Ecology of spionid polychaetes in the swash zone of exposed beaches in Tahiti (French Polynesia)

Abstract The high-energy black sand beaches around the island of Tahiti show low species richness. Most of the individuals collected in the swash zone belong to two recently described species of polychaete Scolelepis sp. A, and Scolelepis sp. B (Spionidae). Densities of the first species can reach up to 1900 individuals.m −2 and biomasses up to 47.5 g dry weight (gD.W.).m −2 . These high densities and biomasses occur because of their adaptation to this high-energy habitat, where they are restricted to the swash zone on the beach. Scolelepis sp. A appears to be a suspension feeder and feeding occurs only as the wave recedes. This suggests that the species is highly efficient at obtaining nutrients in this oligotrophic environment. Scolelepis sp. B, sampled in one station, exhibits the same patterns as Scolepis sp. A. Only three other species are present in this environment; carnivores or suspension feeders, they occur in low densities ( −2 ).