Limnology and Freshwater Biology

Thermohydrodynamic processes in Lake Ladoga

Zverev, Ilia — 2025-12-25

The results of adapting a three-dimensional mathematical model of the hydrodynamics of an inland sea to the conditions of Lake Ladoga are presented, followed by its verification using field and remote measurements. During adaptation, a spherical B-type computational grid with a spatial resolution of 1 km × 1 km was constructed. The equation of state for seawater was replaced by an equation for weakly mineralized water with a maximum density at a temperature close to 4 °C. A procedure was implemented to calculate the inflow of heat and dissolved substances into the lake through liquid boundaries with the waters of tributaries. The flow of the Neva River was taken into account. Atmospheric forcing from NCEP/NCAR reanalysis with a spatial resolution of 2.5°×2.5° has been replaced with the European equivalent ERA5 with a resolution of 0.25°×0.25°. Verification of the new model version was performed for three areas of the lake: the southern shallow area (≤ 40 m), the central area (~50 m), and the northern deep area with depths up to 230 m. To assess the impact of climate change on thermohydrodynamic processes, calculations were performed from 1990 to 2020. Both contact measurements from the Institute of Limnology of the Russian Academy of Sciences and images from NOAA and MODIS Terra/Aqua satellites were used for verification. The verification results showed that the model adequately reproduces the main features of thermohydrodynamic processes in Lake Ladoga, namely: the vertical thermal structure of the lake’s water mass, the beginning of the formation and spread of the vertical frontal zone - the thermobar. Accounting for inflow waters allows tracking their further distribution in the lake. Replacing atmospheric forcing has led to a significant improvement in calculations of ice conditions in the lake. The results of verification of the new version of the model should be considered satisfactory. Some shortcomings of the model have also been noted.

Eutrophication-driven Trichodesmium erythraeum blooms in Karimunjawa National Park, Indonesia

Widiaratih, Rikha — 2025-12-25

Harmful algal blooms (HABs) are increasingly frequent due to anthropogenic nutrient enrichment, posing significant ecological and economic threats. It includes hypoxia, toxin production, and a decline in tourism due to odour pollution. This study investigates the HAB event in Karimunjawa National Park (KNP) on September 19, 2023, attributed to nutrient loading from inadequate wastewater treatment in the shrimp pond. The bloom coincided with the shrimp harvest season, indicating a strong correlation between pond effluents and coastal eutrophication. To identify the dominant algal species and primary environmental drivers of bloom formation, nutrients and water quality parameters were analysed using field and satellite observations from three locations in KNP. Pearson’s correlation analysis was applied to assess linear relationships among variables, while principal component analysis (PCA) was employed to determine key contributors to HAB development. The findings indicate that Trichodesmium erythraeum was the dominant bloom-forming species, proliferating due to biogeochemical imbalances induced by excessive nutrient enrichment. Phosphate (r=0.952), silicate (r=0.832), ammonia (r=0.670), and nitrate (r=0.653) were identified as key factors influencing bloom dynamics. Lower ammonia concentrations suggest uptake by phytoplankton, whereas microbial decomposition contributed to elevated phosphate levels. Additionally, high sunlight exposure (r=0.877) and low-currents hydrodynamic conditions (r=0.197) further facilitated bloom persistence. These findings underscore the urgent need for enhanced wastewater management policies in shrimp ponds and stricter environmental policies to mitigate future HABs occurrences and protect marine ecosystems and coastal economies.

Blood cell morphology of the Mediterranean pond turtle (Mauremys leprosa Schweigger, 1812) from contrasting habitats in northeastern Algeria

Frih , Abdelaziz — 2025-12-25

We examined the blood cell profiles of the Iberian pond turtle, also known as the Mediterranean pond turtle (Mauremys leprosa) in two habitats in northeastern Algeria with markedly contrasting water quality. Blood smears were prepared from 38 adult turtles collected at a polluted reference site (Bouhamra) and an unpolluted site (Brabtia). Differential leukocyte counts and erythrocyte morphometrics (length, width, and surface area) were quantified. At Brabtia Reserve, heterophils were the most abundant leukocyte type (41.35%), followed by lymphocytes (27.54%) and monocytes (10.16%). At the Bouhamra site, heterophils are also dominant (57.86%), followed by monocytes (21.40%) and lymphocytes (12.80%). The average ratio of heterophils to lymphocytes (H/L) was 4.39 in the polluted site, Bouhamra, which is about three times higher than the ratio of 1.60 in the pristine, indicating elevated physiological stress. Erythrocyte dimensions differed significantly between sites. In turtles from Brabtia, mean erythrocyte length, width, and surface were 24.10 µm, 13.68 µm, and 260.97 µm², respectively. Corresponding values in turtles from the degraded habitat (Bouhamra) were larger (25.07 µm, 13.96 µm, and 274.95 µm²). Nuclear length, nuclear width, nuclear surface, and nuclear shape index (NL/NW) did not vary between habitats. Our results show that contamination mainly affects the size of red blood cells, while the morphological parameters of the nucleus remain stable. The higher H/L ratio at the polluted site (Bouhamra) also supports the use of leukocyte profiles as solid indicators of chronic environmental stress in freshwater turtles.

Weakly basic fluorescent dye for vital staining of calcium structures in living organisms

Zelinskiy , S.N. — 2025-12-25

Vital dyes capable of staining developing skeletal elements made of carbonate or calcium phosphate contain carboxyl groups that can interact with calcium ions. These dyes are in demand both in research of the biomineralization mechanisms and in the tagging of fish and mollusks in ecological and aquaculture experiments. At the same time, negatively charged dye molecules such as calcein do not penetrate cell membranes well. This necessitates the use of high concentrations, which can cause toxic effects and non-specific staining. This article describes an effective method for synthesizing a new fluorescent dye, QE2, containing a weakly basic amino group and two carboxyl groups in the form of methyl esters capable of hydrolysis in a weakly alkaline environment or under the action of enzymes. The fluorescence of QE2 and its hydrolysis product significantly depends on the polarity of the environment, intensifying in a nonpolar environment with a simultaneous shift in emission from the green-blue to the blue region. The dye is able to easily penetrate living cells, as shown by the example of dinoflagellate culture. Growing organisms with calcium skeletons (gastropods, fish) in the presence of QE2 leads to fluorescent staining of growth areas (gastropod shell aperture, fish spine and fin elements). The QE2 dye can be used to track areas of calcium mineralization, assess the polarity of cell organelles, introduce markers into fish for experiments in ecology and aquaculture, and stain cell cultures and skeletal elements for confocal microscopy studies.

Invasive fish and its consequences in the freshwater ecosystem of undivided Midnapore, West Bengal, India

Chanda, Angsuman — 2025-12-25

A primary goal of the current study is to conduct a complete survey of the diversity of freshwater exotic fish in Midnapore, West Bengal, India, with special attention paid to their effects on local fish species. Freshwater fish species from all the blocks in the three districts under study have been surveyed. According to observations, there are 14 foreign freshwater fish species in the research region, classified into 12 genera and 7 families. Two species, Barbonymus gonionotus and Piaractus brachypomus, are recorded for the first time from the study area and are comparatively recent phenomena. Most exotic fish species (12 species) were introduced in India as food fish for aquaculture purposes; two species were introduced for mosquito control for their larvicidal feeding habits. Of the twelve food fishes, three are also used in aquariums as pet fish among the residents of the study area. The ecological consequences of the exotic fish species on local fish diversity is an added criterion of the present investigation. All species in the study area have a complete set of distributional information. Thus, the focus of the current study is on the exotic fish faunal diversity in the study area.

Genomic basis of Baikal sponge tissue degradation caused by a free-living Flavobacterium with host-glycan-targeting polysaccharide utilization loci

Panova, Yulia — 2025-12-25

Here we present the complete genome sequence of the Flavobacterium sp. strain PLB03 isolated from the primmorphs cell culture of the Lubomirskia baikalensis sponge and compare it with pathogenic free-living members of the genus Flavobacterium. Strain Flavobacterium sp. PLB03 exhibits pronounced lytic activity towards sponge cells and causes death of symbiotic microalgae (the Trebouxiophyceae). The Flavobacterium sp. PLB03 genome has 5,925,828 bp and a GC content of 34.3%. An average nucleotide identity (ANI) of 98.9% revealed that strain Flavobacterium sp. PLB03 has the highest similarity to Flavobacterium CSZ. Comparative genomic analysis of the strain and phylogenetically related Flavobacterium indicated that Flavobacterium sp. PLB03 has a large genome size characteristic of the environmental genus Flavobacterium, and the peptidase (PEP) to glycoside hydrolase (GH) gene ratio is 1.8, suggesting that strain PLB03 exhibits characteristics similar to nonpathogenic strains.

Nanoplastics as a substrate for fungal growth Lecanicillium coprophilum (Cordycipitaceae, Hypocreales)

Annenkov, Vadim — 2025-12-25

Anthropogenic pollution of the environment by plastic waste represents one of the most serious environmental problems. Nanoplastics, particles smaller than 1000 nm, pose a particular danger, as their small size and high specific surface area result in high bioavailability and toxicity for a wide range of aquatic organisms. Fungi are promising candidates for cleaning contaminated ecosystems due to their metabolic capabilities for breaking down complex molecules. In this study, for the first time, we experimentally investigated the ability of the micromycete, Lecanicillium coprophilum, to use nanoparticles of synthetic polymers–polyvinyl chloride (PVC), polystyrene (PS), and polymethyl methacrylate (PMMA)–as a growth substrate. Fluorescence microscopy and measurements of polymer concentrations in the medium proved that this fungus can not only adsorb nanoplastics on the surface of its hyphae but also metabolize them. Non-parametric analysis of variance (Kruskal-Wallis test) revealed statistically significant differences in mycelial biomass accumulation in media containing different plastics at 10°C. PS was the most favorable substrate for the growth of L. coprophilum. The median mycelial biomass values demonstrated a consistent ranking of polymers by favorability: PS > PMMA > PVC, which remained across different cultivation temperatures. This paper also discusses the enzymatic activity of L. coprophilum and the potential contribution of enzymes, particularly lipases, to the biodegradation of nanoplastics by this fungal species.

Coumarin-based dye for vital staining of cell cultures

Annenkov , Vadim — 2025-12-25

Fluorescent dyes are widely used in modern biochemical and biological research to assess, in particular, the functional state of cells, cellular components, tissues, and organisms. Blue fluorescent dyes offer the advantage of not interfering with the autofluorescence of biological media in the green-red spectrum. This study aims to design a new affordable blue fluorescent dye capable of penetrating living cells. The structure of prepared dye (ZS-833) combines the blue fluorophore 7-(diethylamino)coumarin with the dimethyl-2-butenedioate moiety. The utility potential of ZS-833 was tested with staining heterotrophic as well as naturally pigmented cells (the Saccharomyces cerevisiae yeast and Gymnodinium corollarium dinoflagellate). ZS-833 penetrates readily both types of living cells, making them bright fluorescent in the blue and green spectral ranges but leaving dead cells unstained. These data suggest ZS-833 as a promising agent for intravital cell culture staining and visualization of cellular components, especially nonpolar ones.

Unification of geological and geophysical characteristics of gas hydrate-bearing structures in Lake Baikal

Khabuev, Andrey — 2025-12-25

We carried out the unification of the geological and geophysical characteristics of the gas hydrate-bearing structures of Lake Baikal. For this purpose, we conducted a comprehensive compilation and analysis of all currently available primary and processed data. The study included a detailed examination of >400 seismic and acoustic profiles, 50 sonograms of side-view sonar, 60 bathymetric schemes of multipath echo sounder, and >1,000 primary descriptions of sediment cores. This resulted in the identification of six reference (model and typical) gas hydrate-bearing structures (two mud volcanoes, two hydrate mounds, and two seeps), which most fully characterize each of the listed types. Unification of characteristics of hydrate-bearing structures of Lake Baikal and allocation of supporting structures facilitates the research of already known ones and will help in the search for new places with near-surface gas hydrates in bottom sediments.

Methodological aspects of estimating natural mortality coefficients for the baikal omul: a case study of The selenga population

Anoshko , P.N. — 2025-12-25

This scientific article presents a critical analysis of methods for estimating the instantaneous natural mortality coefficient (M) of the Baikal omul, Coregonus migratorius (Georgi, 1775), in the context of managing its commercial stock. The von Bertalanffy growth equation was parameterized based on growth and age structure data. A comparative analysis of existing M estimates used in the Total Allowable Catch (TAC) materials for 2017–2025 revealed their significant variability, leading to threefold discrepancies in the calculated population biomass under equal recruitment. An important factor determining the dynamics of cohort abundance and biomass is the extremely high post-spawning mortality (>90%) in the Selenga population. The applicability of theoretical models based on life history invariants for calculating average M values (Jensen, 1996) is justified using the concept of maximum age (Shibaev, 2023). The resulting estimate based on maximum age, M_avg=0.19 yr⁻¹, and the ratio M/K≈1.5 yield more realistic projections consistent with historical fishery data. The reliability criterion for any M estimation method should be its consistency with key population indicators, taking into account the spatial heterogeneity of the stock.

The complete chloroplast genome of Chlorella vulgaris strain BAC9706 isolated from Lake Baikal

Panova , Yu.A. — 2025-12-25

We report here the complete chloroplast genome sequence of the strain BAC9706 of green microalga Chlorella vulgaris isolated from Lake Baikal. The chloroplast genome is a circular DNA molecule of 161,721 bp and contains 78 protein-coding genes, 33 tRNA genes, and 3 rRNA genes. Comparative analysis revealed a high level of conservation of gene content and gene order among other C. vulgaris strains with minor differences mainly associated with introns and non-coding regions. Phylogenetic analysis based on concatenated chloroplast protein-coding genes showed that strain BAC9706 clusters within the C. vulgaris clade with high bootstrap support. These results indicate that strain BAC9706 represents a Baikal ecotype of C. vulgaris rather than a new species.

Vertical distributions of dissolved methane concentration in sediments of background areas of Lake Baikal

Ivanov , V.G. — 2025-12-25

For the first time, vertical distributions of dissolved methane concentrations in bottom sediments from background (undisturbed sedimentation) areas of the Southern, Middle and Northern basins of Lake Baikal down to subbottom depths of ~3 m obtained and analyzed. Methane concentration profiles at all stations share common features, characterized by low concentrations in the near-surface layers (≤1–2 µM) and a steady increase of methane with subbottom depth. The highest sedimentary methane concentrations were observed in the Middle basin, somewhat lower values in the Southern, and an order of magnitude lower concentrations in the Northern basin. The exponential decrease in methane concentrations toward the bottom–water interface to equally low values, regardless of its content within the sediment, indicates its significant oxidation and, consequently, minimal influence on methane concentrations in near-bottom water. The obtained results fill a gap in knowledge concerning the vertical distribution of dissolved methane in Lake Baikal sediments and are important for assessing the stability and functioning of hydrocarbon systems in a cold, and deep freshwater reservoir.

Features of polychlorinated biphenyls accumulation in Baikal fishes (initial results)

Kustova , O.V. — 2025-12-25

A detailed systematic analysis of the content of polychlorinated biphenyls (PCBs) in various Baikal fish species was conducted for the first time. Accumulation levels of indicator and dioxin-like PCBs were determined in the muscles of five species of Baikal sculpins of the family Cottidae: Abyssocottus pallidus, Abyssocottus godlewskii, Abyssocottus platycephalus, Leocottus kesslerii and Cottocomephorus comephoroides, and of two species of the family Coregonidae: Coregonus baicalensis and Coregonus migratorius. The features of pollutants accumulation by various fish species depending on habitat specificity and feeding ecology are revealed. The total toxic equivalents of dioxin-like PCBs were calculated despite their extremely low concentrations in the water of Lake Baikal.