Abstract
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.
Highlights
Arctic marine food webs are classically viewed as being supported by two temporally and ecologically distinct types of primary production: ice-associated algae and pelagic open water phytoplankton [1,2,3]
The timing of maximum ice algae polyunsaturated fatty acids (PUFA) availability is important to primary consumers and early melting of sea ice could cause a mismatch between food availability and copepod spring hatch
Emerging evidence of substantial under-ice pelagic production has the potential to fundamentally change our understanding of Arctic marine food webs [9, 11]
Summary
Arctic marine food webs are classically viewed as being supported by two temporally and ecologically distinct types of primary production: ice-associated algae and pelagic open water phytoplankton [1,2,3]. It has generally been accepted that under light-limiting ice/snow cover, the water column is unable to support significant numbers of pelagic autotrophs; ice algae represent the first available food source for zooplankton grazers in the early spring [4,5,6]. Contrary to the classical view, increasing evidence suggests that pelagic blooms occur under sea ice throughout the Arctic, sometimes hundreds of kilometers from open water [8, 9]. Pelagic growth under sea ice may be a significant, yet unaccounted source of PUFA for marine systems and could help buffer food webs from PUFA shortages in years of reduced iceassociated production
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