Reproduction and development of the blue coralHeliopora coerulea (Alcyonaria: Coenothecalia)

Up to the present time, the reproductive cycle and larval development ofHeliopora coerulea, living fossil and sole member of the alcyonarian order Coenothecalia, have been undescribed. Populations ofH. coerulea studied on the Great Barrier Reef between 1984 and 1989 were found to have separate sexes and an annual gametogenic cycle. Mature eggs were large (>800µm diam), and their development was initiated internally. There appeared to be a lunar or semi-lunar periodicity in reproductive behaviour, with brooding of larvae commencing around either full or new moon. Development proceeded via superficial cleavage and a solid stereoblastula. Subsequent development took place on the surface of the colony, within a temporary brood-space created by protracted distension of the polyps. Larvae lacked zooxanthellae and were brooded for between 6 and 14 d prior to leaving the colony. Reproduction and development reflected the taxonomic affinities ofH. coerulea, but brooding and embryological development also appeared to be constrained by its morphology. Reproductive and larval characteristics ofH. coerulea may offer a partial explanation of the current biogeographic range ofH. coerulea.