Abstract

Coral bleaching occurs when cell density or the concentration of photosynthetic pigments of the endosymbionts, zooxanthellae are decreased. This incident may possibly be caused by some environmental stresses, especially under conditions of elevated temperature, decrease in water salinity, or a combination of these factors. To determine the role of temperature and salinity on zooxanthellae and coral bleaching this study was conducted in aquariums under laboratory conditions on cauliflower coral <em>Pocillopora damicornis</em>. The samples were collected from three sites around Samaesan Island, Chonburi, Thailand. Three sets of experiments were conducted at three levels of temperature: room temperature 27 (control), 30, and 33 ^oC respectively. At each temperature level, three levels of salinities; 10, 20 and 30 (control) psu were tested as well. Coral bleaching percentage and zooxanthellae density in the water column were observed every 6 hours during the period of 72 hours. The results showed that when coral exposed to the highest temperature (33 ^oC) under the lowest salinity (10 psu), 50-90% bleaching was found and higher symbiont densities in the water column were detected. These results suggested that the combination of the high temperature and low salinity had synergistic effects on coral bleaching and zooxanthellae.