Aims Limnology and Freshwater Biology is an international peer reviewed open access journal that publishes original articles, reviews, and short communications in the interdisciplinary area of limnology. It links several scientific disciplines including hydrobiology, ichthyology, microbiology, sanitary microbiology, cellular and molecular biology, ecology, genetics, geology, physics and chemistry in an integrated fashion, to address critical issues related to freshwater ecosystems of lakes, rivers, wetlands and reservoirs. Scope hydrological, hydrochemical and geochemical aspects of aquatic ecosystems; molecular and classical biology of ecosystem research; systematics and ecology of aquatic ecosystems; natural and anthropogenic impacts on water systems and resources; paleolimnology and history of the environmental development; field and laboratory studies, and modelling.
This work is distributed under the Creative Commons Attribution-NonCommercial 4.0 International License.
Terrestrial phototrophic biofilms on artificial substrates: diversity of cyanobacteria and microalgae in a small urban town (Pushchino, Russia)
We aimed to study the taxonomic diversity of cyanobacteria and eukaryotic microalgae that form phototrophic biofilms on artificial substrates in a small town. During the study, 19 strains of phototrophic microorganisms were isolated and characterized from various building materials of urban buildings and structures (concrete, cement-sand mortar, plaster, metal, and wood). Combined molecular phylogenetic and morphological analyses permitted the characterization of 5 cyanobacterial and 14 microalgal strains, among which the genera Klebsormidium and Chloroidium predominated. Substrate specificity of the phototrophs was confirmed: the highest taxonomic richness was associated with porous and moisture‑retaining materials (concrete), as well as with metal surfaces. Of particular interest were two strains, Leptolyngbya sp. VKM Al‑382 and Cymatolege sp. VKM Al‑383, which are candidates for species new to science. For the first time, a member of the genus Cymatolege, previously known exclusively as an associated symbiont of marine sponges, was detected in a terrestrial biotope on an anthropogenic substrate, substantially expanding our knowledge of the ecological plasticity of this group. All obtained cultures were deposited in the microbial collection, thereby providing a foundation for further fundamental and applied research in the fields of biocorrosion and the development of bioprotection methods for building materials.
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First records of members of the genus Coelastrella (Chlorophyta) in tundra soils of Duvanny Yar (Sakha Republic, Russia)
The present study provides the results of morphological, molecular genetic, and biochemical analyses of six strains of green microalgae belonging to the genus Coelastrella, isolated from tundra soils of Duvanny Yar, a key reference section of Upper Pleistocene deposits on the right bank of the Kolyma River in the Nizhnekolymsky District of the Republic of Sakha (Russia). Strains were identified using light microscopy and molecular phylogenetic analysis based on internal transcribed spacer ITS2 sequences. Three strains, D2_3c1, D4_8k, and D7_11k, were identified as C. affinis; two strains, D2_6a2 and D4_1/5, –as C. polaris; and one strain, D4_4/5, –as C. multistriata. These findings represent the first documented evidence of the presence of these three species in modern soils of Duvanny Yar. Fatty acid profile analysis revealed that α-linolenic acid dominated in all studied strains, with its concentrations ranging from 35% to 42% of the total fatty acid pool. The highest values were recorded in C. polaris strains (40.4–42.1%). C. polaris and C. affinis strains also exhibited high concentrtions of palmitic (20–23%) and linoleic (9–12%) acids. Strain C. multistriata D4_4/5 showed significant accumulation of 7,10,13-hexadecatrienoic acid (16%), the concentration of which was 1.6–3.3 times higher than in the other studied strains. The obtained results expand our understanding of the species diversity of the genus Coelastrella in Arctic ecosystems and demonstrate the significant biotechnological potential of the isolated strains as producers of polyunsaturated fatty acids for applications in aquaculture and the food industry.
Metagenome-assembled genomes of non-axenic cyanobacteria: taxonomy, functional potential, and selection of promising strains for agrobiotechnologies
The search for novel highly effective microbial strains and the engineering of polyfunctional microbial inoculants based on them represents a key vector in the development of modern agrobiotechnologies. In this study, a comprehensive taxonomic and functional characterization of nine non-axenic strains of soil filamentous cyanobacteria belonging to the order Nostocales was conducted using metagenomic whole-genome sequencing. The assembly of metagenome-assembled genomes (MAGs) allowed for the reconstruction of high-quality genomic sequences of the target taxon, bypassing the labor-intensive step of strain axenization. According to the phylogenomic analysis, the studied cultures occupy a distinct position on the phylogenetic tree and can be considered candidates for novel taxa; however, this requires further verification as the current shortage of reference genomes for soil cyanobacteria is overcome. Based on ribosomal marker genes, the composition of the accompanying satellite microbiota localized within the exopolysaccharide sheaths of the hosts was characterized. The presence of beneficial heterotrophic bacteria from the genera Devosia, Lysobacter, Brevundimonas, Variovorax, Bosea, Achromobacter, and Pseudoflavitalea, which possess pronounced plant growth-promoting and biocontrol potential, was verified. Functional genome annotation revealed that all strains harbor a complete nitrogen fixation gene cluster and well-developed phosphorus mobilization systems. The strain Nostoc sp. VKM Al-56 was distinguished by a unique iron metabolism apparatus, whereas Nostoc edaphicum VKM Al-156 stood out for its aromatic compound degradation pathways. An integrated analysis considering taxonomic and biogeographic diversity, as well as the presence of key agronomically valuable traits (the capacity for phytohormone synthesis, nitrogen fixation, phosphate mobilization, pathogen defense, and abiotic stress tolerance), allowed for the selection of three candidate strains for further applied research on the development of biological formulations for crop production: Nostoc sp. VKM Al-115, Hassallia pseudoramosissima VKM Al-158, and Anabaena pirinica VKM Al-153.
Genomic analysis of picocyanobacteria of the genus Synechococcus from Lake Baikal
The genus Synechococcus comprises photosynthetic picocyanobacteria that, as autotrophic microorganisms, make a significant contribution to the production of organic matter and oxygen in marine and freshwater ecosystems. The wide distribution of representatives of the genus Synechococcus is due to their genetic diversity and ecological plasticity. Of particular interest is the study of these microorganisms in unique natural ecosystems, such as Lake Baikal – a freshwater oligotrophic deep-water lake with a high percentage of endemism among its inhabiting species. This work presents an analysis of two genomes of Synechococcus representatives recovered from metagenomic data of microbial communities from the water of Lake Baikal (MAGs): Synechococcus sp. bin7 and Synechococcus sp. bin8. A structural and functional characterization of the genomes is provided, and genes for antibiotic resistance and secondary metabolite synthesis are identified. Phylogenetic analysis, including 90 closely related freshwater and marine representatives of the genus Synechococcus alongside the studied MAGs, showed that the genomes belong to different, rather distant, phylogenetic clades.
Phytoplankton development in a floodplain water body during winter and ice-free periods under different winter phenology conditions (Lake Lunskoe, Middle Volga basin, Russia)
Climate change is transforming the winter regime of water bodies–reduced ice cover and increased thaws and winter floods require a reassessment of the role of the under-ice period in phytoplankton life. Floodplain water bodies remain especially poorly studied, as their response to winter phenological anomalies can be unpredictable. This study analyzes the seasonal dynamics of phytoplankton in the small eutrophic oxbow Lake Lunskoye (Middle Volga basin) in years with different winter phenology (2023 and 2025–2026). The lake experiences significant anthropogenic pressure and regular outbreaks of cyanobacterial blooms. Winter is demonstrated to be an active period for phytoplankton development. During the cold, snowy winter of 2023, an under-ice bloom (biomass up to 11.8 g/m³) of the non-heterocyst cyanobacteria, Planktothrix agardhii (Gom.) Anagn. et Kom. (up to 86% of total values) and Limnothrix redekei (Van Goor) Meffert (up to 55%), was recorded, remaining dominant throughout the summer. These algal blooms occurred both in the under-ice water and within the ice (especially in the crystalline part), exceeding the growth rates in the under-ice layer by up to twice. During the abnormally warm “Atlantic” winter of 2025, mixotrophic cryptomonads (Cryptomonas spp. and Komma caudata (Geitler) D.R.A. Hill) dominated, creating a winter flood biomass peak of up to 21 g/m³, comparable to summer data. In the winter of 2026, which was similar in phenology to 2023, under-ice phytoplankton was diatom-dominated. Algal development was weak in the ice but more active in the upper snow fraction, which periodically melted during thaws. A seasonal succession was revealed in the ice structure: from a heterogeneous “predecessor” community to monodominance of green algae in white ice, a cryptophyte complex in crystal ice, or complete dominance of diatoms.The obtained results refute the simplified idea that any warming stimulates cyanobacteria and demonstrate that the “atlantization” of winter can lead to the replacement of cyanobacteria by cryptophytes.
Tolerance of regional microalgae strains from the Republic of Tatarstan to heavy metal and acid gas contaminants: implications for carbon capture applications
Green microalgae are attractive biological agents for capturing carbon dioxide from industrial flue gas and for growth on partially treated wastewater, but this dual-source cultivation strategy exposes cultures to heavy metals and the acidic gases sulfur dioxide (SO2) and nitrogen oxides (NOx). This study assessed the lead (Pb), cadmium (Cd), SO2, and NOx tolerance of nine microalgal strains (Chlamydomonas sp., Chlorococcum sp., Edaphochlamys debaryana, Chlorella sp., Chlamydomonas moewusii, Chlorella vulgaris, and Spongiosarcinopsis sp.), isolated in 2024 from various water bodies and surfaces in the Republic of Tatarstan, Russia, and was aimed at selecting the most tolerant strain for further development as a carbon-sequestering candidate. Sampling sites were characterized by redox potential (EMF, 27-1518 mV), pH (6.4-8.0) and spectral absorption coefficient (color of water). EC50 values, determined by dose-response assays, ranged from 31.1 to 238.5 mg/L for Pb and from 8.3 to 176.3 mg/L for Cd, generally exceeding literature values reported for the same or related taxa. Sensitivity to 50 ppm SO2 and 50 ppm NOx was low across all isolates, whereas 100 ppm NOx and 100 ppm NO2 produced significant growth inhibition in three and five isolates, respectively. A point-scoring procedure integrating Pb, Cd, and gas tolerance identified Chlorella vulgaris (isolate 14) as the best-performing strain overall (35 of a maximum 36 points), combining the highest Pb tolerance, a near-maximum Cd tolerance, and complete tolerance across all tested gas conditions. These findings support Chlorella vulgaris as the primary candidate among the isolates examined for further evaluation in the flue gas- and wastewater-based microalgal cultivation systems.
Peculiarities of under-ice phytoplankton development in deep, cold-water lakes: Lake Teletskoye (Altai, Russia) case study
The under-ice phytoplankton was studied in the latitudinal part of Lake Teletskoye in 1997, 2006, 2018, 2023, and 2024 under different ice conditions–partial and complete freeze-up. During the under-ice period, the total diversity and abundance of phytoplankton decreased compared to the period of open water during the spring-summer-autumn growing season. With thick ice cover and a thick snow layer, diatoms and flagellates develop predominantly in numbers–a group of small-celled centric Pantocsekiella teletskoyensis, Stephanodiscus minutulus, S. binatus, and Stephanocostis chantaicus and the cryptophyte algae, Komma caudata. These species dominate in numbers even during the period of open water. Large algae, for example, Mallomonas alpina from golden algae, periodically make a significant contribution to the biomass of phytoplankton. The diversity and abundance of phytoplankton in the pelagic zone are typically lower than in littoral areas. With stable freeze-up, but with thin ice and a thick snow layer, cyanobacteria develop predominantly in the under-ice phytoplankton of Lake Teletskoye; in all other cases, diatoms and cryptophyte algae develop. In littoral areas (with depths down to 30 m), benthic forms and periphyton inhabitants, mainly diatoms, make a significant contribution to the diversity and abundance of winter under-ice phytoplankton, especially to its biomass. Overall, the development of phytoplankton under the ice of Lake Teletskoye in different ice conditions ranged from extremely low to average levels for this water body. Between 1989 and 1997, phytoplankton biomass varied from 0.5 to 1207.5 mg/m3 with a seasonal average of ~150 mg/m3 (Mitrofanova, 2000). In winter phytoplankton, the average biomass over the four studied years was 94.3 ± 21.3 mg/m3 (for the entire dataset) or 175.3 ± 28.7 mg/m3 (for the 0–10 m layer), so according to the trophic scale of lakes by I.S. Trifonova (1990), Lake Teletskoye can be classified as an ultra-oligotrophic water body (0–500 mg/m3). High values of the Shannon-Weaver diversity index may indicate the formation of an under-ice algal community.
Feasibility of microalgae farms as an alternative technology for carbon sequestration under the temperate climate conditions of Central Russia
Microalgae farms offer a promising route for carbon capture owing to the high photosynthetic efficiency of microalgae (10–20%) versus terrestrial plants (1–2%) and to their ability to use industrial CO2 and wastewater nutrients. This study calculates the carbon balance of a hypothetical 100 m2 photobioreactor farm in the temperate climate of Central Russia (Kazan), supplied with thermal-power-plant flue gas and treated municipal wastewater. At a productivity of 3.5 g/L per day, photosynthetic CO2 uptake (642.25 kg/day) exceeds combined emissions (21.7 kg CO2/day), giving a negative footprint of approximately −226.5 t CO2/year and supporting farm feasibility for carbon sequestration in a temperate climate. Achieving this productivity, however, requires strains tolerant to flue gas/wastewater contaminants and pH/temperature fluctuations, making closed photobioreactors a realistic but demanding route to carbon-negative biomass production in temperate regions.
Artificial intelligence and modelling in hydrobiological research
Information technology is essential for the advancement of science. Every day, scientists across all fields face overwhelming data volumes that exceed manual processing capabilities. Mathematical models and artificial intelligence (AI) are introduced as a necessary component for processing environmental information. Environmental AI is used mainly for environmental monitoring, hazard toxicology forecasting, and robotic systems aimed at high sampling depth accuracy. A comparative analysis of convolution neural network (CNN) models shows their potential for successful identification of algal species with sufficient illustrative data for successful machine learning. We systematized the application of modern research methods using AI and mathematical modeling in hydrobiology.
Ultrastructural characterization of lipid droplet biogenesis and microlipophagy in the pennate diatom Encyonema silesiacum
Lipid droplets of diatoms are dynamic organelles essential for energy and lipid metabolism within the cell; however, their intracellular life cycle remains largely unexplored at the ultrastructural level. In this study, we investigated the dynamics of lipid droplets in the pennate diatom, Encyonema silesiacum, using fluorescence and transmission electron microscopy. The size and number of lipid droplets were assessed using BDP 505/515 staining. After five days of cultivation, lipid droplets had a diameter of 0.6±0.1 μm, while with an increase in the cultivation time to 25 days, the diameter decreased to 0.8±0.2 μm. In other words, with increasing culture age, the size increased, indicating stress-induced accumulation of TAGs. We suggest that lipid droplets undergo complete vacuolar engulfment, followed by morphological degradation. Analysis of literature data suggests that complete lipid droplet uptake by vacuoles represents a widespread and conserved microlipophagic pathway in diatoms. These results contribute to our understanding of the lipid metabolism diversity in diatoms.
Study of vertical stratification of freshwater epipelic diatoms under seminatural conditions
This paper proposes a new modification of the method for studying epipelic diatom communities. The proposed modification is based on the use of multiple tissue layers rather than a single layer, placed on the surface of moist bottom sediment, followed by separate studies of their diatom complexes. The modification was probed with materials from Sterlyazhy Pond (Zvenigorod Biological Station MSU). The outcomes of this method highlight substantial epipelic community stratification based on the relative taxon abundance and the community size structure. Differences in sediment microhorizon preferences were also identified among morphologically similar Sellaphora species.
Flagellates and ciliates as biocontrol agents for cyanobacterial blooms
Harmful algal blooms (HABs), particularly cyanobacterial blooms, pose a significant global environmental threat. The existing physical and chemical control methods have significant limitations, highlighting the need for effective and environmentally safe alternatives. This review systematizes and analyses published and original data on the biotic interactions between flagellates, ciliates, and cyanobacteria and evaluates their potential as biocontrol agents. We demonstrate that mixotrophic flagellates of the genera Ochromonas and Poterioochromonas are the most promising candidates, as they combine resistance to toxic strains, the ability to actively graze on various cyanobacterial morphotypes, and the capacity to degrade secondary metabolites. Among ciliates, representatives of the genus Nassula show efficacy against filamentous forms. The efficacy of protist application is governed by multiple biotic and abiotic factors, including prey morphology, predator physiology, predator–prey cell ratios, environmental conditions, and interspecific interactions. Most studies are currently confined to laboratory experiments, and field validation is essential for technology scaling. Combined approaches that integrate biological control with physical or chemical methods are discussed, along with the potential use of machine learning for bloom forecasting and the optimization of inoculation parameters. We propose a conceptual design for a floating modular bioremediation station that combines biomass collection, ultrasonic colony disruption, protist-mediated grazing, and debris sedimentation as a potential solution. This work synthesizes current knowledge and outlines future research directions in protist-based biocontrol of cyanobacterial blooms.
Productivity parameters of Tetraselmis viridis (Chlorophyta) under natural illumination with increased carbon supply
The development of sustainable biotechnologies for microalgal biomass production requires optimization of cultivation conditions and evaluation of productivity under natural illumination, accounting for the natural dynamics of environmental factors. The aim of this study was to assess the effect of carbon supply on production characteristics, diurnal growth dynamics, and night biomass loss during pilot‑scale cultivation of the green microalga Tetraselmis viridis in southern Russia (mid‑latitudes). The experiment was conducted in batch mode in open ponds under natural solar illumination in spring. In the control treatment, no additional carbon source other than atmospheric air was used, while in the experimental treatment, CO2 was supplied to the culture with pH maintained up to 8.5. Biomass concentration, cell number, average daily productivity, daily production, night biomass loss, and photosynthetic efficiency were determined. In the control treatment, batch growth was limited to 8 days, with maximum average daily productivity of 6.5 g m-2 day-1 and a total yield of 43.5 g m-2; growth was constrained by a pH increase to 10.5–10.8. Supplementary CO2 supply increased productivity 1.4‑fold (up to 9.5 g m-2 day-1), daily production 1.9‑fold (up to 14.6 g m-2), maximum biomass to 1.12 g L-1, and total yield 2.4‑fold (103 g m-2). Meanwhile, night biomass loss decreased from 12.5 % to 9.5 % of the evening biomass, and photosynthetic efficiency increased from 7.1 % to 12 % on average (reaching up to 17 % on certain days). Under carbon‑sufficient conditions, night biomass loss was positively correlated with daily production. It was also shown that photosynthetic efficiency was negatively correlated with daily irradiance. Thus, CO2 enrichment of T. viridis culture not only overcomes carbon limitation and extends the linear growth phase but also improves solar energy utilization and reduces night losses. These findings can serve as a basis for optimizing T. viridis cultivation technologies in open systems for biomass production intended for aquaculture, biofuel, and other biotechnological applications.
The use of artificial intelligence technologies as an element of improving the methodology of environmental monitoring of the Black Sea
This article is devoted to the results of an experimental study, the purpose of which was to evaluate the possibility of using artificial intelligence technologies to improve the methodology of environmental monitoring of the Black Sea using the computer vision model (YOLO). The basis of environmental monitoring of water bodies is the determination of pollution, the saprobic index was chosen as its quantitative characteristic in this study. Saprobity is characterized by the degree of contamination of the reservoir with organic substances and their decomposition products. It is determined by the species composition of organisms (saprobionts) living in water and their number (frequency of occurrence). Microalgae of periphyton, which serve as indicators for the presence of organic substances, were selected as saprobionts. The composition and quantity of microalgae involved in the microfouling process were determined using the “fouling glasses” method by installing glasses in the coastal water area under study. The identification and calculation of the frequency of occurrence of microalgae present at a certain point in time in the water area was carried out by microscopy of microfouling samples. A certain composition of microalgae made it possible to calculate the saprobic index of the studied water body and draw a conclusion about its contamination. This method requires the participation of highly qualified specialists and the time required to process the microscopy results. In this regard, artificial intelligence technologies were used to accelerate the process as an element of improving the methodology of environmental monitoring of the Black Sea area. The use of the computer vision (YOLO) model made it possible to reduce the study time and assess the quality of the water body, which confirmed the effectiveness of the proposed technology in order to improve environmental monitoring of water bodies.
New strains of green microalgae from extreme environments in Crimea: identification using an integrative taxonomic approach
This study was conducted as part of a project to establish a bioresource collection of carotenogenic microalgae from the Crimean region with the aim of identifying promising strains adapted to the climatic conditions of southern Russia. A large-scale sampling campaign was carried out in extreme habitats of the western and south-eastern parts of the peninsula, resulting in the isolation and characterization of five novel strains of green algae. Taxonomic identification was performed using an integrative approach that combined analysis of life cycle traits, morphological characterization by light and scanning electron microscopy, and phylogenetic analysis of the nuclear ribosomal DNA region (ITS1–5.8S–ITS2). The strains were assigned to four genera within the classes Chlorophyceae (Coelastrella thermophila IBSS-98, Tetradesmus obliquus IBSS-164, Desmodesmus multivariabilis IBSS-167 and IBSS-171) and Trebouxiophyceae (Dictyosphaerium ehrenbergianum IBSS-163). All strains represent species new to the IBSS collection and were obtained in pure culture from the Crimean algal flora for the first time. The broad range of biotechnological applications for these strains – from environmental remediation to production of high-value compounds for the pharmaceutical, cosmetic, and food industries, as well as biofuels – highlights the importance of further research and supports the potential for regional economic development.
Diatom diversity and community structure of the littoral zone of Lake Ugii, Mongolia
Lake Ugii, one of the largest freshwater lakes in central Mongolia, has experienced increasing anthropogenic pressure and environmental change over recent decades. To evaluate the current ecological condition of the lake shoreline, diatom assemblages were investigated at multiple sampling sites around the lake and associated habitats. A total of 86 diatom taxa were identified in 2024, compared with 110 taxa reported in 2009, indicating a decline in species richness over the past fifteen years. Elevated phosphorus concentration indicators were recorded along the northern and northeastern shoreline, suggesting the influence of organic inputs from surrounding riparian areas. Additionally, there was low substrate stability at sites along the Hooloy River, Hoid Mergen Shanaa, and Saidiin Hoshuu. Multivariate analyses revealed significant spatial variation in diatom community composition among sampling sites (PERMANOVA; R²=0.554; p=0.001), while differences in within-site dispersion were not significant (PERMDISP; p=0.087). Indicator Species Analysis identified five significant indicator taxa, including Diatoma vulgaris Bory, Nitzschia palea (Kützing) W.Smith, Encyonema elginense (Krammer) D.G.Mann, Epithemia sorex Kützing, and Diatoma tenuis C.Agardh. Although measured physicochemical variables (conductivity, temperature, total dissolved solids, salinity, and pH) did not show significant relationships with community composition, spatial differences among assemblages suggest the influence of local shoreline conditions and ongoing land-use changes within the watershed. Comparison with previous surveys indicates a significant decline in diatom diversity and a marked shift in shoreline community composition in Lake Ugii. These findings provide important baseline information for ecosystem monitoring, conservation planning, and sustainable management of the lake and its watershed.
Potential of the green microalgae Tetraselmis viridis and Dunaliella salina for bioremediation of aquatic ecosystems from the organophosphorus herbicide glyphosate
Agricultural activities in Crimea and Sevastopol lead to contamination of aquatic ecosystems with herbicides, particularly glyphosate. A comparative assessment of the physiological response of the green microalgae Tetraselmis viridis and Dunaliella salina to glyphosate exposure (0–2100 μg/L) under optimal (45 μE m⁻² s⁻¹) and high (500 μE m⁻² s⁻¹) irradiance was conducted. The dynamics of algal abundance, physio-biochemical parameters of cells (chlorophyll a content, photosynthetic apparatus efficiency, cell size and granularity, reactive oxygen species production), and the abundance of associated bacteria were evaluated using microscopy, flow cytometry, and PAM fluorometry. It was found that glyphosate stimulates the growth of T. viridis and D. salina, which is reflected in high photosynthetic activity of cells, low oxidative stress levels, and increased biomass production. Under optimal irradiance, T. viridis exhibits growth stimulation at low and intermediate glyphosate concentrations (up to 700 μg/L) and inhibition at high doses. In contrast, D. salina demonstrates exceptional tolerance over a wide range of herbicide concentrations (up to 2100 μg/L). High irradiance enhances both the stimulatory and toxic effects of glyphosate on T. viridis while narrowing the tolerance range of D. salina, reducing the toxicity threshold of cells to the herbicide. It was shown that glyphosate addition stimulates the growth of associated bacteria. However, intensive algal growth outpaces bacterial population growth, indicating direct glyphosate uptake by microalgae as a nutrient source. The ability of both species to directly metabolize glyphosate and the possibility of controlling their physiological state through light conditions determine the high potential of these microalgae for application in biological wastewater treatment systems contaminated with herbicides. The feasibility of using T. viridis for rapid removal of low to moderate glyphosate doses (up to 700 μg/L) is demonstrated. D. salina can be used for the treatment of waters contaminated with high glyphosate concentrations.
Long-term effects of zinc oxide nanoparticles on the autumn phytoplankton of the Black Sea
The widespread use of zinc oxide nanoparticles (ZnO NPs) in human economic activity makes the issue of assessing their impact on the environment relevant. In the presented work, the effects of ZnO NPs (10-60 μg/L) on Black Sea phytoplankton during long-term cultivation (17 days) under experimental microcosm conditions were studied. A dose-dependent effect of nanoparticle impact on the growth and functional state of phytoplankton of the Black Sea was established. The addition of ZnO NPs led to inhibition of growth, photosynthetic activity, and a decrease in the species diversity of phytoplankton. At 10 and 20 μg/L ZnO NPs, the community abundance maintained a positive trend. However, suppression of the growth rate and a decrease in the final algal abundance to 60 and 21% of control values were noted. At the same time, a decrease in the abundance of mass planktonic species, an increase in the contribution of bentho-planktonic forms, and a change in the size structure of the algocenosis toward the predominance of small-celled species were observed. At 30 and 60 μg/L ZnO NPs, at the initial stage of the experiment, the development of acute toxic stress, suppression of photosynthetic activity and cell division, and a decrease in community abundance were noted. However, further cultivation of the microcosms under these conditions led to the recovery of community growth due to the restructuring of the species structure with subsequent dominance of a small number of tolerant species (mainly bentho-planktonic forms of diatoms, coccolithophores Emiliania huxleyi) capable of withstanding a high level of toxic load. Thus, the phytoplankton community is capable of restoring its abundance and photosynthetic activity after acute toxic stress. However, the ability of the community to survive under conditions of chronic contamination is achieved at the cost of simplification of its structure, which leads to a loss of stability and self-regulation and, in the long term, reduces the production potential of the ecosystem.
The structure of phytoplankton in the Votkinsk Reservoir, Russia (2020–2025)
Using data from phytoplankton studies conducted in the Votkinsk Reservoir from July 2020 to 2025, its taxonomic composition, ecogeographic structure, and quantitative indicators were studied. The algal flora includes 379 intraspecific algal taxa from 9 divisions identified, with diatoms and green algae accounting for 61% of the algal flora. The annual list of planktonic algae included between 193 and 301 species and subspecies, with the main species composition remaining relatively constant over several years. In terms of ecogeography, the reservoir’s phytoplankton algae are represented by typically planktonic species, widespread in water bodies worldwide, indifferent to water salinity, and found only in freshwater bodies with neutral waters. The average phytoplankton abundance was 59.6±8.3 million cells/L and was determined by the development of cyanoprokaryotes, predominantly with small cell sizes. The average biomass was 8.89±0.93 mg/L, consisting mainly of cyanoprokaryotes and diatoms. Over the study period, phytoplankton abundance and biomass fluctuated by two orders of magnitude and exhibited increasing trends. The dominant assemblage was formed by cyanoprokaryotes, primarily anheterocystous small-celled representatives of the genera Aphanocapsa, Anathece and Planktolyngbya, diatoms, cryptophytes, and dinoflagellates. In all years of the study, dominant species were Aphanizomenon flos-aquaе and Aulacoseira granulata. Ongoing changes in phytoplankton, particularly the increased coenotic role of small-sized disazotrophic cyanoprokaryotes and dinophytes, indicate progressive eutrophication of the waters of the Kama Reach of the Votkinsk Reservoir due to the combined influence of anthropogenic factors and global warming. The community index Q and saprobity index characterize of the Votkinsk Reservoir as β-mesosaprobic, moderately polluted, corresponding to water quality class III.
The phytotoxicity of non-protein amino acids beta-N-methylamine-L-alanine and meta-tyrosine against cyanobacteria and microalgae
Algae and cyanobacteria synthesize various non-protein amino acids, whose biological functions and mechanisms of action still remain insufficiently studied. Some non-protein amino acids synthesized by plants and microalgae such as beta‑N‑methylamino‑L‑alanine (BMAA) and meta‑tyrosine (m‑tyrosine) exhibit strong allelopathic effects on the growth and development of plants, algae, and cyanobacteria. The phytotoxicity of these amino acids has attracted attention toward them as potential bioherbicides. Proteomics, transcriptomics, and biophysical methods used in photosynthesis research have enabled the identification of key biological effects of BMAA and m‑tyrosine on cyanobacterial and microalgal cells. Both amino acids alter the expression of proteins involved in photosynthesis, ribosomal proteins, amino acid metabolism enzymes, oxidative stress related proteins, chaperones, cell division proteins, and numerous other proteins whose function remains unknown. Research on the specific mechanisms of action of these molecules on various stages of photosynthesis is still in its infancy. This review aim is to draw attention of algologists, microbiologists, and biophysicists to the phytotoxic effect of non–protein amino acids on cyanobacteria and microalgae cells in order to encourage further in-depth experimental study of their mechanisms of action.
Paleohydrology of the Manych Strait in the Khvalynian basin of the Caspian Sea during the Late Pleistocene
The paper discusses controversial issues of the paleohydrology of the Manych Strait—a key element in the water exchange system between the Khvalynian basin of the Caspian Sea and the Neoeuxinian basin of the Black Sea during the Late Pleistocene. Special attention is paid to two parameters: the maximum level of the Khvalynian transgression and the height of the spillway threshold through the Manych depression. Geological-geomorphological analysis, digital terrain modelling, and hydraulic modelling in the HEC-RAS system allowed reconstructing scenarios of Caspian water discharge through the Manych valley. The modelling results indicate that the most probable maximum level of the Caspian Sea during the Early Khvalynian transgression was approximately 40 m a.s.l. with a spillway threshold at 31 m a.s.l. Hypothetical limits of the discharge capacity of the Manych Strait channel of the Khvalynian Caspian basin were also calculated. The results can be used in further research.
Mesohalobic diatom species in the freshwater Lake Itkul (Khakassia, Russia)
This study presents a list of mesohalobic diatom species found in the freshwater Lake Itkul between 2006 and 2025. The lake is located in the steppe zone of the Republic of Khakassia, within the Bele-Shirinsky endorheic region. We identified 28 species and intraspecific taxa of mesohalobic diatoms belonging to 17 genera. Mesohalobes are typically scarce and play no significant role in the algocenosis; however, their diversity and development intensity in the periphyton are slightly greater than in other communities. The occurrence frequency is provided for each taxon. The most active species in the periphyton in terms of relative occurrence frequency are: Navicula capitatoradiata H. Germain ex Gasse (up to 90%), Mastogloia danseyi (Thwaites) Thwaites ex W. Smith (up to 53.3%), M. elliptica (C. Agardh) Cleve (up to 44.2%), and Nitzschia denticula Grunow (up to 69.8%). In 2024–2025, there was a significant increase in the local populations of Navicula capitatoradiata and Mastogloia elliptica in the epilithon and epiphyton communities. A decrease in lake water levels, caused by the annual rise in air and water temperatures alongside localized salinization of the littoral zones, likely impacts the percentage ratio of salinity indicator groups and the proliferation of mesohalobic species.
Relationship between the quantitative development of phytoplankton and environmental factors in lakes of different trophic status in the Belarusian Lakeland
This study examined 11 lakes of the Belarusian Lakeland, encompassing the range from mesotrophic lakes with oligotrophic features to highly eutrophic systems, to evaluate the impact of abiotic factors on the quantitative development of phytoplankton. Sampling was carried out during the growing seasons of 2023–2025 using standard hydrobiological and hydrochemical methods. Phytoplankton biomass showed an increase from 0.46–0.85 mg/L in mesotrophic lakes with oligotrophic features to 22.7–46.75 mg/L in hypereutrophic lakes. Among environmental factors, nitrogen compounds exerted the strongest influence, particularly nitrate nitrogen (rs up to 0.7; p < 0.001), while the role of total phosphorus was less pronounced. The analysis did not consider the concentration of phosphate ions (P–PO₄) because it was mostly below the analytical detection limit, and the number of measurements with non-zero values was insufficient for statistically robust conclusions. Redundancy analysis (RDA) revealed that the combined effect of environmental factors explained up to 55% of the variation in phytoplankton, with the trophic gradient being the dominant driver. Both nitrate and ammonium nitrogen contributed significantly to phytoplankton development; however, the effect of nitrate nitrogen was more pronounced. This was likely due to the rapid uptake and oxidation of NH₄⁺ under conditions of high oxygen concentration, which complicates the evaluation of its impact, whereas nitrate was consumed more slowly, allowing for a more reliable statistical evaluation of its role. The obtained results refine our understanding of the role of different nitrogen forms in shaping the productive state of lakes and may be applied in assessing their trophic status.
Problems of biological invasions in the fish fauna of southern Vietnam: the example of the Dong Nai River basin
Biological invasions of fish are among the key drivers of transformation in freshwater ecosystems, particularly in regions with intensive aquaculture development and high anthropogenic pressure. The aim of this study was to assess the extent of introduction and degree of naturalization of non-native fish species in the Dong Nai River basin (southern Vietnam), as well as to identify patterns of their spatial distribution and main pathways of introduction. Ichthyological sampling was conducted in April–May 2025 at 56 stations in the upper and middle reaches of the Dong Nai River, including the Da Nhim and Da Dang rivers, their tributaries, and lentic water bodies in Dong Nai and Lam Dong provinces. A total of 17 non-native fish species were recorded across 13 of the 17 surveyed areas. The highest diversity of introduced species was observed in large water bodies subjected to significant anthropogenic impact, particularly in Tri An Lake (11 species), as well as in the middle reaches of the Da Nhim River and the Dai Ninh Reservoir (6 species each). In contrast, the number of non-native species was considerably lower in highland areas of the Central Highlands (1–3 species), while no alien species were recorded in water bodies within Cat Tien National Park. Most species exhibited low to moderate occurrence frequency; however, two species—guppy (Poecilia reticulata Peters, 1859) and Nile tilapia (Oreochromis niloticus (Linnaeus, 1758))—showed very high prevalence. The results indicate a substantial scale of biological invasions in the Dong Nai River basin. Aquaculture and the aquarium trade are identified as the primary sources of non-native fish introductions, while their spatial distribution is strongly associated with the level of anthropogenic impact and the type of water body.
Functional digestive morphology and feeding intensity of the halfbeak Zenarchopterus clarus (Hemiramphidae) in a tropical estuarine habitats, southern Vietnam
This study examines the functional digestive morphology and feeding intensity of the halfbeak Zenarchopterus clarus (Hemiramphidae) in a tropical estuarine habitats of southern Vietnam. A total of 892 specimens were collected monthly from August 2024 to July 2025 at two estuarine sites. The species exhibited a superior mouth with an elongated lower jaw, dense conical dentition, well-developed pharyngeal tooth plates, and numerous gill rakers. The digestive tract consisted of a muscular esophagus and a short intestine, lacking a clearly differentiated stomach, indicating rapid processing of soft prey. Feeding intensity was evaluated using the gut-somatic index (GI) and analyzed with generalized linear mixed models. The model indicated significant variation in GI (p < 0.001). The GI differed significantly between sexes and sampling locations, with higher values in females and at Dam Doi. Although the season had no significant main effect, a significant sex × season interaction indicated contrasting seasonal feeding patterns between males and females. Morphological traits and GI collectively suggest that Z. clarus is adapted for surface-oriented feeding on small, mobile prey in dynamic estuarine environments. However, the feeding strategy was inferred from morphological traits and GI, as diet composition was not directly examined. These findings provide baseline insights into the digestive morphology and feeding ecology of an estuarine hemiramphid fish.
A decade of Philippine freshwater goby research (2010–2022): a systematic review and meta‑analysis of ichthyofaunal surveys
Freshwater goby (Family Gobiidae) is one of the diverse and widespread fish species in rivers and lakes, with economic values ranging from ornamental and subsistence provisions. Several ichthyofaunal surveys have been conducted in the Philippines; however, no systematic review and meta-analysis was performed to analyze freshwater goby species richness over fish species richness. Following the PRISMA Protocol, twenty–three (23) studies were assessed and statistically analyzed using JASP Version 0.18.3. Each paper was reviewed to identify study sites, goby genera, diversity indices (Shannon, Pielou’s evenness, and Simpson), and physicochemical parameters, with correlations analyzed across fish species, goby species richness, and diversity indices. Results revealed that most freshwater goby studies take place in Luzon, and the genus Glossogobius is the prevalent goby species at most study sites. The diversity index for introduced fish species ranged from low to medium, as indicated by the enriched biodiversity index score from Guerrero (2014). In terms of physicochemical parameters, all values generally met the standards set by DAO 2016-08. However, the forest plot revealed that the effect size was entirely on the positive side of zero, with a combined effect size of 0.46, suggesting a moderate impact. The funnel plot indicated an asymmetrical pattern among studies, suggesting potential publication bias. Analysis suggests that goby diversity in the Philippines is high in terms of species richness, with a moderate effect size when compared to overall fish species richness based on the collated studies. Taking into account the high publication bias observed, we recommend including more studies from Southeast Asian countries. Researchers are encouraged to prioritize biodiversity studies in the Visayas and Mindanao regions to mitigate study bias. A comparative analysis of native and introduced fish species richness would also be beneficial in determining their potential impact on the overall effect size of species richness.
Assessment of water quality and zooplankton community structure in the Gambhiri River (Chittorgarh, Rajasthan, India)
This study examines water quality parameters and zooplankton community structure in the Gambhiri River, Chittorgarh district of Rajasthan, India, to assess the ecological health and trophic state of this vital freshwater ecosystem. Seasonal sampling was conducted from January to December 2023 at six sampling sites to observe spatial and temporal variations in physicochemical parameters and zooplankton communities. Key water quality parameters, including water temperature, pH, total dissolved solids, turbidity, electrical conductivity, total hardness, chloride, alkalinity, dissolved oxygen, and biological oxygen demand, were measured using standard analytical techniques. Zooplankton samples were collected with a plankton net, preserved, and identified to the lowest possible taxonomic level, following standard keys. In the study period, 65 species of zooplankton were analyzed, of which 26 species of Rotifera, 25 species of Cladocera, 8 species of Copepoda, and 6 species of Ostracoda were recorded. Cladocera appeared as the dominant group of zooplankton with a higher density (38.67%), followed by Rotifera (35.72%), Copepoda (18.57%), and Ostracoda (7.03%). The season-wise zooplankton analysis revealed that Cladocera and Rotifera were the dominant groups across all seasons, while Copepoda and Ostracoda contributed comparatively less to the total density. Cladocera showed higher density than Rotifera during summer and post-monsoon seasons, whereas during monsoon and winter, Rotifera slightly dominated over Cladocera. Copepoda consistently remained the third dominant group in all seasons, while Ostracoda recorded the lowest density throughout the study period. The study highlights the importance of zooplankton as sensitive bioindicators for evaluating the health of freshwater ecosystems and recommends routine monitoring and pollution control measures to preserve the ecological integrity of this crucial water resource in Rajasthan’s semi-arid region.
Seasonal dynamics of rotifer community in relation to water quality at Pravara-Godavari river confluence (Ahmednagar, MS, India)
This study reports the diversity, abundance, and seasonal dynamics of the rotifer community in the Pravara-Godavari river confluence, Ahmednagar, throughout a year, from November 2024 to October 2025. Seasonal sampling was conducted to assess rotifer species composition and density, and to measure key physicochemical water parameters, including temperature, pH, dissolved oxygen, turbidity, alkalinity, hardness, and chloride. A total of 19 rotifer species, representing 4 genera and 3 families, were recorded in the study area. Strong temporal variation in population structure was indicated by the rotifer community’s noticeable seasonal variations in both species richness and density. The summer period recorded the highest rotifer diversity and abundance. At the same time, the monsoon season had the lowest values, perhaps due to a dilution effect, increased water turbulence, and altered habitat stability. Furthermore, correlation analysis showed that important physicochemical parameters such as pH, water temperature, turbidity, alkalinity, total hardness, chloride concentration, and dissolved oxygen had a significant impact on rotifer species richness. These results demonstrate that even small changes in water quality can significantly impact the composition of rotifer communities. Overall, the study highlights rotifers’ sensitivity to environmental factors and underscores their value as reliable bioindicators for evaluating freshwater ecosystems.
Morphological and genetic features of crustaceans Artemia parthenogenetica and A. tibetiana (Crustacea, Anostraca) in different-type hypersaline lakes in the south of Western Siberia
We studied modern morphological features of parthenogenetic and bisexual Artemia populations from 10 different-type hypersaline lakes in the south of Western Siberia (Altai Krai). DNA barcoding of these populations revealed two Artemia species: Artemia parthenogenetica Barigozzi, 1974 and A. tibetiana (Abatzopoulos et al., 1998). The studies were conducted monthly from July to September 2025. Principal component analysis indicated differences in the hydrochemical composition of brine (water) of lakes inhabited by parthenogenetic and bisexual Artemia populations. Comparative analysis of morphological features suggested that females of A. parthenogenetica and A. tibetiana significantly differed in mean values (14 of 16 traits). Cluster analysis of 12 plastic and 4 meristic characters of A. parthenogenetica females demonstrated splitting of its population into three groups with different structural features of the furca: length (fl), number (sf), and length of setae (sl). The Spearman correlation index establishes significant statistical correlations between the morphological features of A. parthenogenetica and A. tibetiana and main environmental factors, i.e. salinity and water temperature.