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Inorganic carbon acquisition is essential to algal growth, while the limitations of dissolved inorganic carbon (DIC) on phytoplankton are still less known in lakes. Sediment is an active hot spot for microbial metabolism, driving the migration and transformation of elements in shallow lakes, which may control the DIC availability to influence algal spatiotemporal dynamics. Hence, we investigated the spatiotemporal changes of phytoplankton, DIC and sediment respiration rates in a eutrophic shallow freshwater lake under non-bloom conditions. There was a widespread deficiency of DIC in the lake, except the estuary. Sediment respiration was positively associated with changes in DIC concentrations, indicating that carbon metabolic activity of sedimentary microorganisms was an important inorganic carbon source for water columns. The availability of DIC in water columns regulated by sediment microbial respiration influenced the algal biomass, composition and productivity. The synergistic effects of seasonal temperature changes and sediment microbial respiration influenced the vertical distribution and migration of phytoplankton. Our results emphasized that carbon metabolic intensity of sediment microorganisms might play a key role in dynamics of phytoplankton, further impacting the spatiotemporal pattern and formation of algal bloom in eutrophic shallow freshwater lakes. [ABSTRACT FROM AUTHOR]

Mixotrophy, a physiological trait combining autotrophy and heterotrophy in one organism, significantly contributes to energy and matter transfer in aquatic ecosystems. However, understanding how environmental factors influence mixoplankton success across freshwater ecosystems has been uncertain. The grand écart hypothesis (GEH) posits that light and nutrient availability are key components of mixotrophs' niche, suggesting that ecosystem properties determine opposing gradients of light and nutrients, creating environmental filtering for mixotrophs. We hypothesized that ecosystem size, a property of lake ecosystems, mediates the prevalence of patterns and control mechanisms predicted by the GEH on mixoplankton relative biomass (MRB). Using data from 98 tropical lakes, we demonstrated that lake size mediates the inverse relationship between light and nutrient availability across ecosystems. Larger lakes have more light but low nutrients, while smaller lakes have more nutrients but greater shading. Light availability better explains MRB in small lakes, and nutrients better explain MRB in large lakes, with MRB values being higher in small lakes, with secondary influence from zooplankton herbivory. Our results validate the GEH as a significant framework for explaining patterns and control mechanisms of mixoplankton across tropical lakes. This study highlights the significance of lake size as an ecosystem property that generates opposing light and nutrient gradients, further emphasizing its importance for understanding mechanisms regulating freshwater phytoplankton community structure and functioning. Integrating lake size within the conceptual framework of the GEH could aid in explaining mixoplankton success over macroecological scales. [ABSTRACT FROM AUTHOR]

This study investigates the escalating impact of wildfire smoke on the remote sensing of phytoplankton biomass in freshwater systems. Wildfire smoke disrupts the accuracy of Chlorophyll-a (Chl-a) retrieval models, with Chl-a often used as a proxy for quantifying phytoplankton biomass. Given the increasing frequency and intensity of wildfires, there is a need for the development and refinement of remote sensing methodologies to effectively monitor phytoplankton dynamics under wildfire-impacted conditions. Here we developed a novel approach using Landsat's coastal/aerosol band (B1) to screen for and categorize levels of wildfire smoke interference. By excluding high-interference data (B1 reflectance > 0.07) from the calibration set, Chl-a retrieval model performance using different Landsat band formulas improved significantly, with R2 increasing from 0.55 to as high as 0.80. Our findings demonstrate that Rayleigh-corrected reflectance, combined with B1 screening, provides a robust method for monitoring phytoplankton biomass even under moderate smoke interference, outperforming full atmospheric correction methods. This approach enhances the reliability of remote sensing in the face of increasing wildfire events, offering a valuable tool for the effective management of aquatic environments. [ABSTRACT FROM AUTHOR]

As environmental indicators, phytoplankton community variations often indicated the effects of anthropogenic activities on aquatic ecosystem. Efficient and accurate monitoring of phytoplankton is of great significance for water ecological assessment and conservation. We aimed to explore the impacts of anthropogenic activities on an urban river ecosystem via environmental DNA metabarcoding biomonitoring of eukaryotic phytoplankton communities at Panlong River in Kunming, Yunnan, China. 257 Species/genera eukaryotic phytoplankton were detected, and distinct spatial and seasonal variations of phytoplankton community (e.g., ASVs number, dominant taxon, the relative abundances) were observed in Panlong River. The species number (170 species/genera in dry period and 236 species/genera in wet period) and the abundances of Cryptophyta increased from dry period to wet period, while the relative abundances of Bacillariophyta and Dinophyta decreased. The diversities were higher in wet period than in dry period, and there were also significant differences among upstream, midstream and downstream. Redundancy analysis showed the water temperature was the key environmental stressor affecting phytoplankton community structures both in dry and wet periods, while the influences of other environmental factors varied in different periods and different sites. This study provides insights on phytoplankton diversity monitoring and the management of urban rivers. [ABSTRACT FROM AUTHOR]

Freshwater biodiversity has been declining in urban areas, which may threaten ecosystem functions. Although many studies have demonstrated a positive correlation between biodiversity and ecosystem functioning (BEF) in terrestrial and marine ecosystems, little is known about the BEF relationship in freshwater environments, especially in highly urbanized regions where water pollution is a major concern. Eutrophication in urban water bodies may trigger algae blooms, decreasing the evenness or functional divergence (FDiv) of phytoplankton communities, thus negatively affecting ecosystem functioning. Through an annual field investigation, we clarified the relationship between phytoplankton diversity and ecosystem functioning, represented as resource use efficiency (RUE), in an urban river in northern China. Results indicated that evenness in the phytoplankton community contributes most to driving ecosystem functioning compared to environmental factors. The relative abundance of dominant Bacillariophyta was positively correlated with the resource use efficiency of phytoplankton (RUEpp) but negatively correlated with the resource use efficiency of zooplankton (RUEzp). Both phytoplankton evenness and functional divergence were negatively linked to RUEpp but positively to RUEzp. Our findings suggest that the reduction of phytoplankton evenness and functional divergence may seriously threaten resource use efficiency (RUE), and its potential mechanism can provide a crucial reference for water quality protection and sustainable water resource utilization in the basin. [ABSTRACT FROM AUTHOR]

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]

Physicochemical properties of water influence planktonic diversity and distribution, which is essential in obtaining basic knowledge of aquatic biodiversity. Thus current study aims to investigate the spatiotemporal diversity, abundance ratio, and distribution of phytoplankton species and their association with water quality parameters of Chashma Lake, Pakistan. During the study period from 2018 to 2019, we measured 13 physicochemical parameters across three selected sampling sites (S1, S2, and S3) in Chashma Lake, revealing both spatial and temporal variability. Dissolved oxygen (DO) was higher in S3, while S1 exhibited higher alkalinity levels, carbon dioxide, phosphorus, and chloride levels. The study identified 77 phytoplankton species grouped into five taxonomic categories, with Cyanobacteria dominating (39.90%), followed by Chlorophyta (33.4%) and Bacillariophyta (24.88%). Euglenozoa and Ochrophyta were less abundant (1.3% and 0.41%, respectively). Spatial variations in phytoplankton distribution were noted, with Chlorophyta being more abundant at S2, Bacillariophyta and Cyanobacteria at S1, and Euglenozoa dominating at S3. Canonical Correspondence Analysis (CCA) revealed the influence of various physicochemical parameters on phytoplankton distribution. This comprehensive study provides valuable insights for the ecological assessment and monitoring of water bodies. It is recommended that continuous monitoring is required to capture long-term trends, further explore the specific environmental drivers impacting phytoplankton dynamics, and consider management strategies for maintaining water quality and biodiversity in Chashma Lake. [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]

Excessive phytoplankton concentrations in rivers can result in the loss of plant and invertebrate communities, and threaten drinking water supplies. Whilst the physicochemical controls on algal blooms have been identified previously, how these factors combine to control the initiation, size, and cessation of blooms in rivers is not well understood. We applied flow cytometry to quantify diatom, chlorophyte, and cyanobacterial group abundances in the River Thames (UK) at weekly intervals from 2011 to 2022, alongside physicochemical data. A niche modeling approach was used to identify thresholds in water temperature, flow, solar radiation, and soluble reactive phosphorus (SRP) concentrations required to produce periods of phytoplankton growth, with blooms only occurring when all thresholds were met. The thresholds derived from the 2011 to 2018 dataset were applied to a test data set (2019–2022), which predicted the timing and duration of blooms at accuracies of > 80%. Diatoms and nano‐chlorophyte blooms were initiated by flow and water temperature, and usually terminated due to temperature and flow going out of the threshold range, or SRP and Si becoming limiting. Cyanobacterial bloom dynamics were primarily controlled by water temperature and solar radiation. This simple methodology provides a key understanding of phytoplankton community succession and inter‐annual variation and can be applied to any river with similar water quality and phytoplankton data. It provides early warnings of algal and cyanobacterial bloom timings, which support future catchment management decisions to safeguard water resources, and provides a basis for modeling changing phytoplankton bloom risk due to future climate change. [ABSTRACT FROM AUTHOR]

The Global Navigation Satellite Systems (GNSS), including the US's GPS, China's BDS, the European Union's Galileo, and Russia's GLONASS, offer real-time, all-weather, any-time, anywhere and high precision observations by transmitting L band signals continuously, which have been widely used for positioning, navigation and timing. With the development of GNSS technology, it has been found that GNSS-reflected signals can be used to detect Earth's surface characteristics together with other signals of opportunity. In this paper, the current status and latest advances are presented on Global Navigation Satellite System-Reflectometry (GNSS-R) in theory, methods, techniques and observations. New developments and progresses in GNSS-R instruments, theoretical modeling, and signal processing, ground and space-/air-borne experiments, parameters retrieval (e.g. wind speed, sea surface height, soil moisture, ice thickness), sea surface altimetry and applications in the atmosphere, oceans, land, vegetation, and cryosphere are given and reviewed in details. Meanwhile, the challenges in the GNSS-R development of each field are also given. Finally, the future applications and prospects of GNSS-R are discussed, including multi-GNSS reflectometry, new GNSS-R receivers, GNSS-R missions, and emerging applications, such as mesoscale ocean eddies, ocean phytoplankton blooms, microplastics detection, target recognition, river flow, desert studies, natural hazards and landslides monitoring. [ABSTRACT FROM AUTHOR]

Algal blooms caused by eutrophication are a major global problem, and the monitoring and prediction of algal densities in lakes are important indicators of eutrophication management. However, the reliability of the commonly used chlorophyll-a (Chl-a) to characterize phytoplankton density in lake environments needs to be further investigated. In this paper, we sampled and analyzed 365 samples from nine plateau lakes in Yunnan Province during the dry and rainy seasons. The Chl-a data measured by the laboratory spectrophotometric method and the portable YSI multi-parameter water quality meter (YSI) directly used in the field were compared, and regression analysis and correlation analysis with phytoplankton density were performed. Most of the Chl-a values measured by the laboratory instrument were greater than those measured by the YSI, and the correlation between the two methods was weak (0.492, p < 0.001). The correlation between Chl-a and phytoplankton density measured by the YSI reached 0.67 (p < 0.001) in the dry season, while the laboratory methods used to measure Chl-a to characterize phytoplankton density may have led to an overestimation of phytoplankton density due to nonspecific sources of Chl-a. However, both methods are relatively inaccurate for characterizing phytoplankton density. For different trophic states of lakes, nutrient concentration changes affect the Chl-a concentration of phytoplankton. During different seasons, changes in the fluorescence intensity of phytoplankton in response to environmental conditions prevent the YSI results from reflecting the authentic phytoplankton density. Furthermore, high species diversity can lead to inconsistent changes in Chl-a and phytoplankton because the content of Chl-a in individual cells of different phytoplankton is different. The relationship between Chl-a and phytoplankton density was species specific. Therefore, when applying Chl-a to characterize phytoplankton density in lakes, it is necessary to consider environmental conditions, phytoplankton community structure and other practical conditions. In addition, laboratory analytical methods and instrumental techniques and instruments need to be improved. [ABSTRACT FROM AUTHOR]

Great importance is given to maintaining lentic ecosystems, threatened by human-induced consequences worldwide. The present study hypothesized to assess differences in species-environment relationships and ecological status of 15 lakes (saline water systems, high-altitude freshwater lakes, and other freshwater lakes) in the Konya Closed River Basin using phytoplankton indices throughout wet and dry periods. Results of canonical correspondence analysis separated saline and freshwater (high-altitude) habitats, which were characterized by different phytoplankton species. Total phosphorus (TP), electrical conductivity (EC), nickel-Ni, and altitude were the most influential environmental factors affecting phytoplankton dispersal in these ecosystems. Saline lakes were under pressure of high EC, TP, and Ni, while high-altitude freshwater ecosystems were associated with the elevation. Lake Uyuz, associated with TP and Ni, is characterized by Anabaenopsis elenkinii, Cocconeis pediculus, Euglena viridis, Lepocinclis acus, Lepocinclis ovum, and Lepocinclis oxyuris. Several phytoplankton species such as Dunaliella salina, Nitzschia communis, Nitzschia inconspicua, Nitzschia vermicularis, and Navicula cincta were found in saline and saline soda lakes with high EC gradients. Freshwater lakes are characterized by Tabellaria flocculosa, Pinnularia anglica, Fragilaria pararumpens, Eunotia bilunaris, and Pinnularia microstauron. Results of the phytoassessment displayed a high ecological status for Lake Sülüklü but a bad ecological status for Lake Uyuz. The modified phytoplankton trophic index can be an appropriate phytoplankton metric for determining the environmental conditions of lakes in the Konya Closed system. The Søndergaard metric based on total phytoplankton and cyanobacteria biovolume also supported the ecological statuses of lakes. This work underlined the importance of phytoplankton ecological integration in saline water systems and high-altitude freshwater lakes, as well as the determination of the ecological statuses of various lakes in the semiarid eco-region. [ABSTRACT FROM AUTHOR]

The composition and intensity of land use significantly influence the aquatic ecological environment, further affecting the physicochemical attributes of the water body, and indirectly modulating the phytoplankton community structure. This study centers around the Danjiangkou Reservoir, investigating the correlation between land use, water environment, and phytoplankton alongside varying intensities of anthropogenic activities, based on the review of land use, phytoplankton, and water quality data of 2021. Firstly, an analysis was conducted over five circular buffer zones generated around sampling points with radii set at 500 m, 1000 m, 1500 m, 2000 m, and 2500 m, wherein the intensity of human activity was categorized into low, medium, and high, in accordance with the human activity intensity level score (HAILS). This study proceeded to explore the correlation between land use and the water environment across different scales, compared phytoplankton density and community structure differences across varied levels of human activity, and analyzed the association between phytoplankton communities in the Danjiangkou Reservoir and environmental variables under various intensities. The findings showed: The land use within the 500 m circular buffer zone has the greatest impact on the water quality of the Danjiangkou Reservoir, especially with the increase in human activities leading to elevated nutrient levels in the water, thereby promoting the growth and reproduction of algae, and increasing the risk of algal blooms. This research scrutinizes the relationship between land use, water environment, and plankton under varying human activity intensities, serving as a foundation for environmental management sectors to make informed decisions and promote the sustainable development of the catchment water environment. [ABSTRACT FROM AUTHOR]

The anticipated long‐term rise in temperature can have numerous effects on freshwater phytoplankton, however, there is a great deal of uncertainty about how biogeochemical processes modify community functioning under a warming climate. Previous works regarding a large shallow lake and a mesocosm study showed a positive relationship between the temporal variability of phytoplankton composition and mean temperature, which might be a sign of warming‐stimulated instability in ecosystem processes. To elucidate whether these observations are part of a more general phenomenon, we combined a numerical model describing the dependence of algal growth on temperature and nutrient concentration with a multispecies, multi‐nutrient model. We ran simulations representative of changes in phytoplankton communities with randomized initial species composition under different temperature scenarios (current annual temperature pattern increased with 1°C, 2°C, or 3°C), various levels of nitrogen and phosphorus supply and different degrees of temporal variability in those supplies. The model outputs showed that seasonal variability in composition can be enhanced by warming through the mechanistic links between nutrient availability, temperature, and species‐specific growth rates, but the rate of increase is also dependent on nutrient ratios and the size of the species pool. Moreover, temporal variability in nutrient loads also enhanced compositional variability, but the rate of increase also depended on the level of nutrient supply. The results of our study hint that the impact of climate change and eutrophication on phytoplankton dynamics can be more intricate than spatiotemporally limited field or experimental observations would suggest. [ABSTRACT FROM AUTHOR]

Owning to their extreme environmental conditions, lakes on the Qinghai-Tibet Plateau have typically displayed a simplistic food web structure, rendering them more vulnerable to climate change compared to lakes in plains. Phytoplankton, undergoing a changing aquatic environment, play a crucial role in the material cycle and energy flow of the food chain, particularly important for the unique fish species of the Tibetan Plateau. To identify the changing environment indexes and determine the response of phytoplankton composition to the environment change in alpine lakes, three lakes--Lake Qinghai, Lake Keluke and Lake Tuosu--were selected as study areas. Seasonal sampling surveys were conducted in spring and summer annually from 2018 to 2020. Our findings revealed there were significant changes in physicochemical parameters and phytoplankton in the three lakes. Bacillariophyta was the predominant phytoplankton in Lake Qinghai from 2018 to 2020, with the genera Synedra sp., Navicula sp., Cymbella sp. and Achnanthidium sp. predominated alternately. Lake Keluke alternated between being dominated by Bacillariophyta and cyanobacteria during the same period. Dolichospermum sp., a cyanobacteria, was prevalent in the summer of 2018 and 2019 and in the spring of 2020. In Lake Tuosu, Bacillariophyta was the predominant phytoplankton from 2018 to 2020, except in the summer of 2019, which was dominated by cyanobacteria. Synedra sp., Oscillatoria sp., Pseudoanabaena sp., Chromulina sp. and Achnanthidium sp. appeared successively as the dominant genera. Analysis revealed that all three lakes exhibited higher phytoplankton abundance in 2018 that in 2019 and 2020. Concurrently, they experienced higher average temperatures in 2018 than in the subsequent years. The cyanobacteria, Bacillariophyta, Chlorophyta and overall phytoplankton increased with temperature and decreased with salinity and NH4-N. Besides, the ratios of cyanobacteria, and the ratios of Bacillariophyta accounted in total phytoplankton increased with temperature. These findings suggest that cyanobacteria and phytoplankton abundance, especially Bacillariophyta, may have an increase tendency in the three alpine lakes under warm and wet climate. [ABSTRACT FROM AUTHOR]

Reservoirs, heavily influenced by artificial management, often harbor phytoplankton assemblages dominated by cyanobacteria or dinoflagellates, triggering significant changes in aquatic ecosystems. However, due to limited sampling frequency and insufficient attention to species composition, the bloom processes and key characteristics of phytoplankton community structure have not been systematically elucidated. During the low-water level period when blooms are most likely to occur (June to September) in a tributary bay of the Three Gorges Reservoir, daily sampling was conducted to investigate phytoplankton community composition, identify significant environmental factors, and evaluate important structure characteristics of phytoplankton community. The results showed that Microcystis aeruginosa maintained a clear dominance for almost a month in stage 1, with low Shannon and evenness but a high dominance index. Phytoplankton total density and biomass decreased drastically in stage 2, but Microcystis aeruginosa still accounted for some proportion. The highest Shannon and evenness but the lowest dominance index occurred in stage 3. Peridiniopsis niei occurred massively in stage 4, but its dominant advantages lasted only one to two days. NH4-N was responsible for the dominance of Microcystis aeruginosa, while TP and PO4-P was responsible for the dominance of Peridiniopsis niei; however, precipitation contributed to their drastic decrease or disappearance to some extent. The TN: TP ratio could be considered as an important indicator to determine whether Microcystis aeruginosa or Peridiniopsis niei dominated the phytoplankton community. Throughout the study period, physiochemical factors explained more variation in phytoplankton data than meteorological and hydrological factors. Pairwise comparisons revealed an increase in average β diversity with stage progression, with higher β diversities based on abundance data than those based on presence/absence data. Repl had a greater effect on β diversity differences based on presence/absence data, whereas RichDiff had a greater effect on β diversity differences based on species abundance data. Co-occurrence networks for stage 1 showed the most complex structure, followed by stage 4, while the network for stage 3 was relatively sparse, although the overall community division remained compact. This study provides a useful attempt to explore the status and changes in phytoplankton community structure during the bloom process through high-resolution investigation. [ABSTRACT FROM AUTHOR]

Efficient means for measuring the abundance and species composition of phytoplankton in situ continue to pose a big challenge to scientists. Hitherto, analyses and interpretations have been based mainly on small numbers of data acquired from microscopic examinations of water samples. Hence, information on devices facilitating such measurements is highly desirable. This paper examines the opportunities offered by the LISST-100X instrument for measuring in situ the concentrations and spatially variable biovolumes of a species dominant in the southern Baltic during the autumnal bloom. Microscopic analysis of phytoplankton in water sampled from different locations in the southern Baltic confirmed earlier results, indicating that this bloom was due to the overriding prevalence of one microplankton diatom species—Coscinodiscus granii. Combining the microscopic measurements of C. granii cell sizes with the size distribution ranges employed by the LISST-100X yielded equivalent spherical diameters (EDSs) ranging from 47.4 to 188.0 µm, with maxima in the 78.4–92.6 and 92.6–109 ranges. Comparative analysis of the particle size distribution (PSD) spectra was used to separate the abundance of C. granii from the total suspended particulate matter (SPM). Spatial in situ measurements in 2012 and 2014 of C. granii concentrations in surface waters showed that both its abundance and its percentage contribution to the total SPM were highly variable. Over a distance of several km, these concentrations varied from values close to zero to 0.2 µL L−1 in 2012 and from 0.3 to 0.9 µL L−1 in 2014, whereas the percentage in the total SPM was found to vary locally from a few to c. 50%. The proposed method and results demonstrate the success of the LISST-100X instrument in detecting size and volume concentrations of phytoplankton in size classes ranging from 1.25 to 250 μm. However, the correct interpretation of LISST data requires that the dominant phytoplankton species concentration in the suspensions be large enough for the signal (peak) to be readily visible against the background PSD of other SPM. [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]

High mountain lakes are increasingly recognized as sentinel ecosystems of global change. Monitoring phytoplankton changes or reconstructing their composition from sedimentary records can help identify systemic changes in these lakes and their catchments.This study aimed to evaluate the distribution of the major phytoplankton groups in high mountain lakes across environmental gradients and identify tipping points in relative dominance. The phytoplankton groups were estimated using pigment‐based chemotaxonomy in 79 lakes in the Pyrenees selected to cover the bedrock and elevation gradients. Fifty‐four environment variables were considered, including in‐lake and catchment descriptors.Redundancy analyses showed that in‐lake descriptors override the explicative capacity of landscape variables. Generalized additive models and multivariate regression trees showed that water hardness, trophic state and food‐web descriptors were, in this order, the most influential factors determining phytoplankton group dominance. Calcium concentration of about 200 μeq L−1 defined the threshold between soft waters—with chrysophytes and chlorophytes showing a higher affinity for them—and harder waters that favour diatoms and cyanobacteria. Across the trophic gradient, there was a threshold at ~5 μg L−1 of total phosphorus (TP), chrysophytes being dominant below that TP value and cryptophytes above. The dominance of chlorophytes and cryptophytes increased with the density of macrozooplankton. Chrysophytes were significantly lower and diatoms higher in lakes with fish.Synthesis. The relative abundance of phytoplankton groups in temperate high mountain lakes responds in a nonlinear way to the hardness of the water in the range 20–1195 Ca2+ μeq L−1 and the trophic state in the range 0.94–19 TP μg L −1. The thresholds across water hardness and trophic state gradients coincide with studies based on other organisms, pointing to a robust typology for mountain lakes that should be considered when selecting global change sentinel lakes and anticipating abrupt transitions across these thresholds. [ABSTRACT FROM AUTHOR]

Climate change is expected to increase the frequency of extreme temperature events. The effect of heatwaves on phytoplankton is of particular concern because they are a key source of C, N, P and essential fatty acids to aquatic ecosystems. Laboratory studies have demonstrated that phytoplankton grown at warmer temperatures are a lower quality food source, but how heatwaves affect phytoplankton quality at the community scale is currently unclear.Here we address this knowledge gap by growing natural assemblages of freshwater phytoplankton at "ambient", "constant warming" or "heatwave" conditions. We next fed these phytoplankton communities to natural assemblages of zooplankton to test the prediction that zooplankton that consume heatwave‐exposed phytoplankton will exhibit reductions in biomass.Our experiment demonstrated that zooplankton that consumed "heatwave" phytoplankton attained lower community biomass than those fed "constant warming" or "ambient" phytoplankton. Additionally, despite receiving similar total heat input, phytoplankton exposed to "heatwave" conditions contained lower C, N, P and fatty acid concentrations compared to phytoplankton grown in "constant warming" conditions.Correlations between zooplankton biomass and all measured phytoplankton traits revealed that decreases in zooplankton biomass were best explained by low quantities of C, N and monounsaturated fatty acids in "heatwave" phytoplankton.Our study demonstrates that the effects of heatwaves on phytoplankton quality are clearly distinct from those caused by constant warming temperatures and that heatwave‐mediated decreases in resource quality have immediate effects on consumer productivity. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Although the general impacts of zooplankton grazing on phytoplankton communities are clear, we know comparatively less about how specific grazing strategies interact with environmental conditions to shape the size structure of phytoplankton communities. Here, we present a new data‐driven, size‐based model that describes changes in the size composition of lake phytoplankton under various environmental constraints. The model includes an ecological trade‐off emerging from observed allometric relationships between (1) phytoplankton cell size and phytoplankton growth and (2) phytoplankton cell size and zooplankton grazing. In our model, phytoplankton growth is nutrient‐dependent and zooplankton grazing varies according to specific grazing strategies, namely, specialists (targeting a narrow range of the size‐feeding spectrum) vs. generalists (targeting a wide range of the size‐feeding spectrum). Our results indicate that grazing strategies shape the size composition of the phytoplankton community in nutrient‐rich conditions, whereas inorganic nutrient concentrations govern phytoplankton biomass. Under oligotrophic regimes, the phytoplankton community is dominated by small cell sizes and the grazers have little to no impact. Under eutrophic regimes, dominating specialist grazers push phytoplankton towards small cells, whereas dominating generalist grazers push phytoplankton towards large cells. Our work highlights that trait‐based modeling, based on realistic eco‐physiological trade‐offs, represents a valuable tool for disentangling the interactive roles played by nutrient regimes and grazing strategies in determining the size compositions of lake phytoplankton. Ultimately, our study offers a quantitative basis for understanding how communities of lake phytoplankton may reorganize in the future in response to changes in nutrient levels and zooplankton grazing strategies. [ABSTRACT FROM AUTHOR]

The Ross Sea is a highly productive system characterized by a seasonal succession of phytoplankton groups. However, most of the current understanding is based on observations on the continental shelf in spring and summer at relatively coarse taxonomic resolution. Here, we characterize community composition (class to species) using V4‐18S rRNA gene metabarcoding on transects to and across the Ross Sea (shelf‐slope and oceanic subregions) during two voyages covering the Austral summer–autumn progression in successive years. Phytoplankton composition shifted from low‐diversity diatom‐dominated (50%) communities during the summer to more diverse dinoflagellate‐dominated (48%) systems during the lower‐productivity autumn season. Prymnesiophyceae abundance was low on both voyages (10%), except on the southeast shelf‐slope, where Phaeocystis antarctica dominated a shallow mixed layer, contrary to its reported preference for deep‐mixing conditions. Amplicon sequence variant analysis identified distinct spatial patterns for two P. antarctica genotypes yet clustered certain species of Bacillariophyta and Prymnesiophyceae, indicating similar environmental preference for genotypes in these groups. Multivariate analysis of environmental drivers found a higher correlation of community composition variation with salinity and macronutrients, but less so with mixed layer depth, considered a primary determinant of taxonomic composition in the Ross Sea. Comparison between years established that community composition was temporally more stable in oceanic relative to shelf‐slope waters. This study of seasonal variation of phytoplankton community composition at finer taxonomic resolution provided insights into species‐ and strain‐specific distribution, ecological preferences, and relationships to environmental conditions in the wider Ross Sea to inform modeling and projection of future regional changes. [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]

Despite management efforts, anthropogenic nutrient enrichments continue to enhance phytoplankton blooms worldwide. Release of nitrogen and phosphorus compounds not only provides surplus of nutrients but also disbalances their stoichiometry. Declines in the relative availability of dissolved silicon might induce limitation in diatoms, major primary producers with silicified shells. We studied experimentally how nutrient enrichment and resulting decline in dissolved silicon to nitrogen ratios (Si:N) affect the structure and functioning of natural plankton communities. Nitrate was added to create a range of Si:N ratios and phosphate was supplied in Redfield ratio to nitrogen. We also manipulated copepod abundance to understand the top-down effects on communities experiencing nutrient enrichment. Nitrogen and phosphorus additions resulted in a steep phytoplankton biomass increase, followed by a post-bloom decline. Phytoplankton bloom biomass was higher in high nitrogen treatments but during the post-bloom period this trend switched. Biomass was sustained longer in high Si:N treatments, indicating that silicon limitation terminates the bloom. Many diatom species did not benefit from nitrogen and phosphorus enrichment and diatom dominance ceased below Si:N of 0.4:1. Under high grazing pressure, silicate was taken up faster suggesting that silicification is important in diatom defense. Copepods shaped plankton communities via feeding on dinoflagellates, chlorophytes and the diatom Skeletonema costatum but there was no significant effect of nitrogen and phosphorus enrichment on copepod abundance. Our results, combined with previous studies, show that while nutrient concentrations define the total phytoplankton bloom biomass, resource ratios are important in sustaining biomass and determining community structure and composition. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) serves as the primary substrate for the photosynthesis of phytoplankton, forming the foundation of marine food webs and mediating the biogeochemical cycling of C and N. We studied the effects of CO2 variation on the Michaelis-Menten equations and elemental composition of Skeletonema dohrnii and Heterosigma akashiwo. CO2 functional response curves were conducted from 100 to 2000 ppm. The growth of both phytoplankton was significantly affected by CO2, but in different trends. The growth rate of S. dohrnii increased as CO2 levels rose up to 400 ppm before reaching saturation. In contrast to S. dohrnii, the growth rate of H. akashiwo increased with CO2 increasing up to 1000 ppm, and then CO2 saturated. In addition, H. akashiwo showed a slower growth rate than S. dohrnii for all CO2 concentrations, aside from 1000 ppm, and the Michaelis-Menten equations revealed that the halfsaturation constant of H. akashiwo was higher than S. dohrnii. An increase in CO2 concentration was seen to significantly affected the POC: Chl-a of both S. dohrnii and H. akashiwo, however, the effects on their elemental composition were minimal. Overall, our findings indicate that H. akashiwo had a more positive reaction to elevated CO2 than S. dohrnii, and with higher nutrient utilization efficiency, while S. dohrnii exhibited higher carbon fixation efficiency, which is in line with their respective carbon concentrating mechanisms. Consequently, elevated CO2, either alone or in combination with other limiting factors, may significantly alter the relative relationships between these two harmful algal blooms (HAB) species over the next century. [ABSTRACT FROM AUTHOR]

Phytoplankton are usually considered autotrophs, but an increasing number of studies show that many taxa are able also to use organic carbon. Acquiring nutrients and energy from different sources might enable an efficient uptake of required substances and provide a strategy to deal with varying resource availability, especially in highly dynamic ecosystems such as estuaries. In our study, we investigated the effects of 31 organic carbon sources on the growth (proxied by differences in cell counts after 24 h exposure) of 17 phytoplankton strains from the Elbe estuary spanning four functional groups. All of our strains were able to make use of at least 1 and up to 26 organic compounds for growth. Pico-sized green algae such as Mychonastes, as well as the nano-sized green alga Monoraphidium in particular were positively affected by a high variety of substances. Reduced light availability, typically appearing in turbid estuaries and similar habitats, resulted in an overall poorer ability to use organic substances for growth, indicating that organic carbon acquisition was not primarily a strategy to deal with darkness. Our results give further evidence for mixotrophy being a ubiquitous ability of phytoplankton and highlight the importance to consider this trophic strategy in research. [ABSTRACT FROM AUTHOR]

Despite advances in phytoplankton ecology through functional approaches, little is known about functional traits highlighting metacommunity processes. Our aim was to highlight and compare the influence of spatial and local environmental factors in a phytoplankton metacommunity, in a subtropical shallow lake system, based on taxonomic composition and different functional trait measures. Environmental filtering significantly explained metacommunity variation in most approaches. The spatial signal found could be interpreted as mass effects, given the scale of the present study, and was also a significantly driver of community variability. Among the functional measures, Morphology-Based Functional Groups revealed a stronger influence of the pure environmental component. Although the taxonomic approach helped capture variability in the local environment in a reliable way, it also showed the highest residual variance. Phytoplankton volume significantly captured both local and spatial processes under low residual variance, which may make it a promising functional trait for metacommunity studies. Our findings demonstrated that the drivers of phytoplankton metacommunity may be differently captured by taxonomic and functional measures, so that the approaches can eventually give more or less weight to the environmental and/or spatial signals. We thus recommend the use of taxonomic and functional approaches in metacommunity studies in a complementary way. [ABSTRACT FROM AUTHOR]

Semi-quantitative microscope counts of phytoplankton are often a compromise between time-consuming cell biomass analyses and no phytoplankton data. We demonstrate how semiquantitative data from a monitoring program can be used to study phytoplankton community composition, its annual cycle, and aspects of the ecosystem it inhabits. Semi-quantitative counts from Agmon Wetlands, Israel, collected monthly from 2008 to 2021, were generated by allocating a score from 1 (rare) to 6 (extremely abundant) to each taxon observed in a sample. Five samples could be analyzed at the time it takes to count one sample by the conventional Utermöhl method. Using an exponential regression equation, the scores were transformed to estimated concentrations (algal units/ml), then summed into taxonomic or other groups of species. A strong annual pattern of the sum of scores for each taxonomic group was observed. The method was useful for assessing ecosystem features based on indicator species, and for presenting the contribution of morpho-functional groups to the phytoplankton community. If making a species list is planned, we recommend assigning scores, creating calibration curves, converting the scores to concentration estimates, and using those estimates to achieve higher resolution and better conclusions than possible with a species list alone. [ABSTRACT FROM AUTHOR]

In 2019, phytoplankton and environmental parameters were analysed monthly during the growing season from April to September at 26 sampling sites in the Danube and 10 additional sampling sites in the main tributaries as part of the Joint Danube Survey 4, organised by the ICPDR. Our results showed that both phytoplankton biomass and composition follow the River Continuum Concept on free-flowing sections, but also responds to hydromorphological changes where the largest dam Iron Gate represents the largest interruption of the river and the phytoplankton continuum. Besides longitudinal interruption, water residence time was the most important factor for phytoplankton composition, while nutrients were less relevant. The low phytoplankton biomass and its composition in the Danube support the oligotrophication trend, but this one-year study could not confirm it with certainty. Phytoplankton is the most important autotrophic component in the Upper and Middle Danube, where environmental conditions do not support the optimal growth of other river flora. The predominant FGs coda were A, C and D as a typical potamoplankton component, while the codon TB occurs throughout the Danube but is more prominent in the Upper reach and other river sections with higher discharge events. [ABSTRACT FROM AUTHOR]

Meteorological and hydrological forcings influence phytoplankton at very short-time scales. The effect of turbulence, dilution, light, and nutrients are highly dynamic. Yet, our knowledge of short-term phytoplankton dynamics associated with discharge disturbances and nutrient inputs remains elusive, especially in large rivers. Based on every three-day monitoring, we studied phytoplankton in the middle Loire River (France) and related to the daily variations in water discharge and the physical and chemical parameters. We focused on summer phytoplankton (2013 and 2014), where dissolved inorganic phosphorus concentration was potentially limiting growth. We identified eight discharge events, which increased suspended matter concentration and decreased chlorophyll-a concentration. The most significant environmental drivers of phytoplankton composition were discharge and water temperature, a sensitive proxy for meteorological forcing at short-time scale. The phytoplankton composition responded to changes in hydrology along with three distinct assemblage types, where even small water discharge increase induced a community response. Meroplanktic algae being able to withstand sedimentation and resuspension could take advantage of hydrological peaks, following the benthic retention hypothesis. Our results suggest that short-term dynamics are crucial to understanding community organization and functioning in large river plankton, with meroplankton playing a decisive role in maintaining phytoplankton diversity and ecosystem functioning. [ABSTRACT FROM AUTHOR]

Phytoplankton is one of the five biological quality elements used to assess the ecological status of lakes within the Water Framework Directive. Classical morphological Utermöhl method and eDNA metabarcoding by Ilumina sequencing the hypervariable V9 region of the eukaryotic SSU rRNA gene were used to analyse the qualitative and quantitative composition of the phytoplankton and compared at the taxonomic and FG level to highlight advantages and disadvantages of eDNA metabarcoding method over classical microscopy. Samples were collected from April to September in seven Croatian natural karst lakes. Cluster analysis based on the Bray–Curtis similarity of taxa biomass (microscopy) and number of sequences (eDNA metabarcoding) clearly separated lakes showing that eDNA metabarcoding is sensitive to species change. Overlap at the species level between methods was found primarily in the taxa of Cryptophyta, Miozoa, and Ochrophyta, while some very common taxa of Bacillariophyta, Charophyta, and Chlorophyta identified by microscopy were not detected by eDNA metabarcoding, possibly due to incompleteness of the reference databases. At a higher organizational level, the results showed poor overlap of taxonomic and functional group composition and poor comparability of relative biomass to relative number of sequences, indicating the need to complete reference databases and standardize quantification to further develop eDNA metabarcoding for ecological status assessment. [ABSTRACT FROM AUTHOR]

Phytoplankton is a well-studied group of organisms that can change rapidly with environmental conditions, providing a reliable response to these changes. We analysed phytoplankton biomass, diversity, and its response to environmental conditions in the shallow brackish Mediterranean Lake Vransko. Although protected as Nature Park, the Lake's succession is enhanced by intensive agricultural activity and an artificial connection to the sea. Analysis of phytoplankton reveals a specific community composition strongly influenced not only by nutrients but also by salinity gradient, with species composition shifting from freshwater to brackish. Conditions of higher salinity support the dominance of brackish species, often with low biomass, while periods of low salinity are characterised by dominance of cyanobacteria or other freshwater species capable of rapidly taking up nutrients and forming algal blooms. Changes in water transparency caused by phytoplankton dynamics strongly influence the overall lake system through the availability of macrophyte growth and sediment fixation. These findings are critical for the future lake management, particularly its hydrological regime and maintenance of natural oligohaline and mesotrophic conditions. Understanding the response of phytoplankton to environmental conditions, exacerbated by anthropogenic influence and recent climate change, contributes to the protection of Mediterranean shallow lakes at local and global scales. [ABSTRACT FROM AUTHOR]

In contrast to pelagic and benthic realms of the aquatic ecosystems, studies on the metaphytic habitats remain underrepresented in the literature. However, this realm may have a potential impact on composition and diversity of the open water assemblages through metacommunity processes (source-sink dynamics, mass-effect) especially in small ponds with extended littoral zone. Using a limnocorral experiment we studied how metaphyton affects diversity and composition of open water phytoplankton in a small eutrophic pond in the vegetation period. The three habitats (metaphyton, isolated and non-isolated open water) showed considerable differences in their taxa and functional group composition. Abundance-based diversity measures did not reveal remarkable differences among the assemblages of the three habitats. However, taxonomic and functional richness of the metaphyton and the non-isolated part of the pelagial significantly exceeded that of the limnocorral. Incidence-based similarity index values also showed closer resemblance of the metaphyton and plankton samples compared to that of the limnocorral. In the case of several functional groups, their functional redundancy in the metaphyton exceeded that in the open water areas. These results suggest that the metaphyton provides a refuge for several euplanktic elements that survive in the littoral and occasionally enrich the phytoplankton of the open water areas, representing that a within–lake metacommunity processes shape the composition and functioning of the open water areas in standing waters. [ABSTRACT FROM AUTHOR]

Phytoplankton species exhibit fundamental temperature niches that drive observed species distributions linked to realized temperature niches. A recent analysis of field observations of Prochlorococcus showed that for all ecotypes, the realized niche was, on average, colder and wider than the fundamental niche. Using a simple trait‐based metacommunity model that resolves fundamental temperature niches for a range of competing phytoplankton, we ask how dispersal and local temperature variability influence species distributions and diversity, and whether these processes help explain the observed discrepancies between fundamental and realized niches for Prochlorococcus. We find that, independently, both dispersal and temperature variability increase realized temperature niche widths and local diversity. The combined effects result in high diversity and realized temperature niches that are consistently wider than fundamental temperature niches. These results have broad implications for understanding the drivers of phytoplankton biogeography as well as for refining species distribution models used to project how climate change impacts phytoplankton distributions. [ABSTRACT FROM AUTHOR]

Phytoplankton guilds are commonly characterised by dominance effects, while the main contribution to biological diversity is given by rare species. Here, we analysed the influence of rare species on taxonomic and functional diversity, which is described by taxa richness and composition, cell size, and size–abundance relationships in phytoplankton guilds. We explore these relationships at global and regional scales by analysing phytoplankton guilds from five biogeographical regions: the Northern Atlantic Ocean (Scotland), the South-Western Atlantic Ocean (Brazil), the South-Western Pacific Ocean (Australia), the Indo-Pacific Ocean (Maldives), and the Mediterranean Sea (Greece and Turkey). We have comparatively analysed the phytoplankton taxonomic diversity of the whole dataset and with the datasets obtained by progressively subtracting taxa occurring in the last 1%, 5%, 10%, and 25% of both numerical abundance and overall biomass. Globally, 306 taxa were identified across five ecoregions with only 27 taxa accounting for 75% of overall numerical abundance and biomass; almost 50% of taxa were lost on every step. The removal of 1% of most rare taxa significantly affected the phytoplankton size–abundance relationships and body-size structure, strongly impacting on small taxa. The progressive removal of additional rare taxa did not further affect phytoplankton size–abundance relationships and size structure. [ABSTRACT FROM AUTHOR]

This study investigates phytoplankton functional group variations in the western Bay of Bengal (WBoB) during the Spring Intermonsoon. Samples were collected from four cross-shore transects: Mahanadi (MN), Vamsadhara (VD), Godavari (GD), and Krishna (KS). East India Coastal Current and warm gyre influenced the southern transects (KS, GD), VD was experiencing moderate upwelling and MN was characterized by low salinity and oligotrophic conditions due to freshwater input. In response to hydrography, phytoplankton biomass and functional types differed within and between the transects. Chlorophyll-a (Chl-a) was spatially high in VD and low in MN. The subsurface Chlorophyll-a maxima (SSCM) was prominent and shallow in the MN and VD, compared to the southern transects. Total diagnostic pigments concentration was high in VD, followed by GD, KS and MN. Phytoplankton functional groups and each groups contribution to Chl-a was calculated through CHEmical Taxonomy (CHEMTAX). Diatoms and cyanophytes were the dominant functional types in the surface layers. Progressive shift from diatoms in the nearshore region to cyanophytes in the offshore was observed. The low saline and low-nutrient conditions were conducible for the growth of cyanophytes, while nutrient-rich optimum light layer of SSCM and upper layer of VD were favorable for diatoms. Cryptophytes contribution to Chl-a was higher in southern transects compared to the north. Prymnesiophytes and prasinophytes were high in the subsurface and deep layers could be due to their adaptions to light and nutrients. The present study highlights the significance of physical processes associated hydrography in structuring the phytoplankton functional types. [ABSTRACT FROM AUTHOR]

We investigated the spatio-temporal dynamics of phytoplankton composition, chlorophyll-a as a proxy for algal biomass, and abundance in relation to environmental parameters in four Ethiopian soda lakes: Arenguade, Beseka, Chittu, and Shala. Triplicate water samples were collected from each lake from January to December 2020, four times in different seasons. Lake Chittu had the highest chlorophyll-a concentration, followed by Lake Arenguade, Beseka and Shala. Chlorophyll-a concentrations generally increased during the post rainy and dry season. The results of LR models are high for lakes Arengude, Beseka and Chittu. Lakes Shala and Beseka had the highest number of phytoplankton taxa, with both taxa composition and abundance dominated by Bacillariophyceae. Cyanoprokaryota, particularly Limnospira fusiformis, predominated in the abundance of Lakes Arenguade and Chittu. Water temperature, Secchi depth, turbidity, electrical conductivity, soluble reactive phosphorus, nitrate and silica significantly influenced the phytoplankton community structure. Long-term trend analysis revealed changes in phytoplankton biomass and lake taxonomic composition. The alteration in phytoplankton biomass and species composition of the lakes could be attributed to three factors: (1) frequent high-velocity explosions conducted for seismological studies in the past. This impact caused a dramatic increase in lake level in the case of Lake Beseka leading to a drop in nutrient concentration; (2) climate change and (3) salt content. Overall, our findings suggest that phytoplankton composition, biomass, and abundance varied according to seasonal fluctuations, emphasizing the possible effects of anthropogenic and natural causes on their community structure. [ABSTRACT FROM AUTHOR]

Estuarine systems, being situated at the interface between land and marine environments, are important sites for nitrate (NO3-) retention and processing due to large inputs, long retention time, and high biogeochemical activity. However, it remains uncertain how pelagic and benthic processes control NO3- cycling and how these differ between contrasting seasons. In this study, we measured pelagic and benthic assimilatory and dissimilatory NO3- processes in a large lagoon (Curonian Lagoon, SE Baltic Sea) to understand changes in NO3- cycling in relation to variation in riverine inputs and shifts in phytoplankton community composition. We show that in spring, benthic dissimilatory and assimilatory NO3- processes were important, while in summer, pelagic assimilatory processes dominated. During spring, diatom blooms promote greater delivery of nitrogen (N) and labile organic matter to the benthos resulting in greater denitrification in the sediments and a net flux of NO3- from the water column to the sediments. In summer, phytoplankton blooms dominated by buoyant cyanobacteria exhibited high rates of assimilatory uptake and greater particulate organic N export to the sea, but low rates of sediment--water exchange. Cyanobacteria blooms were associated with higher absolute rates of NO3- uptake, as well as higher mass-specific rates compared to spring. Given the low dissolved inorganic N in summer, high uptake indicates that the pelagic community possessed a nutritional strategy to efficiently utilize multiple N forms. Overall, our findings show that the seasonal succession from diatom to cyanobacteria-dominated communities is associated with a shift from strong benthic-pelagic coupling to predominantly pelagic-based N cycling. [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 Danjiangkou Reservoir supplies drinking water to most residents in northern China. However, signs of eutrophication have been observed in the inlet tributaries of the reservoir, including the Shending River backwater. This research used data from the Sentinel-2 Multispectral instrument and findings from a 2021 aquatic ecological survey to analyze the spatial and temporal characteristics of phytoplankton distribution in the Shending River backwater region. The average chlorophyll a (Chl-a) concentrations by season, ranked from largest to smallest, are as follows: summer (63.96 μg/L) > autumn (41.26 μg/L) > spring (27.47 μg/L) > winter (16.21 μg/L); the upstream of the backwater area and the near-shore tributary bay had relatively higher Chl-a concentration. Bacillariophyceae (Cyclotella meneghiniana and Synedra sp.) and Cryptophyceae species (Chroomonas acuta) were dominant in spring, whereas Chlorophyceae (Scenedesmus sp. and Chlorella vulgaris) and Cyanophyceae (Dactylococcopsis acicularis, Microcystis aeruginosa and Oscillatoria tenuis) species were dominant in summer. The seasonal succession characteristics of the phytoplankton community were consistent with those of the Plankton Ecology Group model. The average phytoplankton cell density was 4.80 × 107 cells/L, and the Shannon–Wiener average diversity index was 1.95, indicating that the Shending River backwater area was moderately eutrophic. According to Pearson correlation analysis and Mantel test, the main factors causing temporal and spatial differences in phytoplankton production in the Shending River's backwater were water level (WL), water temperature (WT), ammonia nitrogen (NH3-N) and total nitrogen (TN). In particular, WL was significantly positively correlated with Bacillariophyceae, Chlorophyceae and Cyanophyceae, whereas WT was significantly correlated with Cryptophyceae and Chlorophyceae. NH3-N and TN were significantly correlated with Cyanophyceae. Therefore, intensive nitrogen removal from the tailwater of sewage treatment plants may be considered a feasible measure to prevent cyanobacterial bloom in the Shending River backwater of the Danjiangkou Reservoir. [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]

Filamentous algae blooms (FABs) have been increasing globally in recent years, and their presence can have both harmful and beneficial effects on aquatic ecosystems. As one of the most common FABs, Cladophora blooms have been reported in the lakes of the Qinghai-Tibet Plateau during the past few years. However, there have been few studies focused on how FABs impact other aquatic organisms, especially in alpine lakes since these are at the forefront of responding to global climate change. In this study, the phytoplankton communities in different regions of Qinghai Lake were profiled in different seasons using meta-barcode sequencing. The phytoplankton assemblages in areas with Cladophora blooms were compared to those without Cladophora. The phytoplankton community structure correlated with physicochemical properties including water temperature, electrical conductivity, nitrate, and the presence or absence of Cladophora blooms. The relative abundance of Bacillariophytes was found to be higher in zones with Cladophora blooms than in other regions. Significant seasonal changes in phytoplankton biomass and β diversity were observed in zones with Cladophora blooms. Growth and microbial degradation of Cladophora can change the pH, dissolved oxygen, secchi depth, and nitrate. Together with seasonal temperature and electrical conductivity changes, Cladophora growth can significantly impact the phytoplankton biomass, community dissimilarity and assembly process. These results showed that Cladophora plays a key role in littoral aquatic ecosystem ecology. [ABSTRACT FROM AUTHOR]

The effect of climate warming on community composition is expected to be contingent on competitive outcomes, yet approaches to projecting ecological outcomes often rely on measures of density‐independent performance across temperatures. Recent theory suggests that the temperature response of competitive ability differs in shape from that of population growth rate. Here, we test this hypothesis empirically and find thermal performance curves of competitive ability in aquatic microorganisms to be systematically left‐shifted and flatter compared to those of exponential growth rate. The minimum resource requirement for growth, R*—an inverse indicator of competitive ability—changes with temperature following a U‐shaped pattern in all four species tested, contrasting from their left‐skewed density‐independent growth rate thermal performance curves. Our results provide new evidence that exploitative competitive success is highest at temperatures that are sub‐optimal for growth, suggesting performance estimates of density‐independent variables might underpredict performance in cooler competitive environments. [ABSTRACT FROM AUTHOR]

The study was designed to assess the water quality based on physico-chemical parameters and phytoplankton communities of eight lentic water bodies of Haryana which are famous for mass bathing and religious rituals taking place here. To evaluate comparative analysis of composition, diversity and distribution of Phytoplankton and physico-chemical factors, water samples were collected seasonally viz., summer, monsoon, post monsoon and in winters from all the eight sites in triplicate. Total 118 phytoplankton taxa were observed at all sites. Among these cyanophyceae group was found most dominant at sites 1, 2, 4, 5, 7, 8 whereas cholorophyceae at site 6, bacillariophyceae at site 1,3,4,7 whereas xanthophyceae was in abundance at site 5. Population density (nos. L-1) wise phytoplankton trend was Cyanophyceae > Chlorophyceae > Bacillariophyceae >Desmidiaceae and Species diversity wise phytoplankton trend observed was Chlorophyceae > Bacillariophyceae > Cyanophyceae >Desmidiaceae. Correlation of different phytoplankton groups with physicochemical factors revealed a significant negative correlation of Cyanophyceae with pH, whereas a significant positive correlation of ortho-phosphate with Desmids and bacillariophyceae wheareas CO2 showed a positive correlation with Xanthophyceae. Appearance of pollution tolerant taxa of phytoplankton Microcystis aeruginosa, Phormidium sp., Scenedesmus spp., Pediastrum spp., Mougeotia sp., Synedra sp., Pediastrum spp. at most of the sites indicated the sign of the more organic pollution and degradation in the water quality of the selected sites due to religious immersion, mass bathing and by other anthropogenic activities. Suitable remedial actions should be adopted by regulatory bodies and policy makers to maintain the water quality of these aquatic systems. [ABSTRACT FROM AUTHOR]

Functional trait-based approaches have undergone an extraordinary expansion in phytoplankton ecology. Morpho-functional traits have been shown to vary both within and between populations and species, potentially affecting individual fitness and the network of inter-individual relationships. Here we integrate six fully harmonized phytoplankton morpho-functional trait datasets, characterized by a fine data grain, reporting individual-level data over a large biogeographical area. Datasets refer to transitional water ecosystems, from five biogeographical areas: Northern Atlantic Ocean (Scotland), South-Western Atlantic Ocean (Brazil), South-Western Pacific Ocean (Australia), Indo Pacific Ocean (Maldives) and Mediterranean Sea (Greece and Turkey). The integrated dataset includes 127311 individual phytoplankton records with sampling locations, taxonomic and morphometric information according to Darwin Core standards and semantic annotations. The six FAIR datasets are openly available in the LifeWatch Italy data portal. The datasets have already been used for morpho-functional analyses and hypothesis testing on phytoplankton guilds at different levels of data aggregation and scale, from local to global. [ABSTRACT FROM AUTHOR]

The ephemeral saline lakes of Cyprus in the Mediterranean, situated in close proximity to each other, demonstrate pronounced seasonal and interannual fluctuations in their environmental conditions. Despite their extreme saline conditions, these lakes support phytoplankton diversity and bloom-forming species. Anthropogenic activities, particularly urban and artificial land uses within their catchments, contribute to eutrophication, warranting conservation attention within the context of European legislation. Over two years (2018–2019), we examined phytoplankton abundance and diversity alongside salinity in six lakes, with samples collected every three weeks. Chlorophytes were the dominant and most diverse group, followed by cyanobacteria and diatoms. Increasing salinity correlated with reduced compositional diversity and species richness. The proximity of lakes to each other suggested airborne microbe colonization from one lake to another as a significant factor in shaping these communities, while similar land use within each lake's catchment impacted bloom formation. The highly halotolerant chlorophyte Dunaliella frequently dominated phytoplankton blooms, occasionally coexisting with other taxa in less saline lakes. Our findings provide insight into the phytoplankton community dynamics in temporal saline lakes, essential for developing effective conservation strategies and sustainable management practices. [ABSTRACT FROM AUTHOR]

Phytoplankton communities serve as useful bioindicators of environmental changes in aquatic ecosystems and can be used to assess the health of freshwater systems. Their community composition responds sensitively to changes in habitat conditions. As a result, the phytoplankton dynamics of the freshwater reservoir may differ from those of the downstream river. In the present study, we conducted a comparative analysis of the phytoplankton community between a freshwater upstream reservoir (UR) and the downstream river (DR) sections of the temperate freshwater Han River (Korea), using morphological analysis. Both UR and DR exhibited similar seasonal successions of phytoplankton groups. Diatoms dominated in autumn, winter and spring, while cyanobacteria dominated during the summer. However, the composition and frequency of the dominant species varied between UR and DR. Particularly during summer, Anabaena sp. was found to be the most frequent at UR, while Microcystis sp. was the most frequently detected at DR. In addition, high abundances of the chlorophyte Eudorina elegans and the dinoflagellate Unruhdinium penardii var. robustum were found only at DR during the autumn. The dominance and species selection of the phytoplankton community were found to be correlated with water temperature and nutrient concentrations. These results may be helpful to understand the relationship and differences in phytoplankton dynamics in reservoirs and river sections of temperate freshwater and provide guidance for maintaining the health of freshwater systems. [ABSTRACT FROM AUTHOR]

The 2019 Mississippi River flood impacted estuaries and coastal economies across the Gulf Coast, USA. This flood resulted in blooms of toxic cyanobacteria in eastern Louisiana and impacted fisheries region wide. The Atchafalaya-Vermilion Bay System (AVBS) is located along Louisiana's central coast and receives nearly one-third of the Mississippi River's flow through the Atchafalaya River distributary, in addition to localized freshwater inputs. To understand how this extreme flood affected the AVBS, we compared environmental, phytoplankton biomass, and community composition data collected during and after the 2019 flood to historical data from previous years (2016, 2017). Compared to historical data, 2019 was characterized by higher concentrations of silica and nitrate and lower salinities. Following the flood period, increased phytoplankton biomass and relative abundance of potential toxin-producing cyanobacteria were observed at sites farthest from the Atchafalaya River outlet. We found no differences in community composition at sites closer to the river mouth due to hydrologically induced disturbance. Particulate and dissolved microcystins were detected throughout the system. These results suggest that, even in a system that receives regular freshwater input, the extreme 2019 flood resulted in significant alteration of phytoplankton biomass and community composition in the western AVBS. [ABSTRACT FROM AUTHOR]

Phytoplankton are key members of river ecosystems wherein they influence and regulate the health of the local environment. Headwater streams are subject to minimal human activity and serve as the sources of rivers, generally exhibiting minimal pollution and strong hydrodynamic forces. To date, the characteristics of phytoplankton communities in headwater streams have remained poorly understood. This study aims to address this knowledge gap by comparing phytoplankton communities in headwater streams with those in plain rivers. The results demonstrated that within similar watershed sizes, lower levels of spatiotemporal variability were observed with respect to phytoplankton community as compared to plain rivers. Lower nutrient levels and strong hydrodynamics contribute to phytoplankton growth limitation in these streams, thereby reducing the levels of spatiotemporal variation. However, these conditions additionally contribute to greater phytoplankton diversity and consequent succession towards Cyanophyta. Overall, these results provide new insights into the dynamics of headwater stream ecosystems and support efforts for their ecological conservation. [ABSTRACT FROM AUTHOR]

Eutrophication-resistant phytoplankton communities in freshwater ecosystems have a novel lipid potential to contribute to the development of tropical regions. The question that arises due to the unsustainability of their eutrophicated waters is how the recognition of the lipids of the resident phytoplankton progresses. Our aim was to provide an overview of the pico-, nano- and micro-cellular lipids of phytoplankton with a focus on eutrophic tropical freshwater ecosystems. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) framework, global and Latin American publications were retrieved based on search equations and specific questions. In total, 490 studies were reviewed. The inclusion criteria, in order, were (1) peer-reviewed articles, (2) articles investigating phytoplankton strains or communities from any aquatic environment, (3) articles on freshwater ecosystems, and (4) research in tropical climates. The contribution of freshwater phytoplankton was high and discontinuous, with a representation of 63% in the 21st century. Freshwater themes were resolved in the ecological context with phytoplankton or algae keywords, while microalgae were targeted using resource use keywords. On the tropical scale, technological themes on lipid microalgae were related to fatty acids, biofuels, biodiesel, antioxidants, and recombinant DNA. It is concluded that studies of the lipid composition of phytoplankton communities are delayed in the case of eutrophic tropical freshwater ecosystems. [ABSTRACT FROM AUTHOR]