First analysis of an Arctic sea ice meiofauna food web based on abundance, biomass and stable isotope ratios

Particulate organic carbon (POC) produced in sea ice is often included in stable isotopic food web studies of polar seas as a single value of particulate organic matter (POM), i.e. 'ice POM'. During 10 field trips to landfast ice off Alaska's north coast, we examined the seasonal contribution of sea ice-associated meiofauna to total POM and the trophic structure within the sea ice using bulk carbon and nitrogen stable isotope ratios (delta C-13, delta N-15). Algal biomass, POC/particulate organic nitrogen and meiofaunal abundances increased after the polar night, and a suite of different metazoan meiofauna contributed seasonally substantially to total ice POC amount. delta C-13 values of meiofauna generally tracked the seasonal enrichment of delta C-13 in POC suggesting a trophic relationship, also supported by increasing body mass of meiofauna over the seasons. delta N-15 of individual meiofaunal taxa varied by at least 1.5 trophic levels. delta C-13 values of some meiofauna were very close to or below POC values suggesting the use of other carbon sources, perhaps including dissolved organic carbon (DOC) and bacteria. Estimated potential grazing rates, based on generated carbon and nitrogen content of individuals in this study, confirmed earlier generally low estimates of grazing impact of the meiofauna on the ice algal spring bloom, leaving large portions of the produced matter as food for pelagic and benthic organisms. These findings suggest a more complex sea ice-based food web structure that should be more commonly incorporated into food web, conceptual and other models.