An Arctic sea ice spring bloom driven and dominated by Dinoflagellates - a harbinger of the future sea ice?

The sea ice spring bloom is crucial for sustaining Arctic marine food webs, with sea ice algae serving as primary carbon sources for higher trophic levels. Despite the prevailing dominance of diatom species in sea ice spring blooms, our study highlights a notable deviation, showcasing a bloom driven by dinoflagellates. Through field sampling of first-year sea ice cores and subsequent analysis of physical and biogeochemical parameters, combined with amplicon sequencing of the 18S rRNA gene, we investigated the occurrence and implications of this significant dinoflagellate bloom, with a particular focus on Polarella glacialis. Our findings reveal that high irradiances at the top of the ice core, coupled with elevated nutrient availability and warm ice conditions, are key drivers of this phenomenon, as elucidated by redundancy analysis. Moreover, our results suggest a potential climate-driven decline in snow cover on sea ice, increased open leads, and thinner sea ice, which may favor the proliferation of dinoflagellates over diatoms. This alternative dinoflagellate-dominated bloom could have profound ecological consequences, given the enriched omega-3 fatty acid content of dinoflagellates, thereby influencing energy transfer within the Arctic marine food web. Furthermore, our study identifies the presence of not only Polarella glacialis but also Chytridinium, an ectoparasite on copepod eggs, and the green algae Ulothrix in relatively high abundances within the sea ice. These findings shed light on the intricate interplay between environmental factors and microbial community dynamics within Arctic sea ice ecosystems.