CHEMICAL ASPECTS OF MASS SPAWNING IN CORALS .1. SPERM-ATTRACTANT MOLECULES IN THE EGGS OF THE SCLERACTINIAN CORAL MONTIPORA-DIGITATA

This paper provides the first evidence for sperm chemotaxis in the Scl eractinia. Montipora digitata Dana, 1845 (Scleractinia: Coelenterata) is a hermaphroditic coral which reproduces bi-annually, releasing egg- sperm bundles during the mass spawning at Magnetic Island (19 degrees 10'S; 146 degrees 52'E) in late spring-early summer, and autumn each y ear. The buoyant egg-sperm bundles float to the surface where they bre ak apart, releasing eggs and sperm into the ocean. Fertilisation occur s after similar to 30 min. Unfertilized eggs were collected, washed fr ee of sperm, and freeze-dried. The eggs were extracted with dichlorome thane, fractionated by chromatography on silica gel, and the fractions assayed for their ability to attract M. digitata sperm. The active fr action was further fractionated by high-performance liquid chromatogra phy, resulting in the isolation of three highly unsaturated fatty alco hols: (1) dodeca-2,4-diynol; (2) tetradec-13-ene-2,4-diynol; (3) (14Z) -heptadeca-14,16-diene-2,4-diynol. Of these three compounds, only Comp ound 1 attracted sperm of M. digitata. Synthetic Compound 1, produced from simple precursors by known reactions, possessed sperm-attracting activity comparable to the naturally derived attractant. Preliminary e xperiments suggest that the natural mixture of Compounds 1, 2 and 3 in the ratio 1:4:9 is more effective in attracting sperm from M. digitat a than sperm from other Montipora species. Sperm attractants may act t o reduce the incidence of hybridisation between different species of M ontipora.