Marine Polychaete Annelids of Easter Island

This study increases the number of species of marine polychaete annelids known to occur at Easter Island from 11 to 60, of which 43 are identified to species. Nearly 90% of these occur in the tropical Indo‐West Pacific region, but 60% are of circumtropical distribution. The strong Indo‐West Pacific zoogeographic affinity is consistent with other taxa of Easter Island inshore marine animals for which data are available, the fishes, corals, and gastropod molluscs. Polychaete species composition and abundance were determined in substrate samples from two types of microhabitat in a tidepool. A sample of 290 ml of sand and 70 ml of algae contained 1,779 specimens of 41 species of polychaetes (species diversity H′ = 2.57). A basalt boulder of surface area 340 cm 2 contained a polychaete assemblage of 864 specimens of 35 species (H′ = 2.49). Population density of the latter sample is equivalent to 25,400 polychaetes/m 2 . Of the 49 species present in the two samples, 34 were identified to species. Although 27 species (55%) were common to both samples, similarity as measured by C λ , which weighs differences in relative abundance, was only 24%. More than half of all polychaetes present in the two samples belonged to the family Syllidae; they comprised 65% of the individuals in the sand‐algae sample and 35% in the boulder sample. Spirorbinae predominated numerically in the boulder sample (40%). Chaetopteridae (10%) and Spionidae (8%) were the next most abundant families in the sand‐algae sample.