ECOLOGY OF SPIONID POLYCHAETES IN THE SWASH ZONE OF EXPOSED BEACHES IN TAHITI (FRENCH-POLYNESIA)

The high-energy black sand beaches around the island of Tahiti show lo w species richness. Most of the individuals collected in the swash zon e 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 1 900 individuals.m(-2) and biomasses up to 47.5 g dry weight (gD.W.).m(-2). These high densities and biomasses occur becaus e of their adaptation to this high-energy habitat, where they are rest ricted 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 i n this oligotrophic environment. Scolelepis sp. B, sampled in one stat ion, exhibits the same patterns as Scolepis sp. A. Only three other sp ecies are present in this environment; carnivores or suspension feeder s, they occur in low densities(< 10 individuals.m(-2)). ((C) Academie des sciences/Elsevier, Paris.).