Coral bleaching: the winners and the losers

Sea surface temperatures were warmer throughout 1998 at Sesolto Island, Jap an, than in the 10 preceding years. Temperatures peaked at 2.8 degreesC: ab ove average, resulting in extensive coral bleaching and subsequent coral mo rtality. Using random quadrat surveys, we quantitatively documented the cor al community structure one year before and one year after the bleaching eve nt. The 1998 bleaching event reduced coral species richness by 61% and redu ced coral cover by 85%. Colony morphology affected bleaching vulnerability and subsequent coral mortality. Finely branched corals were most susceptibl e, while massive and encrusting colonies survived. Most heavily impacted me re the branched Acropora and pocilloporid corals, some of which showed loca l extinction. we suggest two hypotheses whose synergistic effect may partia lly explain observed mortality patterns (i.e. preferential survival of thic k-tissued species, and shape-dependent differences in colon) mass-transfer efficiency). A community-structural shift occurred on Okinawan reefs, resul ting in an increase in the relative abundance of massive and encrusting cor al species.