Rapid coral decay is associated with marine heatwave mortality events on reefs

Globally coral reefs are increasingly threatened by a rapidly changing climate and the emergence of severe heatwaves. Coral bleaching events and mortality have become more frequent and severe across tropical reef ecosystems as sea surface temperatures rise. Here we show that severe heatwave events drive coral mortality and result in a rapid dissolution of the coral skeleton. During a heatwave-induced mortality, the coral skeletons exposed by tissue loss are, within days, encased by a complex biofilm of phototrophic microbes, whose metabolic activity accelerates calcium carbonate dissolution to rates exceeding accretion by healthy corals and far greater than has been documented on reefs under normal conditions. This dissolution reduces the skeletal density and hardness, and increases porosity.