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

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 δ13C values of essential amino acids (EAAs) (δ13CEAA 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 δ13CEAA values, that is, the basal resource specific δ13CEAA values, and δ13CEAA fingerprints, or mean‐centred baseline δ13CEAA 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, δ13CEAA fingerprints from algae‐associated bacteria were clearly traced to the sponges, with an individually variable kelp use by sea cucumbers. Although mean‐centred δ13CEAA 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 δ13CEAA values as similar microalgae clades occur in both habitats. We suggest that δ13CEAA fingerprints combined with microalgae baseline δ13CEAA values are an insightful tool to assess the effect of ongoing changes in Arctic basal resources on their use by organisms.

Year-round utilization of sea ice-associated carbon in Arctic ecosystems

“…2b) that had exclusively pelagic signatures at the time of sampling. Given these are the only taxa lacking in iPOC signatures entirely, which contrasts other studies 22,23,38 , this is likely the result of rapid HBI turnover rates in zooplankton and sample timing, which does not rule out the utilization of iPOC for these zooplankton species or an exclusive reliance on phytoplankton. Accordingly, we provide the first direct demonstration of the persistent role sea-ice primary production plays in supporting the energy requirements throughout a majority of the marine and coastal food webs across the Arctic, extending beyond the narrow springtime window of initial production (Fig.…”

“…It has also been suggested that bacteria may consume greater proportions of this highly degraded pelagic detritus than benthic macrofauna 22,59 .…”

“…Based on a previously established calibration 8 , we were then able to convert H-Print values into estimates of sea-ice particulate organic carbon (iPOC) directly consumed by animals 8,15 or transferred to higher trophic organisms. So far, this approach has resulted in comparable findings of carbon sources, examples including fatty acid markers [16][17][18] , bulk stable isotopes 19,20 and compound-specific stable isotope analysis of amino acids (CSIA-AA) 21,22 and CSIA of fatty acids (CSIA-FA) 17,23,24 . Stable isotope analysis of carbon for the primary ice-associated HBI, IP 25 , has also confirmed sea ice origins 25 .…”

What we do in the dark: Prevalence of omnivorous feeding activity in Arctic zooplankton during polar night

“…Combinations of multiple independent trophic biomarkers such as essential amino acid carbon isotopic fingerprints may be used to constrain assumptions about the susceptibility of trophic biomarkers to these variations. For example, the general patterns in the importance of sympagic and pelagic diatoms and dinoflagellates for June/July A. glacialis was confirmed in a study using the 13 C signature of essential amino acids and demonstrated that the under‐ice diatom, Melosira arctica , could have significantly contributed to the diatom‐associated fatty acid signal (Vane et al 2023).…”

Quantifying the utilisation of blue, green and brown resources by riparian predators: A combined use of amino acid isotopes and fatty acids

“…Sampling and isolating primary producers in the wild remains challenging, especially for bacteria, whose fingerprinting is typically derived from lab cultures. An alternative approach involves sampling primary consumers, which integrate basal fingerprinting over time and provide a site-specific baseline (Skinner et al, 2021;Vane et al, 2023). However, primary consumers themselves may exhibit overlaps, particularly for brown and blue consumers that derive carbon from bacteria, fungi, and plant, and bacteria, algae, and plant, respectively.…”