Tracing basal resource use across sea‐ice, pelagic, and benthic habitats in the early Arctic spring food web with essential amino acid carbon isotopes

Abstract

Abstract A rapidly warming Arctic Ocean and associated sea‐ice decline is resulting in changing sea‐ice protist communities, affecting productivity of under‐ice, pelagic, and benthic fauna. Quantifying such effects is hampered by a lack of biomarkers suitable for tracing specific basal resources (primary producers and microorganisms) through food webs. We investigate the potential of δ 13 C values of essential amino acids (EAAs) (δ 13 C EAA values) to estimate the proportional use of diverse basal resources by organisms from the under‐ice ( Apherusa glacialis ), pelagic ( Calanus hyperboreus ) and benthic habitats (sponges, sea cucumber), and the cryo‐pelagic fish Boreogadus saida . Two approaches were used: baseline δ 13 C EAA values, that is, the basal resource specific δ 13 C EAA values, and δ 13 C EAA fingerprints, or mean‐centred baseline δ 13 C EAA values. Substantial use of sub‐ice algae Melosira arctica by all studied organisms suggests that its role within Arctic food webs is greater than previously recognized. In addition, δ 13 C EAA fingerprints from algae‐associated bacteria were clearly traced to the sponges, with an individually variable kelp use by sea cucumbers. Although mean‐centred δ 13 C EAA values in A. glacialis , C. hyperboreus , and B. saida tissues were aligned with microalgae resources, they were not fully represented by the filtered pelagic‐ and sea‐ice particulate organic matter constituting the spring diatom‐dominated algal community. Under‐ice and pelagic microalgae use could only be differentiated with baseline δ 13 C EAA values as similar microalgae clades occur in both habitats. We suggest that δ 13 C EAA fingerprints combined with microalgae baseline δ 13 C EAA values are an insightful tool to assess the effect of ongoing changes in Arctic basal resources on their use by organisms.