Evidence for the presence of sexual pheromones in free-spawning starfish

Filtered natural seawater passed through a tank containing ripe female starfish of the forcipulate species Asterias forbesi (Desor 1848) and Orthasterias koehleri (de Loriol 1897) contains low concentrations of a substance which attracts the sperm of these species. Release of this substance is sex specific in at least one species, O. koehleri. Immature females apparently do not release the sperm attractant. Daily testing for sperm attractant in seawater in the Friday Harbor Laboratories' aquarium system, Washington, U.S.A., in the spring and summer of 1986 indicates that incursions of sperm attractant-bearing water occur frequently during the starfish reproductive season. Testing of seawater taken directly from the San Juan Channel in the summer of 1987 reveals that sperm attractant is also present at irregular intervals in natural seawater. There is a definite correlation between the sperm attractant incursions in the laboratory seawater and initiation of spawning of starfish in the laboratory. The periodic presence of a long-lived bio-active sex-specific substance in natural seawater during the reproductive season of starfish suggests that benthic invertebrates may communicate sexual identity and readiness to spawn by means of waterborne pheromones.