physiological responses to both temperature and irradiance exposure. Genetic differences may also occur between coral hosts of the same species. In 1985, colonies of Porites compressa bleached in Hawaii were apparently clone mates of a genotype that was extremely sensitive to elevatedsea temperature(C. Hunterand R.A.Kinziecited in Jokiel and Coles 1990). Similar clone-specific bleaching patterns were reported by Edmunds (1994) in St. John USVI in theCaribbean.Although geneticdifferences were not evaluated, a very high proportion (60—100%) of coral colonies of a single species re-bleached in 1995 after the 1991 bleaching event in Thailand. This result might also suggest a clone-specific bleaching response since the coral colonies were all situated close to each other along transects with minimal micro-climatic variability. Similar results were also obtained by Jokiel and Coles (1990) for coral colonies which re-bleached annually in response to thermal discharges in Hawaii.