Widespread variation in heat tolerance of the coral Acropora hyacinthus spanning variable thermal regimes across Palau

Climate change is poised to dramatically change ecosystem composition and productivity, leading scientists to consider the best approaches to fostering population resilience and diversity in the face of these changes. Here we present results of a large-scale experimental assessment of bleaching resistance, a critical trait for coral population persistence as oceans warm, in 293 colonies of the coral Acropora hyacinthus across 39 reefs in Palau. We find bleaching resistant individuals originate significantly more often from warmer reefs, although they inhabit almost every reef regardless of temperature at low frequency. High levels of variation within reefs, where colonies experience similar temperatures, suggests that bleaching resistance is not solely due to phenotypic plasticity, but also involves adaptive alleles and host-symbiont interactions. To the extent that it is heritable, bleaching resistance could be used in promoting nursery growth, habitat restoration, or breeding, while employing large numbers of resistant colonies to preserve genetic variation.