Deep-sea polychaete communities in the Northeast Pacific Ocean off the Gulf of the Farallones, California

Polychaete communities of the continental slope off the Farallon Islands, California are characterized in terms of their species composition, dominating families and species, and diversity. Extensive material was collected during three cruises in 1990 and 1992 to evaluate several smaller research areas for deep-sea disposal of dredge spoil from the harbor of San Francisco. Nearly 30,000 polychaetes belonging to 382 species in 47 families were identified. The most speciose, and usually most abundant, families were the Paraonidae, Spionidae, and Dorvilleidae. Polychaete abundance ranged from about 2000 to nearly 10,000 ind m(-2) and was influenced by the oxygen minimum zone (OMZ) around 800 in. Below 1900 m, there was a general trend of gradually decreasing abundance with increasing depth. Species richness also increased with increasing depth to about 2000 m and then gradually decreased to 3100 m. Diversity was fairly high with the exception of the shallowest stations where some highly dominant species were found. The Shannon-Wiener indices were generally between 2.5 and 3.5, with peaks below the OMZ at 1200 m, around 20002100 m, and somewhat less pronounced around 2600 m.