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Planktonic unicellular cyanobacteria are the dominant biomass producers and carbon fixers in the global ocean ecosystem, but they are not abundant in polar seawater. The interseasonal dynamics of picocyanobacterial (PC) abundance, picophytoplankton primary production, and phylogenetic diversity of PC Synechococcus were studied in the sub-Arctic White Sea. The PC abundance varied from 0.2–0.3 × 106 cells/L in February to 5.2–16.7 × 106 cells/L in July. Picophytoplankton primary production ranged from 0.22 mg C/m3 per day in winter to 11.32 mg C/m3 per day in summer. Synechococcus abundance positively correlated with water temperature and river discharge that increased in recent years in the White Sea. Phylogenetic analysis of the 16S rRNA gene and ITS region clone libraries from the White Sea and Barents Sea eDNA revealed picocyanobacterial sequences related to marine Synechococcus subclusters 5.1-I, 5.I-IV, 5.2, and 5.3. All Synechococcus S5.1-I were common in the White and Barents seas and were consistently present in the picophytoplankton composition throughout the year. Synechococcus S5.2 and S5.3 appear in the PC community in summer, suggesting their river origin, and Synechococcus S5.1-IV inhabits only the Barents Sea and was not detected in the White Sea. A unique Synechococcus phylotype was revealed. It is expected that the increase in the abundance of PC and their increasing role in ecosystem functioning, as well as the enrichment of the species composition with new phylotypes in the semi-enclosed sub-Arctic White Sea, which is vulnerable to the effects of climate change, will be characteristic of all Arctic seas in general.

Lophozia pallida, the commonly used name for a rare and little-known Sino-Himalayan species, was found to be a synonym of Lophozia dubia, a forgotten and previously misinterpreted species known in Indonesia. A comparative study of herbarium materials and our collections made it possible to ‘extend’ the distribution of Lophozia s. str. southward to Indonesia. The description of oil bodies from the species is provided for the first time. The position of the species in the Lophozia phylogenetic system demonstrates its clear differences from the morphologically similar Lophozia guttulata and its phylogenetic relationship with the Japanese–Korean Lophozia koreana.

Calypogeia is a genus in Pacific Asia that is difficult to classify taxonomically. These difficulties arise from (1) considering the presence of oil bodies as anatomical characters for taxonomic differentiation, (2) the wide occurrence of sibling, semicryptic and geographical vicariant taxa and (3) the inevitable need to organize new datasets for molecular genetic revision of the genus. The present study uses an integrative approach, including molecular genetic, morphological, chorological and ecological methods, to understand the taxonomy of the genus in Amphi-Pacific Asia. As a result, a set of new-to-science taxa was revealed, and the suite of morphological features necessary for reliable discrimination of the taxa was revised. These results are based on the study of a large set of ‘fresh’ collections suitable for molecular analysis and morphological comparison and include data on oil bodies. The most basal branch in Calypogeia s.l. is segregated into a new genus, Asperifolia. Descriptions of the new taxa and the key to Calypogeia in Vietnam are provided.

This survey is the first to explore the seasonal cycle of microbial eukaryote diversity (Micromonas polaris was constantly present throughout the September–June period in the PE community. The obtained results determine the seasonal dynamics of picoplankton in order to improve our understanding of their role in polar ecosystems.

The taxonomic diversity center of Schistochilopsis is in East Asia, where the genus also shows the highest genetic diversity and morphological plasticity. The integrative survey of Schistochilopsis in East Asia was the main goal of the present account. Plant materials were obtained from recent collections made by authors in various parts of amphi-Pacific Asia; several types of specimens were also studied. The study includes phylogenetic reconstructions from nuclear ITS1,2, chloroplast trnL and trnG sequences, and anatomo-morphological, biogeographical, and taxonomical analyses. As a result, it was concluded that S. obscura should be transferred to Lophozia s. str. and S. grandiretis to the newly described genus Protochilopsis. Lophozia boliviensis was found to be part of the Andean–Sino-Himalayan taxon belonging to Schistochilopsis. The species status of S. hyperarctica and S. opacifolia was not confirmed. Substantial genetic variation is observed within S. incisa with possible cryptic sympatric distributed entities. The taxonomical section of the paper provides a discussion on the status, distinctive morphological traits, distribution, and ecology supplemented with the morphological description for poorly understood taxa. In the vast majority of cases, the illustrations and photographs made from the types and living material are provided.