Picophytoplankton in Blagopoluchia Bay (Novaya Zemlya Archipelago) and Adjacent Part of the Kara Sea

Picophytoplankton abundance, biomass, and chlorophyll a concentration as well as contribution of picoalgae to total chlorophyll a , and species composition of phototrophic picoeukaryotes (cells size less than 3 µm) were studied in Blagopoluchia Bay (Novaya Zemlya archipelago) and the northwestern part of the Kara Sea in September 2017. In the Bay, the highest picophytoplankton abundance and biomass were found in the surface layer and averaged 0.75 × 10 9 cell/m 3 and 1.49 mg С/m 3 respectively. In the northwestern part of the Kara Sea, the highest abundance and biomass of picophytoplankton were observed in the 8 m layer and were 2.29 × 10 9 cells/m 3 and 2.76 mg С/m 3 respectively. The contribution of picophytoplankton to total chlorophyll a concentration varied from 12 to 24% in the Bay and reached 46% in the Kara Sea. The Illumina sequencing of the V4 region of 18S rRNA gene revealed eight classes of phototrophic picoeukaryotes. Mamiellophyceae dominated in the number of reads. Arctic endemic ( Micromonas polaris ) and widespread ( Bathycoccus prasinos ) species were revealed in both studied areas.