Climatological context for large-scale coral bleaching

Large-scale coral bleaching was first observed in 1979 and has occurred throughout virtually all of the tropics since that time. Severe bleaching may result in the loss of live coral and in a decline of the integrity of the impacted coral reef ecosystem. Despite the extensive scientific research and increased public awareness of coral bleaching, uncertainties remain about the past and future of large-scale coral bleaching. In order to reduce these uncertainties and place large-scale coral bleaching in the longer-term climatological context, specific criteria and methods for using historical sea surface temperature (SST) data to examine coral bleaching-related thermal conditions are proposed by analyzing three, 132 year SST reconstructions: ERSST, HadISST1, and GISST2.3b. These methodologies are applied to case studies at Discovery Bay, Jamaica (77.27 degrees W, 18.45 degrees N), Sombrero Reef, Florida, USA (81.11 degrees W, 24.63 degrees N), Academy Bay, Galapagos, Ecuador (90.31 degrees W, 0.74 degrees S), Pearl and Hermes Reef, Northwest Hawaiian Islands, USA (175.83 degrees W, 28.25 degrees N), Davies Reef, Australia (147.68 degrees E, 18.83 degrees S), and North Male Atoll, Maldives (73.35 degrees E, 4.70 degrees N). The results of this study show that (1) The historical SST data provide a useful long-term record of thermal conditions in reef ecosystems, giving important insight into the thermal history of coral reefs and (2) While coral bleaching and anomalously warm SSTs have occurred over much of the world in recent decades, case studies in the Caribbean, Northwest Hawaiian Islands, and parts of other regions such as the Great Barrier Reef exhibited SST conditions and cumulative thermal stress prior to 1979 that were comparable to those conditions observed during the strong, frequent coral bleaching events since 1979. This climatological context and knowledge of past environmental conditions in reef ecosystems may foster a better understanding of how coral reefs will respond in future, ocean warming scenarios.