A scientific framework for evaluating coral reef resilience to climate change

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2016The 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.Funding for this research was provided by the Next Wave Fund Fellowship, a National Science Foundation Graduate Student Fellowship, the NSF-funded National Network for Ocean and Climate Change Interpretation, the James Stratton Fellowship, National Science Foundation awards OCE-1220529 and OCE-1031971 to Anne Cohen, The Tiffany & Co. Foundation, The Nature Conservancy, The Dalio Foundation, Inc., through the Dalio Explore Fund, and Ray Dalio through the WHOI Access to the Sea Fund