Search Results (48)

The ecological consequences of the construction and operation of the Three Gorges Reservoir, particularly its unique operation strategy of storing clear water and releasing turbid water, exerts a profound influence on the composition and dynamics of local fish communities. To date, detailed and comprehensive research on seasonal changes in the fish community across the entire reservoir remains scarce. This study aims to fill this research gap by systematically investigating fish diversity through a comprehensive assessment of six main river reaches and eight major tributaries. The investigation employs environmental DNA (eDNA) technology across three critical life-cycle stages: breeding, feeding, and overwintering periods. A total of 124 fish species were recorded, comprising 10 orders, 20 families, and 80 genera. The comparative analyses of historical data suggest a significant decline in lotic and endemic fish populations, accompanied by a concurrent increase in lentic, eurytopic, and non-native fish species. Notably, the composition of fish communities exhibited similarities between breeding and overwintering periods. This study highlights the occurrence of significant seasonal fluctuations in the fish communities, showing a preference for reservoir tails and tributaries as optimal habitats. Water temperature has a predominant influence on structuring fish communities within aquatic ecosystems. This study investigates variations in the biodiversity of fish communities using historical data, with a focus on changes linked to reservoir operations and water impoundment activities. By integrating historical data, this research examines changes in fish diversity that are associated with water storage processes. It provides foundational data on the current composition and diversity of fish communities within the watershed, elucidating the spatiotemporal variations in fish diversity and the mechanisms by which environmental factors influence these communities. Furthermore, the current study serves as a valuable reference for understanding the changes in fish communities within other large reservoirs. Full article

Zooplankton are ubiquitous in aquatic ecosystems and play crucial roles in material cycling and energy flow. However, the mechanisms governing zooplankton community assembly, particularly habitat-specific differences, remain poorly understood. In this two-year study, we monitored zooplankton communities across reservoir and river habitats within the Chayuan watershed, a representative karst region in southwest China. Our findings revealed significant spatial divergence in water-quality variables (including water temperature, pH, total nitrogen, total phosphorus, permanganate index, dissolved oxygen, chlorophyll-a, and ammonia nitrogen) between habitats. Twenty-nine dominant zooplankton species were identified in reservoir and river communities, with only eight shared between the two habitats. The mechanisms underlying the corresponding zooplankton community structures showed distinct segregation between habitats, with deterministic processes predominating in reservoir communities (explaining 25.1% of the variation) and stochastic processes predominating in river communities (3.4% of the variation explained). Environmental drivers differed substantially between habitats: reservoir communities were primarily influenced by total nitrogen, dissolved oxygen, and chlorophyll-a concentrations, whereas river communities responded predominantly to ammonia nitrogen levels. This study provides novel insights into the divergent mechanisms governing zooplankton community assembly in lentic versus lotic systems within a shared karst watershed, offering theoretical foundations for ecosystem-specific management strategies in fragile karst environments. Future research should focus on key climatic variables (e.g., extreme precipitation) and hydrological dynamics (such as flow velocity and water residence time) to further elucidate the mechanisms behind zooplankton community assembly, providing deeper insights to facilitate effective ecosystem management in karst environments. Full article

The responses of benthic fauna to channel modifications of mountain rivers by low-head barriers are poorly understood. The study aimed (1) to estimate the impact of two different low-head barrier types: concrete sills and block ramps, on Oligochaeta and Trichoptera communities in two small Carpathian rivers (Porębianka and Mszanka) in southern Poland, and (2) to determine changes in these communities in the mountain Porębianka River after 50 years by comparing current data with historical data. Both types of channel modifications led to a transformation from lotic to more lentic habitats. The research shows that habitat conditions and induced bed siltation greatly influenced the studied communities. In both rivers, the taxa richness and dominant taxa of Oligochaeta and Trichoptera were similar, alongside similar species compositions of Trichoptera. However, the river with the lower bed siltation rate had a higher Trichoptera density and a greater diversity in their density among habitats. After 50 years, the taxonomic richness of Oligochaeta and Trichoptera remained similar, unlike the considerable shift in their species compositions. Many species typical of mountain rivers have been replaced by species more tolerant to siltation, characteristic of lowland rivers. The family Tubificidae (Oli-gochaeta) and the genus Hydropsyche (Trichoptera) became dominant in both rivers in the early 2020s. Additionally, the functional feeding group (FFG) of Trichoptera changed considerably. Oligochaeta and Trichoptera communities serve as valuable indicators for moni-toring the environmental changes in these ecosystems. Full article

The spread of non-native species threatens biodiversity and exacerbates societal challenges like food security. To address this, effective conservation programs require detection methods that are easy to implement, accurate, and non-invasive. Over the past 15 years, environmental DNA (eDNA) techniques have gained popularity, surpassing traditional sampling methods. In this context, our study focused on tracking the invasive host–pathogen complex Pseudorasbora parva and Sphaerothecum destruens using eDNA metabarcoding. We collected water samples from freshwater canals over five months in the Camargue region, and once in Corsica Island, both in southern France. Total DNA was extracted from filtered water samples, and PCR-amplicons were sequenced using Illumina or Nanopore technologies. Our results revealed a high detection rate of P. parva in lentic ecosystems, aligning with habitat preferences of this small freshwater fish. Additionally, the detection rate in Camargue increased in May and June, likely due to the peak of the spawning season, which leads to more DNA being released into the environment (i.e., concentration and interaction of individuals). While eDNA successfully detected this invasive fish, we were unable to detect its cryptic fungal parasite, S. destruens, highlighting the challenges of identifying intracellular and cryptic fungal pathogens through eDNA methods. Full article

Accurate assessment of species rarity and conservation status requires an approach that integrates data-driven models with established ecological knowledge. In this study, we applied multispecies occupancy (MSO) and latent factor multispecies occupancy (LFMSO) models to estimate the occurrence of 133 Odonata species in South Korea. Using the model outputs, we implemented the Rabinowitz rarity framework to conduct data-based rarity assessments, which were then compared with known ecological information, including geographic ranges, habitat preferences, regional Red List statuses, and citizen science observations. Our findings reveal both alignments and discrepancies between these data-driven rarity assessments and traditional ecological knowledge. For example, species classified as near threatened (NT) or vulnerable (VU) on the regional Red List generally corresponded with high-rarity classifications based on the Rabinowitz framework. However, significant inconsistencies were identified, particularly for certain lentic Odonata species traditionally considered common. These results suggest that spatial biases in field surveys, combined with limited access to data on legally protected species, can impede accurate rarity assessments. These findings underscore the need for standardized survey protocols and improved data-sharing policies for sensitive species to reduce biases and enhance the reliability of rarity assessments. This is essential for effective conservation planning and biodiversity management in freshwater ecosystems. Full article

Giant water bugs (Hemiptera: Belostomatidae) are top predators in wetland ecosystems, serving as biological indicators of the health of lentic ecosystems and as effective biological control agents for freshwater snails and mosquitoes. This study aimed to predict the current and future distribution of two Korean giant water bugs, Appasus japonicus and Diplonychus esakii, under three climate change scenarios, contributing to the sustainable management of wetland ecosystems in South Korea. Using MaxEnt models, we employed seven climatic and three non-climatic variables to investigate the habitat preferences and distribution patterns of the species. The results revealed that A. japonicus is likely to experience a northward range contraction due to climate change, while D. esakii is predicted to expand its distribution northward without losing its current range. These responses may lead to occupancy turnover between the two species, potentially driving reassembly in aquatic organism community. Elevation was the primary factor influencing the distribution of A. japonicus, whereas annual mean temperature was the most informative variable for D. esakii, both factors derived under the current climate conditions. These findings suggest that both species are highly sensitive to climate change, with potential range shifts toward higher latitudes and elevations. This study provides insights into how climate change could impact two giant water bugs, thereby supporting future efforts to manage and conserve wetland ecosystems in this country. Full article

Although somewhat debated, it is generally agreed in Europe that small water bodies comprise lentic ecosystems that are shallow (less than 20 m) and have a surface area of a few hectares (less than 10 ha). In Albania, 84 glacial lakes constitute a substantial portion of the aquatic ecosystems that sustain high levels of biodiversity, metabolic rates, and functionality. This paper discusses the integration of ecological sustainability into ecosystem services (i.e., cultural, regulatory, and sustaining services) and the national ecological networks of protected sites. This integration is particularly important in light of recent advancements regarding European integration. It is also important due to the catchment continuum, which addresses biodiversity values and gradients that, in this work, are considered using rotifer communities and aquatic plant species. The main causes of the stressors on small ecosystems are inappropriate land use, water pollution, altered habitats, non-native species introduction, resource mismanagement in basins, inadequate planning, and a lack of sector integration. The glacial lakes reflect climate change elements through: an increased number of dried glacial lakes, so only 84 remain functioning; the water level is slowly being reduced; the oscillation of the water level is steadily increasing; and the eutrophication process is rapidly advancing. Full article

Freshwater insects are highly significant as ecosystem service providers, contributing to provisioning services, supporting services, and cultural services. Odonates are dominant predators in many freshwater systems, becoming top predators in fishless ecosystems. One service that odonates provide is the export of matter and energy from aquatic to terrestrial ecosystems. In this study, we provide a review of the literature aiming to estimate the density, biomass, and secondary production of odonates and discuss to what extent this order of insects is relevant for the fertilization of terrestrial ecosystems. We found published data on 109 species belonging to 17 families of odonates from 44 papers. Odonata larvae are abundant in freshwater systems, with a mean density of 240.04 ± 48.01 individuals m⁻² (±SE). Lentic habitats show much higher densities (104.40 ± 55.31 individuals m⁻², N = 118) than lotic systems (27.12 ± 5.09, N = 70). The biomass estimations for odonates indicate values of 488.56 ± 134.51 mg m⁻² y⁻¹, with similar values in lentic and lotic habitats, which correspond to annual secondary productions of 3558.02 ± 2146.80 mg m⁻² y⁻¹. The highest biomass is found in dragonflies of the Aeshnidae, Corduliidae, and Gomphidae families. The available evidence suggests a significant potential contribution of Odonata to the exportation of material from water bodies to land. This is further strengthened by the ability of adult odonates to migrate and to colonize different types of water bodies. Full article

Waste Water Treatment Plants (WWTP) aim to reduce contamination in effluent water; however, studies indicate antimicrobial resistance genes (ARGs) persist post-treatment, potentially leading to their spread from human populated areas into the environment. This study evaluated the impact of a large WWTP serving 125,000 people on the Iskar River in Bulgaria, by characterizing the spatial and short-term temporal dynamics in bacterial community dynamics and resistance profiles of the surface water. Pairs of samples were collected biweekly on four dates from two different locations, one about 800 m after the WWTP effluents and the other 10 km downstream. Taxonomic classification revealed the dominance of Pseudomonodota and Bacteriodota, notably the genera Flavobacterium, Aquirufa, Acidovorax, Polynucleobacter, and Limnohabitans. The taxonomic structure corresponded with both lentic and lotic freshwater habitats, with Flavobacterium exhibiting a significant decrease over the study period. Principal Coordinate Analysis revealed statistically significant differences in bacterial community composition between samples collected on different dates. Differential abundance analysis identified notable enrichment of Polynucleobacter and Limnohabitans. There were shifts within the enriched or depleted bacterial taxa between early and late sampling dates. High relative abundance of the genes erm(B), erm(F), mph(E), msr(E) (macrolides); tet(C), tet(O), tet(W), tet(Q) and tet(X) (tetracyclines); sul1 and sul2 (sulphonamides); and cfxA3, cfxA6 (beta-lactams) were detected, with trends of increased presence in the latest sampling dates and in the location closer to the WWTP. Of note, genes conferring resistance to carbapenems blaOXA-58 and blaIMP-33-like were identified. Co-occurrence analysis of ARGs and mobile genetic elements on putative plasmids showed few instances, and the estimated human health risk score (0.19) according to MetaCompare2.0 was low. In total, 29 metagenome-assembled genomes were recovered, with only a few harbouring ARGs. This study enhances our understanding of freshwater microbial community dynamics and antibiotic resistance profiles, highlighting the need for continued ARGs monitoring. Full article

Dramatic land-use changes in urban landscapes can drive water colour darkening by washing compounds, such as organic matter and iron, from terrestrial ecosystems into urban blue space, consequentially affecting aquatic communities. Here, I studied how pond water colour changes along an urban gradient and how diving beetles (Dytiscidae) respond to the water colour gradient in 11 ponds with fish and 15 ponds without fish in the Helsinki Metropolitan Area, Finland. I found that the pond water colour exhibited a non-significant decreasing pattern along the urban gradient, indicating that urbanisation may not necessarily drive brownification in urban ponds. Dytiscid species richness and abundance exhibited significant positive correlations with increasing water colour in ponds with fish but no significant correlation in ponds without fish. Some species, such as Agabus spp. and Dytiscus spp., appeared tolerant to highly coloured water, whereas some species, such as Hyphydrus ovatus and Hygrotus spp., tended to occur in clear water, indicating that brown water may provide dytiscids with prey refuges, but some species are intolerant to brown water. The study highlights the importance of urban pondscape heterogeneity to meet the needs of aquatic invertebrates that prefer different water colours and for the multifunctioning of urban ponds. Full article

Factors responsible for species distribution of benthic macroinvertebrates, including responses at different spatial scales, have been previously investigated. The aim of the present research was to review the most relevant factors explaining chironomid species distribution focusing on factors operating at different spatial scales, such as latitude, longitude, altitude, substrate, salinity, water temperature, current velocity, conductivity, acidity, dissolved oxygen, nutrient content etc. acting at regional levels and at a large or small water basin level. Data including chironomid species abundances from different lentic and lotic waters in Italy and other surrounding countries were analyzed using partial canonical correspondence analysis (pCCA) and multiple discriminant analysis (DISCR). Spatial analyses, including univariate Moran’s I correlograms, multivariate Mantel correlograms and Moran’s eigenvector maps (MEMs), were thereafter carried out. The results showed that habitat type, including different types of lotic waters (i.e., kryal, crenal, rhithral, potamal) and different lake types (i.e., littoral, sublittoral, profundal zones), is the most significant factor separating chironomid assemblages, while spatial factors act only as indirect influencers. Full article

Alien fish invasions are causing devastating impacts on native freshwater fauna; thus, rigorous, non-invasive and cost-effective biomonitoring of lotic and lentic freshwaters to design and implement appropriate prevention and control measures is now a priority. In this study, we used a species-specific qPCR eDNA assay to monitor two of the most invasive fish species (Gambusia holbrooki and Pseudorasbora parva) in 15 river basins of Greece and validated these results with conventional fish sampling as well as existing field sampling data. Our monitoring provided new records of invasive species indicating basins for rigorous future monitoring and possible eradication attempts. The eDNA proved more sensitive as a detection tool (56% detection rate) compared to conventional electrofishing (50% detection rate) for G. holbrooki. In contrast, it proved less sensitive for detecting P. parva (38% accuracy) compared to electrofishing (44% accuracy), as evident by the two locations where the eDNA failed to detect the target species. Our study illustrates the potential of the eDNA method for regular, standardised monitoring of riverine habitats for invasive fish species by local managers for early detection. Finally, we discuss the application of eDNA in management interventions for identifying invasive species’ hotspots for management prioritisation, for early detection of invaders and for the monitoring of eradication/control actions. Full article

Periphytic rotifer assemblages from lentic habitats are understudied. To improve knowledge on the principal environmental determinants of their structure and composition, we examined summer periphyton from 184 freshwater bodies from a taxonomic and multi-trait-based perspective. Only the latter allowed consideration of all bdelloids. Alpha diversity decreased with electrolyte and aluminium concentration but increased with macrophyte richness, pointing at salinization, metal toxicity and loss of structural niche heterogeneity as potential threats for rotifer diversity. Replacement was the prominent component of beta diversity, with acidified sites showing the highest local contributions. Variation partitioning indicated that local conditions explained variation in species composition best, but general setting (soil type, land cover, connectivity) and spatial context were also not insignificant. Redundancy analysis related species composition more particularly to gradients of pH and trophic status, whereas the representation of functional groups was structured mainly by phytoplankton productivity. Mirroring shifts observed in the plankton, high phytoplankton productivity associated with larger size and more detritibacterivory. Dominance of collectors constrained variation in guild ratios, underlining the need for more refined functional approaches. To aid the use of periphytic rotifers in regional water quality assessment, we identified indicators and community thresholds for pH and trophic variables and determined optima and tolerances for individual taxa. Full article

Suckermouth armored catfish (Pterygoplichthys disjunctivus) is one of the most widespread invasive species in Vietnam. However, it is relatively unknown how the species underwent its divergent adaptations to varying local conditions and habitat types, an understanding of which is essential for managing its invasion in Vietnam. We addressed this by analyzing a large number of fish (662 samples) collected in lotic (Dinh River) and lentic (Suoi Trau Reservoir) habitats in southern Vietnam during one year. The allometric growth patterns estimated by von Bertalanffy growth functions were $L_t=483\left(1-e^{-0.71(t-0.40)}\right)$ in Dinh River and $L_t=346\left(1-e^{-1.01(t-0.62)}\right)$ in Suoi Trau Reservoir. The estimated fish ages were 2.9 to 4.2 years old with an average total length from 206.10 ± 2.09 mm in Suoi Trau Reservoir to 319.22 ± 3.29 mm in Dinh River. The percentage of fish with matured ovaries peaked in August (100%) and was lowest in February (<10%), indicating that these fish breed nearly all year round. The main reproductive season is April–October, with a peak in July–August, as indicated by the gonado-somatic index and monthly changes in the percentage of matured fish. The lengths at 50% maturity were 234.3 and 179.7 mm for females from lotic and lentic habitats, respectively. Lotic fish had a fecundity (4812 ± 383 oocytes/ind.) which was five times greater than that of lentic fish (841 ± 91 oocytes/ind.); however, the relative fecundity of the fish was not statistically different between the two habitats (≈13 oocytes/g). This result was consistent with the larger oocytes: 2.95 ± 0.04 and 2.58 ± 0.01 mm for fish from Dinh River and Suoi Trau Reservoir, respectively. The faster growth and bigger fish with higher fecundity in the lotic habitats suggest that their population growth can accelerate more quickly, potentially affecting local communities more than those in lentic habitats. Our study sheds light on substantial phenotypic divergences in the reproduction and growth of the suckermouth armored catfish between lotic and limnetic habitats in Vietnam. Full article

This study aimed to evaluate the effects of the Martil River rehabilitation project and recently constructed dam infrastructures to reduce flood risks and to promote local socio-economic development on the ecological integrity of the river. The assessment focused on changes in fluvial landforms over time and the evaluation of aquatic ecosystems based on six physicochemical parameters (temperature, pH, electrical conductivity, dissolved oxygen, biochemical oxygen demand, and chemical oxygen demand), morpho-hydrological variables (stream width, water depth, and current speed), habitat indices (QBR, IHF, and MQI), and macroinvertebrate assemblages of EPT, OCH, and Chironomidae (Diptera) at five stations from autumn 2015 to spring 2018 (prior to and during the rehabilitation actions). The results showed that the river rehabilitation project led to profound changes in Martil River’s ecosystem and water quality over time. Physicochemical and habitat measurements at the rehabilitated sites revealed a major change in macroinvertebrate communities due to changes in fluvial landforms in relation to flow-sediment regimes. As a result, some typical species of lentic habitats disappeared, while alien, opportunistic, and lotic species appeared. Full article