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

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.

Diatom Biogeography From the Labrador Sea Revealed Through a Trait-Based Approach

“…However, to avoid sinking, healthy diatoms (> 200 µm 3 in cell volume = c.a. 8 µm equivalent spherical diameter) have developed trade-off strategies to encourage positive buoyancy, such as cellular vacuoles filled with low-density ions (Woods and Villareal, 2008), light-weight fatty acids (Duerksen et al, 2014), and extracellular mucous material (Assmy et al, 2013a). Another strategy is the presence of cellular protrusions, such as setae, spines, and long processes, which improves the cell's ability to increase its shear rate (and slow its sinking).…”

Culturable diversity of Arctic phytoplankton during pack ice melting

“…Unfortunately, this strain was lost and no images are available. Coscinodiscus may be abundant under the ice pack (Duerksen et al, 2014) and is often reported in Arctic diversity studies (Booth et al, 2002;Lovejoy et al, 2002).…”

“…However, the salinity decrease in surface waters, resulting from higher ice melting rates and increased river run off, leads to an increase in water column stratification which in turn may impact nutrient availability and plankton diversity (Li et al, 2009). The presence of ice-associated algae may impact the quantity (Leu et al, 2011;Kohlbach et al, 2016) and quality (Duerksen et al, 2014;Schmidt et al, 2018) of secondary production at high latitudes, as well as the recruitment of ice-associated diatoms to the water column (Kauko et al, 2018). Climaterelated changes can also increase Arctic vulnerability to invasive species (Vincent, 2010) as the intrusion of warmer waters "atlantifies" the Arctic Ocean (Årthun et al, 2012) and temperate phytoplankton move northwards, replacing Arctic communities (Neukermans et al, 2018).…”

Culturable diversity of Arctic phytoplankton during pack ice melting

“…However, the salinity decrease in surface waters resulting from higher ice melting rates and increased river run off leads to an increase in water column stratification which in turn may impact nutrient availability and plankton diversity (Li et al, 2009). The presence of ice-associated algae may impact the quantity (Kohlbach et al, 2016; Leu et al, 2011) and quality (Duerksen et al, 2014; Schmidt et al, 2018) of secondary production at high latitudes, as well as the recruitment of ice-associated diatoms to the water column (Kauko et al, 2018). Climate-related changes can also increase Arctic vulnerability to invasive species (Vincent, 2010) as the intrusion of warmer waters “atlantifies” the Arctic Ocean (Årthun et al, 2012) and temperate phy-toplankton move northwards, replacing Arctic communities (Neukermans et al, 2018).…”