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Turbidity and Wave Energy Affect Community Composition and Trophic Interactions

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Turbidity and Wave Energy Affect Community Composition and Trophic Interactions TURBIDITY AND WAVE ENERGY AFFECT COMMUNITY COMPOSITION AND TROPHIC INTERACTIONS A Dissertation by JESSICA LUNT BS, University of West Florida, 2008 Submitted in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY in MARINE BIOLOGY Texas A&M University-Corpus Christi Corpus Christi, Texas August 2014 © Jessica Heath Lunt All Rights Reserved August 2014 TURBIDITY AND WAVE ENERGY AFFECT COMMUNITY COMPOSITION AND TROPHIC INTERACTIONS A Dissertation by JESSICA LUNT This dissertation meets the standards for scope and quality of Texas A&M University-Corpus Christi and is hereby approved. Delbert L. Smee, PhD Thomas C. Shirley, PhD Chair Committee Member Michael S. Wetz, PhD Anna R. Armitage, PhD Committee Member Committee Member Anita J. Reed, PhD Graduate Faculty Representative JoAnn Canales, PhD Dean, College of Graduate Studies August 2014 ABSTRACT Abiotic variables are well known community regulators and can strongly influence species distributions when they are outside of a species physiological tolerance limits. However, environmental variables within tolerance limits may also alter species distributions, morphology, predator-prey interactions, and influence the structure and function of communities. The purpose of this study was to determine how abiotic variables (notably turbidity) alter diversity, species distributions and abundances, predation rates on and species morphology. Texas Parks and Wildlife Department Fisheries Independent Survey Data from 1991- 2008 were used in addition to field surveys of St. Charles Bay to determine the effects of turbidity on fish and crab diversity and abundance. Feeding assays were conducted in the field using groups of 5 mud crabs and 10 juvenile oysters to assess feeding rates in high and low turbidity. Juvenile oysters were also allowed to grow in the field to test the effects of turbidity on oyster growth. In addition, the effects of wave energy on oyster reef species composition and size were assessed using field surveys. I found that turbidity affects top-down control and biodiversity in estuaries and has similar effects to salinity and temperature. Elevated turbidity reduced fish diversity and abundance (p < 0.01), while increasing the diversity and abundance of crabs (p < 0.01). Predation by visual fish predators was also reduced in elevated turbidity (p = 0.02), which leads to an increase in the abundance of crabs and increased predation on mud crabs in high turbidities (p = 0.03). Juvenile oysters respond to increased crab abundance by growing heavier shells, which may lower fecundity. In laboratory assays, increased turbidity decreased the predation v efficiency of visual predators (fish) but not of chemosensory predators (crabs). Differences were found between wave exposed and wave protected areas. Areas with higher wave energy had fewer species (p < 0.001) and the average size of species was smaller. This research identifies turbidity as an important variable within estuarine systems and extends the effects of wave energy from rocky intertidal systems to oyster reef communities. Both of these variables should be considered for effective management and restoration of estuarine communities. vi DEDICATION In dedication to all the people who said I should not be or could not be a Marine Biologist. vii ACKNOWLEDGEMENTS I thank my Chair, Dr. Lee Smee for being a supportive and encouraging mentor through this long process. For never saying no when I needed to talk about data, writing, teaching or life in general. He has taught me what it means to be a mentor and a scientist. He was instrumental in the tough transition from student to professional and helping me learn to argue my own case and present my own interpretations of and ideas for research. He tested my patience and my first aid/responder training but I hope to be half as good an advisor to my own students as he was for me. I thank my committee members: Dr. Thomas Shirley, Dr. Anna Armitage and Dr. Mike Wetz for their insights and criticisms that made this dissertation both better in scope and more polished. You asked the right questions to make sure I could put this dissertation in context. Thank you to the Center for Coastal Studies at TAMU- CC which provided facilities and equipment necessary to accomplish this research. I also thank our funding sources: NSF-MRI Grant #0821215, Texas Sea Grant, the Texas Research Development Fund, a TAMU-CC Faculty Enhancement Grant, the Harvey Weil Sportsman Conservationist Award, and the Ruth A. Campbell Professorship to D.L. Smee. Thank you to my lab mates in the TAMU- CC Marine Ecology Lab, for both logistical assistance and moral support. I specifically thank K. Johnson for training me to successfully operate a boat at the Goose Island State Park boat ramp, A. Scherer for helping me discover the ‘just right’ way to tether and transport a mud crab, and E. Robinson for never saying no to a field day or being a sounding board for my research ideas and frustrations. viii I also thank my family and friends for their unwavering support and conviction that a Ph.D. was mine for the taking. My parents, Kimberly Lunt and Robert Lunt for never sugar coating the trials of life but insisting I could do whatever I set my mind to anyway. I thank my maternal grandparents, Leigh and Don Heath for giving me the kick in the pants I needed when it came time to write this dissertation. I thank my paternal grandparents, Dottie and Jerry Lunt for wanting to hear all about my research and taking me on the most amazing graduation trip, early so I could remember just why being a scientist is so important. Lastly I thank my uncle, Kerry Heath who never let me forget that I needed to be able to communicate with and understand the perceptions of the general public to be successful. ix TABLE OF CONTENTS CONTENTS PAGE ABSTRACT .................................................................................................................................... v DEDICATION .............................................................................................................................. vii ACKNOWLEDGEMENTS ......................................................................................................... viii TABLE OF CONTENTS ................................................................................................................ x LIST OF FIGURES ..................................................................................................................... xiii LIST OF TABLES ....................................................................................................................... xiv INTRODUCTION .......................................................................................................................... 1 Oyster Reefs as a Model System ................................................................................................. 4 Chapter I: Anthropogenic effects indirectly reduce biodiversity .................................................... 7 ABSTRACT ................................................................................................................................ 7 INTRODUCTION ....................................................................................................................... 7 METHODS................................................................................................................................ 10 Long-term monitoring of turbidity on species abundance ..................................................... 10 Field Study ............................................................................................................................. 12 Field Sampling ....................................................................................................................... 14 Collection and Analysis ......................................................................................................... 17 RESULTS.................................................................................................................................. 17 DISCUSSION ........................................................................................................................... 27 x ACKNOWLEDGEMENTS ...................................................................................................... 30 Chapter II: Turbidity influences trophic interactions in estuaries ................................................ 32 ABSTRACT .............................................................................................................................. 32 INTRODUCTION ..................................................................................................................... 32 METHODS................................................................................................................................ 37 Long-term monitoring of turbidity on species abundance ..................................................... 37 Field study ............................................................................................................................. 40 RESULTS.................................................................................................................................. 46 TPWD analysis ...................................................................................................................... 46 Field sampling ......................................................................................................................
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