Compound-Specific Amino Acid Isotopic Analysis of Benthic Food Webs in the Chukchi Sea

Abstract:

The Chukchi Sea is known for locally high standing stocks of benthic macrofauna and strong coupling between pelagic-benthic components of the ecosystem. However, benthic food structure is not fully understood, due to varied sources of particulate organic matter (POM) and the high diversity of benthic invertebrates. We provide the first demonstration of the application of compound-specific amino acid isotope analysis to study the dietary sources and trophic structure for this Arctic marginal sea. About 20 stations in Chukchi Sea were sampled during cruises in August of 2012 and 2013. At each station, phytoplankton, POM and benthic fauna were collected, processed and analyzed using GC-C-IRMS (gas chromatography-combustion-isotope ratio mass spectrometry). Among benthic fauna, dominant species included the following taxonomic groups: Ophiuroidea, Amphipoda, Polychaeta, Gastropoda, Bivalvia, and Cnidaria. The benthic fauna showed similar patterns of individual amino acid δ¹³C, with glycine the most enriched in ¹³C and leucine the most depleted in ¹³C. Specific amino acids including phenylalanine showed spatial variability in δ¹³C and δ¹⁵N values within the sampled area, indicating contributions of different dietary sources including phytoplankton, sea ice algae, benthic algae and terrestrial organic materials. δ¹⁵N values of individual amino acids such as the difference between glutamic acid and phenylalanine, i.e. Δ¹⁵N_glu-phe (δ¹⁵N_glu – δ¹⁵N_phe), were also used to identify trophic levels of benthic invertebrates relative to estimates available from bulk δ¹⁵N values. These data will ultimately be used to evaluate the spatial variability of organic carbon sources and trophic level interactions of dominant benthic species in the Chukchi Sea.