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A mathematical model is (newly proposed) to be defined the interconnection of the four state variables greenhouse gases (GHGs), atmospheric temperature, phytoplankton population and fishery population. Basically, it is a non-linear differential equation mathematical model. It contains environmental parameters related to climate change, caused by quick increment in amount of GHGs, which caused the disturbances in the marine environments that affects marine ecological system especially fisheries and phytoplankton population. The purpose of the study is to explain the current situation of the effect of climate change to marine ecosystem. In the mathematical modeling part, equilibrium analysis, local stability and numerical simulations have been done. A novel model for environment management using the time variant parameters is validated through analysis, and numerical simulations are used to test the study's analytical findings. [ABSTRACT FROM AUTHOR]

Southern Ocean phytoplankton form the base of the Antarctic food web, influencing higher trophic levels through biomass and community structure. We examined phytoplankton distribution and abundance in the Indian Sector of the Southern Ocean during austral summer as part a multidisciplinary ecosystem survey: Trends in Euphausiids off Mawson, Predators and Oceanography (TEMPO, 2021). Sampling covered six meridional transects from 55-80°E, and from 62°S or 63°S to the ice edge. To determine phytoplankton groups, CHEMTAX analysis was undertaken on pigments measured using HPLC. Diatoms were the dominant component of phytoplankton communities, explaining 56% of variation in chlorophyll a (Chl a), with haptophytes also being a major component. Prior to sampling the sea ice had retreated in a south-westerly direction, leading to shorter ice-free periods in the west (< 44 days, ≤65°E) compared to east (> 44 days, ≥70°E), inducing a strong seasonal effect. The east was nutrient limited, indicated by low-iron forms of haptophytes, and higher silicate:nitrate drawdown ratios (5.1 east vs 4.3 west), pheophytin a (phaeo) concentrations (30.0 vs 18.4 mg m-2) and phaeo:Chl a ratios (1.06 vs 0.53). Biological influences were evident at northern stations between 75-80°E, where krill "super-swarms" and feeding whales were observed. Here, diatoms were depleted from surface waters likely due to krill grazing, as indicated by high phaeo:Chl a ratios (> 0.75), and continued presence of haptophytes, associated with inefficient filtering or selective grazing by krill. Oceanographic influences included deeper mixed layers reducing diatom biomass, and a bloom to the north of the southern Antarctic Circumpolar Current Front in the western survey area thought to be sinking as waters flowed from west to east. Haptophytes were influenced by the Antarctic Slope Front with high-iron forms prevalent to the south only, showing limited iron transfer from coastal waters. Cryptophytes were associated with meltwater, and greens (chlorophytes + prasinophytes) were prevalent below the mixed layer. The interplay of seasonal, biological and oceanographic influences on phytoplankton populations during TEMPO had parallels with processes observed in the BROKE and BROKE-West voyages conducted 25 and 15 years earlier, respectively. Our research consolidates understanding of the krill ecosystem to ensure sustainable management in East Antarctic waters. [ABSTRACT FROM AUTHOR]

Perfluorooctanoic acid (PFOA) is a surfactant that is detected in small quantities across various environments away from its manufacturing zones. Despite the widespread detection of PFOA in aquatic ecosystems, the impact of this compound on phytoplankton populations remains poorly understood. This study aimed to determine the physiological effects of PFOA on Microcystis aeruginosa. The cyanobacterium was exposed to 1‒10 000 μg l‒1 PFOA for 7 days under controlled laboratory conditions. The EC50 of PFOA for the test species after 7 days of exposure was 30.03 μg l‒1. Cell density significantly decreased at all PFOA concentrations (1‒10 000 μg l‒1). Chlorophyll a and carotenoid concentrations increased on day 1 (except for 1 μg l‒1, the lowest PFOA treatment) but then decreased across all treatment concentrations on day 7 of the experiment. When M. aeruginosa was exposed to PFOA, the total lipid, protein and carbohydrate content generally increased across all treatment concentrations. The concentration of intracellular hydrogen peroxide increased with increasing surfactant concentrations. In different treatments, lipid peroxidation increased, with 100 μg l‒1 PFOA producing the highest malondialdehyde content. Peroxidase and glutathione S-transferase activities increased across all treatment concentrations, demonstrating progressive changes consistent with the increase in reactive oxygen species observed. Total microcystin concentration increased in cultures exposed to 1000 and 10 000 µg l‒1 PFOA. These findings suggest that PFOA can adversely affect the survival of M. aeruginosa populations in contaminated aquatic ecosystems, with potential cascading effects on the general health of the environment. [ABSTRACT FROM AUTHOR]

The Hawaii Ocean Time‐series (HOT) at Station ALOHA (22.75°N, 158°W) in the North Pacific Subtropical Gyre (NPSG) serves as a critical vantage point for observing plankton biomass production and its ecological implications. However, the HOT program's near‐monthly sampling frequency does not capture shorter time scale variability in phytoplankton populations. To address this gap, we deployed the SeaFlow flow cytometer for continuous monitoring during HOT cruises from 2014 to 2021. This approach allowed us to examine variations in the surface abundance and cell carbon content of specific phytoplankton groups: the cyanobacteria Prochlorococcus, Synechococcus, and Crocosphaera as well as a range of small eukaryotic phytoplankton (≤ 5 μm). Our data showed that daily to monthly variability in Prochlorococcus and Synechococcus abundance matches seasonal and interannual variability, while small eukaryotic phytoplankton and Crocosphaera showed the highest seasonal and interannual fluctuations. The study also found that eukaryotic phytoplankton and Crocosphaera had higher median cellular growth rates (0.076 and 0.090h−1, respectively) compared to Prochlorococcus and Synechococcus (0.037 and 0.045h−1, respectively). These variances in abundance and growth rates indicate that shifts in the community structure significantly impact primary productivity in the NPSG. Our results underscore the importance of daily to monthly phytoplankton dynamics in ecosystem function and carbon cycling. [ABSTRACT FROM AUTHOR]

The Southern Ocean microbial ecosystem, with its pronounced seasonal shifts, is vulnerable to the impacts of climate change. Since viruses are key modulators of microbial abundance, diversity, and evolution, we need a better understanding of the effects of seasonality on the viruses in this region. Our comprehensive exploration of DNA viral diversity in the Southern Ocean reveals a unique and largely uncharted viral landscape, of which 75% was previously unidentified in other oceanic areas. We uncover novel viral taxa at high taxonomic ranks, expanding our understanding of crassphage, polinton-like virus, and virophage diversity. Nucleocytoviricota viruses represent an abundant and diverse group of Antarctic viruses, highlighting their potential as important regulators of phytoplankton population dynamics. Our temporal analysis reveals complex seasonal patterns in marine viral communities (bacteriophages, eukaryotic viruses) which underscores the apparent interactions with their microbial hosts, whilst deepening our understanding of their roles in the world's most sensitive and rapidly changing ecosystem. The study reveals that the Southern Ocean hosts a unique and largely underexplored DNA viral community. It explores the diversity of viral communities infecting all domains of life and their seasonality, emphasizing their role in ecosystem dynamics. [ABSTRACT FROM AUTHOR]

Phytoplankton play an irreplaceable role as producers in maintaining lake ecosystems. Nevertheless, scant attention has been given to investigating the dispersion of phytoplankton communities and the factors influencing them across expansive areas. In this study, we present the results of a survey on the distribution of phytoplankton community and the effects of different driving factors in 11 lakes along Inner Mongolia in July–August 2020. Non-metric multidimensional scaling analysis and variance decomposition (VPA) were used to elucidate the distribution of phytoplankton communities and the response of drivers. A total of 169 species of phytoplankton from 8 phyla were detected. Both the abundance and diversity of phytoplankton in the Inner Mongolia lakes showed a trend of high in the east and low in the west (with Daihai Lake as the boundary). The Margalef index of phytoplankton significantly negatively correlated with salinity (r  = −0.707, P  < 0.05) and total dissolved solids (r  = −0.720, P  < 0.05), and both density and biomass highly significantly positively correlated with the suspended solids, Chlorophyll a and trophic level index. The VPA explained 38.9% of the changes in the phytoplankton community with the highest rate of explanation of land use. Therefore, preventing anthropogenic impacts, as well as reducing nutrient loads, can effectively ensure the ecological diversity of lake phytoplankton in lake populations with large geographical spans and varying levels of nutrients. [ABSTRACT FROM AUTHOR]

Oceanic biogeochemistry plays a pivotal role in regulating Earth's climate system by governing the cycling of key elements such as carbon, oxygen, and nutrients. Various metocean processes including wind, tides, currents, waves, and eddies significantly influence the dynamics of this system. In particular, ocean surface waves contribute to this intricate interplay by facilitating the exchange of heat, gas, and momentum between the atmosphere and the ocean. Although wave‐coupled effects are substantial, studies on their impacts on oceanic biogeochemistry, particularly on phytoplankton abundance are missing in present‐day research. Additionally, wave‐coupled effects cannot be disregarded in regions like the Southern Ocean (SO), where wind and waves activities are prominent. Addressing this gap, we incorporated a parameterization of surface wave mixing into a global ocean biogeochemical model to investigate its effects on upper ocean and biogeochemical parameters. Our results show that surface wave mixing has significant impacts on sea surface temperature (SST), mixed layer depth (MLD), and nutrient distribution—key factors that influence phytoplankton growth. Additionally, we observed significant improvements in model biases against the observations. During austral summer, additional mixing from surface waves can significantly lower SST by 0.5°C, deepen MLD by 13 m, and enhance Chlorophyll‐a (Chl‐a) concentration, an index of phytoplankton population, by 8% in the SO. This observed increase in Chl‐a concentration is mainly driven by enhanced dissolved iron levels resulting from wave‐induced mixing. Our findings underscore the significance of incorporating surface wave mixing in ocean biogeochemistry studies, an aspect that is currently overlooked. Plain Language Summary: Ocean biogeochemistry encompasses the complex interactions of the ocean's biological, geological, and chemical processes and affects the Earth's climate system. This system is highly impacted by various physical forcings such as wind, currents, waves, tides, and eddies. Among these forcings, surface waves play a crucial role by exchanging heat, gas, and momentum between the atmosphere and ocean. Understanding the roles of surface waves on upper ocean mixing and oceanic biogeochemistry is paramount, especially in regions like the Southern Ocean (SO), where wind and waves are prominent. However, present‐day studies lack research on wave‐coupled effects on ocean biogeochemistry, particularly in the SO. Addressing this research gap, we investigated the influence of surface wave mixing on oceanic biogeochemistry by adding a parameterization of surface wave mixing in a global ocean biogeochemical model. From the investigation, we found significant effects of wave coupling on upper ocean and biogeochemical parameters, such as cooling of sea surface temperature, deepening mixed layer depth, enhancing nutrient levels, and consequently, increasing phytoplankton distribution during austral summer in the SO. This study contributes to a deeper understanding of the complex interplay between ocean surface waves and oceanic biogeochemistry, especially in the SO. Key Points: Present‐day studies lack research on the wave‐coupled effects on ocean biogeochemistry, particularly in the Southern OceanA surface wave mixing parameterization is used to investigate the wave‐coupled effects on the upper ocean and biogeochemical parametersWave coupling influences ocean temperature, mixed layer depth, and nutrient levels which are essential for phytoplankton growth [ABSTRACT FROM AUTHOR]

Metacommunity ecology has shown that connectivity is important for the persistence of a species locally and across connected ecosystems, however we do not know if ecological effects in freshwater ecosystems exposed to biocides leaking from agriculture depend on metaecosystem connectivity. We experimentally replicated metaecosystems in the laboratory using gradostats as a model system. We tested the effects of connectivity, in terms of node distance from the pollutant-source, flow rate, and a glyphosate-based herbicide, on phytoplankton productivity, diversity and stability. Gradostats were composed of interconnected equally spaced nodes where resources and phytoplankton move directionally along a gradient of increasing distance from the source of the polluting herbicide. We hypothesised that ecological effects would be stronger in the node situated closer to the point of herbicide input, but that flow would suppress phytoplankton populations in distant nodes. Overall, RoundUp impacted phytoplankton productivity and stability by reducing algal biomass and abundances. This occurred especially in the node closest to the diluted herbicide point-source and under high flow, where species abundances were heavily suppressed by the effects of the rapidly flowing herbicide. At low flow on the other hand, distant nodes where buffered from the effects of the slow-moving herbicide. No differences in beta and gamma diversity among replicate metaecosystems was found; however, a significant loss of alpha diversity in all metaecosystems occurred through time until the end of the experiment. Together, these results point to the importance of considering aquatic connectivity in management plans for monitoring and mitigating unintended ecological consequences of agrochemical runoff. [ABSTRACT FROM AUTHOR]

Deep convection occurs periodically in the Gulf of Lion, in the northwestern Mediterranean Sea, driven by the seasonal atmospheric change and Mistral winds. To determine the variability and drivers of both forcings, multiple 1 year ocean simulations were run, spanning from 1993 to 2013. Two sets of simulations were performed: a control and seasonal set, the first forced by unfiltered atmospheric forcing and the other by filtered forcing. The filtered forcing was bandpass filtered, retaining the seasonal and intraday aspects but removing the high frequency phenomena. Comparing the two sets allows for distinguishing the effects of the high frequency component of the Mistral on the ocean response. During the preconditioning phase, the seasonal forcing was found to be the main destratifying process, removing on average 46% of the stratification needed for deep convection to occur, versus the 28% removed by the Mistral. Despite this, each forcing triggered deep convection in roughly half of the deep‐convection events. Sensible and latent heat fluxes were found to be the main drivers of the seasonal forcing during deep‐convection years, removing 0.17 and 0.43 m2s−2 of stratification, respectively. They were themselves driven by increased wind speeds, believed to be the low frequency signal of the Mistral, as more Mistral events occur during deep‐convection winters (34% vs. 29% of the preconditioning period days). An evolving seasonal forcing in a changing climate may have significant effects on the future deep convection cycle of the western Mediterranean Sea. Plain Language Summary: Deep convection occurs periodically in the Gulf of Lion (located in the northwestern Mediterranean Sea), when water at the surface of the ocean is cooled enough to mix freely with the deeper water below, sometimes reaching the sea floor. It's an important part of the overall circulation of the Mediterranean Sea that leads to an explosion in the phytoplankton population in the following spring. In the gulf, the surface cooling is caused by the atmospheric transition from summer to winter and the Mistral winds. The latter is a cool, dry northerly wind that flows through the Rhône Valley out over the gulf. In our study, we ran ocean simulations that included and excluded the non‐seasonal effects of the Mistral to determine the importance of the seasonal and Mistral forcing on deep convection. The seasonal forcing was found to have a larger role, and contained a low frequency part of the Mistral, elevating the average wind speeds during the winter. Changes in the seasonal forcing and ocean water composition will need to be studied to understand the evolution of deep convection in the Gulf of Lion and its consequences on the Mediterranean Sea dynamics and biology in a changing climate. Key Points: The seasonal atmospheric change is the main driver of destratificationWinters with deep convection have below average levels of stratification that the atmospheric forcing has to overcomeThe Mistral winds have a low frequency signature that elevates the seasonal wind speeds in the winter [ABSTRACT FROM AUTHOR]

The present research article gives an account of the abundance and monthly variation of plankton diversity (i.e., phytoplankton and zooplankton) in Ashwani stream, Solan (H.P.). A total of 17 genera were recorded, out of which 11 belongs to Bacillariophyceae, 5 belongs to Chlorophyceae and 1 belongs to Cyanophyceae. Only single genera (Monostyla) of zooplankton were recorded. Study revealed that phytoplankton population was dominated by members of Bacillariophyceae followed by Chlorophyceae and Cyanophyceae. Relative abundance of plankton was higher during the December and January month (winter season) and lowest in April month. [ABSTRACT FROM AUTHOR]

The past two decades have seen a drastic increase in the availability and use of genetic techniques to study phytoplankton communities. As a result, it is now well documented that phytoplankton populations are genetically diverse, despite predominantly asexual reproduction and minute morphological variation. Genetic variation can lead to variation also in phenotype, and some traits vary more among genotypes than between species. Trait‐based approaches tackle this by focusing on traits rather than on species. However, trait‐based models often have difficulty predicting and explaining the huge trait‐diversity among coexisting individuals competing for the same few resources. Thus, we ask the question: How do hundreds, if not thousands, of genotypes coexist in a highly competitive environment? In this review, we gather information on genetic and phenotypic variations in coexisting genotypes and elaborate on three mechanisms by which broad intraspecific genetic diversity may be possible: neutral mutations, environmental fluctuations, and trade‐offs among traits. These have all been applied on an interspecies level, and we discuss their use also among coexisting genotypes. We find that genetic diversity to be almost exclusively studied in blooming species and that clonal diversity frequently measure above 0.95 (i.e., 95% of individuals sampled are genetically different). Genetic diversity seems stable throughout blooms, suggesting that competitive exclusion is low or that new genetic material is frequently being introduced into populations. Further, we find high intraspecific trait‐variation in several key traits among coexisting strains but also that trait‐variation is often neglected in studies on phytoplankton, making coexistence difficult to predict. [ABSTRACT FROM AUTHOR]

This paper reports an important conclusion that self-diffusion is not a necessary condition for inducing Turing patterns, while taxis could establish complex pattern phenomena. We investigate pattern formation in a zooplankton–phytoplankton model incorporating phytoplankton-taxis, where phytoplankton-taxis describes the zooplankton that tends to move toward the high-densities region of the phytoplankton population. By using the phytoplankton-taxis sensitivity coefficient as the Turing instability threshold, one shows that the model exhibits Turing instability only when repulsive phytoplankton-taxis is added into the system, while the attractive-type phytoplankton-taxis cannot induce Turing instability of the system. In addition, the system does not exhibit Turing instability when the phytoplankton-taxis disappears. Numerically, we display the complex patterns in 1D, 2D domains and on spherical and zebra surfaces, respectively. In summary, our results indicate that the phytoplankton-taxis plays a pivotal role in giving rise to the Turing pattern formation of the model. Additionally, these theoretical and numerical results contribute to our understanding of the complex interaction dynamics between zooplankton and phytoplankton populations. [ABSTRACT FROM AUTHOR]

The hydrographic variability in the fjords of Svalbard significantly influences water mass properties, causing distinct patterns of microbial diversity and community composition between surface and subsurface layers. However, surveys on the phytoplankton-associated bacterial communities, pivotal to ecosystem functioning in Arctic fjords, are limited. This study investigated the interactions between phytoplankton and heterotrophic bacterial communities in Svalbard fjord waters through comprehensive eDNA metabarcoding with 16S and 18S rRNA genes. The 16S rRNA sequencing results revealed a homogenous community composition including a few dominant heterotrophic bacteria across fjord waters, whereas 18S rRNA results suggested a spatially diverse eukaryotic plankton distribution. The relative abundances of heterotrophic bacteria showed a depth-wise distribution. By contrast, the dominant phytoplankton populations exhibited variable distributions in surface waters. In the network model, the linkage of phytoplankton (Prasinophytae and Dinophyceae) to heterotrophic bacteria, particularly Actinobacteria, suggested the direct or indirect influence of bacterial contributions on the fate of phytoplankton-derived organic matter. Our prediction of the metabolic pathways for bacterial activity related to phytoplankton-derived organic matter suggested competitive advantages and symbiotic relationships between phytoplankton and heterotrophic bacteria. Our findings provide valuable insights into the response of phytoplankton-bacterial interactions to environmental changes in Arctic fjords. [ABSTRACT FROM AUTHOR]

Grazing dynamics are one of the most poorly constrained components of the marine carbon cycle. We use inverse modeling to infer the distribution of community‐integrated zooplankton grazing dynamics based on the ability of different grazing formulations to recreate the satellite‐observed seasonal cycle in phytoplankton biomass after controlling for physical and bottom‐up controls. We find large spatial variability in the optimal community‐integrated half saturation concentration for grazing (K1/2), with lower (higher) values required in more oligotrophic (eutrophic) biomes. This leads to a strong sigmoidal relationship between observed mean‐annual phytoplankton biomass and the optimally inferred grazing parameterization. This relationship can be used to help constrain, validate and/or parameterize next‐generation biogeochemical models. Plain Language Summary: To improve predictions of the ocean's ability to feed a growing human population and buffer a changing climate, we need to improve our understanding of what happens to carbon once it is absorbed into the surface ocean. One of the largest knowledge gaps in marine carbon cycling is the role of zooplankton grazing. The rate at which zooplankton graze phytoplankton modifies the size and seasonal evolution of phytoplankton populations and in turn, the associated rates of net primary production at the base of the food‐web, secondary production of grazers (an indicator of fisheries potential) and export production (the biological sequestration of carbon). However, regional differences in grazing, which are difficult to measure outside of the laboratory, remain poorly constrained by observations and thus difficult to model. Here, we run a suite of model simulations, which each simulate grazing differently, then compare the results to infer which grazing dynamics best match observations. We find that there is dramatic spatial variability in how zooplankton, as a community, appear to be grazing and that this variability maps well onto observed phytoplankton abundance, suggesting that the type of zooplankton present may be determined by the amount of prey available. Key Points: Oligotrophic (eutrophic) biomes exhibit more (less) efficient community‐integrated grazing, characteristic of micro‐ (meso‐) zooplanktonWe find a strong link between observed mean‐annual phytoplankton biomass and the grazing dynamics required to recreate its seasonal cycleA type III functional response typically does a better job recreating observed phytoplankton seasonal cycles than a type II response [ABSTRACT FROM AUTHOR]

We carried out measurements of the CO2 system parameters to evaluate the impact of carbonate and nutrients' chemistry on phytoplankton populations in the Gulf of Guinea (GoG). The seasonal variations of the CO2 system parameters (fCO2, DIC, pH and TA) along with nitrates and phosphates were quantified weekly at surface (between 0 and 5 m depth) (5.57°N - 4.57°W) in the GoG from May to December 2020. Seawater pH varied widely during the study period, ranging between 8.10-8.35 pH units; DIC and TA varied between 1810 and 2094 mmol kg-1, and between 2051 and 2216 mmol-1 respectively. DIC peaks coincided with the high upwelling period (August and September). For phytoplankton, a total of 60 species were found belonging to four taxonomic phyla: Bacillariophyta, Dinophyta, Chlorophyta and Dictyochophyta. The highest number of phytoplanktonic species were recorded for Bacillariophyta phylum with 36 species (60%). The phylum Dinophyta comprised 22 taxa (36%) and Chlorophyta and Dictyochophyta recorded only one species (2%). The highest specific diversities were observed in August and September with 29 and 26 taxa respectively and the lowest was found in October-November (5 taxa) and December (one taxa). Bacillariophyta and Dinophyta appeared throughout the entire study period. The only species for Chlorophyta phylum appeared in June and July and the Dictyochophyta's one in May, July and August. In general, the physical (SST, SSS) and chemical (TA, DIC, pH) parameters influenced less than 50% of the phytoplankton population in the coastal area of the GoG. Our study shows that Bacillariophyta population grows up when the physicochemical parameters' variability increase. [ABSTRACT FROM AUTHOR]

Spatiotemporal variations of phytoplankton populations in agricultural irrigation ponds need to be accounted for in order to properly assess water quality. Phytoplankton cell and photosynthetic pigment concentrations are two common metrics used to characterize phytoplankton communities. This work evaluated depth and time of the day as factors affecting discrete sampling of phytoplankton. The abundance of chlorophytes, diatoms, cyanobacteria, flagellates, and dinoflagellates, as well as chlorophyll-a and phycocyanin pigments, were determined in samples taken at the surface and depth, in 0.5 m increments, in three to five spatial replications at 9 a.m., 12 p.m., and 3 p.m. in two ponds in Maryland, USA. Depth was a significant factor for photosynthetic pigment concentration variations in both ponds on most sampling dates and time of day was a significant factor for photosynthetic pigment concentrations in half of the sampling dates. Depth was not a significant factor in cell concentration variations for any of the phytoplankton groups observed, but time of day was a significant factor in 40% of the sampling dates. Two distinct patterns in pigment concentration daily variation were observed. The first featured a continuous increase with depth throughout the day. The second showed maximum concentrations at the surface in the morning changing to maximum concentrations at 0.5 m depth at 12 p.m. and 3 p.m.; these patterns corresponded to different morning solar irradiance levels. This indicates that sampling depth and time can be a significant factor when evaluating photosynthetic pigments and should be accounted for in monitoring programs that rely on pigments for decision-making. [ABSTRACT FROM AUTHOR]

Phytoplankton are primary producers in aquatic ecosystems, their abundance is determined by environmental changes, so phytoplankton are often used as bioindicators of waters. The aim of this research was to determine the diversity and abundance of phytoplankton in Menjer Lake, to measure the environmental factors that determine the diversity and abundance of phytoplankton, and to determine the environmental factors that most influence the diversity and abundance of phytoplankton in Menjer Lake. This research uses a survey method in 5 areas (inlet, middle of the lake, aquaculture using floating net cage, tourism, and outlet). The parameters observed were the diversity and abundance of phytoplankton as well as the concentration of water quality parameters that determine the presence of phytoplankton (temperature, light penetration, pH, DO, TSS, TDS, PO4 and NO3). To determine the environmental factors that most influence the diversity and abundance of phytoplankton were analyzed using the principal component analyses method with Past 4.10 software. The community structure of phytoplankton in Menjer Lake was dominated by Bacillariophyta (83%). The factors determining the development of phytoplankton in Menjer Lake are influenced most by light penetration and PO4 concentration. The input of PO4 concentration from the water catchment area must be controlled to prevent phytoplankton blooming in Menjer Lake. [ABSTRACT FROM AUTHOR]

Autonomous underwater vehicles provide water column observations of phytoplankton biomass using chlorophyll a (Chl a) fluorometers. However, under high incident light, phytoplankton fluorescence yield decreases in a process known as non‐photochemical quenching, resulting in a reduced Chl a fluorescence signal. Methods have been developed to identify and remove the quenched signal from observations by autonomous underwater vehicles. These existing methods rely on assumptions of the homogeneity of the system, both in terms of time (i.e., between day and night observations) and space (i.e., within the water column or between neighboring profiles). These assumptions are not valid in shallow shelf seas or when sampling across different water masses. Thus, we evaluate six new quenching correction methods based on an existing ocean‐based method, but adapted for a continental shelf sea environment where the water mass changes between night and day observations. We have included two main changes to the existing method. First, we interpolate the unquenched, nighttime signal across the daytime observations and use this as a reference for correcting the quenched, daytime signal. Second, we explore the inclusion of a fluorescence quenching depth limit. By interpolating nighttime observations across daytime periods, the diel changes in non‐photochemical quenching were separated from the phytoplankton population changes. The proposed methods all show improved performance compared to existing approach. The methods presented here, and the approach used to evaluate them, are applicable in other shelf sea environments, enabling studies using autonomous Chl a fluorescence data across shelf sea ecosystems. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of phytoplankton assemblages in various and variable aquatic ecosystems is of paramount importance, given the strategic supporting services offered by these organisms. Such knowledge is implicitly based on the analysis of the realized niche of the different populations, i.e. of the sets of conditions within which populations show a positive growth. The range of phytoplankton morphological traits variability is evolutionarily selected to maximize the ecological performance of species while they are entrained in the spectrum of turbulent flows. In addition, most phytoplankton species exhibit high morphological plasticity that can further optimize their performance under reduced environmental variability. Although this plasticity is well known, it is seldom considered in phytoplankton studies. Morphological analysis could therefore be used as a tool to estimate the environmental variability within which a species can persist and, ultimately, the niche width of phytoplankton populations. This opinion paper tries to answer the questions: to what extent can the morphological variability of phytoplankton offer a synthesis of the environmental variability of aquatic ecosystems?. Do the morphological traits contain sufficient information to describe the width of the realized niche of phytoplankton species? What can we do to fill eventual gaps in our knowledge? [ABSTRACT FROM AUTHOR]

We integrated data from field observations during April and March with data from a 2-week mesocosm experiment to investigate changes in phytoplankton populations in southern Korean coastal waters (KCWs) following nutrient enrichment during early spring of 2021. The mesocosm experiments used 1000 L cylindrical plastic containers that had natural seawater (control), a low nutrient (LN) treatment, or a high nutrient (HN) treatment. The field observations showed that increased freshwater runoff following spring rainfall led to elevated levels of dissolved inorganic nitrogen and silicate and a significant increase in total phytoplankton abundance. In March, nutrient enrichment from water mixing and terrestrial runoff led to dominance of cryptophyte Cryptomonas spp. In April, higher nutrient levels than March (p< 0.05) resulting from increased terrestrial runoff after rainfall and dominant species were Skeletonema spp., and Cryptomonas spp. In the mesocosm experiment, a succession from E. zodiacus initially to Chaetoceros spp. in the middle stage, and then to Cylindrotheca closterium and Pseudo-nitzschia spp. finally was observed, depending on the species-specific nutrient availability after nutrient addition. In principal component analysis, the negative correlation between C. closterium and nutrient levels supports their nutrient availability, which is an adaptation to low-nutrient conditions. The combined data from the field observations and mesocosm experiments indicated that nutrient supplementation from terrestrial runoff and tidal mixing played a crucial role in determining the dynamics of phytoplankton populations during early spring in the KCWs. [ABSTRACT FROM AUTHOR]

Mixotrophic eukaryotes are important bacterivores in oligotrophic open oceans, but their significance as grazers in more nutrient‐rich waters is less clear. Here, we investigated the bacterivory partition between mixotrophs and heterotrophs in a productive, estuary‐influenced coastal region in the East China Sea. We found ubiquitous, actively feeding phytoplankton populations and taxa with mixotrophic potential by identifying ingestion of fluorescent prey surrogate and analyzing community 18S rRNA gene amplicons. Potential and active mixotrophs accounted for 10–63% of the total eukaryotic community and 17–69% of bacterivores observed, respectively, contributing 6–48% of estimated in situ bacterivory. The much higher mixotroph fitness outside of the turbid plume was potentially driven by increased light and decreased nutrient availability. Our results suggest that, although heterotrophs dominated overall in situ bacterivory, mixotrophs were abundant and important bacterivores in this low‐latitude mesotrophic coastal region. [ABSTRACT FROM AUTHOR]

The study of time-fractional problems with derivatives in terms of Caputo is a recent area of study in biological models. In this article, fractional differential equations with phytoplankton-toxic phytoplankton-zooplankton (PTPZ) system were solved using the Laplace transform method (LTM), the Adomain decomposition method (ADM), and the differential transform method (DTM). This study demonstrates the good agreement between the results produced by using the specified computational techniques. The numerical results displayed as graphs demonstrate the accuracy of the computational methods. The approaches that have been established are thus quite relevant and suitable for solving nonlinear fractional models. Meanwhile, the impact of changing the fractional order of a time derivative and time t on populations of phytoplankton, toxic-phytoplankton, and zooplankton has been examined using graphical representations. Furthermore, the stability analysis of the LTM approach has been discussed. [ABSTRACT FROM AUTHOR]

Plankton organisms are fundamental components of the earth's ecosystem. Zooplankton feeds on phytoplankton and is predated by fish and other aquatic animals, being at the core of the aquatic food chain. On the other hand, Phytoplankton has a crucial role in climate regulation, has produced almost 50% of the total oxygen in the atmosphere and it's responsible for fixing around a quarter of the total earth's carbon dioxide. Importantly, plankton can be regarded as a good indicator of environmental perturbations, as it can react to even slight environmental changes with corresponding modifications in morphology and behavior. At a population level, the biodiversity and the concentration of individuals of specific species may shift dramatically due to environmental changes. Thus, in this paper, we propose an anomaly detection-based framework to recognize heavy morphological changes in phytoplankton at a population level, starting from images acquired in situ. Given that an initial annotated dataset is available, we propose to build a parallel architecture training one anomaly detection algorithm for each available class on top of deep features extracted by a pre-trained Vision Transformer, further reduced in dimensionality with PCA. We later define global anomalies, corresponding to samples rejected by all the trained detectors, proposing to empirically identify a threshold based on global anomaly count over time as an indicator that can be used by field experts and institutions to investigate potential environmental perturbations. We use two publicly available datasets (WHOI22 and WHOI40) of grayscale microscopic images of phytoplankton collected with the Imaging FlowCytobot acquisition system to test the proposed approach, obtaining high performances in detecting both in-class and out-of-class samples. Finally, we build a dataset of 15 classes acquired by the WHOI across four years, showing that the proposed approach's ability to identify anomalies is preserved when tested on images of the same classes acquired across a timespan of years. [ABSTRACT FROM AUTHOR]

The phytoplankton population of Qionghai Lake was surveyed in December 2015, March 2016, June 2016, September 2016, and March 2017. A total of 196 species (including varieties) belonging to 77 genera of 7 phyla were identified. The phytoplankton communities were dominated by Chlorophyta and diatoms, and there were significant differences across the five sampling sites. The phytoplankton abundance, which ranged between 13.85 × 104 and 335.54 × 104 cells·L−1, was significantly higher in spring and summer than in autumn and winter. Chlorella sp. and Cyclotella sp. were the dominant populations, and their dominance degree reached as high as 0.54 and 0.33, respectively. The diversity of the phytoplankton populations was significantly higher in spring and summer than in autumn and winter, and the Shannon–Wiener index and Margalef index ranged from 2.49–3.65 and 2.47–3.10, respectively. The water quality of Qionghai Lake was generally good. The trophic level index was between 30 and 60, showing that the water body was overall in a mesotrophic to slightly eutrophic state. The Spearman correlation analyses revealed that ammonium nitrogen (NH4+-N), water temperature (WT), permanganate index (CODMn), and transparency (SD) were the most important environmental factors that influenced the phytoplankton communities. For example, NH4+-N was significantly correlated with Chroococcus sp. (r = 0.41, p < 0.05) and Cryptomonas ovata Ehrenberg (r = 0.45, p < 0.05), and WT was significantly correlated with Cryptomonas marssonii Skuja (r = 0.43, p < 0.05) and Cryptomonas ovata (r = 0.53, p < 0.01). [ABSTRACT FROM AUTHOR]

Global change is rapidly and fundamentally altering many of the processes regulating the flux of energy throughout ecosystems, and although researchers now understand the effect of temperature on key rates (such as aquatic primary productivity), the theoretical foundation needed to generate forecasts of biomass dynamics and extinction risk remains underdeveloped. We develop new theory that describes the interconnected effects of nutrients and temperature on phytoplankton populations and show that the thermal response of equilibrium biomass (i.e. carrying capacity) always peaks at a lower temperature than for productivity (i.e. growth rate). This mismatch is driven by differences in the thermal responses of growth, death, and per‐capita impact on the nutrient pool, making our results highly general and applicable to widely used population models beyond phytoplankton. We further show that non‐equilibrium dynamics depend on the pace of environmental change relative to underlying vital rates and that populations respond to variable environments differently at high versus low temperatures due to thermal asymmetries. [ABSTRACT FROM AUTHOR]

The goal of this study was to examine and assess the stability of phytoplankton communities in connection to the different health status type of shrimp pond (healthy and diseased) in an intensive culture. The research was conducted in two ponds located in Probolinggo region, which had different health status until the eight week of harvest period. Several water quality variables and phytoplankton community composition were observed. Non-metric dimensional scaling and analysis of similarity were used to compare the phytoplankton community structure and water quality parameters in both ponds. In addition, the stability of phytoplankton community in these ponds was measured using species turnover rate, rate change of composition community, and community stability indices. The results showed that phytoplankton community structure and water quality factors between a diseased and healthy pond were not statistically significant. On the other hand, the phytoplankton community in the healthy pond was more stable than that of the diseased pond. Furthermore, ammonia and phosphate were found as the dominant factors affecting the phytoplankton community in the studied ponds. [ABSTRACT FROM AUTHOR]

The current investigation was conducted on hydrobiological parameters and plankton diversity in the Yamuna River at Okhla Barrage. The various water quality parameters were investigated, and found that the pH ranged from 7.35±0.02 to 8.10±0.09, temperature varied from 20.79±0.02 to 32.29±0.05!, dissolved oxygen (DO) levels range from 1.72±0.08 to 3.6±0.12 mg/l, total dissolved solids (TDS) ranged from 179.625±36.605 to 382.75±0.875 mg/L, electrical conductivity (EC) went from 759.25±9.37 to 1527.25±3.47 μs/cm and free CO2 levels varied from 8.4±0.93 to 10.5±0.27 mg/L. There are 51 genera of plankton, including 31 genera of phytoplankton and 20 genera of zooplankton. Phytoplanktons are categorized into four major groups: Bacillariophyceae, Chlorophyceae, Cyanophyceae, and Euglenophyceae, and zooplankton belonging to Protozoa, Rotifera, Copepoda and Cladocera. The phytoplankton population exhibited fluctuations, reaching its peak in October (13,000 per litre) and its lowest point in July (10,400 per litre). On the other hand, the highest zooplankton population was recorded in October, reaching 11,600 per litre, while the lowest count was observed in August, with only 5,200 zooplankton per litre. Regarding diversity indices, the highest and lowest values for phytoplankton occurred in July (1.054) and August (0.849), respectively. The diversity index of zooplankton ranged from 1.381 in November to 1.249 in August, with November having the highest diversity index value. [ABSTRACT FROM AUTHOR]

Due to their role as primary producers, phytoplankton are essential to the productivity of estuarine ecosystems. However, it is important to understand how these nearly passive organisms are able to persist within estuaries when river inflow results in a net outflow to the ocean. Estuaries also represent challenging habitats due to a strong salinity gradient. Little is known about how phytoplankton are able to be retained within estuaries. We present a new individual-based Lagrangian model of the Elbe estuary which examines possible retention mechanisms for phytoplankton. Specifically, we investigated how reproduction, sinking and rising, and diel vertical migration may allow populations to persist within the estuary. We find that vertical migration, especially rising, favors retention, while fast sinking does not. We further provide first estimates of outwashing losses. Our simulations illustrate that riverbanks and tidal flats are essential for the long-term survival of phytoplankton populations, as they provide refuges from strong downstream currents. These results contribute to the understanding needed to advance the ecosystem-based management of estuaries. [ABSTRACT FROM AUTHOR]

Populations are generally censused daily, weekly, monthly or annually. In this paper, we introduce a discrete-time nutrients-phytoplankton-oysters (NPO) model that describes the interactions of nutrients, phytoplankton and oysters in a bay ecosystem. We compute the threshold parameter $ \mathcal {R}_N $ R N for persistence of phytoplankton with or without oysters. When $ \mathcal {R}_{N} \lt 1 $ R N < 1 , then both phytoplankton and oysters populations go extinct. However, when $ \mathcal {R}_N \gt 1 $ R N > 1 , we show that the model may exhibit two scenarios: (1) a locally asymptotically stable equilibrium with positive values of nutrients and phytoplankton with oysters missing, and (2) a locally asymptotically stable interior equilibrium with positive values of nutrients, phytoplankton and oysters. We use sensitivity analysis to study the impact of human and environmental factors on the model. We use examples to illustrate that some human activities and environmental factors can force the interior equilibrium to undergo a Neimark–Sacker bifurcation which generates phytoplankton blooms with oscillations in oysters population and nutrients level. [ABSTRACT FROM AUTHOR]

Dokdo, a volcanic island located in offshore waters, is significantly influenced by various currents and the island effect resulting from upwelling events. Despite these factors, there is a limited understanding of the seasonal changes in phytoplankton populations and their relationship with the environmental factors in the waters around Dokdo, even during dramatic shifts in phytoplankton dynamics. We focused on seasonal oceanographic features over three years (2018, 2019, and 2020) to understand the phytoplankton community structure and seasonal species succession. Winter, characterized by thorough mixing, results in high nutrient levels, leading to increased phytoplankton biomass. The dominance of the large-sized diatom Chaetoceros spp. contributes to relatively low diversity (H': 1.14 ± 0.31). In contrast to the typical coastal waters, spring exhibits dominance by the small nano-flagellates and Cryptomonas spp. associated with a lack of surface nutrients due to increased water temperature. Summer, characterized by strong stratification, shows low phytoplankton biomass but high Chl. a concentrations, possibly influenced by picoplankton and the emergence of dinoflagellates, such as Gyrodinium sp. and Katodinium sp., which increases diversity (H': 2.18 ± 0.28). In autumn, there is typically a phytoplankton bloom, but in 2019, an unusually low biomass occurred. This was likely due to the intrusion of deep, cold water from the bottom and low-salinity Changjiang diluted water (CDW) from the surface, increasing the water's stability. This, in turn, led to nutrient depletion, contributing to a rise in diversity (H': 1.14 ± 0.31). These environmentally complex waters around Dokdo result in a distinct pattern of biodiversity indices, with the highest in summer and the lowest in winter, differing from typical temperate waters. In conclusion, this research highlights the substantial influence of distinctive oceanographic features and nutrient dynamics on the phytoplankton biomass and biodiversity in the Ulleung Basin and Dokdo region. Understanding these patterns is vital for the effective management of marine ecosystems and fisheries resources, emphasizing the necessity for continued long-term monitoring in the vicinity of the Dokdo area. [ABSTRACT FROM AUTHOR]

Feeding effects are crucial for evaluating the capacity of zooplankton to regulate phytoplankton populations within freshwater ecosystems. To examine the impact of the bloom-forming cyanobacteria Raphidiopsis raciborskii, which occurs in tropical and subtropical freshwaters, on the growth of zooplankton Daphnia in relation to toxins, filament length and fatty acid content, we fed D. magna with R. raciborskii only (cylindrospermopsin (CYN)-producing and non-CYN-producing, as the negative controls), Chlorella pyrenoidosa only (as the positive control) and a mixed diet containing R. raciborskii (CYN-producing and non-CYN-producing) and C. pyrenoidosa. Consequently, our findings revealed that the toxic effect of CYN-producing R. raciborskii strains on Daphnia was mitigated by the coexistence of C. pyrenoidosa containing stearidonic acid (SDA, C18:4 ω3) in mixed diets. This was evident in the elevated survival rate compared that from diets containing only R. raciborskii and a significantly higher reproduction and population intrinsic increase rate compared to diets consisting of only R. raciborskii or C. pyrenoidos. Additionally, a strong positive correlation was observed between arachidonic acid (ARA, 20:4ω6) and the population intrinsic increase rate of Daphnia; notably, R. raciborskii strains were found to be rich in the ω6 polyunsaturated fatty acid ARA. These outcomes reinforce the crucial role of polyunsaturated fatty acids in predicting the population increase of crustacean zooplankton, which has long been neglected. Furthermore, our results underscore the potential effectiveness of zooplankton, particularly in temperate lakes, in controlling CYN-producing R. raciborskii populations. [ABSTRACT FROM AUTHOR]

Mesoscale eddies modify the vertical structure of the resource environment and affect the horizontal dispersal and mixing of phytoplankton populations. It is useful to characterize the lateral dispersal and trapping properties of eddies for their biogeochemical interpretation. We employ a Lagrangian approach, which provides metrics of material coherence, to identify and track eddies over two decades of remote sensing observations in an intensely studied region of the North Pacific Subtropical Gyre. Emphasizing biogeochemical applications, we use backward-in-time Lagrangian trajectories to compute the coherency of the recent past, synchronize the analysis with ocean color products, and provide a high temporally resolved atlas of coherent eddy boundaries (Jones-Kellett, 2023a, doi.org/10.5281/zenodo.8139149). We compare Lagrangian coherent and Sea Level Anomaly eddy atlases, finding similar variations in temporal and spatial distributions. However, coherent eddies have a more mechanistic relationship between size and longevity and form distinct regional regimes based on polarity. While 65% of tracked Sea Level Anomaly eddies are classified as coherent at some point in their lifetime, only 54% contain a Lagrangian coherent structure at any given time. We illustrate the potential of the coherent eddy atlas for biogeochemical applications by examining the relationship between bloom development and eddy evolution in a case study of a Hawaiian Lee cyclone. [ABSTRACT FROM AUTHOR]

Due to their role as primary producers, phytoplankton are essential to the productivity of estuarine ecosystems. However, it is important to understand how these nearly passive organisms are able to persist within estuaries, when river inflow results in a net outflow to the ocean. Estuaries are also representing challenging habitats due to a strong salinity gradient. So far, little is known about how phytoplankton are able to be retained within estuaries. We present a new individual-based Lagrangian model of the Elbe estuary which examines possible retention mechanisms for phytoplankton. Specifically, we investigated how reproduction, sinking and rising, as well as diel vertical migration may allow for populations to persist within the estuary. We find that vertical migration especially rising favors the retention, fast sinking does not. We further provide first estimates on outwashing losses. Our simulations illustrate that riverbanks and tidal flats are essential for the long-term survival of phytoplankton populations, providing refuges from strong downstream currents. These results contribute to the understanding needed to advance ecosystem-based management of estuaries. [ABSTRACT FROM AUTHOR]

The scientific community lacks models for the dynamic changes in population size structure that occur in colonial phytoplankton. This is surprising, as size is a key trait affecting many aspects of phytoplankton ecology, and colonial forms are very common. We aim to fill this gap with a new discrete, stochastic model of dynamic changes in phytoplankton colonies' population size structure. We use the colonial phytoplankton Dinobryon as a proof‐of‐concept organism. The model includes four stochastic functions—division, stomatocyst production, colony breakage, and colony loss—to determine Dinobryon population size structure and populations counts. Although the functions presented here are tailored to Dinobryon, the model is readily adaptable to represent other colonial taxa. We demonstrate how fitting our model to in situ observations of colony population size structure can provide a powerful approach to explore colony size dynamics. Here, we have (1) collected high‐frequency in situ observations of Dinobryon in Lac (Lake) Montjoie (Quebec, Canada) in 2013 with a moored Imaging FlowCytobot (IFCB) and (2) fit the model to those observations with a genetic algorithm solver that extracts parameter estimates for each of the four stochastic functions. As an example of the power of this model‐data integration, we also highlight ecological insights into Dinobryon colony size and stomatocyst production. The Dinobryon population was enriched in larger, flagellate‐rich colonies near bloom initiation and shifted to smaller and emptier colonies toward bloom decline. [ABSTRACT FROM AUTHOR]

To examine the potential impact of invasive dreissenid mussels on in situ populations of phytoplankton and nutrients in western Lake Erie, we combined mussel population estimates from a 2018 survey, results from mussel excretion, grazing, and in situ growth experiments, along with nutrient measurements on collected lake water. We calculated the proportion of the water column filtered per day, based on both clearance rates from grazing experiments and mussel biomass. In most cases the water column was filtered less than once per day. Based on mussel densities from nearby survey sites, we found that mussels could be expected to clear less than 5% of phytoplankton from the water column each day. We combined measurements of nitrogen and phosphorus excretion by mussels with survey densities and found that concentrations of nitrogen and phosphorus from excretion were much less than the ambient inorganic nitrogen and phosphorus measured throughout the season. Despite the modest potential impact that we measured, spatial variability in mussel density and temporal variability in nutrients and seston suggest that more substantial impact likely occurs in some conditions. Lastly, we used a mass balance approach to compare flows of nitrogen and phosphorus attributable to mussel assimilation, growth, and excretion. The proportion of assimilated nitrogen (0.01-0.21) and phosphorus (0.007-0.08) due to growth changed markedly throughout the season, but the excretion rate sometimes exceeded the apparent assimilation rate. These differences in growth:assimilation suggest changes in food quantity or quality, fluctuations in growth rates over time, or other physiological effects can lead to short-term imbalance in nutrient cycling by mussels, which could lead to locally important impacts on phytoplankton and algal blooms. Moreover, this work underscores the importance of mapping mussel densities at fine spatial scales and across interannual variation. [ABSTRACT FROM AUTHOR]

Ecological interactions among phytoplankton occur in a moving fluid environment. Oceanic flows can modulate the competition and coexistence between phytoplankton populations, which in turn can affect ecosystem function and biogeochemical cycling. We explore the impact of submesoscale velocity gradients on phytoplankton ecology using observations, simulations, and theory. Observations reveal that the relative abundance of Synechoccocus oligotypes varies on 1–10 km scales at an ocean front with submesoscale velocity gradients at the same scale. Simulations in realistic flow fields demonstrate that regions of divergence in the horizontal flow field can substantially modify ecological competition and dispersal on timescales of hours to days. Regions of positive (negative) divergence provide an advantage (disadvantage) to local populations, resulting in up to ∼20% variation in community composition in our model. We propose that submesoscale divergence is a plausible contributor to observed taxonomic variability at oceanic fronts, and can lead to regional variability in community composition. Plain Language Summary: Oceanic phytoplankton populations, which play an essential role in regulating the carbon and oxygen in our atmosphere and oceans, are shaped by their fluid environment. Ocean currents can alter the diversity and distribution of these populations. However, little is known about the ecological impact of submesoscale flows (1–10 km), which are challenging to observe and model but have a number of interesting features, including increased variability and vertical motion. Here we combine an unprecedented high‐resolution spatial survey of closely related cyanobacterial populations with simulations and theory. We find that previously underappreciated submesoscale flows can drive significant local and regional changes in community composition and biodiversity. Key Points: Unexplained genetic variability is observed among phytoplankton populations at a front in the Mediterranean SeaA theoretical relationship is derived for the influence of horizontal velocity divergence on population dynamicsSubmesoscale velocity divergence is proposed as a mechanism for generating genetic variability in frontal regions [ABSTRACT FROM AUTHOR]

Marine viruses play a key role in regulating phytoplankton populations, greatly affecting the biogeochemical cycling of major nutrients in the ocean. Resistance to viral infection has been reported for various phytoplankton species under laboratory conditions. Nevertheless, the occurrence of resistant cells in natural populations is underexplored due to the lack of sensitive tools to detect these rare phenotypes. Consequently, our current understanding of the ecological importance of resistance and its underlying mechanisms is limited. Here, we sought to identify lipid biomarkers for the resistance of the bloom-forming alga Emiliania huxleyi to its specific virus, E. huxleyi virus (EhV). By applying an untargeted lipidomics approach, we identified a group of glycosphingolipid (GSL) biomarkers that characterize resistant E. huxleyi strains and were thus termed resistance-specific GSLs (resGSLs). Further, we detected these lipid biomarkers in E. huxleyi isolates collected from induced E. huxleyi blooms and in samples collected during an open-ocean E. huxleyi bloom, indicating that resistant cells predominantly occur during the demise phase of the bloom. Last, we show that the GSL composition of E. huxleyi cultures that recover following infection and gain resistance to the virus resembles that of resistant strains. These findings highlight the metabolic plasticity and coevolution of the GSL biosynthetic pathway and underscore its central part in this host-virus arms race. [ABSTRACT FROM AUTHOR]

The biogeochemistry of waters is an essential regulator of phytoplankton dynamics, determining the level of species bloom and the change in dominants. This paper investigated the seasonal dynamics of phytoplankton and the nutrient concentrations and their ratios in the northeastern Black Sea in 2017–2021. Two taxonomic groups, diatoms and coccolithophores, determine the seasonal dynamics and significantly contribute to the total phytoplankton biomass. Coccolithophores formed blooms in early June annually, except in 2020. Large diatoms dominated in summer with a biomass exceeding 1000 mg m−3 annually, except in 2019. During the blooms of these taxonomic groups, their contribution to the total phytoplankton biomass exceeded 90%. Each group has characteristic biogeochemical niches in the nitrogen and phosphorus concentration coordinates. The position of the seasonal thermocline regulates the biogeochemistry of the water. With a high-lying and sharp gradient thermocline (the average for five years is 6.87 m), low nitrogen concentrations and a nitrogen-to-phosphorus ratio below the Redfield ratio are created in the upper mixed layer. These conditions are optimal for the dominance of coccolithophores. When the thermocline is deepened (the average for five years is 17.96 m), the phosphorus concentration decreases significantly and the ratio of nitrogen to phosphorus is significantly higher than the Redfield ratio, and these conditions lead to the dominance of large diatoms. The results of experimental studies with nitrogen and phosphorus additives in the natural phytoplankton population confirm the above statements. The addition of phosphorus leads to the increased role of coccolithophores in the total phytoplankton biomass, the addition of nitrogen alone contributes to the growth of large diatoms, and the combined addition of phosphorus and nitrogen in a ratio close to the Redfield ratio leads to the dominance of small diatoms. [ABSTRACT FROM AUTHOR]

The particle size distribution (PSD) of suspended particles in near-surface seawater is a key property linking biogeochemical and ecosystem characteristics with optical properties that affect ocean color remote sensing. Phytoplankton size affects their physiological characteristics and ecosystem and biogeochemical roles, e.g., in the biological carbon pump, which has an important role in the global carbon cycle and thus climate. It is thus important to develop capabilities for measurement and predictive understanding of the structure and function of oceanic ecosystems, including the PSD, phytoplankton size classes (PSCs), and phytoplankton functional types (PFTs). Here, we present an ocean color satellite algorithm for the retrieval of the parameters of an assumed power-law PSD. The forward optical model considers two distinct particle populations: phytoplankton and non-algal particles (NAPs). Phytoplankton are modeled as coated spheres following the Equivalent Algal Populations (EAP) framework, and NAPs are modeled as homogeneous spheres. The forward model uses Mie and Aden–Kerker scattering computations, for homogeneous and coated spheres, respectively, to model the total particulate spectral backscattering coefficient as the sum of phytoplankton and NAP backscattering. The PSD retrieval is achieved via spectral angle mapping (SAM), which uses backscattering end-members created by the forward model. The PSD is used to retrieve size-partitioned absolute and fractional phytoplankton carbon concentrations (i.e., carbon-based PSCs), as well as particulate organic carbon (POC), using allometric coefficients. This model formulation also allows the estimation of chlorophyll a concentration via the retrieved PSD, as well as percent of backscattering due to NAPs vs. phytoplankton. The PSD algorithm is operationally applied to the merged Ocean Colour Climate Change Initiative (OC-CCI) v5.0 ocean color data set. Results of an initial validation effort are also presented using PSD, POC, and picophytoplankton carbon in situ measurements. Validation results indicate the need for an empirical tuning for the absolute phytoplankton carbon concentrations; however these results and comparison with other phytoplankton carbon algorithms are ambiguous as to the need for the tuning. The latter finding illustrates the continued need for high-quality, consistent, large global data sets of PSD, phytoplankton carbon, and related variables to facilitate future algorithm improvements. [ABSTRACT FROM AUTHOR]

Based on the ecological interpretation of the results of the Lake Baikal ecosystem monitoring in 2014–2021 and in view of the optimization of the observation system on the lake, the directions of a further development of integrated monitoring in the areas of strong anthropogenic impact are presented. [ABSTRACT FROM AUTHOR]

The occurrence of cyanobacterial blooms in summer are frequently accompanied by the succession of phytoplankton communities in freshwater. However, little is known regarding the roles of viruses in the succession, such as in huge reservoirs. Here, we investigated the viral infection characteristics of phytoplankton and bacterioplankton during the summer bloom succession in Xiangxi Bay of Three Gorges Reservoir, China. The results indicated that three distinct bloom stages and two successions were observed. From cyanobacteria and diatom codominance to cyanobacteria dominance, the first succession involved different phyla and led to a Microcystis bloom. From Microcystis dominance to Microcystis and Anabaena codominance, the second succession was different Cyanophyta genera and resulted in the persistence of cyanobacterial bloom. The structural equation model (SEM) showed that the virus had positive influence on the phytoplankton community. Through the Spearman's correlation and redundancy analysis (RDA), we speculated that both the increase of viral lysis in the eukaryotic community and the increase of lysogeny in cyanobacteria may contributed to the first succession and Microcystis blooms. In addition, the nutrients supplied by the lysis of bacterioplankton might benefit the second succession of different cyanobacterial genera and sustain the dominance of cyanobacteria. Based on hierarchical partitioning method, the viral variables still have a marked effect on the dynamics of phytoplankton community, although the environmental attributes were the major factors. Our findings suggested that viruses played multiple potential roles in summer bloom succession and may help the blooms success of cyanobacteria in Xiangxi Bay. Under the background of increasingly serious cyanobacterial blooms worldwide, our study may have great ecological and environmental significance for understanding the population succession in phytoplankton and controlling the cyanobacterial blooms. [ABSTRACT FROM AUTHOR]

Surface seawater and phytoplankton samples were collected from different stations covering the areas of six harbors in the Egyptian Red Sea during 2019-2021. The obtained results revealed 119 phytoplankton species, including 80 species of diatoms, 27 species of dinoflagellates, and six species of both cyanophytes and chlorophytes. Diatoms such as Proboscia alata var. gracillima, Chaetoceros curvisetus, Asterionellopsis glacialis, and Licmophora flabellata produced the highest phytoplankton peak in most harbors. A relatively high phytoplankton population density was recorded at stations near Port Tawfiq Harbor, followed by Zaytiyat. This could be due to the relatively high impacts from various petroleum factories as well as the Sewage Treatment Company, which reflect the area's eutrophic conditions. In general, the highest phytoplankton population density was observed in February 2021, with average counts of 7112 units/L. This is primarily due to the diatom Licmophora flabellata, which accounted for approximately 44% of all phytoplankton in Safaga Harbor waters. However, most of the phytoplankton species in the current study were unique to the Egyptian Red Sea region. On the other hand, several of the harmful species, such as the dinoflagellates Prorocentrum, Goniaulax, and Dinophysis spp., as well as the Cyanobacterium Oscillatoria sp., were found in low counts at some sites of the Egyptian harbors. The statistical analysis of the data indicated that dissolved nitrate (0.81-18.45µM) and ammonium (0.47-5.01µM) were the most effective factors controlling phytoplankton abundance. The multiple regression analysis was calculated to show the relationship between phytoplankton abundance and the most effective environmental factors. A regression equation was obtained and could be applied in the future to predict the total phytoplankton abundance in the coastal waters of the investigated Red Sea harbors. [ABSTRACT FROM AUTHOR]

Phytoplankton growth and microzooplankton grazing are two critical processes in marine food webs, but they remain understudied in the vast area of the subarctic western Pacific and the Bering Sea. In this study, we measured phytoplankton growth and microzooplankton grazing rates in these less‐explored regions to demonstrate their spatial patterns and investigate underlying mechanisms driving the planktonic food web dynamics. Our results showed that the phytoplankton growth in these regions was determined by nutrient availability and temperature. In the high‐nutrient, low‐chlorophyll regions (HNLC), iron availability was the primary factor limiting phytoplankton growth. In contrast, phytoplankton growth in the Gulf of Anadyr and Kamchatka Strait was mainly limited by inorganic nitrogen exhausted by the summer blooms. We found that microzooplankton grazing rate was affected by temperature and prey availability, highlighting the positive effect of temperature. Strong top‐down control on phytoplankton by microzooplankton in the Gulf of Anadyr and Kamchatka Strait indicated an active microbial food web with high turnover rates. In contrast, the decoupling of phytoplankton growth and microzooplankton grazing in the HNLC regions illustrates a weak role of microzooplankton in the marine food web. These results indicated different food web structures in the areas with and without riverine iron input. By revealing the roles of temperature and nutrient or prey availability in regulating the spatial variability of plankton rates, we expect that the plankton will respond differently to ocean warming between the HNLC and coastal regions of the subarctic Pacific due to different nutrient conditions. Our study helps understand how marine plankton will respond to environmental changes at high latitudes. [ABSTRACT FROM AUTHOR]

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We studied the characteristics of plankton community and its response to water environmental factors at the early stage of COVID-19 outbreak (2019–2020) in the Tianjin coastal waters of Bohai Bay. The water quality showed a good trend during this period, due to the reduction of pollution brought by the runoff rivers and water exchange driven by the circulation. In the survey area, 68 species of diatomata and dinoflagellata phytoplankton were found, where diatomata was the dominant population. The number of phytoplankton increased from 636,000 in 2019 to 1,642,600 in 2020. Compared with 2019, the impact factors of water environment in the surveyed area changed greatly, where nitrogen was the main impact factor in 2020. The adjustment of production and lifestyle in the early stage of COVID-19 outbreak suddenly slowed down the growth of the secondary industry, which contributed a lot to the improvement of water quality in 2020.' • Water quality improved and phytoplankton populations increased in coastal waters in 2020. • The environmental factors of phytoplankton distribution in 2019 and 2020 are different. • The decline of secondary and tertiary industry is the main reason for environmental improvement. [ABSTRACT FROM AUTHOR]

The proliferation of certain phytoplankton species may lead to harmful algal blooms (HABs) that can affect living resources and human health. Therefore, an accurate identification of phytoplankton populations is essential for the sustainable management of some activities relevant for the blue economy, such as aquaculture, being also relevant for environmental monitoring and marine research purposes. Microalgae taxonomic discrimination, based on their pigment composition, is a versatile and promising technique to detect and identify potential HABs. In this work, a portable and low-cost device for taxonomic identification of microalgae, based on the pigment composition of 16 species belonging to 6 different phyla, was developed. It uses the fluorescence intensity signal emitted by each species at three wavelengths (575 nm, 680 nm and 730 nm) when excited at five wavelengths (405 nm, 450 nm, 500 nm, 520 nm and 623 nm) to create a fluorescence signature for each species. Furthermore, several machine learning classifiers were studied using this fluorescence signature as features to train and classify each species according to their respective taxonomic group. The Extreme Gradient Boosting (XGBoost) classifier was able to correctly predict microalgae monocultures with 97 % accuracy at the phylum level and 92 % accuracy at the order level. The obtained results confirm the potential of this technique for fast, accurate and low-cost identification of microalgae. [Display omitted] • Portable/low-cost optical device for harmful algal blooms taxonomic discrimination. • Microalgae fluorescence signatures combined with machine learning classification methods. • Detecting the high diversity of phytoplankton communities present in seawater. • Accuracy of 97 % at the phylum and 92 % at the order levels for microalgae monocultures. [ABSTRACT FROM AUTHOR]

To test the possibility of nickel (Ni) limitation and nickel‑nitrogen (Ni-N) colimitation on phytoplankton growth, seven urea/Ni enrichment experiments were conducted in the subtropical and subarctic Pacific Ocean. Effects of additions of urea, nickel, and combination of urea and nickel were examined by monitoring the growth of the whole phytoplankton community and three different phytoplankton populations, Synechococcus , Prochlorococcus , and eukaryotes. In all the experiments in the subtropical regions, urea addition significantly increased the total chlorophyll a concentration as compared to the unamended control after two days of incubation, confirming widespread nitrogen limitation and high accessibility of the urea‑nitrogen to phytoplankton in the subtropical Pacific. In contrast, Ni addition did not affect the total chlorophyll a concentration, whether it was added alone or in combination with urea. To elucidate population-level responses to urea and/or Ni addition, cellular and population chlorophyll content and carbon content were estimated using flow cytometric parameters. Synechococcus and Prochlorococcus mainly responded to the urea enrichment. The addition of Ni alone did not show a significant effect on the chlorophyll or carbon content of any phytoplankton population in most of the experiments. Ni-N colimitation was evident only for Synechococcus , and not for Prochlorococcus or eukaryotic phytoplankton. Ni-N colimitation was evident in the urea drawdown rates only for one experiment out of the six experiments. In contrast, in the subarctic region, urea drawdown decreased with Ni addition, although the reason for this was unclear. The present study demonstrates that Ni bioavailability in the subtropical Pacific can evoke Ni-N colimitation in the pico-sized cyanobacteria Synechococcus , but it does not seem to affect phytoplankton biomass at the community level. • Nickel / urea enrichment experiments were conducted in the Pacific Ocean. • Synechococcus responded positively to nickel additions when amended with urea. • Nickel addition partly enhanced drawdown of the added urea in the subtropical waters. • Nickel‑nitrogen colimitation was not a general phenomenon in the Pacific. [ABSTRACT FROM AUTHOR]

• Nutrient stoichiometry modulates phytoplankton during summer monsoon (SM) in the eastern Arabian Sea (EAS) • High N/P ratio favours diatom dominance throughout the SM in EAS coastal waters. • Low N/P ratio favours pico-nano plankton abundance in the offshore EAS waters. • Proliferation of pico-nano plankton in offshore EAS points towards the existence of a microbial food web. The basin-wide phytoplankton succession and community behaviour in response to varying nutrient patterns during various upwelling phases are detailed, for the first time, in the eastern Arabian Sea (EAS, ∼6◦ to 22◦N) during the summer monsoon (SM) of 2018. Three consecutive observations were carried out during early SM (June-July), peak SM (August), and late SM (September-October), representing different phases of upwelling. During the early phase of upwelling, high phytoplankton biomass was observed in the south (column-integrated chlorophyll a : 74.09 ± 60.05 mg m−2) and moderate levels in the central (25.75 ± 6.51 mg m−2) and north (30.31 ± 12.32 mg m−2) EAS coastal waters. Diatoms were the dominant group (60–90 %) in the coastal stations throughout the upwelling period. Offshore regions characterised by deeper nutriclines (>50 m) had pico-phytoplankton dominance, including cyanobacteria (14–30 %), chlorophytes (19–24 %) and prochlorophytes (12–15 %); however, due to low nitrogen to phosphorous ratio (N/P: 2.6 ± 1.31) during this period, the contribution of diatoms decreased to less than 20 % in the offshore waters compared to the coastal EAS. During peak SM, upwelling induced shoaling of nutriclines and high N/P conditions (8.4 ± 5.25) in the mixed layers of south EAS coastal waters substantially enhanced phytoplankton biomass (chlorophyll a : 129.06 ± 96.24 mg m−2). Additionally, the shallow nutriclines supported diatoms dominance in offshore waters, particularly in the central EAS (up to 65 %), relative to the south and north EAS (22 to 33 %), where the upwelling intensity was weaker. The withdrawal of upwelling led to a deepening of nutricline and low N/P conditions (3.33 ± 2.77 in coastal and 3.35 ± 2.26 in offshore waters) during late SM. This supported the occurrence of cyanobacteria and dinoflagellates, as the contribution of diatoms to the total phytoplankton community sharply decreased to 50 %. In other words, upwelling in the EAS brings nitrogen-deficient (denitrified) waters; the available nitrogen is immediately consumed by the diatom community, resulting in low N/P conditions that favour the dominance of the cyanobacterial population towards late SM. Overall, substantial intra-seasonal variability was observed in nutrient stoichiometry, strongly modulated by the intensity of physical processes affecting the phytoplankton populations. Continuous monitoring is required to understand the phytoplankton populations, their impact on higher trophic levels, and the overall health of aquatic food web structure in the EAS. [ABSTRACT FROM AUTHOR]