In a coral-algae symbiotic system, heat-dependent photoinhibition of photosystem II (PSII) leads to coral bleaching. When the reef-building coral Acropora digitifera was exposed to light, a moderate increase of temperature induced coral bleaching through photobleaching of algal pigments, but not through expulsion of symbiotic algae. Monitoring of PSII photoinhibition revealed that heat-dependent photoinhibition was ascribed to inhibition of the repair of photodamaged PSII, and heat susceptibility of the repair machinery varied among coral species. We conclude that the efficiency of the photosynthesis repair machinery determines the bleaching susceptibility of coral species under elevated seawater temperatures.