Large, omega-3 rich, pelagic diatoms under Arctic sea ice: sources and implications for food webs

• Published in: PloS one 2014-12, Vol.9 (12), p.e114070-e114070
• Main Authors: Duerksen, Steven W, Thiemann, Gregory W, Budge, Suzanne M, Poulin, Michel, Niemi, Andrea, Michel, Christine
• Format: Article
• Language: English
• Subjects: Algae; Animals; Arctic Regions; Arctic sea ice; Bacillariophyta; Biology and Life Sciences; Cabassous centralis; Chaetoceros; Diatoms; Diatoms - cytology; Diatoms - growth & development; Diatoms - metabolism; Earth Sciences; Ecology and Environmental Sciences; Eicosapentaenoic acid; Fatty acids; Fatty Acids, Omega-3 - metabolism; Food Chain; Food chains; Food production; Food quality; Food sources; Food webs; Herbivores; Ice breakup; Ice Cover; Ice environments; Isotopes; Nutrients; Omega 3 fatty acids; Pack ice; Pelagic zone; Phytoplankton; Polar environments; Polyunsaturated fatty acids; Primary production; Sea ice; Stable isotopes; Thalassiosira; Unsaturated fatty acids; Zooplankton
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0114070

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) Coscinodiscus centralis 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 C. centralis: 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, C. centralis had significantly greater proportions of the long chain omega-3 fatty acid, eicosapentaenoic acid (EPA), than ice algae (24.4 ± 5.1% versus 13.7 ± 5.1%, respectively). Thus, C. centralis 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 C. centralis. Our results suggest that C. centralis 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.