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Primary productivity mostly relies on marine cyanobacteria in the oligotrophic north-eastern Mediterranean (NEM). However, wide shelf basin is fed by nutrient-rich rivers (namely Goksu, Lamas, Seyhan, Ceyhan, Asi) leading to apparent increase in algal production at coastal regions. In the present study, variation of picophytoplankton (pico-eukaryotes, Synechococcus and Prochlorococcus) abundance of at different trophic levels of NEM were investigated. Sample collection was carried out at 50 different stations including Mersin Bay, Goksu River discharge area and oligotrophic offshore waters during October 2017, February, April and July 2018. Minimum and maximum abundance of pico-eukaryotes, Synechococcus and Prochlorococcus were found as 1-1x104, 10³ - 3.3x104 and 8x10¹ -7.3x104 cell/ml, respectively. Eukaryotic picoplankton are observed mainly in Goksu River discharge area and could not compete with marine cyanobacteria in offshore waters. Annual average ofpico-eukaryotes abundance was decreased by 1.4 folds from inshore to offshore; while, annual average of Synechococcus abundance was increased by 1.2 folds. Prochlorococcus abundance did not vary from inshore to offshore but decreased by 4 folds from river discharge area to offshore area. Synechococcus and Prochlorococcus have displayed similar abundance profiles with peak levels near the Deep Chlorophyll Maximum (DCM) in October and July. Results showed that Synechococcus was the most abundant regardless of location or season. Even though Synechococcus abundance was found to be higher than Prochlorococcus abundance, a significant increase in the contribution of Prochlorococcus to the total picophytoplankton was observed in July. [ABSTRACT FROM AUTHOR]

We investigated at the single cell level during 16 months (June 2012 to September 2013) the temporal distribution of picophytoplankton (picoeukaryotes, Synechococcus and Prochlorococcus ) communities in two contrasted ecosystems: the Bay of Bizerte characterised by an oligotrophic regime typical of the Mediterranean Sea and the Bizerte Lagoon that exhibits a mesotrophic/eutrophic state. We aimed at depicting seasonal variations and quantifying the relationships between the environmental factors and the structure and abundance of picophytoplankton communities. Results showed that picophytoplankton groups were able to grow under a wide range of environmental conditions varying seasonally, although their abundances and contributions to the total chlorophyll biomass significantly varied and showed importance in the Bay of Bizerte. Synechococcus was the most abundant group reaching 225 ∗ 10 3 cells·cm − 3 in the Bay and 278 ∗ 10 3 cells·cm − 3 in the lagoon. This group was present all over the year in both ecosystems. Structural equation model results pointed out a different configuration regarding the picophytoplankton environmental drivers. The complexity of the configuration, i.e. number of significant links within the system, decreased under enhanced eutrophication conditions. The less exposure to anthropogenic stress, i.e. in the Bay of Bizerte, highlight a larger role of nutrient and hydrological conditions on the seasonal variations of picophytoplankton, whereas a negative effect of eutrophication on picophytoplankton communities was unveiled in the Bizerte Lagoon. We stress that such influence may be exacerbated under expected scenarios of Mediterranean warming conditions and nutrient release in coastal ecosystems. [ABSTRACT FROM AUTHOR]

A comprehensive analysis on the phytoplankton ecology with special reference to different phytoplankton size classes was carried out at green Noctiluca scintillans (hereafter Noctiluca ) bloom and non-bloom locations in offshore waters of the northern Arabian Sea. At the bloom locations, green Noctiluca represented a dense mono-specific proliferation with average cell density of 10.16 ± 5.806 × 10 4  cells-L −1 and relative abundance share of 98.63%. Active photosynthesis through prasinophytic endosymbiont was depicted from net community production magnitude reaching 85.26 mgC/m 3 /Day under low prey abundance. Parallel swarming of Porpita porpita , a voracious copepod feeder signified the competitive advantage of Noctiluca to have the phytoplankton prey. Average concentration of picophytoplankton biomass was eleven times lower in surface waters of non-bloom stations in comparison to bloom. Higher N:P ratio in subsurface waters of non-bloom stations signified non-utilization of nitrogenous nutrients. Green Noctiluca bloom onset subsequent to diatom rich conditions was evident from spatio-temporal ocean colour satellite imageries. [ABSTRACT FROM AUTHOR]

Mesoscale eddies have been reported to have a substantial impact on the distribution of phytoplankton through the regulation of environmental variables in the open ocean. However, the influence of warm eddies on phytoplankton in continental slopes remains largely unknown. To reveal the impact of mesoscale eddies within slope regions, we conducted a field investigation of picophytoplankton on the northern slope of the South China Sea during an anticyclonic warm eddy propagation. We observed different picophytoplankton distribution patterns. Synechococcus dominated the picophytoplankton community in the Kuroshio-affected eddy core rather than the previously reported Prochlorococcus , and Prochlorococcus dominated outside the eddy in the shelf. In addition, through further vertical study of typical layers, we found that the influence of warm eddy varied in different layers. Analysis of the mechanisms indicated that the distributions were attributed to warm eddy-induced nutrients and light variations and the physical processes in it. [Display omitted] • Analysis of warm eddy impacts on picophytoplankton in South China Sea slope area • Different distribution pattern of picophytoplankton was observed. • The warm eddy changed the distribution of nutrients and light intensity. • The warm eddy affected the composition of water masses. • The distribution of picophytoplankton was influenced by physical-chemical variations. [ABSTRACT FROM AUTHOR]

Mesoscale eddies have been reported to have a substantial impact on the distribution of phytoplankton through the regulation of environmental variables in the open ocean. However, the influence of warm eddies on phytoplankton in continental slopes remains largely unknown. To reveal the impact of mesoscale eddies within slope regions, we conducted a field investigation of picophytoplankton on the northern slope of the South China Sea during an anticyclonic warm eddy propagation. We observed different picophytoplankton distribution patterns. Synechococcus dominated the picophytoplankton community in the Kuroshio-affected eddy core rather than the previously reported Prochlorococcus , and Prochlorococcus dominated outside the eddy in the shelf. In addition, through further vertical study of typical layers, we found that the influence of warm eddy varied in different layers. Analysis of the mechanisms indicated that the distributions were attributed to warm eddy-induced nutrients and light variations and the physical processes in it. [Display omitted] • Analysis of warm eddy impacts on picophytoplankton in South China Sea slope area • Different distribution pattern of picophytoplankton was observed. • The warm eddy changed the distribution of nutrients and light intensity. • The warm eddy affected the composition of water masses. • The distribution of picophytoplankton was influenced by physical-chemical variations. [ABSTRACT FROM AUTHOR]

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Abstract: Photosynthesis and nutrient status measurements were compared in size fractioned water samples collected in southern Lake Malawi in three different seasons. The size fractions analyzed were 0–2.0μm, 0–20μm, and 0–200μm. Total chlorophyll concentrations were relatively invariant at about 1μgL−1 in all seasons (wet stratified, deep mixing, dry stratified). Over 90% of total chlorophyll was < 20μm and 40–50% < 2μm. Stoichiometric ratios of carbon (C):nitrogen (N) and C:phosphorus (P) for the < 2-μm seston were similar to < 20-μm and < 200-μm seston samples and indicated that all size fractions were moderately N and P deficient in all seasons. N and P uptake experiments demonstrated that when the < 2-μm picoplankton were isolated from the larger sizes, they showed high N and P nutrient debts, apparently in response to the removal of nano- and micrograzers. This effect was strongest for N debt in the dry stratified season, but was apparent for P debt in all seasons. The chlorophyll-normalized light saturated rate of photosynthesis, Pb, was always higher in whole water samples compared to the rates of the isolated picophytoplankton which were lowest in the dry season. We infer that nano- and micrograzers were an especially important source of regenerated nutrients when the lake was stratified although their removal as a source of nutrient to the picophytoplankton may affect Pm in all seasons. Nitrogen regeneration was especially critical to the picophytoplankton in the dry stratified season but less important in the windy deep mixing season. [Copyright &y& Elsevier]b m in all seasons. Nitrogen regeneration was especially critical to the picophytoplankton in the dry stratified season but less important in the windy deep mixing season. [Copyright &y& Elsevier]

cophytoplankton (0.2-2.0 μm in size) is the smallest group of autotrophic plankton, being abundant and widespread in the world ocean and playing an important role in the organic matter cycling in ocean. By the method of epifluorescence microscopy (EFM), the abundance and its spatial and diurnal variations of the picophytoplanktons in Qingdao offshore and its adjacent waters in winter were investigated. The results showed that in the study area in winter, phycoerythrin-rich (PE) Synechococcus cells were dominant, followed by Picoeukaryote (Euk) cells, while the abundance of phycocyanin-rich (PC) Synechococcus cells was low and no Prochlorococcus (Pro) cells were observed. The abundance of Synechococcus (Syn) and Euk varied from 8.97x10³ to 1.95x105 cells·ml-1(averaged 4.67x104 cells·ml-1) and from 1.95x10² to 1.01x104 cells·ml-1(averaged 2.39x10³ cells·ml-1), respectively. There was a high-value of Syn abundance in Jiaonan offshore and a low-value in Jimo and southeast Laoshan off-shores, while a high-value of Euk abundance in Rizhao offshore and a low-value in Laoshan offshore. No significant difference was observed in the vertical distribution of Syn and Euk abundance among four water layers (P>0.05) at a continuous station located in the center of Jiaozhou Bay, the abundance had an obvious diurnal fluctuation. Pearson correlation analysis indicated that Syn was positively correlated with water temperature and electrical conductivity (P<0.01) but negatively correlated with dissolved oxygen concentration (P<0.01), and Euk was negatively correlated with water salinity and dissolved oxygen concentration. In the study area in winter, picophytoplankton contributed about 20% to the total phytoplanktonic biomass. [ABSTRACT FROM AUTHOR]

Understanding picophytoplankton variations that play important roles in the material circulation and energy flow are critical to assessing overall status of waterbody, especially for clean reservoirs which remain a relatively stable community structure and high species diversity due to lower nitrogen and phosphorus nutrients. However, their response to key environmental factors and tightly acting microbial remains poorly understood. Traditional quantification methods are limited, such as chlorophyll-a, turbidity and microscope. There are still many defects with present molecular analysis. In this study, a flow cytometric analysis and high-throughput sequencing combination methodology was developed and tested on clean water from a reservoir, by a monthly dynamic for a vegetative period April-September in 2019 to improve the accuracy of dynamic monitoring for the picophytoplankton system. More species of Pico-Cyanobacteria and Pico-Eukaryotes were discovered. The increased percentage of pigment compounds from 8.2% to 76.3% proves the effective reduce of heterotrophic disturbing and enrichment of target populations. Picophytoplankton that was previously neglected due to their low relative abundance has once again entered the scope of our eyes. Phytoplankton were divided into three categories. The first one was the highly abundant and frequently present taxa, the second one was the low-abundance but highly-transient population, and the third one was the low abundance and stable group. Synechococcus, Emiliania, Tetraselmis and Thalassiosira were dominant picophytoplankton and displayed obvious temporal and spatial distribution characteristics. Pico-PE rich Cyanobacteria and Nano-Eukaryotes with high transience abnormally increased in summer. Temperature, ammonia-N, nitrate-N, turbidity and total nitrogen were most influencing factors, while some picophytoplankton with special physiological structure showed distinct competitive advantages in the microbial community. As for the off-flavor compounds, the concentration of 2-methylisoborneol and geosmin were high even 66.7% and 20.8% of the samples exceeded their olfactory threshold. Chrysochromuina , Planktothrix and Microcystis might be the potential producers. [Display omitted] • Combination methodology of flow cytometry and high-throughput sequencing can improve detection accuracy for picophytoplankton. • Picophytoplankton with special structure showed distinct competitive advantages and made contribution to community stability. • Chrysochromuina , Planktothrix and Microcystis might be the potential producers of off-flavor compounds. [ABSTRACT FROM AUTHOR]