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Species diversity of phototrophic eukaryotes (PEs) with cell size <3 µm in autumn phytoplankton of the Kara and Laptev seas was studied. High-throughput sequencing of the 18S rRNA gene V4 region revealed 15 classes of algae in the plankton pico-sized fraction, which belonged to five divisions: Haptophyta, Cryptophyta, Chlorophyta, Ochrophyta, and Dinoflagellata. Dinoflagellata and green algae of the class Mamiellophyceae were the main contributors to total PE sequences. Chlorophyta was the most diverse section, represented by seven classes: Mamiellophyceae, Trebouxiophyceae, Nephroselmidophycea, Palmophyllophyceae, Pyramimonadophyceae, Chlorodendrophyceae, and Chlorophyceae. Bolidophyceaea species Triparma strigata and T. laevis, as well as the diatom Skeletonema marinoi, were first identified in the Kara and Laptev Seas, respectively. The hydrological conditions on the stations determined the PE taxonomic composition. The diversity indices were higher at the stations located in the upper estuary of river Khatanga and at the areas of both seas adjacent to the Khatanga and Ob estuaries than at the northernmost Laptev Sea station. The obtained data showed that the taxonomic composition of the smallest phytoplankton fraction of the two shelf seas of the Russian Arctic was similar to that found in other Arctic regions. [ABSTRACT FROM AUTHOR]

Seasonal dynamics of phytoplankton production and structural characteristics was studied at two closely located stations in the open part of the Sevastopol Bay mouth, one of which was a mussel farm. The net primary production, chlorophyll a content, total phytoplankton biomass, the quantitative ratio between small and large algal cells, and their seasonal dynamics were the same for both stations. Linear dependencies were observed between the relevant parameters of the stations, with the angular regression coefficients close to 1. The phytoplankton production and biomass peaked during the summer period, reaching 350 ± 43 mg C/(m3 day) and 450 ± 50 mg C/m3, respectively. Chlorophyll a content varied from 0.5 to 3 mg/m3, with the minimum in January‒February and the maximum in summer. The assimilation number values for chlorophyll a during the light period corresponded to those reported for production waters and correlated with the temperatures during the year. Total oxygen consumption by bacterio- and phytoplankton during the summer period was 30–70% of net photosynthesis. The data were obtained on seasonal biomass variations in three groups of algae (Synechococcus, picoeukaryotic phytoplankton, and nanophytoplanktom); on average, picoalgae constituted 30% of the phytoplankton biomass, with maxima during the winter-spring and summer periods. Bacterioplankton abundance was determined using flow cytometry and the SYBR Green I vital fluorochrome. A positive relation between bacterial abundance and water temperature was shown. [ABSTRACT FROM AUTHOR]

Abundance and seasonal trophodynamics (specific growth rate, daily production, and grazing mortality) of the major picophytoplankton components, Synechococcus cyanobacteria (Syn) and picoeukaryotes (Pico-E), were studied at three stations in Sevastopol Bay and adjacent coastal waters (the Black Sea) in 2014 by flow cytometry and the dilution method. Pico-E abundance was shown to increase along the nutrient and pollution gradient from the coastal waters outside the bay (annual average of 7.3 ± 5.4 × 10 cells mL) to the eastern corner of the bay (28.7 ± 11.4 × 10 cells mL), while no relation was found between the water pollution status and Syn abundance (9.9 ± 8.7 × 10 cells mL; at all the stations, n = 27). Matter flows through the communities (daily production for Syn and Pico-E 06.6 and 09.3 µg C L day, respectively; grazing mortality for Syn and PicoE 0-3.6 and 0-21.2 µg C L day, respectively) were comparable to or even exceeded their biomass stocks (>0.05-6.8 and 0.9-26.5 µg C L for Syn and PicoE, respectively), indicating high biomass turnover rates. The highest flow-to-stock ratio (up to 6 for Syn) and a significant imbalance between daily production (P) and grazing mortality ( G) were observed in the most polluted and eutrophic waters of the bay in spring (Pico-E: P/G < 1) and late summer (Syn: P/G > 1). Black River inflow to the bay was hypothesized to be among the mechanisms maintaining this pronounced and long-term imbalance in the open system without any negative consequences for the picophytoplankton assemblages. [ABSTRACT FROM AUTHOR]

In July-August 2009, the abundance of picophytoplankton (Pico) in the Velikaya Salma strait varied from 3.4 × 10 to 19.4 × 10 cells/L, while its biomass (B) was 0.8-3.3 mg C/m. In August 2010, Pico abundance was significantly higher (up to 216 × 10 cells/L and 36.8 mg C/m). Pico consisted mainly of cyanobacteria. It constituted 13 (2009) to 28% (2010) of the total phytoplankton biomass. In April 2010, Pico numbers varied from 0.1 × 10 to 0.22 × 10 cells/L and its biomass was 0.05-0.28 mg C/m. Picoeukaryotes were predominant. Pico constituted not more than 2.7% of the phytoplankton biomass. In the ice column, the integrated Pico abundance was 430 × 10 cells/m and the integrated biomass was 365 μg C/m. [ABSTRACT FROM AUTHOR]