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 corals. Pocillopora damicornis, Seriatopora hystrix, and Stylophora pistillata are all brooders and release planulae having symbiotic zooxanthellae. Planulae showed a great size variation, especially at peaks of planulation, and we found negative correlations between zooxanthella density and planula size in S. hystrix and S. pistillata. Studies of the larval life of planulae under both light and dark conditions have revealed that larger planulae have a longer lifetime. When planulae of the same size were compared, it was found that they lived longer under light conditions than under dark conditions. These findings suggest that planulae utilize energy from photosynthetic products of zooxanthellae and that these corals enjoy long-distance dispersal by producing larger planulae with greater dispersal potential. It is conceivable that variation in the dispersal potential of planulae is a means of adaptation by which planulae can increase their chances of finding a suitable habitat.