Growth and Elemental Stoichiometry of the Ecologically-Relevant Arctic Diatom Chaetoceros gelidus: A Mix of Polar and Temperate

Abstract

In the wake of modest surface blooms that occur at the onset of the growth season in the nitrogen-poor surface waters of the Beaufort Sea, subsurface chlorophyll maxima (SCM) develop and persist within the nutrient-rich halocline. Algal communities of these SCM can realize a major portion of annual net primary production and are often dominated by the widespread diatom Chaetoceros gelidus in coastal waters. In order to assess how changing growth conditions at the SCM may affect the biological carbon pump, grazer nutrition, and dissolved nutrient inventories across the transpolar Pacific-Atlantic conduit, the elemental stoichiometry of a C. gelidus strain (RCC2046) isolated from the Beaufort Sea and its response to the availability of light and different forms of nitrogen (N) were examined in the laboratory. The cells were grown in semi-continuous batch cultures at 0 • C under sub-saturating (LL; 5.5 µmol photons m −2 s −1 ) or saturating irradiance (HL; 200 µmol photons m −2 s −1 ) and with ammonium (NH + 4 ), nitrate (NO − 3 ) or urea as sole N form in nutrient-replete conditions. The growth rate, cell size, maximum quantum efficiency of photosystem II (F v /F m ) and the concentrations of chlorophyll a (Chl a), biogenic silica (Si) and particulate N, phosphorus (P), and organic carbon (C) were measured during the exponential growth phase. Despite a clear response of volumetric quotas to N form, the growth rates and elemental ratios of the cells were unaffected by N form in the two irradiance treatments. Elemental ratios were affected by light and the responses were remarkably similar to those observed for temperate diatoms. Overall, this study shows that the growth and elemental composition of C. gelidus in the Arctic Ocean are highly resistant to changes in nitrogen form at near-freezing temperatures and suggests that this diatom possesses the ability to remain competitive despite ongoing environmental changes.

Arctic phytoplankton spring bloom diversity across the marginal ice zone in Baffin Bay

“…The increase in Chaetoceros spp. observed here in the OW sector, especially in the upper layers within the 3-20 µ m size fraction, may reflect an ecological advantage within a post-bloom scenario, since this genus has a high growth irrespective of nitrogen source in polar (Schiffrine et al 2020) and subtropical (Morando and Capone 2018) environments. The only abundant diatoms flagged as indicator ASVs for OW or MIZ+OW sectors belonged to Thalassiosira and Eucampia , two genera that were also reported to be effective scavengers for different nitrogen sources, out-competing other plankton community members within nutrient poor waters (Morando and Capone 2018).…”

Environmental and Biological Determinants of Algal Lipids in Western Arctic and Subarctic Seas

“…Relatively frequent or pronounced environmental fluctuations at SUR in terms of pH, salinity or temperature may also blur the relationship since algae may often modulate the degree of FA unsaturation in order to adjust membrane fluidity in changing environments (Tatsuzawa et al, 1996;Bigogno et al, 2002;Los et al, 2013). In this respect, the SCM is generally sheltered within the pycnocline and thus tends to maintain relatively stable physicochemical conditions over time (Martin et al, 2010;Schiffrine et al, 2020). This creates a setting in which the influence of phytoplankton assemblage composition on lipid profiles is less prone to be obscured by short-term physiological responses to fluctuating temperature, salinity, pH or light.…”

Ecological Responses of Core Phytoplankton by Latitudinal Differences in the Arctic Ocean in Late Summer Revealed by 18S rDNA Metabarcoding

“…The pan-Arctic C. gelidus is widely distributed in the Arctic, and remains abundant in the summer and early autumn seasons (Tremblay et al, 2006). In particular, this psychrophilic diatom thrives despite the depletion of inorganic nitrogen concentrations at near-freezing temperatures (Schiffrine et al, 2020). Micromonas spp.…”