The importance of ice algae-produced carbon in the central Arctic Ocean ecosystem: Food web relationships revealed by lipid and stable isotope analyses

Abstract

To better predict ecological consequences of changing Arctic sea ice environments, we aimed to quantify the contribution of ice algae-produced carbon (a Ice ) to pelagic food webs in the central Arctic Ocean. Eight abundant under-ice fauna species were submitted to fatty acid (FA) analysis, bulk stable isotope analysis (BSIA) of nitrogen (d 15 N) and carbon (d 13 C) isotopic ratios, and compound-specific stable isotope analysis (CSIA) of d 13 C in trophic marker FAs. A high mean contribution a Ice was found in Apherusa glacialis and other sympagic (ice-associated) amphipods (BSIA: 87% to 91%, CSIA: 58% to 92%). The pelagic copepods Calanus glacialis and C. hyperboreus, and the pelagic amphipod Themisto libellula showed substantial, but varying a Ice values (BSIA: 39% to 55%, CSIA: 23% to 48%). Lowest a Ice mean values were found in the pteropod Clione limacina (BSIA: 30%, CSIA: 14% to 18%). Intra-specific differences in FA compositions related to two different environmental regimes were more pronounced in pelagic than in sympagic species. A comparison of mixing models using different isotopic approaches indicated that a model using d 13 C signatures from both diatomspecific and dinoflagellate-specific marker FAs provided the most conservative estimate of a Ice . Our results imply that ecological key species of the central Arctic Ocean thrive significantly on carbon synthesized by ice algae. Due to the close connectivity between sea ice and the pelagic food web, changes in sea ice coverage and ice algal production will likely have important consequences for food web functioning and carbon dynamics of the pelagic system.

Carbon geochemistry of plankton-dominated samples in the Laptev and East Siberian shelves: contrasts in suspended particle composition

“…For example, stable carbon isotopes of marine phytoplankton are used for palaeo-pCO 2 reconstructions over geological timescales (Hoins et al, 2015;Pagani et al, 1999;Popp et al, 1999;Rau, 1994). The δ 13 C signature also provides a solid tool for marine food web and ecosystem structure investigations (Dunton et al, 2006;Iken et al, 2005;Kohlbach et al, 2016). Furthermore, dual-carbon isotope mixing models (δ 13 C and 14 C) are commonly used to quantify the relative proportion of marine and various allochthonous sources (e.g.…”

Spatio-temporal variability in the winter diet of larval and juvenile Antarctic krill, Euphausia superba, in ice-covered waters

“…The proportions of the individual FAs were expressed as mass percentage of the total FAs. Details on the procedure and analytical equipment were reported by Kohlbach et al (2016).…”

“…Furthermore, the laboratory standards isoleucine and peptone were analysed every 5 samples (Sigma Aldrich), indicating errors of ± 0.3 ‰ for nitrogen and ± 0.6 ‰ for carbon isotope ratios of isoleucine (representing ±1 SD of 16 analyses) and ± 0.3 ‰ for both peptone measurements (representing ±1 SD of 8 ana lyses). For details on the verification of accuracy and precision of the BSIA measurements, see Kohlbach et al (2016). Samples of particulate organic matter (POM) from surface water and sea ice were collected to provide a baseline for BSIA.…”

“…The analysis of stomach contents can provide essential information on the recent diet composition of a consumer. Combined with lipid and fatty acid (FA) compositions, it is possible to elucidate trophic interactions over larger temporal scales (Falk-Petersen et al 1999, Dalsgaard et al 2003, Kohlbach et al 2016. Zooplankton lack the ability to biosynthesize certain FAs de novo.…”

“…Furthermore, the isotopic fractionation of carbon (δ 13 C: 13 C/ 12 C) was measured to assess the potential contribution of ice algae-derived carbon to the diet of overwintering krill. This is possible because the δ 13 C values of sea ice-derived carbon are often higher compared to pelagic produced carbon (Fry & Sherr 1984, Hecky & Hesslein 1995, Jia et al 2016, Kohlbach et al 2016). The isotopic composition of nitrogen (δ We used this comprehensive methodical approach for a detailed analysis of the spatial variability of the trophic ecology of overwintering krill across a geographically large research area in the northern Weddell Sea, aiming to: (1) assess the importance of sea ice-associated carbon sources in the diet of overwintering krill; (2) investigate the association of the diet composition with spatio-temporal patterns in the environmental properties of the research area; and (3) analyse correlations between the size and stage composition of different krill cohorts and recent and long-term dietary sources.…”