T. A. Belevich

Metagenomic analyses of white sea picoalgae: First data

Picoalgae (defined as cells smaller than 2-3 μm) include members of diverse taxonomic groups. They are an important constituent of marine plankton and ice biota and play a significant ecological role in biogeochemical cycles. Despite their importance, the true extent of their diversity has only recently been uncovered by molecular surveys. The diversity of picoeukaryotes has not yet been studied in the White Sea, which is a unique marine environment combining features of temperate and Arctic seas. Here, we investigated the taxonomic composition of eukaryotic picoalgae in ice and under-ice water at a station located in the Kandalaksha Bay of the White Sea. We applied metagenomic survey using Illumina sequencing. Eight main algae phyla, namely, Chlorophyta, Katablepharidophyta, Haptophyta, Dinophyta, Cercozoa, Bacillariophyta, Cryptophyta, and Ochrophyta were identified. The genera Paraphysomonas and Micromonas and the order Pedinellales were most numerous in plankton; the genera Paraphysomonas, Micromonas, and Metopion were most abundant in ice. The number of “rare” phylotypes was 80 in under-ice water and 112 in ice. Some taxa of nanoand microalgae are identified for the first time in the White Sea phytoplankton. Our data provide a basis for further research of tiny phototrophs in the Russian Arctic.

Metagenomics of bolidophyceae in plankton and ice of the White Sea

The molecular diversity of poorly studied algae of Bolidophyceae class was first estimated by Illumina sequencing of V4 region of 18S rRNA gene in ice, under-ice water and summer water of the subarctic White Sea. We used two clustering thresholds–93 and 97%–and revealed 31 phylotypes of Bolidophyceae. Triparma pacifica and Т. strigata were identified to species level. The association of individual phylotypes to certain biotopes (ice or plankton) and stages of seasonal succession (under ice or summer plankton) has been established. Some phylotypes are found in different biotopes and over a wide temperature range. Due to changing their genetic composition, Bolidophyceae are a constant component of the photoautotrophic plankton and ice communities.

Fluorescence Parameters of Marine Plankton Algae at the Assimilation of Organic Nitrogen

Abstractfluorescence parameters of marine plankton algae Pseudo-nitzschis delicatissima, Thalassiosira weissflogii, and Tetraselmis viridis were estimated after the addition of organic (urea and glycine) and inorganic (nitrate and ammonia) nitrogen to nitrogen-limited cultures acclimated to limited and saturated irradiance. The photochemical efficiency of photosystem 2, the maximum relative electron transport, and the light saturation index increased in the algae assimilating organic nitrogen. The dynamics of parameters depended species specifically on the nitrogen source and irradiance. The ecological role of organic nitrogen in the seasonal dynamics and vertical distribution of phytoplankton is discussed.

Fluorescence parameters of White Sea phytoplankton under different nitrogen sources

We investigated dependence of fluorescence parameters and phytoplankton biomass on the nitrogen source and irradiance in enriched flask studies with White Sea plankton from August-September 2007. Phytoplankton was exposed in situ for 18 d with addition of 180 μM/L of nitrogen in the forms of nitrate, urea, ammonia, and glycine under two levels of irradiance. Maximum quantum efficiency of PS2 (Fv/Fm) was determined in the samples adapted to darkness. Rapid light curves were obtained for each sample with the sequential increase of light intensity (8 levels). The maximal relative electron transport rate (rETRmax), the maximum light utilization coefficient (α), and the nonphotochemical quenching (NPQ) were calculated. The phytoplankton abundance increased on nitrogen addition, and the photosynthetic parameters changed. The values Fv/Fm reached 0.64–0.71, which indicated a good physiological state of algae and lack of nitrogen limitation. The dynamics of rETRmax and NPQ depended of the nitrogen source and irradiance, while α did not depend on nitrogen addition.

Phototrophic Picoeukaryotes of Onega Bay, the White Sea: Abundance and Species Composition

The abundance, biomass, and composition of phototrophic picoeukaryotes (PPE, cell size less than 3 μm) were studied in Onega Bay of the White Sea in June 2015. The highest PPE abundance and biomass were registered in the 0–5-m water layer. In the bay, in the 0–5-m water layer, the average abundance and biomass varied from 0 to 36.8 × 104 cell/L and from 0 to 117 μg С/m3, respectively. The Illumina sequencing of V4 region of 18S rRNA gene revealed eight classes of PPE. Mamiellophyceae dominated both by number of reads and by operational taxonomic units. The green algae Bathycoccus prasinos, Ostreococcus tauri, and Micromonas pusila, as well as diatoms Skeletonema marinoi and Minidiscus trioculatus, were identified to the species level.

Diatoms in the ice of Velikaya Salma strait, the White Sea, before the spring algal bloom

Diatom species composition in the ice of Velikaya Salma strait of Kandalaksha Bay of the White Sea was studied in 5 stations in March, 2013–2014—prior to the spring algal bloom. Under-ice water salinity and ice thickness did not differ significantly between the two years. In total 59 diatom taxa (47 species and 12 taxa of higher taxonomic ranks) were found in the ice of Velikaya Salma strait, which makes 61% of the number of diatom taxa found in Velikaya Salma ice during the whole ice period and 22% of all the White Sea ice species. Species Stenoneis obtuserostrata (Hustedt) Poulin and Gyrosigma concilians (Cleve) Okolodkov were identified in the White Sea ice for the first time. Szymkiewicz-Simpson similarity coefficient for pairs of stations with significant difference was 0.44–0.80.

Spatial Distribution of Picophytoplankton in the White Sea in the Beginning of Summer

Biomass of photosynthetic picoplankton (Bpic), its contribution to the total phytoplankton biomass (Bpic%), chlorophyll a concentration (Chl), and associated hydrophysical characteristics of the water masses in the White Sea were estimated in June 2015 at 47 stations located in the open parts and in the inlets of the Onega and Kandalaksha Bays and in the western part of the Basin. Spatial variability of mean values of Bpic in the photic layer (0.01–1.91 mg C/m3) was preconditioned by sub- and mesoscale heterogeneity of the hydrological conditions. The values of Bpic were higher near the frontal zones than those in the water masses characterized by quasi-homogeneous distribution of the thermohaline characteristics. The relative contribution of Bpic did not exceed 1% at half of the stations and varied from 1 to 8% for the rest of the studied water area. The value of Bpic% reached 40.5% in the Basin and did not exceed 2% during the phytoplankton bloom in Knyazhaya Inlet (Chl > 3 mg/m3) accompanied by the dominance of Skeletonema costatum sensu lato.

Structure of the community of planktic algae of the white sea in relation to availability of oxidized or reduced forms of nitrogen and level of illumination

Phytoplankton sampled in Kandalaksha Bay of the White Sea in late June 2006 was exposed in situ for 14 days under two levels of illumination (E1 > E2) with the addition of 180 μM of nitrogen as nitrate, urea, ammonium, and glycine. Every 3 days, species composition, abundance, and biomass of algae were estimated. The maximum biomass (Bmax) of phytoplankton depended on nitrogen substrates and level of illumination. The differences in Bmax between phytoplankton assimilating different nitrogen substrates became more apparent under E2. Phytoplankton assimilating nitrates, urea, and ammonium had higher Bmax under E1, but algae grown with glycine had higher Bmax under E2. Although the values of Bmax differed, the structures of all assemblages were similar except for that grown on ammonium under E1. Competitive parameters of algae populations depended on the form of nitrogen and level of illumination in a species-specific manner. Comparison of the present data with results of similar experiments in 2005 revealed that structure of assemblages formed after nitrogen pulse additions depended not only on nitrogen forms and illumination level but also on initial (before pulse) structure of community and availability of nitrogen for algae.