Patterns of variability in the fatty acid and stable isotope profiles of ice algae, phytoplankton, and zooplankton during early spring in the Canadian High Arctic

Sea ice-associated primary producers are a major source of energy within Arctic marine ecosystems, particularly when pelagic primary growth is temporally and spatially limited. Using samples and data collected in spring 2011 and 2012, the variation in the fatty acid composition and stable isotopes of ice-based primary producers and primary consumers were investigated over several spatial scales in the Canadian Arctic Archipelago. Snow and ice thickness significantly affected ice algae fatty acid composition. Broad scale year-to-year variation in snow and ice conditions indirectly affected the fatty acid compositions, particularly the levels of polyunsaturated fatty acids, of a keystone zooplankton species. Environmental influence on fatty acid composition decreased as trophic level increased. Despite the presence of high quality pelagic phytoplankton under the sea ice, the data suggest herbivores rely mainly on ice algae

Fatty acids and stable isotope signatures of first-year and multiyear sea ice in the Canadian High Arctic

Ice algae are critical components to the lipid-driven Arctic marine food web, particularly early in the spring. As little is known about these communities in multiyear ice (MYI), we aimed to provide a baseline of fatty acid (FA) and stable isotope signatures of sea-ice communities in MYI from the Lincoln Sea and compare these biomarkers to first-year ice (FYI). Significant differences in the relative proportions of approximately 25% of the identified FAs and significantly higher nitrogen stable isotope values (δ15N) in bottom-ice samples of FYI (δ15N = 6.4 ± 0.7%) compared to MYI (δ15N = 5.0 ± 0.4%) reflect different community compositions in the two ice types. Yet, the relative proportion of diatom- and dinoflagellate-associated FAs, as well as their bulk and most of the FA-specific carbon stable isotope compositions (δ13C) were not significantly different between bottom FYI (bulk δ13C: –28.4% to –26.7%, FA average δ13C: –34.4% to –31.7%) and MYI (bulk δ13C: –27.6% to –27.2%, FA average δ13C: –33.6% to –31.9%), suggesting at least partly overlapping community structures and similar biochemical processes within the ice. Diatom-associated FAs contributed, on average, 28% and 25% to the total FA content of bottom FYI and MYI, respectively, indicating that diatoms play a central role in structuring sea-ice communities in the Lincoln Sea. The differences in FA signatures of FYI and MYI support the view that different ice types harbor different inhabitants and that the loss of Arctic MYI will impact complex food web interactions with ice-associated ecosystems. Comparable nutritional quality of FAs, however, as indicated by similar average levels of polyunsaturated FAs in bottom FYI (33%) and MYI (28%), could help to ensure growth and reproduction of ice-associated grazers despite the shift from a MYI to FYI-dominated sea-ice cover with ongoing climate warming

Status and trends in the structure of Arctic benthic food webs

On-going climate warming is causing a dramatic loss of sea-ice in the Arctic Ocean and it is projected that the Arctic Ocean will become seasonally ice-free by 2040. Many studies of local Arctic food webs now exist and with this review paper we aim to synthesize these into a large-scale assessment of the current status of knowledge on the structure of various Arctic marine food webs, and their response to climate change, and to sea-ice retreat in particular. Key drivers of ecosystem change and potential consequences for ecosystem functioning and Arctic marine food webs are identified along the sea-ice gradient with special emphasis on the following regions: seasonally ice free Barents and Chukchi Seas, loose ice pack zone of the Polar Front (PF) and Marginal Ice Zone (MIZ), and permanently sea-ice covered high Arctic. Finally, we identify gaps existing in the knowledge of different Arctic marine food webs and provide recommendations for future studies

Large, Omega-3 Rich, Pelagic Diatoms under Arctic Sea Ice: Sources and Implications for Food Webs

<div><p>Pelagic primary production in Arctic seas has traditionally been viewed as biologically insignificant until after the ice breakup. There is growing evidence however, that under-ice blooms of pelagic phytoplankton may be a recurrent occurrence. During the springs of 2011 and 2012, we found substantial numbers (201–5713 cells m⁻³) of the large centric diatom (diameter >250 µm) <i>Coscinodiscus centralis</i> under the sea ice in the Canadian Arctic Archipelago near Resolute Bay, Nunavut. The highest numbers of these pelagic diatoms were observed in Barrow Strait. Spatial patterns of fatty acid profiles and stable isotopes indicated two source populations for <i>C. centralis</i>: a western origin with low light conditions and high nutrients, and a northern origin with lower nutrient levels and higher irradiances. Fatty acid analysis revealed that pelagic diatoms had significantly higher levels of polyunsaturated fatty acids (mean ± SD: 50.3±8.9%) compared to ice-associated producers (30.6±10.3%) in our study area. In particular, <i>C. centralis</i> had significantly greater proportions of the long chain omega-3 fatty acid, eicosapentaenoic acid (EPA), than ice algae (24.4±5.1% <i>versus</i> 13.7±5.1%, respectively). Thus, <i>C. centralis</i> represented a significantly higher quality food source for local herbivores than ice algae, although feeding experiments did not show clear evidence of copepod grazing on <i>C. centralis</i>. Our results suggest that <i>C. centralis</i> are able to initiate growth under pack ice in this area and provide further evidence that biological productivity in ice-covered seas may be substantially higher than previously recognized.</p></div

Stable carbon and nitrogen isotope values for <i>C. centralis</i> (circles) and ice algae (triangles).

<p>Stable carbon and nitrogen isotope values for <i>C. centralis</i> (circles) and ice algae (triangles).</p

Mean abundance (±SD) of selected fatty acids (expressed as mass % of total fatty acids) in ice algae and pelagic diatom <i>Coscinodiscus centralis</i> collected in spring 2012.

<p><i>*Thirteen fatty acids used for MANOVA, cluster and principal component analyses</i></p><p><i>EPA eicosapentaenoic acid, SFA saturated fatty acids, MUFA monounsaturated fatty acids, PUFA polyunsaturated fatty acids</i>.</p><p>Mean abundance (±SD) of selected fatty acids (expressed as mass % of total fatty acids) in ice algae and pelagic diatom <i>Coscinodiscus centralis</i> collected in spring 2012.</p

Distribution of <i>C. centralis</i> near Cornwallis Island, Nunavut, Canada.

<p><b>A</b>) Qualitative estimates of <i>C. centralis</i> abundances in spring, 2011. <b>B</b>) Densities (cells m⁻³) of <i>C. centralis</i> in the water column in spring 2012. Interpolation of cell densities was plotted using Ocean Data View v 4.6.1 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114070#pone.0114070-Schlitzer1" target="_blank">[23]</a>. Station colours correspond to the clusters identified in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114070#pone-0114070-g004" target="_blank">Fig. 4</a>; black indicates cluster 1, red is cluster 2 and green is cluster 3.</p

Relationship between δ¹⁵N and A) concentrations (mg m⁻³) of <i>C. centralis</i> fatty acids in the water column and B) PUFA (%) of <i>C. centralis.</i>

<p>Colours correspond to the clusters identified in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114070#pone-0114070-g004" target="_blank">Fig. 4</a>; black indicates cluster 1, red is cluster 2 and green is cluster 3.</p

Hierarchical clusters of ice algae (triangles) and <i>C. centralis</i> (circles) fatty acid profiles overlaid on the first two principal component axes.

<p>Hierarchical clusters of ice algae (triangles) and <i>C. centralis</i> (circles) fatty acid profiles overlaid on the first two principal component axes.</p