Marine Micro- and Macroalgae in the Polar Night

Microalgae have unique adaptions including low metabolic activity, utilization of lipid storage, and resting stage formation to survive the Polar Night. Some species are mixotrophic or heterotrophic and do survive periods that are not favorable for photosynthetic (autotrophic) growth, such as the Polar Night. In addi- tion, the autotrophic and mixotrophic species seem to maintain the key components of the photosynthetic apparatus intact during the dark period, which allows them to resume growth rapidly once light comes back in spring. In contrast, some macroal- gal species may act as “season anticipators” and utilize the winter darkness or early spring period as their major growth seasons. This chapter elucidates aspects of the ecology of micro- and macroalgae with a focus on the dark season. It is comprised of six parts and starts with an introduction (Sect. “Introduction”) about Arctic marine micro- and macroalgae. Section “The Key Abiotic Environmental Variables Related to Micro- and Macroalgae” reviews the key abiotic environmental variables related to micro- and macroalgal growth and survival. The seasonal development of the different groups of microalgae is described in Sect. “Microalgae”, comprising phytoplankton, microphytobenthos, and sea-ice algae. Section “Macroalgae” intro- duces the three classes of macroalgae (phaeo-, rhodo-, and chlorophytes) with infor- mation about biological variables, seasonal processes, and habitats. Section “Ecophysiology of Algae in the Polar Night” sheds light on the ecophysiology of microalgae and macroalgae in the Polar Night, using selected examples. The last Section “Conclusive Remarks” summarizes our current state of knowledge and provides some conclusions derived from it

Seasonal patterns in Arctic prasinophytes and inferred ecology of Bathycoccus unveiled in an Arctic winter metagenome

14 pages, 5 figures, 3 tables, supplementary Information https://www.nature.com/ismej/journal/v11/n6/suppinfo/ismej20177s1.htmlPrasinophytes occur in all oceans but rarely dominate phytoplankton populations. In contrast, a single ecotype of the prasinophyte Micromonas is frequently the most abundant photosynthetic taxon reported in the Arctic from summer through autumn. However, seasonal dynamics of prasinophytes outside of this period are little known. To address this, we analyzed high-throughput V4 18S rRNA amplicon data collected from November to July in the Amundsen Gulf Region, Beaufort Sea, Arctic. Surprisingly during polar sunset in November and December, we found a high proportion of reads from both DNA and RNA belonging to another prasinophyte, Bathycoccus. We then analyzed a metagenome from a December sample and the resulting Bathycoccus metagenome assembled genome (MAG) covered ~90% of the Bathycoccus Ban7 reference genome. In contrast, only ~20% of a reference Micromonas genome was found in the metagenome. Our phylogenetic analysis of marker genes placed the Arctic Bathycoccus in the B1 coastal clade. In addition, substitution rates of 129 coding DNA sequences were ~1.6% divergent between the Arctic MAG and coastal Chilean upwelling MAGs and 17.3% between it and a South East Atlantic open ocean MAG in the B2 Clade. The metagenomic analysis also revealed a winter viral community highly skewed toward viruses targeting Micromonas, with a much lower diversity of viruses targeting Bathycoccus. Overall a combination of Micromonas being relatively less able to maintain activity under dark winter conditions and viral suppression of Micromonas may have contributed to the success of Bathycoccus in the Amundsen Gulf during winterThis study was part of the Circumpolar Flaw Lead—International Polar Year (CFL-IPY) study supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Network of Centers of Excellence ArcticNet. NJ received scholarships from Université Laval and the Canadian Excellence Research Chair—Remote Sensing of Canada’s New Arctic Frontier (CERC) grant to Marcel Babin. Additional support came from an NSERC Discovery and Northern Supplement grants to CL and the Fonds de recherche du Québec Nature et Technologies (FRQNT) to Quebéc-OcéanPeer Reviewe