Search Results (12)

The nutritional needs of anadromous fish species must be met for successful annual spawning migration and reproduction. Despite its widespread distribution throughout Europe, little is known about the composition of the twaite shad, Alosa fallax, diet in freshwater ecosystems. To redress this, we studied the composition of stomach contents extracted from 287 A. fallax sampled during their spawning migration from the Baltic Sea to the Curonian Lagoon (Lithuania). We found that the diet comprised 32 types of prey, with Insecta (unknown Order), Chironomidae and Daphniidae being the most prevalent taxonomic categories consumed. Our analyses revealed significant differences in the abundance of prey categories (Chironomidae, Insecta—unknown order, and Mysidae) among several size groups of A. fallax, associated with stage of maturity inferred from body length. Despite this being a spawning aggregation, juveniles were also present among the A. fallax we collected. The results imply that feeding behavior and morphometry may be responsible for the differences observed, and further investigation of this topic is warranted. Full article

Cyanobacterial harmful blooms (CyanoHABs) in lakes, estuaries, and freshwater reser-voirs represent a significant risk to water authorities worldwide due to their cyanotoxins and economic impacts. The duration, spread, and severity of CyanoHABs have markedly increased over the past decades. The article addresses CyanoHABs, cyanotoxins, and monitoring methodologies in post-Soviet and Central Asian countries. This particular region was selected for the systematic review due to its relative lack of representation in global CyanoHABs reporting, particularly in Central Asia. The main aim of this systematic review was to analyze the primary literature available from 2010–2024 to examine the current situation of CyanoHAB detection, monitoring, and management in Central Asia and post-Soviet countries. Following a detailed database search in several selected data-bases (Google Scholar, Pubmed, Web of Science (WOS), Scopus, Elibrary, ENU, and KazNU) along with additional hand searching and citation searching, 121 primary articles reporting 214 local cyanobacterial bloom cases were selected for this review. Aquatic cyanotoxins were reported in water bodies of eight countries, including high concentrations of microcystins that often exceeded reference values established by the World Health Organization (WHO). Advancing monitoring efforts in Baltic countries, Belarus, and the Russian Federation differed from only a few Central Asian reports. However, Central Asian aquatic ecosystems are especially threatened by rising anthropogenic pressures (i.e., water use, intensive agriculture, and pollution), climate change, and the lack of adequate ecological surveillance. We hypothesize that recent Caspian seal mass mortality events have been caused by a combination of infection (viral or bacterial) and exposure to algal neurotoxins resulting from harmful algal blooms of Pseudo-nitzschia. We conclude that there is an urgent need to improve the assessment of cyanobacterial blooms in Central Asia and post-Soviet countries. Full article

Freshwater ecosystems in Lithuania are threatened by the introduction of invasive fish species including Neogobius fluviatilis, N. melanostomus, Perccottus glenii, and Pseudorasbora parva. Data on helminth parasites of these fishes have not been comprehensively studied, with only two reports on parasites of N. melanostomus from the Curonian Lagoon and Baltic Sea, Lithuania. We examined 278 fish individuals representing 4 invasive species from 13 waterbodies. Using morphological and molecular analyses, we identified 29 helminth taxa representing 15 digenean trematodes, 6 nematodes, 4 cestodes, 2 acanthocephalans, and 2 monogeneans. With 18 species, N. fluviatilis had the highest helminth diversity, followed by N. melanostomus (11 species) and Ps. parva (8 species). Perccottus glenii was found to be free from helminth infection. The availability of historical information on the native fish parasites in Lithuania allowed us to conclude that out of the 29 recorded species, invasive fish serve as hosts for 22 local fish helminth species, while 7 helminth species have been reported exclusively in invasive fish. Based on newly obtained and previously published data, a total of 34 helminth species parasitise invasive fish in Lithuania, of which 30 use these fish as intermediate or paratenic hosts. Full article

The proposed study is focused on an ecological analysis of Latvian coastal lagoons, emphasizing their unique but vulnerable nature. Coastal lagoons are recognized as fragile ecosystems of significant ecological, social, and economic value, as recognized by the European Directive 92/43/EEC (Habitats Directive). Despite their protected status, the existence of these ecosystems can be threatened by morphological, hydrological, and anthropogenic changes. The uniqueness of these ecosystems can be determined by the large number of influencing factors and their dynamics. They are affected by seawater, their level of fluctuation, wind exposure, overgrowing with macrophytes, freshwater sources, and water flow generated streams affecting sediment transport and accumulation. All the influencing factors determine a highly trophic ecosystem, which in the studied lagoons is rated as medium to poor ecological status, which confirms the above-mentioned vulnerability and fragility. The aim of this study was to analyze two lagoons in the coastal area of the Baltic Sea in the Riga Gulf, by characterizing, for the first time, their current conditions and ecological parameters because understanding such ecosystems is only partial. The physicochemical composition of lagoon sediments and water shows the impact of seawater by increased electrical conductivity and the concentration of SO₄²⁻ and Cl⁻ in water, while the presence of detritus in sediments is almost non-existent; thus, the content of organic matter is low with relatively variable pH. The results show that the diversity of studied benthic macroinvertebrates, macrophytes, zooplankton, and even phytoplankton species is low, but there is higher diversity in lagoons and their parts with regular water exchange with the sea. The study provides valuable insight into the ecological dynamics of coastal lagoons in Latvia, shedding light on their current conditions, anthropogenic impact, and the need for sustainable management measures. Full article

In recent years, the study of marine viromes has become one of the most relevant areas of geoecology. Viruses are the most numerous, genetically diverse and pervasive biological entities on Earth, including in aquatic ecosystems. Information about viral diversity in aquatic ecosystems remains limited and requires more research. This work provides the first-ever look at the current DNA virome of the Northern Caspian Sea. A comparison with other freshwater and marine viromes revealed that the North Caspian Sea virome has the greatest similarity with those of the Baltic Sea and Lake Baikal. The study described in this article expands the knowledge about aquatic viromes and provides key data for a more comprehensive analysis of viruses circulating in the Caspian Sea, the largest inland body of water on Earth. Full article

Coastal lakes are subject to multiple stressors, among which land use, hydrological connectivity, and salinity have the greatest effect on their biodiversity. We studied the effects that various land cover types (CORINE) of coastal lake watersheds had on macrophyte diversity in ten coastal lakes along the southern Baltic coast as characterised by twelve phytocenotic indices: these being a number of communities, Shannon–Wiener diversity, evenness, and indices of taxonomic distinctiveness of plant communities: vegetation coverage; colonisation index; share of the phytolittoral area in the total lake area, as well as shares of nympheides, pondweeds, charophytes, marine, emerged and submerged communities in the total lake area. The effects were checked for three groups of lakes distinguished by differences in salinity–freshwater (F, 5), transitional (T, 4), and brackish (B, 1)—in which a total of 48 macrophyte communities were identified. The most abundant in aquatic phytocoenoses were lakes of T type. A partial least squares regression model (PLS-R) showed a stronger impact of land-use types in immediate vicinities and entire watersheds than the impact of physico-chemical properties of water on phytocenotic indices in the lakes. Macrophyte diversity was relatively low in urban and agricultural catchments and relatively high in forest and wetland areas. Agriculture had a negative impact on the number of macrophyte communities in F lakes and, in T lakes, on the number of macrophyte communities, biodiversity, evenness, and proportion of emerged, submerged, and marine communities. Urban areas contributed to lower values of evenness, vegetation coverage, and share of marine communities in F, but, in T, to lower the number of macrophyte communities, evenness, and proportion of submerged and marine communities. Our results confirm the significant impact of land use on macrophyte diversity in coastal aquatic ecosystems. Combined analysis of anthropogenic and natural descriptors is a prerequisite for analysing human threats to biodiversity in coastal lakes. Macrophyte community-based measures of biodiversity are sensitive indicators of anthropogenic impact on the ecological condition of coastal ecosystems. Full article

Non-indigenous species may pose a threat to native ecosystems worldwide. In aquatic environments, invasives may have a negative impact on human food security and livelihoods. Several water fleas (Crustacea: Branchiopoda: Cladocera) are notorious invasive alien species influencing large freshwater lake systems and even inland seas. In the current review, we discuss the state of knowledge regarding non-indigenous species in the Cladocera and their invasiveness potential in different continents. We argue that the potential impacts and occurrence of cladoceran exotics may be higher than generally assumed. We critically review 79 cases from literature sources, involving 61 cladoceran taxa where records outside of their natural distribution ranges were previously interpreted as invasions. We assessed the probability of natural range expansions versus human-mediated introductions and we discuss several major corridors of invasion. We estimate human-mediated transportations for at least 43 taxa (out of 61; ca 70%), while other cases can be seen as natural expansions of their distribution ranges (not necessarily/not likely human-mediated) and/or taxonomical confusion. We confirm non-indigenous presence in recipient regions for at least 41 cladoceran taxa, of which several are true invasives (i.e., with negative impacts on native ecosystems). The majority are zooplankters with effects on pelagic freshwater ecosystems, yet we also report on introductions by littoral taxa. We argue that cryptic introductions of cladocerans are taking place on a global scale, yet they remain under the radar. We highlight several striking case studies, such as the Ponto–Caspian onychopods that have invaded the Baltic Sea and the Laurentian Great Lakes, and several clones of the anomopod genera Daphnia and Bosmina that have successfully colonised new environments, causing equilibria shifts in native aquatic worlds. At the same time, we dispel some myths about taxa that were misconstrued as invasive in certain localities. Based on our review, the first of its kind for freshwater zooplankton, future environmental monitoring tools including molecular techniques and detailed surveys with rigorous and critical taxonomical assessments may help to provide a clearer picture on the extent of invasiveness of cladocerans. Full article

Riparian forests are important ecosystems located along the margins of freshwaters. Riparian zones provide many ecosystem services, such as nutrient modification, erosion and temperature control, leading to improvements in water quality in adjacent water ecosystems. In many areas, riparian forest management is restricted to improve adjacent water quality. The potential influence of forest management on water quality of small streams was assessed by analysing species composition and structural diversity in riparian forests. We collected data in riparian forests along 15 streams in the eastern Baltics (Latvia) with different water quality classes. We used detrended correspondence analysis and indicator species’ analysis to determine relationships between woody plants and understory vegetation. We also used ADONIS and ANOSIM analysis to determine possible factors that affect species composition. Our results suggested that water quality is affected by ground vegetation, which in turn was altered by stand density and total yield. Site-specific decision making in management is required in riparian forests to ensure the required conditions in the streams, because species composition differs between sites, dominant tree species and stand parameters (density, total yield, stand age). Introduction of Betula pubescens Ehrh. in coniferous stands is favourable to ensure litter fall quality and provide shade for streams during summer. Full article

The response of bacterioplankton structure to salinity level in coastal lakes (n = 9) along the southern Baltic Sea coastline was studied. In terms of mean salinity levels (0.2–5.2 PSU), the lakes represented freshwater, transitional, and brackish types. Results showed that salinity determines the spatial and seasonal distribution patterns of microorganisms in costal lakes. Increased salinity contributed to a significant decline in total bacterial numbers (TBN). The TBN was lowest in brackish lakes in autumn (4 × 10⁶ cells/mL) and highest in freshwater lakes in summer (7.11 × 10⁶ cells/mL). The groups of Proteobacteria are appropriate bioindicators in any classifications of coastal ecosystems, particularly at low-haline stress. Alpha- and Gamma- subclasses of Proteobacteria are identifiers for brackish habitats, while Betaproteobacteria, due to their intolerance to haline stress, prefer freshwater habitats. Counts of euryhaline Actinobacteria, the dominant group of bacterioplankton (31.8%), decreased significantly with increased salinity. Actinobacteria and Deltaproteobacteria were identifiers of transitional lakes. Cytophaga-Flavobacteria showed affinity with freshwater ecosystems, but this relation was not statistically significant (p > 0.05). The bacteria groups correlated with other physico-chemical parameters of water, such as oxygenation (Actinobacteria) or organic carbon (Betaproteobacteria, Deltaproteobacteria). The impact of hydrological connectivity and salt-water interference on the microbiota structure and biogeochemistry of coastal waters should be considered in the assessment of the ecological status of coastal lakes. Full article

Toxicity of cyanobacteria is the subject of ongoing research, and a number of toxic metabolites have been described, their biosynthesis pathways have been elucidated, and the mechanism of their action has been established. However, several knowledge gaps still exist, e.g., some strains produce hitherto unknown toxic compounds, while the exact dynamics of exerted toxicity during cyanobacterial growth still requires further exploration. Therefore, the present study investigated the toxicity of extracts of nine freshwater strains of Aphanizomenon gracile, an Aphanizomenon sp. strain isolated from the Baltic Sea, a freshwater strain of Planktothrix agardhii, and two strains of Raphidiopsis raciborskii obtained from 25- and 70-day-old cultures. An in vitro experimental model based on Cyprinus carpio hepatocytes (oxidative stress markers, DNA fragmentation, and serine/threonine protein activity) and brain homogenate (cholinesterase activity) was employed. The studied extracts demonstrated toxicity to fish cells, and in general, all examined extracts altered at least one or more of considered parameters, indicating that they possess, to some degree, toxic potency. Although the time from which the extracts were obtained had a significant importance for the response of fish cells, we observed strong variability between the different strains and species. In some strains, extracts that originated from 25-day-old cultures triggered more harmful effects on fish cells compared to those obtained from 70-day-old cultures, whereas in other strains, we observed the opposite effect or a lack of a significant change. Our study revealed that there was no clear or common pattern regarding the degree of cyanobacterial bloom toxicity at a given stage of development. This means that young cyanobacterial blooms that are just forming can pose an equally toxic threat to aquatic vertebrates and ecosystem functioning as those that are stable or old with a tendency to collapse. This might be largely due to a high variability of strains in the bloom. Full article

The Baltic Sea represents one of the largest brackish ecosystems where various environmental factors control dynamic seasonal shifts in the structure, diversity, and function of the planktonic microbial communities. In this study, despite seasonal fluctuations, several bacterial populations (<2% of the total OTUs) that are highly dominant (25% of relative abundance) and highly frequently occurring (>85% of occurrence) over four seasons were identified. Mathematical models using occurrence frequency and relative abundance data were able to describe community assembly persisting over time. Further, this work uncovered one of the core bacterial populations phylogenetically affiliated to SAR11 subclade IIIa. The analysis of the hypervariable region of 16S rRNA gene and single copy housekeeping genes recovered from metagenomic datasets suggested that the population was unexpectedly evolutionarily closely related to those inhabiting a mesosaline lacustrine ecosystem rather than other marine/coastal members. Our metagenomic results further revealed that the newly-identified population was the major driver facilitating the seasonal shifts in the overall community structure over the brackish waters of the Baltic Sea. The core community uncovered in this study supports the presence of a brackish water microbiome distinguishable from other marine and freshwater counterparts and will be a useful sentinel for monitoring local/global environmental changes posed on brackish surface waters. Full article

Cyanobacterial blooms are a major and growing problem for freshwater ecosystems worldwide that increasingly concerns public health, with an average of 60% of blooms known to be toxic. The most studied cyanobacterial toxins belong to a family of cyclic heptapeptide hepatotoxins, called microcystins. The microcystins are stable hydrophilic cyclic heptapeptides with a potential to cause cell damage following cellular uptake via organic anion-transporting proteins (OATP). Their intracellular biologic effects presumably involve inhibition of catalytic subunits of protein phosphatases (PP1 and PP2A) and glutathione depletion. The microcystins produced by cyanobacteria pose a serious problem to human health, if they contaminate drinking water or food. These toxins are collectively responsible for human fatalities, as well as continued and widespread poisoning of wild and domestic animals. Although intoxications of aquatic organisms by microcystins have been widely documented for freshwater ecosystems, such poisonings in marine environments have only occasionally been reported. Moreover, these poisonings have been attributed to freshwater cyanobacterial species invading seas of lower salinity (e.g., the Baltic) or to the discharge of freshwater microcystins into the ocean. However, recent data suggest that microcystins are also being produced in the oceans by a number of cosmopolitan marine species, so that Hepatotoxic Seafood Poisoning (HSP) is increasingly recognized as a major health risk that follows consumption of contaminated seafood. Full article