A scientific framework for evaluating coral reef resilience to climate change

Abstract

The 21 century warming and acidification of tropical oceans will impact the structure and function of coral reef ecosystems. Consequently, conservation efforts are increasingly focused on identifying and protecting reef communities that demonstrate resilience to these changes. In this thesis, I develop a scientific framework for identifying climate change resilience in coral communities and, using Palau's coral reefs as a case study, demonstrate the application of this approach. First, I use coral skeletal records to evaluate the sensitivity of coral communities to episodes of severe thermal stress. This information reveals coral reef communities that consistently exhibit weak responses to multiple high temperature events. Second, I evaluate coral reef community structure across a strong, natural pH gradient using metrics informed by laboratory ocean acidification studies. The coral communities of Palau's Rock Island reefs show a level of pH tolerance that is unique amongst reefs studied to date. Third, I conduct laboratory and field experiments to constrain the pH thresholds of these resilient corals and investigate potential mechanisms for pH tolerance. Finally, I combine archipelago-wide coral temperature and pH sensitivity data to construct climate change resilience indices. My study succeeds in identifying a small number of coral communities that have the potential to withstand 21 century climate change and highlights the spatial variability in community responses to ocean warming and acidification. Critically, I present a set of scientific tools and approaches for identifying resilient coral reef communities that has applicability to coral reefs worldwide. I thank all of the members of the Cohen Lab past and present -Katie Shamberger, Liz Drenkard, Alice Alpert, Tom DeCarlo, Sara Bosshart, Hanny Rivera, Nathan Mollica, Michael Holcomb, and Neal Cantin -for their scientific knowledge, assistance in the field, camaraderie in research, and friendship. I am grateful to Kathryn Pietro and Pat Lohmann for their help in collecting field samples; Liz Bonk, Katherine Hoering, Dave Wellwood, and Paul Henderson for assistance in carbonate chemistry, salinity, and nutrient analyses; Julie Arruda and Scott Cramer for CT-scanning my coral cores; and Ed O'Brien and the WHOI Diving Program for helping with SCUBA diving operations. In addition, I thank the WHOI Academic Programs Office for their tireless assistance, support, and guidance.My extensive field research was made possible by the scientists and staff of the Palau International Coral Reef Center, who provided me with essential logistical aid during six field expeditions to Palau, drove me all over the archipelago to sample water and coral, helped me set up my laboratory experiments, and taught me about Palau's coral reefs. Sulang! The completion of this five-year journey is very much a result of the amazing love and endless support of my incredible family and friends. In particular, I thank my parents, Ron and Barbara, and my brother, Ben, who have celebra...