A framework for comparing coral bleaching thresholds

Coral reefs are highly vulnerable to bleaching under elevated temperature. Since 2002, NOAA Coral Reef Watch has used a bleaching threshold based on global sea surface temperatures to provide operational bleaching warnings. Recent studies suggest that modifications to the current global bleaching prediction method may result in higher predictive power. Here, we present a method for comparing four bleaching prediction methods at different spatial and temporal resolutions, each calibrated against the global bleaching observational dataset from ReefBase between 1985 and 2005. We identify one method (“MMMmax”) that consistently gives the highest predictive power at all spatial and temporal resolutions examined. An improved bleaching threshold will refine future bleaching projections under climate change and provide more reliable real-time bleaching alerts to international coral reef managers.