With rapid economic and social development, eutrophication in coastal areas is currently one of the most severe environmental problems worldwide. However, our understanding of the response of the phytoplankton community structure to the intensification of coastal eutrophication is still relatively limited. Here, seasonal phytoplankton, environmental factors, and nutrients were investigated in 2009 and 2019 in Zhanjiang Bay, where eutrophication has intensified in recent years, to analyze the variation in nutrient structure and its impact on the phytoplankton community. The results revealed that the DIP and DSI concentrations in 2019 were higher than those in 2009. However, dissolved inorganic nitrogen (DIN) has decreased substantially over the past several decades, which is due mainly to the decrease in anthropogenic nitrogen emissions, the substantial increase in the intrusion of high-salinity seawater, and the high-phosphorus wastewater discharged from urban industries. This resulted in a decrease in phytoplankton cell abundance, phytoplankton composition, and species diversity (H′) in 2019 compared with 2009. In addition, the superior N transport, storage, and response strategy to a low N supply of diatoms, especially Skeletonema and Chaetoceros, might benefit the growth of diatoms under low DIN conditions. The lower DIN/DIP ratio in 2019 favored the growth of diatoms, especially Skeletonema and Chaetoceros, leading diatoms to dominate the phytoplankton assemblage. This study demonstrates how changes in nutrient structure alter the community structure of phytoplankton, providing new insights into deepening our understanding of eco-environmental evolution.

Reservoirs constitute critical freshwater ecosystems that influence regional hydrology and energy production in Nigeria; however, they are susceptible to anthropogenic impacts that alter water quality and aquatic biota. This study investigated the spatial-temporal dynamics of phytoplankton assemblages and corresponding limnological variables in ten reservoirs across Niger State, Nigeria, over two consecutive hydrological seasons (wet and dry) spanning June 2019 to March 2021. Multivariate statistical analyses, including two-way ANOVA, demonstrated significant spatial and seasonal variability in physical and chemical water parameters (p < 0.05). Canonical correspondence analysis (CCA) elucidated key environmental drivers shaping phytoplankton community structure, revealing strong correlations with nutrient concentrations and organic loading indicators. Application of the Palmer Algal Index (PAI) facilitated quantitative assessment of organic pollution gradients, corroborating phytoplankton as sensitive bioindicators of trophic status and ecosystem integrity. The results underscore the imperative for integrative monitoring and management frameworks to mitigate eutrophication and preserve aquatic biodiversity within these reservoirs, contributing to sustainable water resource management in Nigeria.

Phytoplankton is the most important primary producer in lakes， and its community structure can reflect the changes in lake ecosystems. In order to understand the changes of phytoplankton functional community structure and its influencing factors in Erhai Lake， a plateau lake， the phytoplankton community composition， water quality changes， and zooplankton and zoobenthos abundance in Erhai Lake were continuously observed every quarter from 2022 to 2023. The results showed that 7 phyla and 81 genera of phytoplankton were identified from 2022 to 2023. Bacillariophyta density and biomass decreased， while cyanobacteria， chorophyta， and cryptoalgae increased. The density of phytoplankton was low in spring and high in autumn， and the biomass reached its peak in summer. The density and biomass of algae were higher in the northern lake area and increased in the central and southern parts of the lake. The Shannon Wiener （H） diversity index and Pielou （J） evenness index were 0.82-2.43 and 0.34-0.97， respectively， which decreased. There were 16 genera of dominant phytoplankton in Erhai Lake， which were divided into 13 functional groups. The phytoplankton community structure changed from P functional groups to M， H1， and K functional groups. Phytoplankton evolved from Fragilaria sp. and Dolichospermum sp. to Melosira sp.， filamentous cyanobacteria， and Microcystis sp.. The number of dominant functional groups increased， and the change of functional community structure was unstable. Water temperature （WT）， turbidity （NTU）， pH， water surface wind speed （WS）， total nitrogen （TN）， electrical conductivity （EC）， and transparency （SD） were the key environmental factors affecting the changes of phytoplankton functional groups. The biomass of the P functional group was positively correlated with SD and EC； the density of the M and H1 functional group was significantly positively correlated with pH， NTU， and WT； and the density and biomass of the K functional group were positively correlated with NTU， WT， and WS. Cladocera and Copepoda zooplankton， as well as aquatic insects， gastropods， and crustacean benthos， were positively correlated with the H1， S1， SN， and P functional groups， while protozoa， bivalves， oligochaetes， and leeches were positively correlated with the K， C， B， X2， and Lo functional groups. The T and E functional groups were positively correlated with rotifers and protozoa. The correlation between the M and Y functional groups and zooplankton and zoobenthos was not obvious or negatively correlated.

Phytoplankton communities play an important role in marine food webs and biogeochemical cycles. The transition zones between ocean gyres and surrounding waters represent critical ecological boundaries where environmental gradients drive significant shifts in phytoplankton community structure. This study investigates how nutrient availability and temperature shape the size distribution and composition of small phytoplankton (< 5 [Formula: see text]m) communities across the North Pacific Subtropical Gyre (NPSG) boundaries, testing several ecological hypotheses that explain phytoplankton size distribution patterns in relation to environmental variability. We used high-resolution, underway flow cytometry data collected during eight oceanographic cruises from 2016 to 2021 to assess changes in phytoplankton biomass and growth rate across the gyre boundaries. The cyanobacterium Prochlorococcus dominated within the gyre, with biomass ranging from 3.2 to 13.1 [Formula: see text]gC L-1, and its relative contribution to total phytoplankton biomass varied among cruises (31% to 81%, average 60 [Formula: see text] 16%). Prochlorococcus growth rates were significantly higher within the gyre (0.43 [Formula: see text] 0.18 per day) than outside the gyre (0.28 [Formula: see text] 0.16 per day) (one-sided t-test, p < 0.001). Northward in the gyre, Prochlorococcus biomass and growth rates declined. Some variations in biomass and growth rates were observed southward and eastward, with biomass ranging from 3 to 10 [Formula: see text]gC L-1 and growth rate ranging from 0.2 to 0.6 per day. Outside the NPSG, total phytoplankton biomass increased, with nanoeukaryotes becoming the predominant contributors (up to 71%, 9.1 [Formula: see text] 7.3 [Formula: see text]gC L-1). Picoeukaryote biomass also increased outside the gyre (up to 28 [Formula: see text] 12% of total biomass). Nutrient concentrations increased by nearly two orders of magnitude outside the NPSG, coinciding with the shift towards larger phytoplankton. The dominance of Prochlorococcus within the gyre emphasizes its adaptation to oligotrophic conditions, while the shift towards larger size classes outside the gyre likely reflects the relatively higher nutrient availability. The relatively low abundance of Synechococcus even in nutrient-rich regions suggest that that factors beyond nutrient availability, such as grazing, may influence its distribution. These findings have implications for understanding how phytoplankton communities will respond to future changes in oceanographic conditions, such as warming and altered nutrient regimes.

To investigate the impact of freshwater discharge variations from the Nanliu River on the phytoplankton community structure in Lianzhou Bay, we conducted surveys of total chlorophyll-a (Tchl-a) concentrations and specific pigment groups during wet and dry seasons of 2016. During wet season, freshwater discharge introduced substantial freshwater, nutrients, and suspended particulate matter into Lianzhou Bay. Due to reduced light availability, Tchl-a concentrations at most stations were lower compared to dry season. The result indicated that light availability often exerts a greater influence than nutrient availability in estuarine environments. Furthermore, the spatial distribution of Tchl-a concentrations in Lianzhou Bay is correlated with the feeding activities of bivalve aquaculture and water movement within the bay. During the high-water period, the phytoplankton community was primarily composed of diatoms (35.0%), cyanobacteria (21.0%), prasinophytes (13.0%), chlorophytes (19.0%), and cryptophytes (11.0%). In contrast, the low-water period saw a phytoplankton community dominated by diatoms (62.0%), prasinophytes (18.0%), cyanobacteria (12.0%), and cryptophytes (7.0%). The absence of osmotic regulation in chlorophytes restricts their distribution primarily to estuarine environments characterized by high water availability. In contrast, diatoms exhibit a greater affinity for well-illuminated conditions, thereby contributing significantly to primary productivity in neritic zones and during periods of low water flow.

Abstract Anthropogenic salinization resulting from road salt application can degrade aquatic environments by altering the structure and function of phytoplankton communities, ultimately reducing flows of resources through aquatic food webs. However, physiological mechanisms underlying taxon‐specific responses to salinization are often poorly linked to higher‐order ecosystem dynamics, limiting our ability to predict community responses to salinization. To this end, we tested hypotheses derived from Subsidy‐Stress and Ecological Stoichiometry theory by growing two cosmopolitan genera, Dolichospermum (prokaryotic, cyanobacteria) and Scenedesmus (eukaryotic, green algae), across NaCl gradients and contrasting differences in their growth rates, degree of Na homeostasis, and cellular C : N : P ratios. We found mixed support for the subsidy‐stress hypothesis, with only stress responses observed for both species. Instead, growth declines appeared to be linked to stoichiometric tradeoffs between growth and homeostatic regulation, with stronger homeostatic Na regulation coinciding with a greater reduction in Scenedesmus growth rates and higher variation in their stoichiometric C : N : P ratios across NaCl gradients. Nonhomeostatic Na regulation allowed Dolichospermum to sustain higher growth rates, which appeared to constrain variation in their stoichiometric C : N : P ratios along with their stronger physiological regulation of intracellular P storage molecule production. Differences in phytoplankton growth responses were consistent with stoichiometric theory and field observations documenting shifts from green algae to cyanobacteria in response to freshwater salinization. Our results suggest that these shifts could take place below existing North American chronic threshold limits, resulting in decreased production at higher trophic levels by reducing phytoplankton biomass production rates and inducing nutritional stress in consumers.

Studying the coupled effects of environmental factors on the structure of phytoplankton communities can deepen our understanding of the stability of aquatic ecosystems in extreme environments. This study examined the phytoplankton community structure and environmental factors of saline a lake during spring, summer, and autumn in 2019. A total of 95 phytoplankton species (belonging to 47 genera and 7 phyla) were identified in Ebinur Lake, reflecting a species richness lower than those of freshwater lakes while being greater than the levels observed in other saltwater lakes. Bacillariophyta dominated the phytoplankton assemblage, followed by Chlorophyta and Cyanophyta, with lesser diversity in other algal species, suggesting that the species composition was similar to that observed in other saltwater lakes. There was considerable spatiotemporal variation in the structure of the phytoplankton community, with the biomass of phytoplankton displaying notable seasonal variation. In spring, the biomass of Bacillariophyta was dominant; in summer, as the climate warmed, the biomass of phytoplankton reached its peak and the biomass of Chlorophyta was dominant; in autumn, the biomass was the lowest, and Chlorophyta and Bacillariophyta shared dominance. The spatial distribution was relatively consistent, as reflected in the distribution of phytoplankton in the three seasons, with the southeastern area of the lake generally exhibiting higher biomass than other lake areas. Bacillariophyta and Chlorophyta were significantly correlated with water transparency (SD); Cyanophyta was significantly correlated with water temperature (WT), and Cryptophyta was significantly correlated with pH. The interaction effects of various environmental factors, including pH, SD, Chlorophyll-a (Chl-a), ammonia nitrogen (NH4 +-N), and salinity (S), jointly affect the dynamics of the phytoplankton community structure in Ebinur Lake. This study investigated the effects of physicochemical factors on the structure of the phytoplankton community in a high salinity lake, thereby providing a basis for ecological protection and environmental management of aquatic ecosystems in extreme environments.

Response of diatoms to environmental changes in the Porphyra cultivation system in Haizhou Bay using GBT model and GAM.

Abstract Ocean mesoscale eddies are important drivers of upper ocean physical and biological processes. However, owing to their ephemeral nature and limited observational data, the impact of eddies on three‐dimensional biogeochemical cycles and hence related phytoplankton phenology remains unclear. Here, from ship‐based surveys, we assessed the impact of two eddies of opposite polarity on phytoplankton biomass and community structure, in the upper 200 m of the northwest South China Sea (SCS), as well as their effect on the diapycnal nutrient fluxes and oxygen concentration. These observations revealed that pico‐phytoplankton dominated phytoplankton community, whereas the fraction of micro‐ and nano‐ phytoplankton (Fmicro and Fnano) increased with depth, reaching a maximum near the SCM layer (located between 50 and 100 m). The magnitude of SCM and total phytoplankton Chl were greater within the cyclonic eddy (CE) compared to those influenced by the anticyclonic eddy due to the enhanced vertical diapycnal fluxes of nutrients within the CE. The elevated diapycnal nutrient flux in the CE resulted from an increase in turbulent kinetic energy dissipation coefficient and steeper vertical gradients in inorganic nutrients. Pigment‐based chemotaxonomy further indicated that eukaryotes increased significantly in the SCM layer with concentrations reaching 0.16 ± 0.08 mg m−3; the enhancement of Fmicro in the CE was mainly attributed to the increased contribution of diatoms. The vertical biogeochemical dynamics revealed by this research may showcase fundamental characteristics of oligotrophic ecosystems, where mesoscale perturbations are vertically heterogeneous, improving our understanding of the complex biophysical interactions within mesoscale eddies.

Distinct patterns and processes of eukaryotic phytoplankton communities along a steep elevational gradient in highland rivers.

The effect of the aging processes of Ulva prolifera-derived dissolved organic nitrogen associated with green tide on the diatoms-dinoflagellates succession in the Southern Yellow Sea, China.

Influence of bloom stage on the effectiveness of algicidal bacteria in controlling harmful cyanobacteria: A microcosm study.

Kolam marikultur yang mengalami akumulasi sisa pakan dari biota, seperti udang dibiarkan menumpuk sehingga berpotensi menjadi toksik akibat senyawa amonia dan nitrit yang tinggi, terutama jika tidak dilakukan pembersihan rutin serta pemberian probiotik guna menguatkan peran fitoplankton sebagai dekomposer. Kondisi tersebut dapat menimbulkan dampak negatif, khususnya terhadap mahluk renik dan biota marikultur dalam perairan. Keanekaragaman fitoplankton adalah mahluk alami yang digunakan sebagai dekomposisi zat-zat organik tanpa menyebabkan kualitas air menurun. Penelitian ini untuk mengetahui suatu komunitas fitoplankton di tambak udang vannamei di Desa Kedongkelor dengan masa pemeliharaan yang sudah berjalan selama 1 bulan (30 hari). Penelitian ini menggunakan metode analisis data untuk mendukung indeks ekologi seperti: indeks keanekaragaman, keseragaman, dominansi dan saprobik. Hasil berdasarkan penelitian menunjukkan jenis fitoplankton memiliki kelimpahan yang berbeda berdasarkan presentase (%) yaitu Green Algae (GA) dengan 41,8, Bacillariophyceae dengan 23,7, Cyanophyceae dengan 29,3, Dinophyceae dengan 5,2. Kategori keanekaragaman fitoplankton tergolong rendah berdasarkan indeks diperoleh 1,22. Kategori keseragaman fitoplankton tergolong tinggi dan kategori dominansi fitoplankton tergolong tidak ada yang dominan. Kategori saprobik pada 4 kolam tergolong dalam pencemaran sedang (fase α-Mesosaprobik) dan berat (fase Polisaprobik). Mariculture Mariculture ponds that accumulate leftover feed from cultured organisms, such as shrimp, are often left unmanaged, leading to the potential buildup of toxic compounds, particularly ammonia and nitrite. This risk is exacerbated in the absence of regular cleaning and probiotic application, which otherwise support the role of phytoplankton as natural decomposers. Such conditions may have detrimental effects, especially on microfauna and cultured aquatic organisms. Phytoplankton diversity represents a natural mechanism for decomposing organic matter without compromising water quality. This study aims to assess the phytoplankton community structure in a vannamei shrimp pond located in Kedongkelor Village after one month (30 days) of cultivation. The study employed ecological index-based data analysis, including diversity, evenness, dominance, and saprobic indices. The findings revealed that phytoplankton abundance varied among groups, with the following relative percentages: Green Algae (GA) 41.8%, Bacillariophyceae 23.7%, Cyanophyceae 29.3%, and Dinophyceae 5.2%. The phytoplankton diversity index was categorized as low, with a value of 1.22. Evenness was classified as high, while dominance was negligible, indicating no single dominant group. Saprobic index analysis showed that water quality in the four ponds ranged from moderately polluted (α-Mesosaprobic phase) to heavily polluted (Polysaprobic phase).

ABSTRACTThis study explores the impacts of climatic phenomena, including the El Niño‐Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), marine heatwaves (MHWs), and the North Pacific Gyre Oscillation (NPGO), on phytoplankton dynamics in Todos Santos Bay (TSB) from 2010 to 2022. Analysis of the anomalies of the sea surface temperature (SSTa), phytoplankton biomass (CHLa), upwelling indices (Bakun and BEUTI), and absolute dynamic topography (ADTa) revealed substantial effects on nutrient dynamics and primary productivity. The results indicate a significant reduction in phytoplankton biomass during El Niño due to increased ADT that weakened nutrient upwelling. In contrast, La Niña periods were associated with enhanced nutrient flow and phytoplankton biomass due to intensified coastal upwelling. The study also highlights the impact of the NPGO’s warm phase in reducing the influx of cold, nutrient‐rich subarctic water, influencing the phytoplankton community structure towards smaller phytoplankton and dinoflagellates. Notably, a positive correlation was found between ADTa and the dominance of smaller phytoplankton and dinoflagellates, suggesting that higher sea levels and increased stratification favor these groups over larger phytoplankton like diatoms. This shift suggests potential long‐term ecological implications, including effects on marine biodiversity and fisheries. The findings underscore the complex interplay between global climatic phenomena and marine ecosystem productivity, emphasizing the necessity of adaptive ecosystem management in the face of climatic variability.

ABSTRACT Seasonal water mass dynamics and terrigenous inputs (aquaculture, industrialization, sewage discharge, river inputs, etc.) create environmental gradients between inshore and offshore the Beibu Gulf. This study analyzed summer-autumn phytoplankton community structure, revealing higher inshore nutrients (NO3 −, NO2 −, NH4 +, PO4 3− and SiO3 2−) and phosphorus limitation in northern inshore waters. Inshore phytoplankton assemblages showed higher abundance but lower diversity than those in the offshore areas. Inshore riverine silicate inputs skewed Si/N/P ratios above Redfield values, causing nutrient imbalance that promoted the growth of red tide species (e.g., Skeletonema costatum). Seasonal water masses transported coastal nutrients offshore, reducing the offshore phytoplankton diversity and fostering late-autumn harmful algal blooms (HABs) by Phaeocystis globosa and Thalassiosira subtilis. These HAB species exhibit small cell size, high specific surface area and enhanced material exchange capacity, enabling ecological dominance under nutrient-enriched conditions.

Water quality of Lake Tana has been deteriorating due to nutrient enrichment associated with various anthropogenic stressors including domestic and industrial effluents, and agricultural runoff. Changes in the ecological health of a lake are better understood by studying the community structure of phytoplankton as they react quickly to environmental changes. Human-induced stressors can lead to changes in the taxonomic composition and Reynolds functional groups (RFGs) of phytoplankton resulting in biodiversity impoverishment. RFGs are more effective in detecting stressor-induced alterations in phytoplankton compared to taxonomy-based assemblages as the former reflect common adaptive or functional traits. Information on RFGs of phytoplankton in the northern gulf of Lake Tana, Ethiopia, is however non-existent. Therefore, this study aimed to assess the spatio-temporal changes in phytoplankton community structure and identify the variables influencing the dynamics of RFGs in the lake. Samples were collected from five sampling sites between May 2023 and April 2024. A total of 113 phytoplankton species belonging to six taxonomic groups and 11 RFGs were identified. The predominant RFGs which collectively accounted for 97% of the total phytoplankton abundance were M, B, N, D, Lo, P and S2. Other RFGs, such as J and X1–X3, constituted 2.4% and 0.8% of the total abundance, respectively. Redundancy analysis indicated significant association of RFGs with electrical conductivity, pH, turbidity and some algal growth limiting nutrients. This suggests that both biotic and anthropogenic stressors have a substantial impact on RFGs. Therefore, continuous monitoring is essential to prevent future ecological imbalances in the lake.

Temporary ponds in agricultural landscapes, highly vulnerable to anthropogenic pressure and climatic variation, constitute unique habitats for microalgae and endangered filter feeders (large branchiopods). Such ponds play a crucial role in the functioning of farmland ecosystem, yet they remain largely understudied. Our study is the first to examine changes in phytoplankton communities in temporary kettle hole ponds in relation to rapid shifts in biotic (large branchiopods) and physical and chemical parameters of water. We conducted our research over a three-year cycle (in nine ponds in western Poland), with sampling starting in spring when inundation usually occurs, and continuing until the ponds dried out. Among 406 phytoplankton taxa (mainly euglenoids, but also diatoms and chlorophytes), locally rare species (e.g. Desmatractum indutum) were noted. When branchiopods occurred in the ponds, the phytoplankton communities shifted towards unicellular chlorophytes. Furthermore, nitrogen forms, temperature, conductivity, and pH were the abiotic factors altering the studied communities. Surprisingly, the diversity of phytoplankton species did not decrease with increasing temperature, which is inconsistent with the trend observed in permanent water bodies. The study identified specific drivers of phytoplankton community structure and dynamics, underscoring their ecological significance and management implications. These insights will be valuable for future conservation strategies of temporary ponds, crucial in sustaining biodiversity in farmland areas.

Abstract. While the sources of dissolved organic matter (DOM) in the open ocean are relatively well identified, its fate due to microbial activity is still evolving. Here, we explored how microbial community structure, growth, and grazing of phytoplankton and heterotrophic bacteria influenced the DOM pool and the transformation of its fluorescent fraction. Dilution experiments were performed during the productive season on the Patagonian Shelf (SW Atlantic Ocean), a region of intense biological activity, with peak productivity observed at the shelf break front. Although phytoplankton biomass was higher than that of bacteria, protists selectively preyed on the faster-growing bacterial population, denoting trophic specificity of grazers. High trophic coupling was suggested by the biomass distribution of protistan consumers and their prey, which predominantly exhibited an inverted trophic pyramid structure. An exception to this pattern was observed at the highly productive shelf break front, where a traditional bottom-heavy pyramid emerged, indicating that most phytoplankton evaded protist predation despite evidence of herbivory. Bacterial consumption of DOM appeared uncoupled from its total amount but was influenced by DOM complexity, while the bacterial production of humic-like substances from protistan plankton precursors observed in most experiments highlighted a potential pathway for carbon sequestration. Protistan grazers also significantly influenced DOM dynamics by scaling their DOM contribution in response to the intensity of grazing on heterotrophic bacteria, regardless of productivity levels. This effect likely arises from reducing the number of active DOM-consuming bacteria and by providing egestion DOM compounds. At the onset of the productive season, high bacterial growth rates stimulate protistan grazing, which serves as a link between bacterial biomass and higher trophic levels. However, as grazing pressure increases, protists can also contribute to the accumulation of a fraction of DOM.

To evaluate the change trends of plankton in inland saline–alkaline water bodies, this study investigated the ecological restoration and rational development of saline–alkaline lakes in northwest China. From June to October 2023, phytoplankton communities in a high-salinity lake in Alar City, Xinjiang, were analyzed using standard survey methods for inland natural waters. Biodiversity indices were calculated, and redundancy analysis (RDA), Spearman’s correlation analysis, and Mantel test were carried out to assess the functional community structure of phytoplankton and its environmental drivers. In total, 115 phytoplankton taxa belonging to seven phyla were identified. The densities ranged from 23.76 × 105 to 53.54 × 107 cells/L. Bacillariophyta and Cyanophyta were the dominant phyla, accounting for 41.7% and 27.8% of the total taxa, respectively. The dominant species included Microcystis spp., Merismopedia sp., Cyclotella meneghiniana, and other algae. Spearman correlation analysis revealed that salinity, water temperature (WT), Na+, TDS, HCO3−, Cl−, and K+ were key environmental factors significantly influencing phytoplankton community structure. Mantel tests confirmed that salinity (SAL), TDS, DO, and major ions (K+, Na+, CO32−) served as key determinants of spatiotemporal phytoplankton community distribution (p &lt; 0.05). RDA results indicated that WT, TDS, alkalinity (ALK), pH, salinity, and Na+ were the key factors driving seasonal variations in phytoplankton communities. Notably, decreasing salinity and ion concentrations stabilized the phytoplankton community structure, maintaining high-diversity indices. This highlights the positive impact of ecological restoration measures, such as fisheries-based alkalinity control and systematic environmental management, on the health of saline–alkaline lake ecosystems. These findings provide important insights for the sustainable development of saline–alkaline fisheries and the conservation of aquatic biodiversity in arid regions.

Single and combined effects of diclofenac, ibuprofen, and paracetamol on phytoplankton community structure and dynamics