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Picophytoplankton are a ubiquitous component of marine plankton communities and are expected to be favored by global increases in seawater temperature and stratification associated with climate change. Eukaryotic and prokaryotic picophytoplankton have distinct ecology, and global models predict that the two groups will respond differently to future climate scenarios. At a nearshore observatory on the Northeast US Shelf, however, decades of year-round monitoring have shown these two groups to be highly synchronized in their responses to environmental variability. To reconcile the differences between regional and global predictions for picophytoplankton dynamics, we here investigate the picophytoplankton community across the continental shelf gradient from the nearshore observatory to the continental slope. We analyze flow cytometry data from 22 research cruises, comparing the response of picoeukaryote and Synechococcus communities to environmental variability across time and space. We find that the mechanisms controlling picophytoplankton abundance differ across taxa, season, and distance from shore. Like the prokaryote, Synechococcus, picoeukaryote division rates are limited nearshore by low temperatures in winter and spring, and higher temperatures offshore lead to an earlier spring bloom. Unlike Synechococcus, picoeukaryote concentration in summer decreases dramatically in offshore surface waters and exhibits deeper subsurface maxima. The offshore picoeukaryote community appears to be nutrient limited in the summer and subject to much greater loss rates than Synechococcus. This work both produces and demonstrates the necessity of taxon- and site-specific knowledge for accurately predicting the responses of picophytoplankton to ongoing environmental change., (© 2024 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Based on the field surveys aimed at understanding the variations of Synechococcus (Syn) abundance in the Pearl River Estuary during different seasons. We found that heavy terrestrial precipitation result in significant riverine runoffs and promote Syn growth, extension and blooms during warm and wet seasons. To understand the ecological role of Syn play in this estuary during wet seasons, we combined flow cytometry and high throughput sequencing (HTS) of 16S rDNA to investigate the phytoplankton distribution patterns and the potential shaping mechanisms during a typical wet season. During the cruise, picophytoplankton, especially Syn, and Nano-eukaryotes contributed importantly to the total phytoplankton biomass of the estuary. Syn can be further divided into phycoerythrin (PE)-rich Syn and phycocyanin (PC)-rich Syn, with PC-rich Syn about 1.5 times higher than PE-rich Syn in abundance. Both PE-rich Syn (60.75 × 10 3  cells ml -1 ) and PC-rich Syn (604.05 × 10 3  cells ml -1 ) reach the highest abundance at the lower part of the estuary. Moreover, PE-rich Syn can be divided into two subgroups which showed different salinity preference, with PE1 distributed in the high salinity area (with salinity >25) while PE2 in the middle salinity area (with salinity 7-20). Our results from the 16S rDNA sequencing also indicated abundant diversity and different niche adaptation of Syn with the operational taxonomic units (OTUs) along the estuary. Besides, analysis also indicated a tight correlation between estuarine Syn and active heterotrophic bacteria, especially groups of Rhodobacteria and Actionobacteria., (Copyright © 2019. Published by Elsevier B.V.)

We investigated at the single cell level during 16months (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., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Phytoplankton photosynthesis is often inhibited by ultraviolet (UV) and intense photosynthetically available radiation (PAR), but the effects on ocean productivity have received little consideration aside from polar areas subject to periodic enhanced UV-B due to depletion of stratospheric ozone. A more comprehensive assessment is important for understanding the contribution of phytoplankton production to the global carbon budget, present and future. Here, we consider responses in the temperate and tropical mid-ocean regions typically dominated by picophytoplankton including the prokaryotic lineages, Prochlorococcus and Synechococcus. Spectral models of photosynthetic response for each lineage were constructed using model strains cultured at different growth irradiances and temperatures. In the model, inhibition becomes more severe once exposure exceeds a threshold (E max ) related to repair capacity. Model parameters are presented for Prochlorococcus adding to those previously presented for Synechococcus. The models were applied to estimate midday, water column photosynthesis based on an atmospheric model of spectral radiation, satellite-derived spectral water transparency and temperature. Based on a global survey of inhibitory exposure severity, a full-latitude section of the mid-Pacific and near-equatorial region of the east Pacific were identified as representative regions for prediction of responses over the entire water column. Comparing predictions integrated over the water column including versus excluding inhibition, production was 7-28% lower due to inhibition depending on strain and site conditions. Inhibition was consistently greater for Prochlorococcus compared to two strains of Synechococcus. Considering only the surface mixed layer, production was inhibited 7-73%. On average, including inhibition lowered estimates of midday productivity around 20% for the modeled region of the Pacific with UV accounting for two-thirds of the reduction. In contrast, most other productivity models either ignore inhibition or only include PAR inhibition. Incorporation of E max model responses into an existing spectral model of depth-integrated, daily production will enable efficient global predictions of picophytoplankton productivity including inhibition., (© 2016 John Wiley & Sons Ltd.)

Temporal and spatial variations in Synechococcus abundance were investigated over an annual cycle (February'10-January'11) along a salinity gradient (0-35) in the tropical Zuari estuary, influenced by south-west monsoons. Synechococcus exhibited salinity preferences with phycoerythrin-rich cells at salinities >2 (Synechococcus-PEI), >20 (Synechococcus-PEII) and <1 (Synechococcus-PEIII) whereas phycocyanin-rich (Synechococcus-PC) dominant at lower salinities. Downstream stratification during monsoon caused Synechococcus group segregation in the surface and near-bottom waters. During monsoon-break and non-monsoon period stabilized waters, increased salinity, temperature, solar radiation and low rainfall favored high Synechococcus abundance whereas unstable waters, increased turbidity and low solar radiation during active monsoon lowered abundance. SYN-PC positively co-related with nitrate and phosphate and SYN-PEI with phosphate. Synechococcus contribution to phytoplankton carbon biomass ranged from 9 to 29%. In monsoonal estuaries, rainfall intensity regulates freshwater runoff which modulates the estuarine environment, creating temporal-spatial niche segregation of Synechococcus groups thereby serving as indicator organisms of the estuarine hydrodynamics., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The marine phytoplankton community responds to latitudinal, longitudinal (coast to ocean), and vertical environmental gradients, an important subject in Oxygen minimum zones (OMZ). The phytoplankton structure and the effect of environmental gradients along the central Mexican Pacific, an area within an OMZ, were studied, especially the importance of size fractions and taxonomic groups. A combination of various methods and protocols, such as microscopic analysis, flow cytometer, and pigment analysis, were followed in this study. Oceanographic conditions included thermal gradients along the study area and unreported evidence of a weak upwelling in the southern zone (Acapulco). Vertical distribution of chlorophyll a showed subsurface maxima (SCM, 15-45 m depth) in all stations, and deeper chlorophyll-a maxima (DCM, 85-95 m depth) in more oceanic stations. Chain-forming diatoms dominated in the northern zone stations. Prochlorococcus, Synechococcus, and picoeukaryotes abundances ranged between 0.01 to 21.7 cells×104 mL-1, although most samples showed the highest contribution to biomass (47.95 µg C L-1) by picoeukaryotes. Expected tendencies of Prochlorococcus distribution were observed: highest densities coincided with the DCM and divinyl chlorophyll-a distribution at oceanic stations. Fucoxanthin had the highest concentrations, whereas fucoxanthin and zeaxanthin concentrations were higher at SCM depths. We documented the co-dominance of the pico- and microplankton: picoplankton was important at the DCM, related to oligotrophic and more stratified water column, whereas microplankton prevailed in coastal stations, with mixed water column, high nutrient concentrations, and diatoms as the dominant group. Picoeukaryotes abundances were related to the concentration of prasinoxanthin, which suggests an important mamiellophyte component not previously revealed. [ABSTRACT FROM AUTHOR]

Marine picophytoplankton plays a major role in marine cycling and energy conversion, and its effects on the carbon cycle and global climate change have been well documented. In this study, we investigated the response of picophytoplankton across a broad range of physicochemical conditions in two distinct regions of the tropical western Pacific. Our analysis considered the abundance, carbon biomass, size fraction, distribution, and regulatory factors of the picophytoplankton community, which included the cyanobacteria Prochlorococcus and Synechococcus, and small eukaryotic phytoplankton (picoeukaryotes). The first region was a latitudinal transect along the equator (142–163° E, 0° N), characterized by stratified oligotrophic conditions. The second region was a meridional transect (143° E, 0–22° N) known for its high‐nutrient and low‐chlorophyll (HNLC) conditions. Results showed that picophytoplankton contributed >80% of the chlorophyll a (Chl a), and was mainly distributed above 100 m. Prochlorococcus was the dominant organism in terms of cell abundance and estimated carbon biomass in both latitudinal and meridional transects, followed by Synechococcus and picoeukaryotes. In the warm pool, Prochlorococcus was primarily distributed below the isothermal layer, with the maximum subsurface abundance forming below it. The maximum Synechococcus abundance was restricted to the west‐warm pool, due to the high temperature, and the second‐highest Synechococcus abundance was associated with frontal interaction between the east‐warm pool and the westward advance of Middle East Pacific water. In contrast, picoeukaryotes formed a maximum subsurface abundance corresponding to the subsurface Chl a maximum. In the mixed HNLC waters, the cell abundance and biomass of the three picophytoplankton groups were slightly lower than those in the warm pool. Due to a cyclonic eddy, the contours of the maximum subsurface Prochlorococcus abundance were uplifted, evidently with a lower value than the surrounding water. Synechococcus abundance varied greatly in patches, forming a weakly high subsurface peak when the isothermal layer rose to the near‐surface (<50 m). The subsurface maximum picoeukaryote abundance was also highly consistent with that of the subsurface Chl a maximum. Correlation analysis and generalized additive models of environmental factors showed that nutrient availability had a two‐faceted role in regulating the spatial patterns of picophytoplankton in diverse latitudinal and meridional environments. We concluded through regression that temperature and light irradiance were the key determinants of picophytoplankton variability in the tropical western Pacific. This study provides insights into the changing picophytoplankton community structure with potential future changing hydroclimatic force. [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]

The picophytoplankton Synechococcus is a globally abundant autotroph that contributes significantly to primary production in the oceans and coastal areas. These cyanobacteria constitute a diverse genus of organisms that have developed independent niche spaces throughout aquatic environments. Here, we use the 16S V3–V4 rRNA gene region and flow cytometry to explore the diversity of Synechococcus within the picophytoplankton community in the Gullmar Fjord, on the west coast of Sweden. We conducted a station-based 1-year time series and two transect studies of the fjord. Our analysis revealed that within the large number of Synechococcus amplicon sequence variants (ASVs; 239 in total), prevalent ASVs phylogenetically clustered with clade representatives in both marine subcluster 5.1 and 5.2. The near-surface composition of ASVs shifted from spring to summer, when a 5.1 subcluster dominated community developed along with elevated Synechococcus abundances up to 9.3 × 104 cells ml–1. This seasonal dominance by subcluster 5.1 was observed over the length of the fjord (25 km), where shifts in community composition were associated with increasing depth. Unexpectedly, the community shift was not associated with changes in salinity. Synechococcus abundance dynamics also differed from that of the photosynthetic picoeukaryote community. These results highlight how seasonal variations in environmental conditions influence the dynamics of Synechococcus clades in a high latitude threshold fjord. [ABSTRACT FROM AUTHOR]

Picophytoplankton (pico) in the eastern Indian Ocean (EIO) were investigated during the inter-monsoon periods. They were found to typically comprise Prochlorococcus (Pro), Synechococcus (Syn), and Picoeukaryotes (PEuks). In the survey area, the pico showed two different vertical distribution patterns in different regions, whereby the Syn abundance decreased with depth, whereas those of Pro and PEuks increased and then decreased with depth, with the maximum depths ranging from 50 to 100 m. The cell abundance and community structure of the pico were similar at the equator (EQ) and the eastern boundary of the Indian Ocean near Sumatra (EB), but the pico cell abundance was significantly lower in the Bay of Bengal (BOB). Pro dominated most regions of the entire EIO and were approximately one-to-two orders of magnitude more abundant than Syn and PEuks. The distributions of Syn and PEuks showed little difference across various regions. Influenced by the physicochemistry of circulation and water masses, there were many different environmental factors in the different regions. The abundance of pico domination by Pro showed a strong positive correlation with the nutrients and salinity in the survey area, indicating increasing nutrient availability, particularly in the oligotrophic EIO. Generalized additive models (GAMs) analysis showed the differences in their responses to environmental variability. Pro and PEuks both increased strongly with warming up to below 26 °C, and Pro and PEuks were more responsive to chemical (nutrient) variability. Syn showed a broader tolerance of low-salinity conditions. In a certain range, an increase in nitrite and nitric acid can improve the cell abundance of Pro. As a significant contributor to primary productivity in oligotrophic waters, this study provides essential information for studying pico communities in the EIO and its adjacent marine ecosystems. [ABSTRACT FROM AUTHOR]

The picophytoplankton Synechococcus is a globally abundant autotroph that contributes significantly to primary production in the oceans and coastal areas. These cyanobacteria constitute a diverse genus of organisms that have developed independent niche spaces throughout aquatic environments. Here, we use the 16S V3–V4 rRNA gene region and flow cytometry to explore the diversity of Synechococcus within the picophytoplankton community in the Gullmar Fjord, on the west coast of Sweden. We conducted a station-based 1-year time series and two transect studies of the fjord. Our analysis revealed that within the large number of Synechococcus amplicon sequence variants (ASVs; 239 in total), prevalent ASVs phylogenetically clustered with clade representatives in both marine subcluster 5.1 and 5.2. The near-surface composition of ASVs shifted from spring to summer, when a 5.1 subcluster dominated community developed along with elevated Synechococcus abundances up to 9.3 × 104 cells ml–1. This seasonal dominance by subcluster 5.1 was observed over the length of the fjord (25 km), where shifts in community composition were associated with increasing depth. Unexpectedly, the community shift was not associated with changes in salinity. Synechococcus abundance dynamics also differed from that of the photosynthetic picoeukaryote community. These results highlight how seasonal variations in environmental conditions influence the dynamics of Synechococcus clades in a high latitude threshold fjord.

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]

The distribution of picocyanobacteria from two genera, Synechococcus and Prochlorococcus, and picoeukaryotes in surface water (0.5 m) was investigated by flow cytometry in the southeastern coast of Peninsular Malaysia during the Southwest monsoon in August 2014. During the cruise, Synechococcus cells were predominant throughout the study area, contributing as much as 50% to the total picophytoplankton population, whereas picoeukaryotes and Prochlorococcus constituted only 31% and 19% of the population, respectively. Spatially, Synechococcus and picoeukaryotes were more dominant in coastal waters, while Prochlorococcus appeared to be more highly abundant in offshore waters. Furthermore, the percentage contribution of each population to total picophytoplankton also exhibited different spatial distribution patterns along a coastal-offshore gradient. The percentage contribution of Synechococcus was spatially constant throughout the study area, while the fraction contributed by picoeukaryotes showed a reduced contribution from coastal to offshore waters. In contrast, Prochlorococcus exhibited an increased proportion to total picophytoplankton across a coastal-offshore gradient, suggesting the increasing importance of this population in offshore waters of the study area. As revealed by Canonical Correlation Analysis, the abundance of Synechococcus and picoeukaryotes increased significantly with reducing dissolved oxygen levels and pH, and with increasing total chlorophyll. In contrast, temperature was the only factor influencing the abundance of Prochlorococcus significantly increased with decreasing water temperature in the study area. Overall, results of the present study provide valuable information on the role of regional environmental factors in the distribution and dominance of picophytoplankton communities that are not only critical for the ocean productivity but also the impact on the carbon cycle in the study area. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine phytoplankton community structure in February 2018 at Laguna Ojo de Liebre, a relevant site for biodiversity at El Vizcaino Biosphere Reserve. The parameters: diversity and abundance indices of the main phytoplankton groups were used to relate them to the oceanographic variables temperature and salinity. Phytoplankton was quantified in three size groups: microphytoplankton (diatoms, dinoflagellates), nanophytoplankton (Chromophytes, Cryptophytes), and picophytoplankton (Cyanobacteria, Prochlorophytes) using optical microscopy and chemotaxonomy (HPLC) analyses. This last method indicated fucoxanthin (pigment characteristic of diatoms) was the most abundant and predominant photosynthetic carotenoid in the whole lagoon. Temperature showed an inverse relationship with microphytoplankton and a direct relationship with nanophytoplankton and picophytoplankton; saline gradient showed a direct association with the distribution of total chlorophyll. [ABSTRACT FROM AUTHOR]

Pico-sized Synechococcus, Prochlorococcus, and eukaryotes are the dominant photosynthetic organisms in the vast warm and oligotrophic regions of the ocean. In this paper, we aim to characterize the realized niches of the picophytoplanktonic community inhabiting the Red Sea, the warmest oligotrophic sea, which is considered to be a model for the future ocean. We quantify population abundances and environmental variables over several oceanographic surveys, and use stepwise regression, principal-component analysis (PCA), and compositional-data analysis to identify the realized niches of the three picophytoplanktonic groups. Water temperature varied from 21.4 to 32.4°C within the upper 200-m water column, with the warmest waters being found in the South, where nutrients increased. Synechococcus dominated the biomass, contributing 47.6% to the total picophytoplankton biomass, followed by picoeukaryotes (26.4%) and Prochlorococcus (25.9%), whose proportions contrast significantly with those reported in the subtropical ocean, where Prochlorococcus prevails. There were positive and significant relationships between temperature and the three populations, although these were weak for Prochlorococcus (R2 = 0.08) and stronger and steeper for Synechococcus (R2 = 0.57). The three populations centered their maximum abundances (Lorentzian fits) at similar low nutrient values. Synechococcus were centered close to the surface at ≈77% of surface photosynthetically active radiation (PAR) and ≈30.6°C. The picoeukaryotes were centered at lower light (≈6.4% surface PAR) and warm waters (≈30°C). Prochlorococcus was segregated from the surface waters and centered deep at low light (≈3.2% surface PAR). Light and temperature were the most influential factors determining the community composition, with Synechococcus dominating ∼74% of the picophytoplankton biovolume in the warmest (>30°C) waters. In the warm and mesotrophic southern Red Sea, the moderate abundances of picoeukaryotes and Synechococcus suggest increasing competition with nano and microphytoplankton. Our observations agree with predictions of increasing vertical segregation of picophytoplankton communities with future warming and reveal Synechococcus’s significant capacity to adapt to warming.

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]

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]

The deepening of mixed layer and ensuing changes in optical and physicochemical properties of euphotic zone can influence phytoplankton community dynamics in the northeastern Arabian Sea during winter monsoon. The response of picophytoplankton community to such changes during winter convective mixing is not well understood. Herein, we have compared variations in the picophytoplankton community structure during early (November–December 2012), peak (end-January 2014) and late (mid-February 2015) winter monsoon from three separate cruises in the southern northeastern Arabian Sea. The higher Synechococcus abundance owing to entrainment of nutrients in mixed layer was observed during peak winter monsoon, while the concomitant changes in nitrate concentration, light and oxygen environment restricted Prochlorococcus growth resulting in lower abundance during the same period. This highlights the diverse responses of picophytoplankton groups to physicochemical changes of water column during winter convective mixing. The divinyl chlorophyll b / a ratio (marker for Prochlorococcus ecotypes) indicated prevalence of one low-light adapted ecotype (sensitive to light shock) in sub-surface water, one high-light adapted ecotype in surface water during early winter monsoon and both disappeared during intense mixing period in peak winter monsoon. Subsequently, a distinct low-light adapted ecotype, capable to tolerate light shock, was noticed during late winter monsoon and we argue that this ecotype is introduced to southern northeastern Arabian Sea through advection from north by sub-surface circulation. The total picophytoplankton biomass available to microbial loop is restored during late winter monsoon, when stratification begins, with a higher abundance of Synechococcus and the re-occurrence of Prochlorococcus population in the region. These inferences indicate that variability in picophytoplankton community structure and their contribution to the microbial loop are driven by convective mixing and advection, which in turn influence ecosystem functioning and trophodynamics of the southern northeastern Arabian Sea. [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]

We investigated the distribution of several picophytoplankton groups (Prochlorococcus, Synechococcus, and picoeukaryotes) in relation to a warm eddy in the northern South China Sea in summer 2012. An anticydonic eddy centered on 117°E longitude was identified during the sampling period using satellite data and hydrologic mapping. The layer of maximum Prochlorococcus and Synechococcus abundance within the eddy core dropped from 50 to 75 m, which was consistent with the subsurface chlorophyll a maximum. The water-column integrated abundance of Prochlorococcus, Synechococcus, and picoeukaryotes in the eddy core (9.67±0.23,1.56±0.04, and 0.28±0.01 x 103 cells ml-1, respectively) was significantly lower (P<0.05) than that of the reference stations (25.10±2.32,2.71±0.63, and 0.92±0.15 x 103 cells ml-1, respectively), and the abundance of Prochlorococcus in the core was also significantly lower than that at eddy edges (15.75±1.78 x 103 cells ml-1). However, there were no differences in the water-column integrated Chi a between the eddy core and edge. Our findings show that the warm eddy led to the reduced picophytoplankton abundance, especially of Prochlorococcus and picoeukaryotes, causing the layer of maximum picophytoplankton abundance to differ from that of the subsurface Chl a maximum. [ABSTRACT FROM AUTHOR]

The Costa Rica Dome (CRD) is a unique open-ocean upwelling system, with picophytoplankton dominance of phytoplankton biomass and suppressed diatoms, yet paradoxically high export of biogenic silica. As a part of Flux and Zinc Experiments cruise in summer ( June-July 2010), we conducted shipboard incubation experiments in the CRD to examine the potential roles of Si, Zn, Fe and light as regulating factors of phytoplankton biomass and community structure. Estimates of photosynthetic quantum yields revealed an extremely stressed phytoplankton population that responded positively to additions of silicic acid, iron and zinc and higher light conditions. Size-fractioned Chl a yielded the surprising result that picophytoplankton, as well as larger phytoplankton, responded most to treatments with added silicic acid incubated at high incident light (HL + Si). The combination of Si and HL also led to increases in cell sizes of picoplankton, notably in Synechococcus. Such a response, coupled with the recent discovery of significant intracellular accumulation of Si in some picophytoplankton, suggests that small phytoplankton could play a potentially important role in Si cycling in the CRD, which may help to explain its peculiar export characteristics. [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]

Eutrophication is a major problem in coastal water bodies. Information about the trophic status of water bodies will enable proper management of coastal ecosystems. In this regard, biological organisms which are sensitive to environmental changes can serve as indicators of ecosystem trophic status. In this study, seasonal and spatial variations of picophytoplankton (PP; <3 μm size) community structure was assessed in the Cochin backwaters (CB) with respect to the prevailing environmental conditions during three seasons, post-monsoon (PM-I; October 2011 and PM-II; November 2012), pre-monsoon (PrM; May 2012) and monsoon (MON; August 2012). CB, along the west coast of India, receives continuous load of nutrients throughout the year through anthropogenic wastes. Trophic status index (TRIX) scores showed that CB is highly eutrophic with a high phytoplankton biomass. Synechococcus was the dominant PP observed in the study area. Seasonal and spatial salinity variations influenced the PP distribution, especially Synechococcus where PE-rich Synechococcus ( SYN -PE) were dominant in higher saline (>30) and PC-rich Synechococcus ( SYN -PC) in lower saline (<30) waters. SYN -PC showed a significant positive relation with chlorophyll a suggesting that this group contributes substantially to the total phytoplankton biomass. TRIX scores and SYN -PC: SYN -PE abundance ratio were negatively correlated with salinity suggesting an influence of the tidal amplitude. SYN -PC correlated positively and SYN -PE negatively with TRIX scores suggesting that these groups occupy contrasting ecological niches. These findings imply that PP distribution pattern can serve as an indicator of the trophic status of coastal water bodies. [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]

Structure and functions of picophytoplankton and their links to the water column density stratification and nutrient vertical profiles were studied in the Black Sea open waters along a transect from the Western Gyre to the NW shelf during spring homothermy in April of 2017. Abundances of picocyanobacteria of the genus Synechococcus (0.85 ± 0.96 (SD) × 103 cells ml−1) and eukaryotic picoalgae (5.74 ± 5.99 × 103 cells ml−1) and their intracellular pigment (chl a , phycoerythrin) contents were quantified using flow cytometry. The distribution of these variables in the upper 100-m layer was non-uniform. Along the whole transect, Synechococcus and picoeukaryote abundance maxima (up to 4 × 103 and 3 × 104 cells ml−1, respectively) were observed at the water temperature of 8–8.5°С in the depth range between 30 and 40 m. Picoeukaryotes dominated the total community. The share of Synecococcus averaged about 22% and increased with depth up to 80%. Picophytoplankton abundance dropped abruptly through the oxycline but the cells were found in the suboxic layer at about 103 cells ml−1 and in a sample from the anoxic zone at 102 cells ml−1. Intracellular chl a maxima were revealed in the nitrate peak at sigma- t density of 15.5. In the surface and suboxic layers, non-specific green autofluorescence (GAF) was detected in picophytoplankton cells that might provide evidence of their stress state in adverse environment. Multivariate analysis has revealed tight coupling between abiotic and microbiological variables in three statistically distinct pelagic regions of the transect, corresponding to the abyss, the continental slope and the shelf. [Display omitted] • Picoeukaryotes dominated picophytoplankton but the proportion of Synecococcus increased with depth. • Picophytoplankton abundance dropped abruptly through oxycline but still survived in suboxic layer. • Non-specific green autofluorescence (GAF) was detected in picophytoplankton by flow cytometry. • Picophytoplankton GAF maxima were revealed in surface and suboxic layers, indicating stress conditions. [ABSTRACT FROM AUTHOR]

Coastal upwelling occurred along the west coast of Guangdong in the northern South China Sea during the summer of 2006. The effects of upwelling on the vertical and horizontal distributions of Prochlorococcus and Synechococcus were investigated. A distinct vertical temperature difference between the surface water and water at a depth of 30 m was observed in the coastal upwelling region. There was a clear spatial variability of temperature, and an increasingly obvious horizontal gradient was created from the coast to offshore waters. Picophytoplankton communities observed from the coast to offshore waters were significantly different. In the coastal upwelling waters, the picophytoplankton community was dominated by Synechococcus within the euphotic zone. Prochlorococcus dominated the picophytoplankton community in the euphotic zone in the non-upwelling region. This difference in the picophytoplankton community structure was due to different hydrodynamics. The results of canonical correspondence analysis demonstrate that temperature, salinity, and phosphate concentration may be important factors affecting the distribution of Prochlorococcus and Synechococcus. [ABSTRACT FROM AUTHOR]

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Abstract: Although the importance of picophytoplankton (<3μm) as the major primary producers is well established in the oceanic and coastal marine environment, occurrence of this community in the marine biofilms is not explored. Considering their small size and high abundance which is next to bacteria, the initial heterotrophic colonizers, it was hypothesized that picophytoplankton are the first autotrophic colonizers in marine biofilms. In this study biofilms were developed by immersing glass slides in the tropical waters of the Dona Paula Bay up to a period of 192h. The presence of picophytoplankton and the temporal variations in community structure was investigated flow cytometrically after every 24h. Biofilms were also developed in the laboratory by immersing the glass slides in fresh natural seawater and the sequence of appearance of the microorganisms was assessed with high frequency samplings. Field observations showed the presence of three groups of picophytoplankton, two prokaryotes, Prochlorococcus-like organisms (PRO), Synechococcus (SYN) and the picoeukaryotes (PEUK). Nanoeukaryotes, which are mostly represented by diatoms were also monitored. In the total biofilm community, prokaryotes were dominant throughout the study period wherein contribution of SYN was highest (50%) in the earlier stages which were later overtaken by PRO-like cells. The contribution of PEUK and nanoeukaryotes was always below 20%. Picophytoplankton contribution to the total photosynthetic biomass was >60% in the initial period of biofilm formation, both in terms of numbers and biomass with PEUK as the major contributors. However, after 2days of incubation, their contribution to total chlorophyll declined thus revealing that although their numbers were increasing, picophytoplankton were succeeded by nanoeukaryotes in terms of biomass. Laboratory experiments revealed that heterotrophic bacteria and picophytoplankton appeared within 5min in the biofilms which were followed by the nanoeukaryotes after 5h. This study shows that picophytoplankton are the pioneer autotrophic colonizers in the tropical marine biofilms, suggesting an essential role in the biofilm food web dynamics, especially in the initial stages. [Copyright &y& Elsevier]

Abstract: The influence of hydrography on the picophytoplankton (PP) abundance in estuaries was studied by sampling along a salinity gradient for the first time in an Indian estuary. Prochlorococcus-like cells were detected at salinities ranging from 0.06 to 35, which otherwise is reported from offshore regions, thereby showing that this group is capable of surviving in estuarine waters. PP also comprised picoeukaryotes and two groups of Synechococcus, one rich in phycoerythrin (SYN-PE) and other in phycocyanin (SYN-PC). Salinity played an important role in the picophytoplankton distribution. SYN-PE was represented by two sub-groups, one which was found only in saline waters (SYN-PEII) and the other throughout the salinity gradient (SYN-PEI). SYN-PEI and SYN-PC dominated downstream and upstream, respectively but were present throughout the salinity gradient unlike in other estuarine regions. Picoeukaryotes abundance showed an increasing trend from saline to brackish water and decreased in freshwater. The entry of seawater into the estuary regulated SYN-PE and Prochlorococcus-like cells downstream whereas their higher abundance in freshwater could be due to different strains of freshwater origin. The average contribution of PP to the total photosynthetic biomass during spring and neap tides was 43% and 29% respectively, which highlights the importance of PP in estuaries. [Copyright &y& Elsevier]

This work describes the dynamics of the autotrophic plankton community in Lim Bay in the north-eastern part of the Adriatic Sea from June 2008 to September 2009. There was an evident shift between microphytoplankton and picophytoplankton domination in summer and autumn periods, while nanophytoplankton contributed negligibly. Picophytoplankton dominated in June 2008 and September 2009 (contributing up to 84 % of the total phytoplankton biomass), while the micro-fraction dominated in September 2008 and June 2009 (contributing up to 97.2 % of the total biomass). The pico- fraction was dominated by Synechococccus in terms of abundance and biomass, with the highest abundances in September of 2009. Picoeukaryotes were not that prominent in terms of abundance or biomass, but they exceeded Synechococcus in terms of biomass in November 2008 and February 2009, and proved to be an important and consistent component of the Lim Bay phytoplankton community. Our results indicate that seasonal variability in the community structure was more affected by specific environmental perturbations occurring in Lim Bay than by availability of nutrients. [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]

Synechococcus species are important primary producers in coastal and open-ocean ecosystems. When nitrate was provided as the sole nitrogen source, nickel starvation inhibited the growth of strains WH8102 and WH7803, while it had little effect on two euryhaline strains, WH5701 and PCC 7002. Nickel was required for the acclimation of Synechococcus WH7803 to low iron and high light. In WH8102 and WH7803, nickel starvation decreased the linear electron transport activity, slowed down QA reoxidation, but increased the connectivity factor between individual photosynthetic units. Under such conditions, the reduction of their intersystem electron transport chains was expected to increase, and their cyclic electron transport around PSI would be favored. Nickel starvation decreased the total superoxide dismutase (SOD) activity of WH8102 and WH7803 by 30% and 15% of the control, respectively. The protein-bound 63Ni of the oceanic strain WH8102 comigrated with SOD activity on nondenaturing gels and thus provided additional evidence for the existence of active NiSOD in Synechococcus WH8102. In WH7803, it seems likely that nickel starvation affected other metabolic pathways and thus indirectly affected the total SOD activity. [ABSTRACT FROM AUTHOR]

Changes in abundance and biomass of Synechococcus were studied during five cruises carried out between November 2004 and September 2005 in the Iskenderun Bay, northeastern Mediterranean. In addition, spatial and temporal variations in physico-chemical factors and Chl a were measured. Abundance ranged from 0.2×104 to 23.09×104 cells ml-1, whereas the biomass ranged from 0.19 1 to 23.01 µgC l-1 in the bay. Synechococcus was found most numerous during September 2005 in the shallower part of the bay while the population was observed least during November 2004 and January 2005. The contribution of <3 µm size fraction to total Chl a ranged between 48% and 74%, being low during the cold period and higher during the warm period. The observed spatial and temporal fluctuations in abundance seemed to be closely related to environmental conditions in the area. Small-sized phytoplankton dominated the bulk of biomass, at least for the summer period. [ABSTRACT FROM AUTHOR]

Abstract: Climatological variability of picophytoplankton populations that consisted of >64% of total chlorophyll a concentrations was investigated in the equatorial Pacific. Flow cytometric analysis was conducted along the equator between 145°E and 160°W during three cruises in November–December 1999, January 2001, and January–February 2002. Those cruises were covering the La Niña (1999, 2001) and the pre-El Niño (2002) periods. According to the sea surface temperature (SST) and nitrate concentrations in the surface water, three regions were distinguished spatially, viz., the warm-water region with >28°C SST and nitrate depletion (<0.1μmolkg-1), the upwelling region with <28°C SST and high nitrate (>4μmolkg-1) water, and the in-between frontal zone with low nitrate (0.1–4μmolkg-1). Picophytoplankton identified as the groups of Prochlorococcus, Synechococcus and picoeukaryotes showed a distinct spatial heterogeneity in abundance corresponding to the watermass distribution. Prochlorococcus was most abundant in the warm-water region, especially in the nitrate-depleted water with >150×103cellsml-1, Synechococcus in the frontal zone with >15×103cellsml-1, and picoeukaryotes in the upwelling region with >8×103cellsml-1. The warm-water region extended eastward with eastward shift of the frontal zone and the upwelling region during the pre-El Niño period. On the contrary, these regions distributed westward during the La Niña period. These climatological fluctuations of the watermass significantly influenced the distribution of picophytoplankton populations. The most abundant area of Prochlorococcus and Synechococcus extended eastward and picoeukaryotes developed westward during the pre-El Niño period. The spatial heterogeneity of each picophytoplankton group is discussed here in association with spatial variations in nitrate supply, ambient ammonium concentration, and light field. [Copyright &y& Elsevier]

Seasonal variations in the picophytoplankton community structure (Synechococcus spp. and picoeukaryotes) were studied by flow cytometry in the coastal ecosystem of the subtropical western Pacific from October 2019 to September 2020. Synechococcus spp. was dominant in abundance during the study period, with its density ranging from 0.05 to 5.6 × 104 cells mL−1; its maximum occurred in July 2020. Picoeukaryotes were less abundant, with their density ranging from 0.2 to 13.6 × 103 cells mL−1. Their highest abundance was recorded in January 2020. The growth rates of Synechococcus spp. and picoeukaryotes ranged from −0.39 to 1.42 d−1 and 0.38 to 2.46 d−1, respectively, throughout the study period. Overall, the growth rate of the picoeukaryotes was significantly higher than that of Synechococcus spp. It is interesting to note that the grazing mortality of Synechococcus spp. and picoeukaryotes during the warmer period (April to September) was relatively low. Based on this study, we suggest that mixotrophic nanoflagellates lowered their feeding activity that obtained nutrients from prey and instead used additional nutrients during the incubation experiments. Our study demonstrated that a shift in the picophytoplankton community composition and grazing activity of predacious nanoflagellates in cold and warm periods can impact on the seasonal dynamics of the microbial food web. [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]

In oceanic communities, picophytoplankton often dominates phytoplankton biomass and productivity. Diel variations in picophytoplankton abundance and growth have been well documented. In the current study, we used flow cytometry to assess the short-term variations (3 h) of the abundance of the most dominant picophytoplankton, Synechococcus spp. and picoeukaryotes, in the coastal regions of northeastern Taiwan. To explore the change in growth and mortality rate in the daytime and over 24 h incubation, we performed a two-point modified dilution experiment for measuring growth, viral lysis, and nanoflagellate grazing rate. In this study, the growth rates of picoeukaryotes were 0.21 and 0.06 h−1, and those of Synechococcus spp. were 0.15 and 0.06 h−1 for daytime and 24 h incubation, respectively, and the values were higher at significant levels in the daytime than those for 24 h incubation. These growth rate values of picoeukaryote and Synechococcus spp. after incubation for 24 h were approximately underestimated at 71% and 55%, respectively. This finding suggests that estimates based on 24 h sampling may not accurately reflect the true growth rate of these populations on ecologically relevant timescales. [ABSTRACT FROM AUTHOR]