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Ecology and Ecophysiology of Zostera capensis: Responses and Acclimation to Temperature Cloverley Mercia Lawrence Thesis presented for the degree of Doctor of Philosophy in the Department of Biological Sciences Faculty of Science University of Cape Town 2019 University of Cape Town Supervisors Dr Deena Pillay, Professor Astrid Jarre, Emer. Professor John Bolton The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non- commercial research purposes only. Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author. University of Cape Town This thesis is dedicated to my parents. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Declaration I, hereby declare that all the work presented in this thesis is my original work in both concept and execution (except where otherwise indicated), and that this thesis has not been submitted in whole or in part for another degree in this or any other university. Cloverley Mercia Lawrence Table of Contents Acknowledgements………………………………………………………………………………….iii Summary.…………………………………………………………………………………………….…v Chapter One General overview and background ……………… ……... ………………………………. .. 1 1.1. Seagrass Ecosystems…………………………………………………………… …… …... 3 1.1.1. Glo bal importance and distribution of seagrasses…………………… ……... 3 1.1.2. Biodiversity in seagrass ecosystems ……………………………… ….… ….…. 6 1.2. Threats to seagrasses………………………………………………………… ….. .…. …. 8 1.2.1. The influenc e of temperature on seagrasses……………………… ……….. .. 9 1.2.2. Epiphytes and fou ling in seagrass ecosystems……………………… …….. .. 12 1.3. Respo nses of seagrasses to threats………………………………………… ….. ….. …. 12 1.3.1. Acclimations in seagrasses…… .. ………………………………… …… ….. …… 12 1.3.2. Chemi cal defence in seagrasses…………………………………… …… ... .. …. 15 1.4. Trophic interac tions in seagrass ecosystems……………………………… …… ….… 17 1.4.1. Temperature effe cts on trophic interactions………………………… …….. .. 20 1.4.2. Top down contr ol and effects of grazing……………………………… ..... ... ... .. 22 1.5. Seagrasses in South Africa…………………………………………………… ….. ….. .. 25 1.5.1. Zostera capensis in Langebaan L agoon……………………………… …… ….. 28 1.6. Mesocosm expe riments in seagrass research………………………………… ….. …. 30 1.7. Aims and overview of thesis…………………………………………… ………… .. .. … 31 Chapter Two Spatial and temporal variability of Zostera capensis in Langebaan Lagoon ... 35 2.1. Introduction… ……………………………………………………………….…… …... ......... 36 2.2. Methods……… ……………………………………………………………… …… …… ……. 40 2.3. Results… ………………………………………………………………………… …… ……… 46 2.4. Discussion ……………………………………………………………………… …… ……….. 62 2.5. Conclusions… …………………………………………………………………… …... .. ......... 70 Chapter Three Spatial and temporal differences in macro-epifaunal assemblages associated with Zostera capensis in Langebaan Lagoon: influences of environmental variables and seagrass structure ………………………………..………………………... 72 3.1. Introduction ……………………………………………………………………… ……. …… 73 i 3.2. Methods………………………………………………………………………… …….. ……... 78 3.3. Results………………………………………………………………………… …….. ………. 84 3.4. Discussion………………………………………………………………… …….. ……… …... 99 3.5. Conclusions ……………………………………………………………… …….. ……………. 10 6 Chapter Four Effects of temperature on small and la rge -leaved morphotypes of Zostera capensis – a mesocosm approach ……………………………………………………….. 108 4.1. Introduction……………………………………………………………… …….. …… …… 109 4.2. Methods………………………………………………………………… …….. ……… ...… 114 4.3. Results……………………………………………………………………… …….. …… .... 118 4.4. Discussion……… …………………………………………………………… …….. ……... 124 4.5. Conclusions… ………………………………………………………………… …….. ……. 12 9 Chapter Five Top -down effects of grazing on the ecophysiology of two morphotypes of Zostera capensis under warming in a mesocosm experiment …………………. 131 5.1. Introduction…… ……………………………………………………………… ……….. .. 132 5.2. Methods……………………………………………………………………… …..… ……. 13 8 5.3. Results………………………………………………………………………… …….. …… 14 7 5.4. Discussion……………………………………………………………………… ……... .… 15 8 5.5. Conclusions……………………………………………………………………..… …….. 16 5 Chapter Six General Discussion .…………….………..….………………………………….…………… 168 Literature Cited ……………….…………………...…………………………………………. 180 Appendices …………………………………………………………………….……………….. 239 ii Acknowledgements I believe one’s character is defined during times of challenge and my PhD journey has indeed provided me with great challenge and enormous opportunity for learning and growth - I am wiser and richer for it. There are many people who have remained unwavering in their support, which has contributed to the completion of this work, and to them, I am forever grateful. Thank you to my supervisors Prof Astrid Jarre, Prof John Bolton and Dr Deena Pillay for input and advice. I am deeply grateful to Astrid for her valuable insights and most especially her patience. A heartfelt thank you to John whose wisdom and encouragement helped me immensely in navigating many complexities. I am grateful for the generosity and financial support provided by Prof Astrid Jarre and the National Research Foundation. Further gratitude for financial assistance is expressed to Dr Clive and Ms Camilla McDowell and the McDowell Trust. For additional advice and guidance on various aspects of my PhD, I am profoundly indebted to Henning Winker, George Branch, Jean Harris, AJ Smit, Maya Pfaff, Sean Marr, Bhavani Krishna and Anusuya Chinsamy-Turan. Henning, thank you for teaching me about statistical modelling, for being a great listener, for the coffee breaks and when needed, tequila shots. To Jean - thank you for being my champion, mentor and friend. My most sincere gratitude is extended to AJ for stimulating discussions, lending me the oxygen chamber and providing student assistants. A huge thank you to all the willing and enthusiastic volunteers who assisted with field and lab work: Alex Rabelo, Chanel Rampartab, Isabel Micklem, Imogen Weideman, Jireh Mannesseh, Lauren Fonto, Martin Emmanuel, Mujahiddin Philander, Pierre Nel, Pumza Mpange, Raquel Flynn, Ropafadzo Moyo, Ross Copin, Saarchi Sadcha, Sam Bolton and Tesrey Linevee. Heartfelt gratitude is expressed to Welly Qwabe, who accompanied me on almost every fieldtrip - even if it meant taking a train at five in the morning in the dead of iii winter. Thank you for the adventures, for building cages with me, and for the many insightful discussions on science and life. Vincent Naudé is acknowledged for his assistance with the design and construction of the mesocosm system. I am especially grateful to George Du Plessis for technical support and going above and beyond - even assisting me on his days off. Thanks also to Andrea Plos and Granville Faulmann for technical assistance. Prof Charles Griffiths is acknowledged for assistance with species identification. The Microbiology Lab at UCT is recognized for their facilitation of my chemistry analyses, with special thanks to Keren Cooper for answering many questions, and running my samples through the HPLC. Thanks also to John Lanham and Ian Newton at the Stable Light Isotope Lab in the Archaeology Department, UCT for measuring nutrients at no cost. Prof Denzil Beukes, University of the Western Cape, is acknowledged for his advice on analysing phenolics in seagrasses, and undertaking preliminary NMR analyses. I am also grateful to Prof Derek du Plessis, Nelson Mandela University, for loan of the PAM fluorometer. Studying part-time has its distinct set of challenges. I am thankful to my employer, South African National Parks for advocating the completion of this PhD. Special thanks to Anè Oosthuizen and Jayshree Govender for support and encouragement. Profound appreciation is expressed to my amazing woman’s circle: Cara, Claire, Emma, Heike, Joanne, Judy (posthumously), Lara, Lindi, Susan and Vicki. I am forever blessed for your wise, loving and empowering support. To my accountability partner and friend, Aline – thank you for helping me stay optimistic and motivated through this PhD journey. I would not have accomplished this feat were it not for the steadfast and relentless love and encouragement from family and friends. To Jireh, Jediael, Craig, Desiree, Melanie, Toufiek, Maya, Henning, Welly, Lorien, Jean, Sean, Charles, Daniel, Yossie, Ayesha and Frank - you are my champions and the faces I look for from the arena of life. iv Summary As environmental norms deviate further from long-established patterns, understanding strategies that allow habitats to persist under sub-optimal conditions is critical for effective mitigation and management. It has therefore become profoundly important to understand the capacity of ecosystems to respond to anthropogenically-driven change, and maintain their function and provision of services to humankind. Species and populations that lack the ability to persist in a changing environment run the risk of declining or going extinct. Two key evolutionary processes available to organisms to cope with shifting environments are adaptation and acclimation. Adaptation is a genetically-based response, while acclimation or phenotypic plasticity is a prompt, non-genetic strategy usually triggered by a change in environmental conditions. Both adaptive and acclimative mechanisms can co-occur producing varied effects at the population level. Seagrasses are ecosystem engineers responsible for providing an important habitat in many estuaries and on coastlines worldwide. They are, however on a global decline due to threats