Grazing dynamics of the pinfish (Lagodon rhomboides) on Thalassia testudinum and Halimeda incrassata across a temperature gradient in the Florida Keys and implications for Ciguatera Fish Poisoning A Thesis Presented to The Faculty of the College of Arts and Sciences Florida Gulf Coast University In Partial Fulfilment of the Requirement for the Degree of Master of Science By Kathryn Alissa Ribble 2019 i Florida Gulf Coast University Thesis APPROVAL SHEET This thesis is submitted in partial fulfillment of the requirements for the degree of Master of Science Kathryn Alissa Ribble Approved: December 2, 2019 ___________________________ Michael Parsons, Ph.D., Advisor ___________________________ James Douglass, Ph.D., Committee Member ___________________________ Brian Bovard, Ph.D., Committee Member The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above-mentioned discipline. ii ACKNOWLEDGMENTS Writing these acknowledgments allows me the time to reflect on the knowledge and experience I have gained from pursuing my Master of Science degree. When I started this program, I was unaware of how immense some of the challenges and opportunities would be that came from attending graduate school. I have learned just how much effort goes into completing a masters degree and how willing people are to help you pursue your endeavors. Through hard work and with the support of many others I was able to successfully earn my Masters of Science degree! I would first like to thank my advisor Dr. Mike Parsons who initially gave me a job in his lab years ago and ultimately inspired me to get my masters degree. He has guided me through the challenges of creating a research project and enhanced my scientific writing skills in addition to providing myself and lab mates with awesome places to conduct field research and giving us the opportunities to experience and participate in scientific conferences around the country. Additionally, my committee members Dr. James Douglass and Dr. Brian Bovard were an integral part in helping me write and interpret the data I collected for this project. Funding and support were provided by the NOAA NCCOS ECOHAB program (award N1A17NOS4780181), the Florida Gulf Coast University Department of Marine and Earth Sciences, the Jean and Bill Wilshere Endowment for Innovative Research in Environmental Science scholarship, the Wanda G. Tolley Scholarship Endowed Fund, the Dan Cassani Memorial Fund for Marine Fish Research and Conservation, the Community Foundation of Sarasota County, and the Angler Action Foundation for providing me the iii funding to go back to school for my masters degree. These organizations made it financially possible for me to achieve this goal. There are many individuals who were a large part in helping me throughout this experience. Of them, Nicholas Culligan has been my rock. Whether it was helping me set up and break down the same 50-gallon seagrass tank for the 7th time, collect samples for my many attempts at setting up my experiment, making me laugh when I had a bad day, or inspiring me when I felt uninspired, he helped make the difficult parts of this experience a little less difficult. I would also like to acknowledge the help and support that my family gave me throughout this process; thank you Andrea, Steven, and Kimbra Ribble. Lastly, I would like to thank Anne Smiley, Andrea James, Adam Catasus, Jeff Zingre, and Allie Bury for being such good friends and helping me with this project in various ways. Attending graduate school has been a rewarding challenge that I would not have wanted to do without the help and support of all the people aforementioned. As the quote by Helen Keller goes, “alone we can do so little; together we can do so much”, I too believe that this project and experience would not have been as successful without the support from all of them. Thank you all so much! iv ABSTRACT Seagrass beds are an important component of coastal environments and serve as important nursery grounds for juvenile and commercially important fish species. Seagrass beds are often monospecific, composed of just one species of seagrass. However, macroalgal species such as Halimeda, Laurencia, and Dictyota (among others) can also be found in seagrass beds in quantities that vary depending on many factors including grazing pressures. This study focuses on the grazing dynamics of Lagodon rhomboides (commonly referred to as pinfish) between two different macrophytes (Thalassia testudinum and Halimeda incrassata) over a temperature gradient in a laboratory setting representative of a seagrass bed from the middle Florida Keys (Heine Grass Bed; HGB). HGB, where samples were collected for this study, is a long-term study site for Ciguatera Fish Poisoning (CFP) research as well. CFP is a form of food poisoning in humans who consume tropical reef fish that have accumulated high levels of ciguatoxins. Ciguatoxins are naturally produced lipid-soluble toxins produced by the benthic dinoflagellate, Gambierdiscus, which enter reef food webs through the consumption of these epiphytic cells by herbivorous fishes. Thalassia testudinum and Halimeda incrassata are known to harbor high quantities of toxic Gambierdiscus species within their associated epiphytic community in areas such as HGB. The overall objective of this study is to examine the grazing dynamics of pinfish on Thalassia testudinum and Halimeda incrassata under varying temperatures within a seagrass bed environment (HGB) in the middle Florida Keys. This study will also aid in determining how ciguatoxins are being introduced into the marine food web through grazing processes occurring within seagrass beds in the middle Florida Keys and assist modeling efforts for CFP outbreaks. Additionally, it will v identify if specific temperatures influence the grazing behaviors of pinfish which will lend insight into how grazing pressures change seasonally and how they may change as the climate warms. This study found that pinfish did not consume one macrophyte agar (Thalassia testudinum or Halimeda incrassata) at a significantly higher amount than the other at ambient temperature. In addition, the results also suggest that pinfish are not significantly increasing their grazing intensity on Thalassia testudinum agar across a temperature gradient (22°C – 30°C). However, the grazing intensity of pinfish on Halimeda incrassata agar did significantly increase with increasing temperature but the strength of this linear correlation is fairly weak (R2 = 0.2154). Finally, pinfish ate a marginally significantly larger amount of the Halimeda incrassata agar cubes than the Thalassia testudinum agar cubes over the temperature gradient tested (22°C – 30°C; p = 0.052). vi TABLE OF CONTENTS ACKNOWLEDGMENTS .............................................................................................. iii ABSTRACT .......................................................................................................................v TABLE OF CONTENTS .............................................................................................. vii LIST OF FIGURES ........................................................................................................ ix LIST OF TABLES ......................................................................................................... xii 1. INTRODUCTION .........................................................................................................1 1.1. Importance of Seagrass Ecosystems .............................................................1 1.2. Role of Grazers in Seagrass Ecosystems ......................................................3 1.3. Target Species .................................................................................................6 1.3.1. Thalassia testudinum ......................................................................6 1.3.2. Halimeda incrassata ........................................................................8 1.3.3. Lagodon rhomboides (Pinfish) ....................................................10 1.4. Ciguatera Fish Poisoning ............................................................................12 1.5. Study Overview ............................................................................................20 2. RESEARCH PURPOSE .............................................................................................21 3. METHODS ..................................................................................................................22 3.1. Study Site ......................................................................................................22 3.2. Field Collection Procedures ........................................................................23 3.3. Experimental Set Up ....................................................................................27 3.3.1. Control Trial ...................................................................................31 3.3.2. Experimental Trials .......................................................................32 3.4. Data Analysis ................................................................................................34 4. RESULTS ....................................................................................................................36 4.1. Overview .......................................................................................................36