Identification of the sea ice diatom biomarker IP25 in Arctic benthic macrofauna: direct evidence for a sea ice diatom diet in Arctic heterotrophs

Abstract

Currently, the impact of declining seasonal sea ice extent in the Arctic on polar food webs remains uncertain. Previously, a range of proxy techniques has been employed to determine links between sea ice or phytoplankton primary production and the Arctic marine food web, although it is accepted that such approaches have their limitations. Here, we propose a novel approach to tracing sea ice primary production through Arctic food webs using the sea ice diatom biomarker, IP25. Various benthic macrofaunal specimens were collected between March and May 2008 from Franklin Bay in the Amundsen Gulf, Arctic Canada, as part of the International Polar Year–Circumpolar Flaw Lead system study. Each specimen was analysed for the presence of the sea ice diatom biomarker IP25 in order to provide evidence for feeding by benthic organisms on sea ice algae. IP25 was found in nineteen out of the twenty-one specimens analysed, often as the most abundant of the highly branched isoprenoid biomarkers detected. The stable isotope composition of IP25 (δ13C = −17.1 ± 0.5‰) in the sea urchin (Strongylocentrotus sp.) specimens was similar to that reported previously for this biomarker in Arctic sea ice, sedimenting particles and sediments. It is concluded that detection of IP25 in Arctic benthic macrofauna represents a novel approach to providing convincing evidence for feeding on sea ice algae. It is also proposed that analysis of IP25 may be used to trace trophic transfer of sea ice algal-derived organic matter through Arctic food webs in the future.