Effect of mass coral bleaching on the community structure of small animals associated with the hermatypic coral Pocillopora damicornis

In the summer of 1998, mass coral bleaching occurred in many reefs around the Ryukyu Islands. Various sized colonies of completely bleached Pocillopora damicornis were collected in order to study the effect of the coral bleaching on the structure of its associated community. Although six species of Trapezia were collected in this survey, and it was comparable to its species richness on healthy Pocillopora, bleached colonies harbored fewer individuals and species of obligate symbionts than unbleached colonies, before the bleaching event. Even on the larger colonies, of which the volume of interbranch space was > 222cm3, no obligate symbionts were found. Heterosexual pairs of the symbionts such as Trapezia spp., Alpheus lottini and Paragobiodon spp. were rather uncommon and the abundance of ovigerous females of Trapezia was lower and their clutch size was smaller than usual. It was quite unusual that large numbers of the symbiont crab Cymo melanodactylus were found on completely bleached colonies of P. verrucosa and Acropora aspera.