Distribution and Phylogenetic Diversity of -like Cyanobacteria in the Late Autumn Picophytoplankton of the Kara Sea: The Role of Atlantic and Riverine Water Masses.

Increased Atlantic water transport and river discharge are more pronounced effects of global warming at high latitudes. Both phenomena may lead to changes in the species composition of small-celled algae populations in marine ecosystems, as well as to the emergence of new species. This study investigated the spatial distribution of picocyanobacterial (PC) abundance and the phylogenetic diversity of PC in the Kara Sea. PC abundance varied from 2 to 88 cells mL and increased with warming temperatures and decreasing salinity caused by river water influence. The contribution of to the total picophytoplankton biomass was low (<16%). The community was characterized at deep taxonomic level using amplicon sequencing targeting the gene. Diversity was low, revealing only subcluster 5.1 polar lineages I and IV, and euryhaline subcluster 5.2. subcluster 5.1.I represented on average 97% of the total reads assigned to cyanobacteria. For the first time, the presence of estuarine subcluster 5.2 was documented as far north as 82° N. Modified Atlantic water was the main source of cyanobacteria in the Kara Sea, followed by river discharge. Our study contributes to the understanding of PC sources in the Kara Sea and allows for the further monitoring of PC distribution and evolution.