Experience shapes the susceptibility of a reef coral to bleaching

Individual zooxanthellate corals vary in their susceptibility to bleaching, caused by the loss of symbiotic algae in response to increased temperatures and solar radiation. In 1995 at Phuket, Thailand, the west face of colonies of the massive coral Goniastrea aspera displayed bleaching in January-March, mediated by high solar radiation. By May, when sea temperatures were anomalously high but solar radiation much reduced, the east sides preferentially bleached. Cores from the east faces of corals exposed to elevated temperature under low irradiance in a laboratory experiment also bleached in response to elevated temperature. The algae in G. aspera were Symbiodinium sp., and the rDNA (both ssu and ITS regions) sequences did not differ between the east and west faces, indicating that the bleaching responses cannot be attributed to genetic factors in the symbiotic algae of the type described in other coral species. It is concluded that, in this system, bleaching is shaped by experience, and that the algae may acquire cross-protection against bleaching from solar to temperature stresses. The impact of experience on bleaching susceptibility may become increasingly important in shaping coral responses to temperature and solar radiation stresses in the coming decades.