LONGEVITY, COMPETENCE AND ENERGETIC CONTENT IN PLANULAE OF THE SOFT CORAL HETEROXENIA-FUSCESCENS

The longevity and competence period of the azooxanthellated planulae o f the soft coral Heteroxenia fuscescens, a common shallow-reef inhabit ant on the Red Sea reefs, were studied for the first time. The caloric content of the planulae in the course of their life is determined and its possible significance for the longevity and competence periods is considered. H. fuscescens planulae are able to metamorphose immediate ly upon release and tend to settle adjacent to their parent colonies. The current study presents evidence for absence of a pre-competence pe riod. A maximal longevity of 50 days and a competence of 49 days were recorded, providing an effective dispersal time which encompasses virt ually the entire lifespan of the planulae. A monthly variation was fou nd in longevity and competence, possibly temperature related; signific antly higher metamorphosis rates occurred during the hotter months of the year, indicating the occurrence of additional temporal variations related to the species reproduction. During late stages of the experim ents most of the planulae underwent partial metamorphosis, probably du e to a lack of necessary inducers for settlement. It is hypothesized t hat these polyps may obtain zooxanthellae through their mouth opening, thus acquiring the energy to extend their pelagic life, until they en counter such settlement inducers. Two-day old planulae had a caloric c ontent of 0.58 +/- 0.05 cal x planula(-1); which decreased gradually w ith age, to a minimum of 0.35 +/- 0.005 cal x planula(-1) in 16-day ol d planulae. H. fuscescens has a wide distribution along the eastern co ast of Africa, probably due to the longevity and competence of its pla nulae.