Spatial and temporal variations in benthic bivalve stable isotopic composition in the Chukchi Sea, Arctic Ocean

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Nguyen, Hoang Minh

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The Chukchi Sea is one of the most productive marine ecosystems in the world. Around 10% of its net primary production originates from sea ice algae, much of which falls ungrazed to a relatively shallow (40 - 50 m) shelf. The chlorophyll α derived from sinking ice algae is thought to support a robust macrobenthic faunal community, dominated by bivalves, which in turn supports higher trophic organisms such as Pacific walrus (Odibenus rosmarus divergens), and bearded seal (Erignathus barbatus). However, reductions in sea ice extent and earlier break-up could reduce epontic ice algal production and enhance the contribution by phytoplankton, decreasing the relative proportion of ice algal carbon delivery to benthic consumers. To address this question, we examined the stable isotope composition of ten common benthic bivalve taxa, collected in summer and spring between 2002 and 2016, to determine if their spatial and temporal variability revealed changes in diet with respect to sea ice conditions and to identify any differences among feeding guilds. The results showed no interannual variations but revealed a significant northeast to southwest increase in δ¹³C values. Benthic bivalves across feeding guilds also appear to assimilate a greater proportion of isotopically heavier carbon in locations with earlier ice break-up. The findings indicate high level of diet fidelity among the selected taxa and suggest there exists a ‘food bank’ in the Chukchi Sea sediments that is highly enriched in ¹³C. This sedimentary food bank could serve as a buffer to protect benthic bivalve community from changes in the delivery of ice algal carbon in response to shifting ice conditions. However, long-term changes in the delivery of reduced ice algal carbon to the seabed could result in changes in benthic community structure and production that could eventually cascade to higher trophic levels.



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