The reproductive biology of the scleractinian coral Plesiastrea versipora in Sydney Harbour, Australia

The scleractinian coral Plesiastrea versipora occurs throughout most of the IndoPacific; however, the species is only abundant in temperate regions, including Sydney Harbour, in New South Wales, Australia, where it can be the dominant sessile organism over small spatial scales. Population genetics indicates that the Sydney Harbour population is highly isolated, suggesting long-term persistence will depend upon on the local production of recruits. To determine the potential role of sexual reproduction in population persistence, we examined a number of features of the reproductive biology of P. versipora for the first time, including the sexual system, the length of the gametogenetic cycles and size-specific fecundity. P. versipora was gonochoric, supporting recent molecular work removing the species from the Family Merulinidae, in which the species are exclusively hermaphroditic. The oogenic cycle was between 13 and 14 mo and the spermatogenetic cycle between 7 and 8 mo, with broadcast spawning inferred to occur in either January or February. Colony sex was strongly influenced by colony size: the probability of being male increased with colony area. The longer oogenic cycle suggests that females are investing energy in reproduction rather than growth, and consequently, males are on average larger for a given age. Alternatively, colonies may change sex from female to male as they grow. In contrast, per polyp fecundity did not vary with colony size. We conclude that the Sydney Harbour population is reproductively active and therefore has the potential to maintain current levels of abundance even without an external supply of propagules.