Present and future bright and dark spots for coral reefs through climate change

Marine heatwaves can cause coral bleaching and reduce coral cover on reefs, yet few studies have identified “bright spots,” where corals have recently shown a capacity to survive such pressures. We analyzed 7714 worldwide surveys from 1997 to 2018 along with 14 environmental and temperature metrics in a hierarchical Bayesian model to identify conditions that contribute to present‐day coral cover. We also identified locations with significantly higher (i.e., “bright spots”) and lower coral cover (i.e., “dark spots”) than regionally expected. In addition, using 4‐km downscaled data of Representative Concentration Pathways (RCPs) 4.5 and 8.5, we projected coral cover on reefs for the years 2050 and 2100. Coral cover on modern reefs was positively associated with historically high maximum sea‐surface temperatures (SSTs), and negatively associated with high contemporary SSTs, tropical‐cyclone frequencies, and human‐population densities. By 2100, under RCP8.5, we projected relative decreases in coral cover of >40% on most reefs globally but projected less decline on reefs in Indonesia, Malaysia, the central Philippines, New Caledonia, Fiji, and French Polynesia, which should be focal localities for multinational networks of protected areas. This study identified "bright spots," where corals have recently shown a capacity to survive marine heatwaves. The study also projected future coral cover, globally, based on temperature changes. By 2100, under RCP8.5, the study projected a relative decline in coral cover >40% on most reefs, globally, but less of a decline on reefs in Indonesia, eastern Malaysia, the central Philippines, New Caledonia, Fiji, and French Polynesia. These projections provide information for management decisions at a local level and predict localities that could be considered for multinational, marine‐protected‐area networks.