Trophic relationships and infaunal community structure of the Beaufort Sea Shelf

Kenneth H Dunton1, Susan V Schonberg2, Carolynn M Harris2, Christina Elisa Bonsell2, Katrin Iken3, Bodil Bluhm4 and Lorena Edenfield5, (1)University of Texas at Austin, Austin, TX, United States, (2)University of Texas Marine Science Institute, Port Aransas, TX, United States, (3)University of Alaska Fairbanks, College of Fisheries and Ocean Sciences, Fairbanks, AK, United States, (4)University of Tromso, Arctic and Marine Biology, Tromso, Norway, (5)University of Alaska Fairbanks, School of Fisheries and Ocean Sciences, Fairbanks, AK, United States
Abstract:
The shelf of the Beaufort Sea is defined by dynamic physical and biological gradients that have a distinctive influence on benthic standing stocks and trophic structure. These gradients occur over both longitudinal and latitudinal scales and are reflected in the character of the benthic community and its long-lived benthic fauna. We sampled the benthic infauna and epifauna along the shelf of the north coast of Alaska in summers 2014 and 2015 to examine both species composition and distribution and the stable isotopic patterns in both carbon and nitrogen of the predominant fauna. A total of 50 stations were sampled between 153° W and 141° W that ranged in water depths from 6 to 500 m. Greatest abundance and biomass of infaunal species were found in waters greater than 20 m to the shelf break which then dropped sharply at 50 m west of 147° W and more gradually east of 147° W. The infaunal populations at depths less than 20 m, which included the mouths of the Colville and Sagavanirktok Rivers, were relatively depauperate, which we attribute to a combination of bottom fast ice, scour by deep-draft ice, and extreme salinity changes during spring breakup. Dominant infauna throughout the Beaufort shelf were polychaetes, crustaceans (amphipods and cumaceans) and molluscs (bivalves and gastropods). Preliminary data on the stable carbon and nitrogen isotopic composition of these benthic organisms, along with isotopic analyses of POM and zooplankton collected in situ, reveal a mixture of carbon sources available to benthic consumers. Within the coastal Beaufort Sea, between 50 and 75% of carbon in marine sediments are terrestrial in origin. Along with sources of marine carbon, terrestrial organic matter (identified by depleted δ13C values) provides a food subsidy to a system that receives relatively little advected marine-derived carbon compared to the northern Chukchi. Our δ15N values also reveal complex food webs dominated by decidedly omnivorous consumers.
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