Mass bleaching of soft coral, Sarcophyton spp. in Thailand and the role of temperature and salinity stress

From June to October 2006 and 2007, mass bleaching of the soft coral, Sarcophyton spp., occurred for the first time in the upper Gulf of Thailand. Approximately 90% of the populations experienced extensive bleaching, and almost 95% of colonies were affected. Field observations also revealed that fragmentation of Sarcophyton spp. set in 1 month after the onset of bleaching. Some colonies started to recover to some extent by the end of July, with 95% of the population of Sarcophyton spp. recovering by October. Both acute and chronic trials were conducted to determine whether temperature and/or salinity triggered bleaching. In the acute tests, Sarcophyton spp. at 40 degrees C and salinity 20 psu were completely bleached, and death occurred after 57 and 204 h, respectively. However, the colonies at 40 psu could survive through the experimental trial. In the chronic tests, Sarcophyton spp. died when exposed to 34 degrees C, whereas complete bleaching and mortality of Sarcophyton spp. occurred at salinities of 10 and 49 psu. We conclude that elevated temperatures had a greater effect on the bleaching of Sarcophyton spp. than did salinity.