Sipunculan fauna in the Pacific Arctic region: a significant component of benthic infaunal communities

The Sipuncula show low species diversity in the Arctic Ocean, but they often occur in very high numbers and biomass, and can dominate shelf benthic communities. We describe here the patterns of sipunculan diversity, abundance, biomass, and species distribution in the Pacific Arctic, and the relation of those patterns to controlling environmental factors. Five species (including two subspecies) belonging to two families and three genera are known to be present in Pacific-influenced Arctic waters. Although sipunculans were found at only about 30% of sampled stations, they constituted, if present, up to about 10% of the total macrobenthic abundance, and over 80% of the total infaunal biomass, particularly in many locations in the Chukchi Sea. The mean sipunculan abundance was 24.5 ± 155.9 individuals m −2 , with a maximum of 1745 individuals m −2 . The mean sipunculan biomass was 14.0 ± 73.8 g wet weight m −2 , with a maximum of 698.7 g wet weight m −2 in the northwest Chukchi Sea. The sipunculan abundances and biomass observed were related to latitude, depth, and sediment characteristics. The populations observed should be considered significant and characteristic components of the Pacific Arctic shallow shelf systems and food webs. This conclusion proves to be true also for other Arctic shelf seas like the Barents Sea, and deep Arctic ecosystems.