Decline of forereef corals in response to recent warming linked to history of thermal exposure

Rising ocean temperatures have reduced rates of coral calcification and increased rates of coral mortality, thereby negatively impacting the health of coral reef ecosystems(1,2). Nevertheless, the response of corals to thermal stress seems to vary spatially across the reef environment(3,4). Here, we show that between 1982 and 2008 in the western Caribbean Sea, skeletal extension within forereef colonies of the reef-building coral Siderastrea siderea declined with increasing seawater temperature, whereas extension rates of backreef and nearshore colonies were not impacted. These results suggest that forereef S. siderea corals are more vulnerable to ocean warming than their backreef and nearshore counterparts. This may arise from backreef and nearshore coral colonies experiencing greater baseline diurnal and seasonal thermal fluctuations than forereef colonies, which may promote acclimatization and/or adaptation to more recent anthropogenic thermal stress. These findings reveal how corals have responded to recent anthropogenic warming, offer insights into how they are likely to respond to future warming and highlight the importance of understanding cross-reef differences in coral thermal tolerance for managing coral reef ecosystems in an era of rapid regional and global climate change.