Pelagic-benthic coupling on the shelf of the northern Bering and Chukchi Seas. II. Benthic community structure

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Abstract
Benthic fauna abundance, biomass and diversity were investigated in the northern Bering and Chukchi Seas to determine factors influencing faunal distribution in this polar region. The hypothesis tested whether sediment grain size and water mass characteristics, such as organic carbon supply to the benthos and temperature, are regulating factors in benthic community structure. Benthic communities under the cold, highly productive (.apprx. 250 to 300 g C m-2 yr-1) Bering Shelf-Anadyr Water (BSAW) are dominated by a high biomass of amphipods (F. Ampeliscidae and F. Isaeidae) and bivalves (F. Nuculidae and F. Tellinidae). A diverse, low biomass fauna exists in benthic communities under the warmer, less productive (.apprx. 50 g C m-2 yr-1) Alaska Coastal Water (ACW) [USA], including amphipods (F. Isaeidae and F. Ampeliscidae), bivalves (F. Tellinidae and F. Thyasiridae), polychaetes (F. Maldanidae and Nephytidae), and sand dollars (F. Echinarachniidae). Faunal diversities are lowest for stations under BSAW, characterized by high food supply and moderately homogeneous (well-stored), sandy sediments. Highest diversities occur at stations in ACW, which is characterized by low food supply and a more heterogeneous (poorly-sorted) mixture of silt and clay, sand and gravel sediments. Faunal diversity also increased to the north in the Chukchi Sea, where food availabilty in the bottom water and surface sediments was greater and more heterogeneous, finer-grain sediments occur. The findings indicate that sediment heterogeneity, silt and clay fractions, and temperature are major regulating factors on benthic community structure, with each positively influencing faunal diversity. Lower diversity was correlated to an increase in fine sand fractions. Food supply, both in the bottom water and surface sediments, has a more variable influence on benthic community structure, although it has a direct positive influence on benthic biomass.

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