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The port ecosystems are prone to deterioration due to the maritime and coastal activities and as a major source of the country's economy need efficient management. Phytoplankton communities can serve as reliable indicators of the prevailing environmental conditions due to their short life cycles. Seasonal sampling was conducted at 26 stations from October 2014 to February 2016 at Kandla port situated in a creek, along the west coast of India. The post-monsoon and monsoon water temperatures were higher (30 °C) whereas pre-monsoon were lower (21 °C). The salinity varied from polyhaline (18–30; monsoon) to euhaline (30 to 45; non-monsoon). The strong currents, high tidal activity, shallow depth areas, and the creek backwater systems make this ecosystem well-mixed and turbid. The annual average trophic index (TRIX) scores indicated very good water quality and low eutrophication, except during pre-monsoon (2.3 ± 0.7 to 4.1 ± 0.2). Based on the cell size, the phytoplankton community was classified into two main groups, i.e., nano-microphytoplankton, which comprised forty-seven species (represented by diatoms, dinoflagellates, and silicoflagellates) and picophytoplankton including two groups (picocyanophytes and picoeukaryotes). The diatoms and picophytoplankton dominated the total biomass and cell abundance, respectively. Only the picophytoplankton exhibited significant seasonal variations in cell abundance and carbon biomass. The lowest monsoon phytoplankton abundance coincided with high turbidity and vice versa during the post-monsoon. The hypersaline pre-monsoon environment with lower annual temperature, relatively lower turbid waters, and increased nutrients favoured higher diatom diversity. These conditions also supported potentially harmful Gymnodinium sp. and bloom-forming Tripos furca and Pyrophacus sp. Overall, ten non-toxic but bloom-forming species were observed. The study provides insights into the phytoplankton community's response to environmental conditions that can have repercussions on the ecosystem's functioning. [ABSTRACT FROM AUTHOR]

Phytoplankton phenology, connected to the seasonal variation in physiology, populations, community composition or whole community aggregated and biological interactions, responds to downwelling irradiance, temperature and nutrient supply. Quantitative niche models estimate picophytoplankton cell abundance based on photosynthetic active radiation (PAR), temperature and nitrate and thus can be used to study picophytoplankton phenology. We used quantitative niche models to estimate the abundance of picophytoplankton groups for the global ocean in 1-degree grids and the upper 200 m of the water column. The inputs of the models were the monthly climatology of temperature and nitrate from the World Ocean Atlas (WOA) and PAR from the Moderate Resolution Imaging Spectroradiometer (MODIS-Aqua). We aimed to study phenological cycles of picophytoplankton and establish a mean baseline to contrast changes in the distribution of Prochlorococcus, Synechococcus and picoeukaryotic phytoplankton. Prochlorococcus presented high abundances in ≥ 9 months in an uninterrupted area between 20ºN-S, whereas Synechococcus and picoeukaryotic phytoplankton showed high abundances in three areas: between 20ºN-S, and around 45ºN and 45ºS. Abundance seasonal change was 7, 15 and 28% around the annual mean, respectively, and the three groups presented two peaks. The seasonality of picophytoplankton was among the lowest compared to other phytoplankton groups and processes in the global ocean. The combined effects of groups' ecological sensitivity captured by the niche models and basins environmental variability provided by the WOA shaped the uneven phenological cycle of picophytoplankton groups. [ABSTRACT FROM AUTHOR]

For the first time in the Mekong delta (Vietnam), the abundance and biomass of the main components of the planktonic microbial food web, and namely: bacteria, picophytoplankton, and heterotrophic and phototrophic flagellates were determined; the features of their spatial distribution and the species diversity of heterotrophic flagellates were studied. In this productive polluted tropical river ecosystem, heterotrophic bacteria were large in size and their biomass reached high values characteristic of hypertrophic waters. They made the main contribution (73.8%, on average) to the formation of the total biomass of the planktonic microbial community. The contribution of picophytoplankton and heterotrophic and phototrophic flagellates was 20.5, 3.9, and 1.9%, respectively. Twenty-nine species and forms of heterotrophic flagellates belonging to eight large taxa and a group of uncertain taxonomic position were identified. [ABSTRACT FROM AUTHOR]

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]

The phytoplankton community structure exhibits seasonal and spatial variations in response to the environmental conditions, which aids in understanding the ecosystem's health. Given this, four samplings were conducted between October 2013 to April 2015, encompassing the monsoon, post-monsoon, and pre-monsoon seasons, from the Haldia port ecosystem of India. The samples were collected from the flowing estuary and an extended semi-enclosed dock. We hypothesized that the seasonal phytoplankton community (diversity, abundance, and carbon biomass) response will differ based on the environmental and hydrographical characteristics of the study site. Picophytoplankton and nano-microphytoplankton dominated the phytoplankton community in terms of numbers and biomass, respectively. Bacillariophytes dominated the nano-microphytoplankton abundance and total biomass, except during the monsoon when Dinophytes contributed (inner-zone). The dominance of Bacillariophytes and Chlorophytes in the outer-zone with picophytoplankton and Dinophytes in the inner-zone indicated group-specific hydrographic preferences that supported the hypothesis. The positive correlation of the picophytoplankton abundance (pre-monsoon) with Secchi disc depth and the negative correlation of diatoms (post-monsoon) with temperature signify the seasonal role of light and temperature, respectively. The highest nano-microphytoplankton species diversity (Shannon–Wiener's index) during the pre-monsoon (inner-zone) with more rare species indicated the probable influence of stable waters with increased water transparency. However, the community was unevenly distributed in the estuary due to the high abundance of the diatom, Aulacoseira granulata. Although harmful algal blooms were not detected, the higher temperature and nutrient concentrations could have favoured potentially harmful species (Pseudonitzschia delicatissima, Dinophysis acuta) during the monsoon. The system ranged from oligo- to mesotrophic state with moderate pollution levels (Carlson's Trophic State Index and Shannon's Index), indicating a reduction of the nutrient accumulation effects by the existing water renewal frequency. This study recommends incorporating qualitative and quantitative phytoplankton assessment in ecological monitoring of the stable coastal sites to prevent future harmful algal episodes. [ABSTRACT FROM AUTHOR]

Marine picophytoplankton (Pico) as a major contributor to primary productivity in oligotrophic waters, play a very important role in marine material cycle and energy conversion, and their key role in the carbon cycle and global climate change is increasingly emphasized. To study the factors affecting the dynamic distribution of Synechococcus, Prochlorococcus, and picoeukaryotes in the East China Sea (ECS), a marginal sea of the Northwest Pacific, we investigated 27 stations in May 2017, and collected 148 samples of Pico and nutrients from the surface to the bottom. By means of flow cytometry, the abundance of Pico was measured, and then we estimated the carbon biomass and analyzed the distribution of Pico. Finally, combined with the ECS unique geographical situation and hydrological regime, we evaluated various factors affecting the Pico in the ECS. In Pico community, the picoeukaryotes cell abundance was between 0.49×102−1.44×104 cells/mL. Prochlorococcus ranged from 1.36×103−3.47×104 cells/mL and Synechococcus ranged from 0.69×103−1.15×105 cells/mL. Synechococcus was the most, both in abundance and in carbon biomass. Picoeukaryotes were the least in abundance, but has larger contribution to carbon biomass than Prochlorococcus. Water temperature, salinity, and stability of water column influenced Pico distribution. Picoeukaryotes were abundant in the shelf sea, whereas Synechococcus and Prochlorococcus were detected in the northeast of Taiwan, China. This study provided basic information for the study of Pico communities in the ECS and its adjacent marine ecosystem. [ABSTRACT FROM AUTHOR]

Picoeukaryotes constitute an important component of the living biomass of oceanic communities and play major roles in biogeochemical cycles. There are very few studies on picoeukaryotes found in the Chukchi Sea. This work shows the relationship between community distribution and composition of picoeukaryotes residing in water masses and physicochemical factors in the southern Chukchi Sea studied in both midsummer (July) and early autumn (September), 2012. Illumina 18S V4 rDNA metabarcoding were used as the main tool. In July, Mamiellophyceae, Dinophyceae, and Trebouxiophyceae were the main microbial classes, with Micromonas, Prasinoderma, Telonema, Amoebophrya, Bathycoccus, Picomonas, and Bolidomonas representing the main genera. In September, Trebouxiophyceae surpassed Dinophyceae and was the second main microbial class, with Micromonas, Prasinoderma, Bathycoccus, Bolidomonas, Telonema, Choricystis, and Diaphanoeca representing the main genera. Water mass was the primary factor determining the community composition and diversity of picoeukaryotes. Abundance of Bathycoccus was found to be highly correlated with Alaskan Coastal Water and that of Prasinoderma, Bolidomonas, and Diaphanoeca with Bering Seawater. Nitrate and phosphate content of water in midsummer and dissolved oxygen (DO) and temperature in early autumn were the main factors that shaped the abundance of the picoeukaryote community. [ABSTRACT FROM AUTHOR]

The long-term trend in satellite retrieved phytoplankton size classes (PSC) such as picophytoplankton (PP), nanophytoplankton (NP), and microphytoplankton (MP) was studied in the three zones falling under different ecological provinces in open ocean regions of the Arabian Sea. A regionally tuned three-component "abundance" model was used to compute PSC biomass from Moderate Resolution Imaging Spectroradiometer onboard Aqua (MODISA) satellite data for the period of 17 years (2003 to 2019). The overall trend indicated the highest concentration of all PSC in the northern Arabian Sea (ARAB province) which gradually decreased to the southern region (MONS province). All PSC biomass showed a peak during the winter monsoon period in ARAB province attributed to the recurring algal bloom. The long-term temporal trend showed relatively lower concentration (most of the times < 0.1 mg m−3) of all PSC biomass in MONS in comparison with ARAB. However, the monthly climatology of total phytoplankton biomass exhibited a similar pattern in all the provinces. The temporal distribution of the PSC biomass discerned rank order of MP > PP > NP in ARAB. In contrast, MONS displayed PSC rank order as PP > NP > MP. A sharp decline in the concentration of MP biomass was observed during the onset of summer monsoon period in comparison with other PSC in MONS. [ABSTRACT FROM AUTHOR]

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 × 109 cell/m3 and 1.49 mg С/m3 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 × 109 cells/m3 and 2.76 mg С/m3 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. [ABSTRACT FROM AUTHOR]

Abundance and biomass of small photosynthetic flagellates (SPF; 3–10 µm), chlorophyll a concentration, and the contribution of SPF to total phytoplankton biomass at different stages of seasonal succession in ice and in surface water were studied in Kandalaksha Bay of the White Sea in September 2016 and February and July 2017. In summer, SPF biomass in the photic layer averaged 38.36 ± 9.77 mg C/m3, 2.22 ± 1.43 mg C/m3 in autumn, 2.6 ± 1.72 mg C/m3 in under-ice water, and 14.79 ± 11.25 mg C/m3 in ice. The contribution of SPF to total phytoplankton biomass depended on the season and ranged from 29 to 95%; the contribution of SPF to sympagic communities averaged 66%. The size structure of photosynthetic flagellates varied by seasons. Flagellates with a cell size of 6–10 µm dominated in summer plankton and in the ice. Flagellates with a cell size of 3–6 µm prevailed in autumn and in the under-ice water. The obtained data of SPF abundance showed higher values of the total phytoplankton biomass of the White Sea in the autumn–winter period compared with the estimates obtained previously. Applying the method of epifluorescence microscopy confirmed the idea that photosynthetic flagellates were the main producers in the winter period as well as in the summer when the biomass of planktonic algae with cell size exceeding 10 µm is low. [ABSTRACT FROM AUTHOR]

The spatial distribution of picophytoplankton abundance, biomass, chlorophyll a and the contribution of picoalgae to the total chlorophyll a was studied in the outer Ob River estuary with the adjacent shelf and in the western part of the Kara Sea. In August–September, the picophytoplankton abundance and biomass varied from 0.1 to 17.3 × 106 cell/L and from 0.06 to 9.20 mg С/m3, respectively. Photosynthetic picoeukaryotes dominated in the plankton picofraction; the contribution of cyanobacteria to the total picophytoplankton biomass did not exceed 11%. The highest contribution of picophytoplankton to the total phytoplankton abundance was observed at a lower (<11 mg/m2) euphotic zone integrated chlorophyll a. The spatial heterogeneity of picoforms contribution was determined by the silicon concentration. [ABSTRACT FROM AUTHOR]

For the first time, the species composition of heterotrophic nanoflagellates, their quantitative characteristics, and abundance and biomass of their main food objects—bacteria and picophytoplankton, were determined in the water column and sediments of the Laptev Sea. In early autumn, an increase in the number and biomass of planktonic flagellates was recorded on a meridional transect from the Lena River delta to the deep-sea zone in the area of the internal shelf impacted by freshwater input from the Lena River. The pattern of the vertical distribution of planktonic flagellates differed in different parts of the sea, but everywhere their largest number was confined to either the surface or near-bottom layers. The quantitative parameters of planktonic flagellates correlated positively with the temperature, bacterial abundance, and biomass, and negatively correlated with water salinity. The abundance and biomass of heterotrophic flagellates in surface sediments was three to four orders of magnitude higher than in the water column and exceeded those of planktonic flagellates at shallow sites under 1 m2. A total of 28 species and forms of heterotrophic flagellates have been identified. Representatives of two taxonomic groups—Kinetoplastea and Stramenopiles, the most tolerant to the salinity—dominated in the community. The species richness of the flagellates decreased with water depth, it was minimum in less saline coastal waters, and it increased in the deep-sea area. [ABSTRACT FROM AUTHOR]

The spatial distribution of picocyanobacteria at the arctic longitude section passing through the shelf of the Kara, Laptev, and East Siberian seas from 58° to 168° E was studied. The average abundance of picocyanobacteria was 0.48 ± 1.2 × 109 cells/m3 in the Kara Sea, 0.16 ± 0.24 × 109 cells/m3 in the Laptev Sea, and 0.25 ± 0.43 × 109 cells/m3 in the East Siberian Sea. The fluctuations of picocyanobacterial abundance were determined by their presence in allochthonous sources: river flow and transformed North Atlantic waters. The highest abundance was observed in the areas of the runoff influence of the Ob, Khatanga, Indigirka, and Kolyma Siberian rivers: 0.5 × 109, 0.2 × 109, 0.4 × 109, and 1.6 × 109 cells/m3, respectively. The average contribution of picocyanobacteria to the total abundance and biomass of picophytoplankton in the western part of the Kara Sea was 37 and 36%, respectively. In other regions, the average contribution of picocyanobacteria to the total abundance and biomass of phototrophic picoplankton did not exceed 7 and 6%, respectively. A highly reliable (p 0.01) positive correlation between the abundance and biomass of picocyanobacteria and the water temperature (p = 0.003) was revealed in the entire dataset obtained. [ABSTRACT FROM AUTHOR]

The naupliar forms are important intermediaries between microbial and classical food web as they can efficiently graze on autotrophic picophytoplankton and heterotrophic bacteria in diverse aquatic ecosystems. Current knowledge on feeding behavior of the naupliar grazing on picophytoplankton is limited and need to be explored. Nauplii (NII and NIII instar) of Amphibalanus amphitrite and Artemia salina were used as candidate grazer organisms in feeding experiments in the presence of picophytoplankton Synechococcus. Substantial grazing was observed from these two instars, and feeding behavior exhibited typical Holling type III functional response. At low prey concentration, the adapted foraging technique during food acquisition by the nauplii of both grazers pointing toward sigmoid type III is best suited than the other functional response types. However, lower carbon ingestion rate of NIII than NII and survival only up to NIV instar indicate that picophytoplankton are unable to meet the energy requirement for advanced instar stages of both the grazers. These inferences suggest that picophytoplankton occupy a key position in naupliar diet and should be taken into consideration when assessing mesozooplankton grazing and food web dynamics. [ABSTRACT FROM AUTHOR]

Okinawa is the southwesternmost part of Japan and represents the northern limit of coral reefs that are influenced by the Kuroshio warm current. We have been studying two coral reefs off Sesoko Island, in northern Okinawa, to evaluate coral reef environments since 2014. In this study, we applied a metagenomic approach to analyze the seasonal composition of picophytoplankton at these two reef sites (Sesoko Minami and Ishikawabaru). The two sites were selected for their differences: Sesoko Minami faces the open ocean and experiences relatively small land effects, while Ishikawabaru experiences relatively high land effects and is surrounded by barrier reefs. Seawater samples were collected from these two sites and filtered through a 1.6 μm pore filter followed by a 0.2 μm membrane filter. DNA was extracted from the 0.2 μm filters, and the V1-V2 region of the 16S rRNA gene (260 bp) was amplified before sequencing using next-generation sequencing techniques. Cyanobacteria or chloroplast sequences were selected for further metabarcording analyses. Interestingly, almost no differences were indicated between the two sites and more than 95% of the picophytoplankton at both sampling sites was composed of only 5 to 7 OTUs. The seasonal composition of picophytoplankton clearly changed; in summer (Jul 2014, May to Jul 2015, and May to Aug 2016) OTU 1 (Synechococcus sp. NC007513) was most abundant. OTU 4 (Prochlorococcus marinus NC009091) also reached its maximum abundance in summer (May to Aug 2016), while OTU 6 (Bathycoccous prasinos FN563099) increased in winter. OTU 8 (Micromonas commoda RCC299 FJ858267) was present at every sampling period and accounted for 5-20% of the total picophytoplankton contig numbers. Our results indicate that seasonal changes clearly influence fluctuations in picophytoplankton community compositions. [ABSTRACT FROM AUTHOR]

The abundance and biomass of bacterioplankton, phototrophic picoplankton, and heterotrophic nanoflagellates has been determined in lakes, rivers, and reservoirs located in the Valley of the Lakes and Great Lakes Depression (Mongolia). The species richness of the heterotrophic flagellates and their consumption of bacteria are estimated. Pico- and nanoplankton are the most abundant in shallow mineral lakes Orog and Tatsyn and in the freshwater Durgun Reservoir. Heterotrophic nanoflagellates consume 26-92% (on average 66%) of the daily bacterioplankton production. Thus, flagellates are important in the transfer of bacterial carbon to the higher levels of planktonic trophic webs. A total of 30 species and their forms of heterotrophic flagellates from 14 large taxa are identified. The highest species diversity of these protists are found in the Durgun and Taishyr reservoirs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Picophytoplankton (Pico) seasonal dynamics and ecology were investigated in three eutrophic coastal lagoons (Calich, Santa Giusta, and Corru S'Ittiri) located in the same geographic region (Sardinia, Mediterranean Sea). Pico dynamics were examined to determine a relationship with variability in environmental conditions characterizing the three sites, and identify which parameters affected observed Pico dynamics. Results showed Pico density reached 10 cells L and biomass values did not exceed 72.8 μg C L. Statistical analyses detected significant differences in hydrographic and nutrient conditions among lagoons, which were also characterized by variable Pico seasonal dynamics and composition. Calich and Santa Giusta were dominated all year around by picocyanobacteria. Maximum picocyanobacteria abundance was observed during summer in both lagoons, associated with the highest temperatures recorded. Picocyanobacteria abundance and nutrient concentrations showed a significant negative and positive correlation in Calich and Santa Giusta, respectively. In contrast, picoeukaryotes dominated Pico assemblages in Corru S'Ittiri, where the highest transparency and salinity and the lowest seasonal variation in salinity were recorded. In Corru S'Ittiri, the maximum Pico abundance was observed in autumn, when lower temperature and the highest nutrient concentrations were observed. Our study provides information on Pico assemblage ecology, which remains scarce in coastal and transitional environments, particularly in Mediterranean climate regimes. [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]

Picophytoplankton are important primary producers in oligotrophic waters and sensitive to environmental changes. However, little is known about their ecophysiology in the northern Bering Sea with complex water masses. The distribution of picophytoplankton with their optical physiological features and physicochemical characteristics as well as water masses were investigated on the northern Bering Sea Shelf during the summer of 2008. Flow cytometry and statistical analysis including Pearson correlation analysis and cluster analysis were the main methods used. Synechococcus and picoeukaryotes were the primary existing picophytoplankton assemblages, with their respective abundances ranging from 0 to 2.69 × 10 and 0.47 × 10 to 13.20 × 10 cells l and peaking at water depths of 10-30 m with surface light levels of 30-50 %. Larger Synechococcus cells contained larger amounts of chlorophyll a (Chl a) and phycoerythrin. Low temperature, high nutrient concentrations and a high N/P value (>7) might limit cell abundance of picoeukaryotes, as shown by their close relationships. With an increase of temperature and oligotrophic freshwater input, smaller picophytoplankton would thrive and the cellular Chl a (Chl a/cell) increase with higher contribution to total Chl a. Seven water types with different physicochemical and biological characteristics were differentiated using the mini-ecosystem (a descriptor of a composite of parameters defining a composite water type community, including temperature, salinity, macronutrients and community abundance of picophytoplankton) as an indicator. They are Alaska Coastal Water, Bering Shelf Surface Water, 20-40 m of Bering Shelf Water, Bering Shelf Cold Water, Anadyr Water, Anadyr-Bering Shelf Water (Bering Sea Water) and Cold Pool. [ABSTRACT FROM AUTHOR]

The species composition and phytoplankton biomass, concentrations of chlorophyll ' a' (Chl) and nutrients in the surface water layer, and accompanying hydrophysical conditions were studied in Onega Bay of the White Sea in June 2015. The temperature and salinity of surface water layer and the water column stability varied greatly in the bay. The nutrients' concentrations exceeded the limiting threshold necessary for the phytoplankton development. The phytoplankton abundance was relatively low, averaged as 13.46 ± 9.00 mg C/m (total phytoplankton biomass), 0.78 ± 0.43 mg/m (concentration of chlorophyll ' a'), and 0.18 ± 0.27 mg C/m (picophytoplankton biomass). The highest phytoplankton biomass has been registered along the frontal zones. Three phytoplankton communities that differed significantly in their structure have been found. [ABSTRACT FROM AUTHOR]

In order to better understand the picophytoplankton (PP) dynamics in tropical monsoon influenced coastal regions, samples were collected daily (June-September 2008: monsoon, December 2008: post-monsoon and April 2009: pre-monsoon) from a fixed station in Dona Paula Bay, India. Eight PP abundance peaks comprising Prochlorococcus-like cells, picoeukaryotes, and three groups of Synechococcus occurred. The chlorophyll biomass and PP abundance were negatively influenced by reduced solar radiation, salinity and water transparency due to precipitation and positively influenced by the stabilized waters during precipitation break/non-monsoon periods. Responses to environmental conditions differed with PP groups, wherein the presence of Synechococcus-PEI (phycoerythrin) throughout the year suggested its ability to tolerate salinity and temperature variations and low light conditions. Synechococcus-PEII appearance toward monsoon end and non-monsoon during high water transparency suggests its tidal advection from offshore waters. Dominance of Synechococcus-PC (phycocyanin) at intermediate salinities under low water transparency during MON and high salinities in PrM coinciding with high nitrate concentrations implies a greater influence of light quality or nutrients. Cyanobacteria and not picoeukaryotes were the dominant picophytoplankton in terms of numbers as well as biomass. This study suggests that PP could be used as tracers of environmental forcing driven by tides and freshwater influx and also highlights the importance of high-frequency samplings in dynamic coastal regions through which transient responses can be captured. [ABSTRACT FROM AUTHOR]

Picophytoplankton are the main primary producers in oligotrophic oceans. They account for more than 90 % of the phototrophic biomass. Investigations of picophytoplankton in the central Arctic Ocean region are rare because these waters used to be completely covered with sea ice. Large, newly exposed water areas, however, appeared in the sea ice zone during the summer of 2010. This provided the first opportunity to study the Arctic picophytoplankton community in these newly open surface waters. This study focuses on the picophytoplankton in the areas near the Alpha-Mendeleev Ridge and Makarov Basin. Here, HPLC pigment analysis with CHEMTAX was used to study community populations, and 454 pyrosequencing with bioinformatics analysis was used to identify the dominant genera (species). Both Pearson correlation analysis and canonical correlation analysis were used to study the relationships between the community and environmental factors. We found chlorophyll a concentrations were low (0.05-0.39 μg l), and picophytoplankton dominated these areas. The abundances of picophytoplankton were 1.58 × 10-9.47 × 10 cells l and made up 44-80 % of the total chlorophyll a. Prasinophytes made up 0-88 % of the picoplanktonic chlorophyll a with the following distributions: diatoms (2-80 %), cyanobacteria (0-20 %), haptophytes (4-14 %), and dinoflagellates (2-11 %). The dominant genera (species) in the picoeukaryotes were Pyramimonas ( Pyramimonas gelidicola), Micromonas ( Micromonas pusilla), and Phaeocystis. Salinity and latitude were the primary factors controlling the community structure of the picophytoplankton. [ABSTRACT FROM AUTHOR]

Synechococcus, the most dominant picophytoplankton in coastal regions, exhibits diurnal variations in the open ocean. The aim of this study was to assess its short-term population dynamics and cell cycle phases through DNA analysis in a coastal region (Sagami Bay, Japan) by sampling at fixed intervals vertically across the euphotic zone. Day-to-day variations in physical processes such as mixing, induced by wind, and advective events played an important role in structuring Synechococcus population. Compared to sub-surface population, surface cells entered S phase earlier in the day and were arrested and accumulated in the S phase for a longer time suggesting an inhibitory effect by higher irradiance. Increase of G-phase cells during the dark suggests progression of cells through S phase in absence of light. Although the length of G-phase was not known, subsequent increase in G-phase cells in the early morning and late evening suggests occurrence of two cohorts of cells which divided in the dark phase or late evening of the cycle. This study showed that the population responds differently across the euphotic zone depending on the physical structure of the water column and its cell cycle phases are controlled by the vertical irradiance availability. [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]

The spatial distribution of heterotrophic ciliates, environmental factors and potential food items (bacteria, Synechococcus spp. and nanoflagellates) were measured in the East China Sea to examine which variables contributed importantly to the long-term distribution of ciliates between 1998 and 2007. In July 1998 and June 2003, heterotrophic ciliates were found to be abundant (1,000-2,000 × 10 cells m) in regions where surface salinity <32 but extremely low (<500 × 10 cells m) in shelf waters of surface salinity >32. After August 2003, shortly after the completion of the Three Gorges Dam, we found no significant areal differences in the abundance of heterotrophic ciliates (HC). However, we found a significantly negative correlation between temperature and HC abundance of surface water after the completion of the dam, suggesting that temperature had a greater influence on HC abundance, once the original saline state had changed. For the long-term trends on the vertical distribution of HC, their abundance was significantly higher in the upper 50 m of the water column than at either 75 or 100 m. Abundance of Synechococcus spp. at these levels varied significantly in regions of surface salinity <32, suggesting that ciliates and picophytoplankton contribute greatly to mediating the transfer of organic matter to higher trophic levels in this marine ecosystem. [ABSTRACT FROM AUTHOR]

ian dust storms (ADSs) are the major source of dust deposition in the Northwest Pacific Ocean. To gain a better understanding on how ADSs affect the ecology of picophytoplankton in this oligotrophic region, five oceanographic cruises were conducted between March 15 and April 15, 2006 on a segment of the Kuroshio Current near the shelf break of the East China Sea (25.05° N, 123.15° E). During the study period, three ADS events were recorded and increases in nutrient concentrations as well as mixing depths were observed. Most of the ADS events stimulated the growth of Synechococcus, but the abundance of Prochlorococcus either remained unaffected or showed mild declines. A more detailed study was conducted during the ADS event between March 16 and 19. Phylogenetic analysis of 16S ribosomal RNA nucleotide sequences revealed that most of the newly appeared Synechococcus belonged to the clade II lineage. Furthermore, messenger RNA (mRNA) levels of three nutrient deficiency indicators, including idiA (an iron deficiency indicator), ntcA (a nitrogen deficiency indicator), and pstS (a phosphorus deficiency indicator), were analyzed by real-time quantitative reverse-transcription polymerase chain reaction. As this ADS event proceeded, mRNA levels of all these indicators decreased from relatively high to non-detectable values. These results suggest that the contributions of iron, nitrogen, and phosphate by the dust deposition from ADSs promote the growth of Synechococcus in the Kuroshio Current. [ABSTRACT FROM AUTHOR]

Information on genetic diversity of picoeukaryotes (<2–3 μm) comes mainly from traditional gene cloning and sequencing, but this method suffers from cloning biases and limited throughput. In this study, we explored the feasibility of using the cloning-independent and massively parallel 454 pyrosequencing technology to study the composition and genetic diversity of picoeukaryotes in the coastal waters of the subtropical western Pacific using the hypervariable V4 region of the 18S rRNA gene. Picoeukaryote assemblages between two sites with different hydrography and trophic status were also compared. The approach gave a high coverage of the community at genetic difference 5% but still underestimated the total diversity at a genetic difference 2%. Diversity of picoeukaryotes was higher in an oligomesotrophic bay than in a eutrophic bay. Stramenopiles, dinoflagellates, ciliates and prasinophytes were the dominant groups comprising approximately 27, 19, 11 and 11%, respectively, of the picoeukaryotes. Water samples collected from the two bays contained different high-level taxonomic groups and phylotype operational taxonomic units of picoeukaryotes. Our study represents one of the first and most comprehensive examinations of marine picoeukaryotic diversity using the 454 sequencing-by-synthesis technology. [ABSTRACT FROM AUTHOR]

Filter fractionated picophytoplankton from Antarctic coastal waters (summer 2001) represented only 7–33% of total phytoplankton, even though total stocks were low (average Chl a = 0.32 μg l−1, range = 0.13–1.03 μg l−1). Though all cells passed a 2 μm filter, electron microscopy revealed most cells were over 2 μm, principally Parmales, Phaeocystis sp., and small diatoms. CHEMTAX analysis of HPLC pigment data suggested type 8 haptophytes (e.g. Phaeocystis sp. plus Parmales and pelagophytes) contributed 7–58% of picoplanktonic chlorophyll a, type 6 haptophytes (e.g. coccolithophorids) 18–59%, diatoms 0–18% (mostly type 2 diatoms, e.g. Pseudonitzschia sp., 0–15%), prasinophytes 0–17%, with cell fragments of cryptophytes 0–40%, and dinoflagellates 0–11%. Only stocks of type 8 haptophytes and prasinophytes differed significantly due to successional changes. Zeaxanthin concentrations exceeded estimates from previous cyanobacterial counts and may derive from non-photosynthetic bacteria. [ABSTRACT FROM AUTHOR]

Seasonal change in the abundance of autotrophic picoplankton (APP) was investigated once or twice a week in relation to some environmental variables in a hypereutrophic pond, from July 1999 to June 2000. Cell density of APP ranged between 0.3×105 and 10.1×105 cells ml−1, overlapping the lower range of APP abundances given in the literature for hypereutrophic systems. The pattern of seasonal change in concentration of dissolved inorganic phosphorus (0.3–20.3 μ mol P l−1) was similar to that of cell density of APP, suggesting that phosphorus limitation on APP abundance. By contrast, nitrogen limitation seemed unlikely since the pattern of seasonal change in concentration of dissolved inorganic nitrogen was different from that of APP cell density. We could not find any coupled oscillations between APP abundance and heterotrophic nanoflagellates, or between that of APP and ciliates. The dominant ciliate taxa, based on their cell densities, were Cinetochilum margaritaceum, Cyclidium glaucoma, Halteria grandinella, Strobilidium sp. and Urotricha spp. The relative contribution of the < 2 μm fraction to total chlorophyll concentration was seasonally high (up to 16.2%), indicating seasonal importance of APP abundance as food for heterotrophs. [ABSTRACT FROM AUTHOR]

The ability of photoautotrophic picoplankton Synechococcus to degrade urea was examined in the euphotic zone of Lake Biwa. Samples were divided into pico (0.2–2.0 μm) and larger (>2.0 μm) size fractions by filtration. The rates of urea degradation (the sum of the rates of incorporation of carbon into phytoplankton cells and of liberation of CO2 into water) measured by radiocarbon urea were 8 and 17 μmol urea m−3 day−1 in June and July, respectively, for the picophytoplankton in the surface water, and 196 and 96 μmol urea m−3 day−1, respectively for the larger phytoplankton. The rates decreased with depth, somewhat similar to the vertical profiles of the photosynthetic rate. The urea degradation rates were obviously high under light conditions. In daylight, urea was degraded into two phases, carbon incorporation and CO2 liberation, whereas in the dark it was degraded only into the CO2 liberation phase. The contribution of picophytoplankton to total phytoplankton in urea degradation was high in the subsurface to lower euphotic layer. Urea degradation activity was higher in the picophytoplankton fraction than in the larger phytoplankton fraction. Shorter residence times of urea were obtained in the upper euphotic zone. The contribution of picophytoplankton to urea cycling was 4% to 35%. The present results suggest that the picophytoplankton Synechococcus is able to degrade urea and effectively makes use of regenerated urea as a nitrogen source in the euphotic layer, and that picophytoplankton play an important role in the biogeochemical nitrogen cycle in Lake Biwa. [ABSTRACT FROM AUTHOR]

A sensitive and specific technique is described for the estimation of phycobiliprotein in freshwater and marine picophytoplankton. The method uses fluorescent properties to detect phycoerythrin concentrations as low as 40 ng L-1 from a 1 L water sample and is capable of distinguishing between R-phycoerythrin, C-phycocyanin and C-phycoerythrin. The application of the method to the study of natural picophytoplankton populations in marine and freshwater environments is described. Nitrate concentrations appear to influence picophytoplankton cellular C-phycoerythrin concentrations in surface waters and increasing cellular C-phycoerythrin fluorescence with water depth suggests that this pigment plays a role as a photosynthetic accessory pigment. [ABSTRACT FROM AUTHOR]