ORCID

Abstract

We investigated diets of 24 Barents Sea zooplankton taxa to understand pelagic food-web processes during late summer, including the importance of sea ice algae-produced carbon. This was achieved by combining insights derived from multiple and complementary trophic marker approaches to construct individual aspects of feeding. Specifically, we determined proportions of algal-produced fatty acids (FAs) to reflect the reliance on diatom- versus dinoflagellate-derived carbon, highly branched isoprenoid (HBI) lipids that distinguish between ice-associated and pelagic carbon sources, and sterols to indicate the degree of carnivory. Copepods had the strongest diatom signal based on FAs, while a lack of sea ice algae-associated HBIs (IP25, IPSO25) suggested that they fed on pelagic rather than ice-associated diatoms. The amphipod Themisto libellula and the ctenophores Beroë cucumis and Mertensia ovum had a higher contribution of dinoflagellate-produced FAs. There was a high degree of carnivory in this food web, as indicated by the FA carnivory index 18:1(n−9)/18:1(n−7) (mean value < 1 only in the pteropod Clione limacina), the presence of copepod-associated FAs in most of the taxa, and the absence of algal-produced HBIs in small copepod taxa, such as Oithona similis and Pseudocalanus spp. The coherence between concentrations of HBIs and phytosterols within individuals suggested that phytosterols provide a good additional indication for algal ingestion. Sea ice algae-associated HBIs were detected in six zooplankton species (occurring in krill, amphipods, pteropods, and appendicularians), indicating an overall low to moderate contribution of ice-associated carbon from late-summer sea ice to pelagic consumption. The unexpected occurrence of ice-derived HBIs in pteropods and appendicularians, however, suggests an importance of sedimenting ice-derived material at least for filter feeders within the water column at this time of year.

Publication Date

2021-01-14

Publication Title

Frontiers in Marine Science

Volume

7

Acceptance Date

2020-12-17

Deposit Date

2021-01-18

Embargo Period

2021-01-21

Funding

This work was funded by the Research Council of Norway through the project The Nansen Legacy (RCN # 276730). Contributions by KS, SB, and AA were funded by the UK’s Natural Environment Research Council MOSAiC-Thematic project SYM-PEL: “Quantifying the contribution of sympagic versus pelagic diatoms to Arctic food webs and biogeochemical fluxes: application of source-specific highly branched isoprenoid biomarkers” (NE/S002502/1).

Keywords

food web, Barents Sea, sea ice, carbon sources, trophic markers, fatty acids, highly branched isoprenoid (HBI) lipids, sterols

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