Size variation of planulae and its effect on the lifetime of planulae in three pocilloporid corals

Dispersal of propagules plays an important role in the distribution of cora ls. Pocillopora damicornis, Seriatopora hystrix, and Stylophora pistillata are all brooders and release planulae having symbiotic zooxanthellae. Planu lae showed a great size variation, especially at peaks of planulation, and we found negative correlations between zooxanthella density and planula siz e in S. hystrix and S. pistillata. Studies of the larval life of planulae u nder both light and dark conditions have revealed that larger planulae have a longer lifetime. When planulae of the same size were compared, it was fo und that they lived longer under light conditions than under dark condition s. These findings suggest that planulae utilize energy from photosynthetic products of zooxanthellae and that these corals enjoy long-distance dispers al by producing larger planulae with greater dispersal potential. It is con ceivable that variation in the dispersal potential of planulae is a means o f adaptation by which planulae can increase their chances of finding a suit able habitat.