Chemical signals in gametogenesis, spawning, and larval settlement and defense of the soft coral Sinularia polydactyla

Mass spawning strategies of hard and soft corals on the Great Barrier Reef, Australia have been described in recent years. Nonetheless, the applicabil ity of those studies to corals on other reef systems has not been well docu mented. Here we describe the mass spawning behavior of the soft coral Sinul aria polydactyla on coral reefs surrounding Guam; specifically we describe the events in an annual gametogenic cycle including steroidogenesis, spawni ng, settlement and early life history defense. The gametogenic cycle of fem ale colonies lasted 12 months while male colonies produced viable sperm wit hin 9 months. Sinularia polydactyla exhibited a split spawn between March a nd June that correlated with a significant reduction in tissue concentratio ns of progesterone and testosterone. Estradiol was released into the water column, apparently by female colonies, just prior to spawning. There was a trend for preferential larval settlement in the presence of the crustose co ralline algae Hydrolithon reinboldii rather than coral rubble, a natural bi ofilm, or filtered seawater. The defensive compounds pukalide and 11 beta-a cetoxypukalide were found in eggs and larvae at adult level and three-fold lower than adult-level concentrations, respectively. These compounds provid ed some predator deterrent and antimicrobial protection against an ecologic ally relevant omnivorous fish Canthigaster solandri and a sympatric microbe Vibrio sp.