Gastropods as Predators and Prey at Easter Island!

First observations are reported of predator-prey relationships among gastropod mollusks of the depauperate, Indo-West Pacific derivative, intertidal and shallow subtidal benthic fauna of Easter Island. Conus miliaris, which will be reported in detail in a separate paper, and Pisania decapitata englerli prey on polychaete annelids; Mitraflavocingulata preys on sipunculans; and Neothais nesiotes preys on barnacles intertidally and gastropods subtidally. Gastropods of at least three species are eaten by the most common Easter Island starfish, Astrostole paschae. EASTER ISLAND, THE MOST ISOLATED island in the Pacific Ocean, may be viewed as a natural experiment in the assembly of biotic communities (Diamond and May 1976). For this reason, its inshore marine biota has been studied increasingly in recent years; the primarily tropical Indo-West Pacific affinity and limitednumbef of species 6nhe fishes and invertebrates have drawn particular attention (Devaney 1973, Fell 1974, Garth 1973, Kohn and Lloyd 1973, Randall 1976). However, the biological interactions of these animals have remained unstudied. In the course of an ecological study of the predatory gastropod Conus miliaris at Easter Island, I examined individuals of three cooccurring predatory gastropod species for evidence of the nature of their prey, and I examined specimens of the starfish Astrostole paschae (Clark) to determine whether its diet includes gastropods. The results of the Conus study will be published separately; here, I report briefly on an initial effort to determine predator-prey relationships involving the other gastropods.