: Evidence That Regional Effects Dominate Eelgrass (Zostera marina L.) and Mesograzer Community Structure in Upwelling-Influenced Estuaries.……… 6 2.1 Abstract………………………………………………….……………………..7 2.2 Introduction…………………………………………………………..………...9 2.3 Methods…………………………………………………………………….…14 2.3.1 Study Sites…….………………………………………………………...14 2.3.2 Observational field surveys……………………………………………..15 2.3.3 Sample processing…………………..……………..……………………16 2.3.4 Statistical analyses………………………………………………………17 2.4 Results……………………………………………………………...…………18 2.4.1 Patterns of eelgrass, macroalgae, and epiphytes..………….…………..18 2.4.2 Patterns of epifauna and fish…………………………………………...19 2.4.3 Variance components of primary producers, epifauna, and fish…...…..20 2.4.4 Patterns of mesograzer distribution, variance, and composition…….…21 2.4.5 Correlations among eelgrass community variables………………….…22 2.5 Discussion…………………………………………………………………….23 2.5.1 Empirical patterns compared to hypotheses……………………………23 2.5.2 Possible drivers of primary producers at regional and local scales…….24 2.5.3 Relationships between primary and secondary producers……………...25 2.5.4 Evidence for localized mesograzer control of eelgrass community structure…………................................................................................27 2.5.5 Management implications……………………………………………...29 2.6 Acknowledgements…………………………………………………………...31 2.7 Tables…...…………………………………………………………………….32 2.8 Figures……………...…………………………………………………………39 3 Chapter 3: General Conclusion ……………………………………………………48 4 Bibliography.…….….…………………………………………………………..…51 5 Appendices…….…………………………………………………………………..65 LIST OF FIGURES Figure Page 1. Map of study area………………………………………...……………………….40 2. Mean cross-shore and alongshore transport across estuaries………….…………41 3. Patterns of eelgrass, macroalgae, and epiphytes within and across estuaries…....42 4. Patterns of epifauna and fish within and across estuaries..………………………43 5. Variance components of primary producers and macrofauna...………………….44 6. Patterns of mesograzers within and across estuaries..……………………………45 7. Variance components of mesograzers………………………...………………….46 8. Comparison of Phyllaplysia taylori abundance, epiphyte load, and fish abundance..……………………………………………………………..……47 LIST OF TABLES Table Page 1.A Estuarine characteristics of Netarts, Yaquina and Coos Bays…………….33 1.B Site locations and local conditions in Netarts, Yaquina, and Coos Bays.…33 2.A Nested ANOVA model results and variance components for primary producers …...……………………………………………………..……….34 2.B Nested ANOVA model results and variance components for epifaunal taxon richness, abundance, and fish abundance………………………………......35 2.C Nested ANOVA model results and variance components for mesograzers..36 3 Pearson’s correlation of eelgrass community variables………………………………………….………………………....37 LIST OF APPENDIX FIGURES Figure Page B.1 Temporal patterns of eelgrass, ulvoid macroalgae, and epiphytes across estuaries…………………………………………...………………………....69 B.2 Temporal patterns of taxon richness, epifaunal abundance, and fish abundance across estuaries…………………………………………………….………...70 B.3 Temporal patterns of four most common mesograzers across estuaries….….....71 LIST OF APPENDIX TABLES Table Page A.1 Cumulative abundance of epifauna from dip net sweeps………………………66 A.2 Cumulative abundance of fish from dip net sweeps……...………….………...68 C.1 Cumulative abundance of epifuana from grab samples………………………...72 C.2 Cumulative abundance of fish from cage method……...………………………74 D.1 Tukey’s linear contrasts from significant factors…………...………………….75 E.1 Means of variables across estuaries…………………………………………….96 E.2 Means of variables within estuaries…………………………………………….97