Search Results (760)

Three locally calibrated Indices of Biotic Integrity (IBIs) based on macroinvertebrates (B-IBI), zooplankton (Z-IBI), and phytoplankton (P-IBI) were developed to characterize relative aquatic ecological condition at impaired sites in Dongjiang Lake, a deep reservoir-type lake in China, during 2021–2023. Using synchronous monitoring data, candidate metrics for the three biotic groups were screened and assembled by integrating taxonomic diversity, community composition, pollution-tolerance attributes, trophic indicators, and functional feeding groups. Metric values were standardized using a linear transformation, and site conditions were classified using a unified five-class grading scheme under the present local calibration framework. A total of 327 taxonomic units (species or morphospecies) were recorded across the three biotic groups, indicating relatively high biodiversity in the study area. Under the present locally calibrated framework, most impaired sites were classified within the moderate-to-good range, with clear interannual variation and spatial heterogeneity. Upstream and downstream sections showed greater fluctuations in IBI classes than the lake area. The macroinvertebrate-based IBI was more sensitive to long-term and cumulative habitat disturbance, whereas the zooplankton- and phytoplankton-based IBIs responded more rapidly to short-term variation in nutrients and water quality. Together, these results indicate that multitaxon IBIs can provide complementary information on relative ecological condition within Dongjiang Lake and may support ecological zoning, pollutant management, and restoration prioritization in similar deep reservoir-type lake systems. Full article

Rotifers are a key group in freshwater food webs, with diverse feeding and defensive traits that enable them to dominate tropical zooplankton. However, whether these traits trade off at the community level remains unclear. We investigated rotifers monthly in two tropical reservoirs in South China, with different hydraulic retention times (HRTs) from 2023 to 2024, comparing patterns between the dry and wet seasons. Functional diversity (Rao’s Q) and community-weighted sum (CWS) of traits were measured for both feeding and defensive traits. Rao’s Q for both traits showed no significant differences between the dry and wet seasons in either reservoir. Feeding trait composition, based on CWS, differed significantly between the dry and wet seasons in both reservoirs, whereas defensive trait composition changed significantly only in the shorter-HRT reservoir (SZ). The relative abundance of suctor feeders was significantly negatively correlated with that of loricate and loricate-spined rotifers, particularly in the wet season. RDA and hierarchical partitioning revealed that the change in feeding traits was mainly driven by water temperature and cladocerans, whereas that in defensive traits was mainly governed by predation pressure from cyclopoid copepods. Rotifers achieve functional trait trade-offs through species turnover. Under high predation pressure, communities may shift from species with more efficient feeding traits to those with stronger defensive traits, thereby enhancing survival. Full article

Ochetobibus elongatus (Kner) is a migratory fish found in the Yangtze River basin and areas south of it, and listed as a critically endangered (CR) fish on the China Red List of Vertebrates. To achieve group recovery and artificial breeding, this study investigated the dietary characteristics of O. elongatus based on high-throughput sequencing of its intestinal contents, and its digestive system morphology, and its histology. Results showed that the digestive system of O. elongatus lacked a stomach and mainly consisted of the oropharynx, pharyngeal teeth, esophagus, intestine, and anus. The gut index was 0.88, with clear segmentation of the foregut, midgut, and hindgut, and the visceral mass index was 7.35%. Histological analysis of the digestive system revealed the presence of keratinized dental plates or pharyngeal teeth in the pharynx, as well as a high density of taste bud cells in the soft palate of the oral cavity. The surface layer of the intestinal villi contained numerous mucous cells, with the average number of mucous cells per villus gradually increasing from the esophagus to the hindgut, and the foregut having the longest and most abundant mucosal folds. The esophagus exhibited well-developed circular and longitudinal muscle layers, while in the hindgut, both the circular and longitudinal muscle layers were slightly thicker than those in the midgut. High-throughput sequencing of the intestinal contents of O. elongatus revealed the following phyla based on 18S V4 meta-barcoding: Chlorophyta, Diatoms, Arthropoda, Basidiomycetes, and Ascomycetes, with the genus Hypophthalmichthys and algae being the main classifications. In contrast, based on COI meta-barcoding, the study newly identified the phyla Cnidaria and Mollusca, with the genera Chlorophyta, Scenedesmus, Pectinodesmus, and zooplankton such as Pseudodiaptomus. Metagenomic sequencing revealed that the gut microbiota at the phylum level was predominantly composed of Pseudomonadota, Ascomycota, Basidiomycota, Chytridiomycota, and Bacillota, with key genera including Cetobacter, Pseudomonas, Acinetobacter, Aeromonas, and Clostridium. This study indicates that O. elongatus is an omnivore with carnivorous tendencies. Basic biological research on O. elongatus is of great significance for the restoration of the population, artificial breeding, and the development of its artificially formulated feed. It also provides important data for the formulation of biodiversity conservation measures. Full article

Studying zooplankton in freshwater ecosystems is crucial for ecological research, providing insight into ecosystem health, biodiversity, and water quality. This study focuses on developing a hybrid approach for studying and analyzing zooplankton communities using machine learning and human expert analysis. The goal of the study was to automate the labor-intensive process of zooplankton analysis as part of a long-term Lake Baikal monitoring program (since 1945), while maintaining continuity with traditional methods. A software and algorithmic system were developed to automate the analysis: images were processed using a two-stage pipeline (object detection using YOLO V11, classification using metric learning and visual transformers), and complex cases and new species were sent to specialists for verification. Over 240,000 images from 811 samples were processed, and models are updated using verified data to adapt to seasonal changes. An updatable database of labeled zooplankton images suitable for statistical analysis and research has been created. A comparison of manual and machine analysis revealed no significant differences in species composition, with accurate detection in 87% of images. This approach allows for scalable monitoring and the accumulation of labeled data arrays for the development of computer vision methods and the assessment of the state of Lake Baikal’s ecosystem. Full article

Macrobrachium nipponense is one of the major economic species in freshwater aquaculture in China. As an important component of aquaculture ecosystem, microorganisms participate in key processes such as material cycling and water quality regulation, exerting significant impacts on the cultured organisms. In this study, high-throughput sequencing of the 16S rRNA, 18S rRNA, and ITS regions was employed to comparatively analyze the characteristics of microbial communities before and during the cultivation period, combined with correlation analysis of environmental factors. The results showed that the dominant microbial groups in the prawn pond water were Proteobacteria, Cyanobacteria, Ascomycota, Basidiomycota, Chlorophyta, and Arthropoda. The microbial community structure differed significantly between the pond water during the culture period and the pre-culture external river baseline: manifested as an increase in the relative abundances of Cyanobacteria, Chytridiomycota, and zooplankton, and a decrease in the abundances of Ascomycota, Basidiomycota, and Chlorophyta. Analysis of LEfSe revealed that the low-nitrogen pond was enriched with taxa such as Muribaculaceae; the high-nitrogen pond was enriched with taxa such as Cyanobium_PCC-6307; and the control pond was enriched with taxa such as CL500-29_marine_group. Functional prediction indicated that heterotrophic metabolism-related functions dominated the microbial communities. The abundance of fungal pathogens was significantly higher in the low-nitrogen group, while potential pathogenic bacteria were enriched in the high-nitrogen group. Ammonia nitrogen is a core environmental factor associated with differences in microbial community structure. The findings of this study can provide theoretical references and data support for water quality optimization and the construction of healthy aquaculture models in freshwater shrimp and crab farming waters. Full article

Coastal port ecosystems serve as critical interfaces between marine environments and anthropogenic activities, yet zooplankton community dynamics in these transitional zones remain poorly understood. This study investigated seasonal variations in zooplankton assemblages and their environmental drivers in the coastal waters surrounding Lanshan Port, northern Yellow Sea, through quarterly field surveys spanning spring to winter. A total of 33 zooplankton species and 16 planktonic larval categories were identified, with Hydromedusa, Copepoda, and planktonic larvae comprising the three dominant groups. Marked seasonal disparities were observed in species richness (spring: 21 species and 11 larvae categories; winter: 8 species and 3 larvae categories), biomass (autumn: 333.7 mg/m³; winter: 34.0 mg/m³), and abundance (spring: 185.3 ind/m³; winter: 25.7 ind/m³). Notably, Aidanosagitta crassa maintained perennial dominance across all seasons. Principal component analysis of dominant zooplankton taxa across seasons indicated that the first two principal components explained 70.05% and 15.97% of the total variance in zooplankton community structure, respectively, with distinct seasonal clustering of sampling sites along PC1 reflecting pronounced seasonal succession in community composition. Redundancy analysis revealed seasonal-specific correlations between dominant taxa and nutrients: nitrate concentration was negatively correlated with the relative abundance of Sergestidae in both spring and summer, whereas ammonium concentration was negatively correlated with Hydromedusa; by contrast, the abundances of Chaetognatha and Tunicata exhibited a significant positive correlation with nitrate. We also found water temperature only drove communities in autumn, while salinity had little effect. These findings elucidate the mechanisms structuring zooplankton communities in temperate coastal port ecosystems and underscore the necessity of seasonally resolved monitoring frameworks for effective marine environmental management. Full article

The aim of this study is to conduct a comprehensive assessment of the water quality of the Sidi Mohammed Ben Taiba (SMBT), one of the largest drinking water reservoirs in northwestern Algeria, by integrating chemical and biological indicators. The assessment combines the Drinking Water Quality Index (DWQI), the Irrigation Water Quality Index (IWQI), the Organic Pollution Index (OPI) and zooplankton-based biological indicators (Zoo-IQ). A total of 23 physicochemical parameters were analyzed and interpreted using multivariate statistical approaches. This study fills an important knowledge gap by evaluating long-term temporal variability (January 2018–May 2025) and recent spatial heterogeneity (June 2023–May 2025), aiming to support sustainable water management. The results indicate that the reservoir water quality is generally suitable for drinking purposes (22.3 < DWQI < 54.0), is deemed excellent for agricultural irrigation (65 < IWQI < 69) and that the reservoir surface waters are slightly polluted to unpolluted (0.3 < OPI < 1.1). However, a deterioration in water quality has been detected in recent years, linked to increasing nutrient concentrations, as confirmed by the TSI–SD index. Despite the early signs of nutrient enrichment, the Zoo-IQ index remained within the moderate to good range, suggesting a certain degree of resilience in the zooplankton community. However, pronounced seasonal fluctuations observed in the Zoo-IQ and species diversity (H′) during periods of environmental stress serve as an early warning signal of emerging problems that may negatively affect water quality indices (WQI, IWQI, OPI). Station S4, located at the confluence of Wadi Belhassen and Wadi Farhat, descending from the Dahra mountain range in Algeria, has been identified as the most sensitive area and a potential hotspot for future pollution. The study provides robust data on the quality of reservoir water, offering a valuable decision-making tool for artificial reservoir managers and contributing to sustainable water management by identifying risk areas and supporting the implementation of preventive measures. Full article

Deposit-feeding aquatic oligochaete worms are abundant and widely distributed benthic animals in lakes that affect the nutrient cycling between sediments and the water and thus the water quality. This effect can be density-dependent and affected by the presence of filter-feeding bivalves, which can modulate the worms’ impact. We conducted a mesocosm experiment with high, medium, and low densities of the tubificid worms Limnodrilus hoffmeisteri (Oligocheata, Tubificida, and Naididae) in the presence of the filter-feeding bivalve Hyriopsis cumingii. In the low-density treatment, the concentrations of nitrate nitrogen (NO₃⁻-N), ammonium nitrogen (NH₄⁺-N), and organic suspended solids (OSSs) increased moderately compared with the control. In the medium- and high-density treatments, there were also increases in total nitrogen (TN), total phosphorus (TP), soluble reactive phosphorus (SRP), total suspended solid (TSS) and inorganic suspended solid (ISS) concentrations. Moreover, the biomass of phytoplankton (Chl a), the light attenuation coefficients, and the abundance of both cladoceran and rotifer zooplankton rose with increasing worm densities. Water quality deteriorated in both the medium and high worm density treatments, likely due to increased nutrient leading to an increase in the biomass of phytoplankton in our mesocosms, even though plankton-consuming bivalves were present. Thus, during the restoration of eutrophic shallow lakes with a high density of worms, more bivalves are needed to compensate for the negative impact of worms on water quality. Full article

Microplastics (MPs) are emerging contaminants in freshwater ecosystems, yet their ingestion by zooplankton remains poorly documented in large European lakes. This study provides the first evidence of MPs in zooplankton from Lake Como (Northern Italy), a major subalpine lake of ecological and socioeconomic relevance. Using high-resolution digital microscopy (detection limit: 2 µm), we quantified MPs across four sampling years (2016, 2017, 2018, 2025), capturing small size fractions typically overlooked by conventional methods. MPs were consistently detected, with mean concentrations of 0.06 ± 0.08 MPs ind.⁻¹ and 1.14 ± 1.22 MPs mg⁻¹ d.w., values comparable to those reported for freshwater zooplankton worldwide. No significant differences were observed between the lake’s two main branches, supporting a lake-wide interpretation of exposure. Clear seasonal patterns emerged, with higher MPs loads in autumn and winter. These findings highlight the potential for MPs to enter pelagic food webs and contribute to a lake-wide baseline for future harmonized monitoring and polymer-specific assessments. The main limitation of this study is the exclusive quantitative approach, which does not provide qualitative information on polymer composition. Overall, these results underscore the need to integrate zooplankton-based monitoring into freshwater microplastic risk assessment frameworks. Full article

This study investigates the spatiotemporal dynamics of zooplankton communities in the tropical low-latitude Northwestern Pacific Ocean based on field surveys conducted in August 2021 and November 2022. Redundancy analysis identified nitrate, silicate, temperature, and salinity as the primary factors influencing community structure. The distribution of dominant zooplankton groups exhibited close correlations with key environmental gradients, showing distinct habitat preferences corresponding to different hydrographic conditions. Zooplankton abundance in August 2021 was significantly higher than that in November 2022, which is presumably attributed to eddy-induced nutrient upwelling and enhanced primary productivity. Comparisons with adjacent marine regions reveal general consistency in overall zooplankton abundance and community species composition, while the observed seasonal discrepancies are closely associated with local unique hydrographic characteristics. These results highlight the role of nutrient–temperature–salinity interactions in structuring zooplankton communities and underscore their sensitivity to environmental variability. The findings provide a scientific basis for understanding pelagic ecosystem dynamics in oligotrophic waters and for developing management strategies under changing climate and oceanographic conditions. Full article

The effects of environmental factors on zooplankton within the marginal ice zone (MIZ) of the Barents Sea remain poorly understood. To address this knowledge gap, we investigated mesozooplankton communities across the central, northern, and northeastern regions in April 2016. Abundance and biomass ranged from 90 to 997 individuals m⁻³ and from 1.1 to 48.6 mg dry mass m⁻³ (0.3 to 13.6 g dry mass m⁻²), respectively. Oithona similis was the most abundant taxon, while calanoid copepods, including Calanus spp., Metridia longa, and Pseudocalanus spp., dominated total biomass. The spatial distribution of mesozooplankton communities was closely linked to the physical properties of water masses. Cluster analysis identified two distinct assemblages associated with Polar Front Water and Arctic Water. Redundancy analysis and generalized linear models identified temperature, mean salinity, mean chlorophyll a concentration, and sea ice concentration as significant predictors of abundance and biomass. The dominance of older life stages within major copepod taxa indicated a winter status for the mesozooplankton community. Regional and temporal comparisons of mesozooplankton biomass with prior May–June data from central and northwestern areas highlighted higher productivity in the northern and northeastern MIZ. This increase is potentially related to the warming trends observed in the Arctic since the 2000s. Our research provides novel insights into Arctic marine zooplankton assemblages and serves as a valuable baseline for future ecological monitoring and modeling of the Barents Sea ecosystem in the context of global climate change. Full article

Reconciling hydropower development with aquatic biodiversity conservation is a central challenge for sustainable river management worldwide. Cascade dam configurations, in which multiple impoundments are arranged in series along a single channel, impose longitudinal environmental gradients that restructure biological communities across trophic levels. Whether the resulting multi-trophic responses are independently driven by shared abiotic gradients (environmental filtering) or mechanistically coupled through direct food-web interactions (trophic cascading) remains unresolved. We surveyed phytoplankton, zooplankton, and benthic macroinvertebrates simultaneously at seven stations along a 430 km gradient downstream of Danjiangkou Dam in the Hanjiang River, the largest tributary of the Yangtze River and the source of China’s South-to-North Water Diversion Middle Route, over eight seasonal campaigns (2015–2017). Variance partitioning, piecewise structural equation modeling, Mantel tests, and co-occurrence network analysis were applied to partition environmental and trophic pathways. Environmental filtering dominated community restructuring at all three trophic levels, while the biotic proxy for direct trophic interactions explained less than 0.4% of community variation, consistent with weak detectable trophic coupling at seasonal resolution. Distance from Danjiangkou Dam shaped downstream transparency and turbidity gradients that mediated trophic-level-specific responses along distinct environmental axes (pH and water temperature for phytoplankton, conductivity for zooplankton, and transparency for benthic macroinvertebrates). Benthic macroinvertebrates were systematically decoupled from the pelagic analytical framework, absent from the cross-trophic co-occurrence network and structured more by spatial configuration than by water-column variables. Hub species in the network were associated with downstream mineralized conditions, confirming that network architecture reflects shared environmental preferences rather than biotic interactions. These findings support a management shift from single-dam mitigation toward cascade-scale coordination of environmental flow regimes, sediment connectivity, and substrate restoration as integrated strategies for sustaining multi-trophic biodiversity in regulated rivers. Full article

Global freshwater scarcity is a pressing environmental challenge, particularly in Egypt, which depends entirely on the Nile River and its tributaries. Rapid population growth, domestic wastes, agricultural runoff, and rapid industrial expansion exert highly anthropogenic stress on aquatic ecosystems, including Bahr Yusuf and Ibrahimia Canals in Upper Egypt. This study aimed to evaluate the ecological health and sustainability status of the two canals using an integrated multi-metric framework combining physicochemical variables, microbiological indicators, and community structures of zooplankton and benthic fauna. Multivariate statistical analyses (PCA, CCA), and ecological indices, including the water quality index (WQI), microbial assessment index (MAI), Rotifer-Based Index (TSI_Rot) and Hilsenhoff Biotic Index, were applied to determine pollution gradients. The results revealed that Bahr Yusuf suffers from higher pollution levels than the Ibrahimia Canal. Canonical correspondence analysis (CCA) showed that nutrient enrichment and elevated organic load are responsible for over 72% of the variance in zooplankton and benthic invertebrate assemblage in both water bodies. The dominance of pollution-tolerant species, Philodina roseola and B. calyciflorus of zooplankton and Limnodrilus udekemianus, Chironomidae larvae, Melanoides tuberculate and Cleopatra bulimoides of benthic taxa, further indicates a direct increase in organic loading and nutrient enrichment from agricultural and domestic sources. According to the Integrated Water Quality–Biotic Health Index (IWQ-BHI), the downstream stations of Bahr Yusuf are critical risk zones, with scores below 50.0, while the upstream stations of Ibrahimia Canal fell within the “good” category, with scores exceeding 70.0. Overall, both waterbodies are approaching a critical threshold of ecological instability and require urgent, integrated and sustainable management to restore and preserve these vital freshwater ecosystems. Full article

Polyunsaturated fatty acids (PUFAs), especially the long-chain omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are essential nutrients for aquatic organisms and play key roles in growth, reproduction, neural development, and immune function. In freshwater ecosystems and aquaculture systems, the availability of these lipids depends on complex interactions within aquatic food webs, where PUFAs are produced by primary producers and transferred to higher trophic levels. This review summarizes current knowledge on the biosynthesis, regulation, and trophic transfer of PUFAs in freshwater aquaculture food webs, with particular emphasis on interactions among microalgae, zooplankton, and fish larvae. The main biochemical pathways and regulatory mechanisms responsible for PUFA synthesis in microalgae are described, together with the environmental factors that influence their production. The role of zooplankton at an intermediate trophic level is discussed, highlighting their ability to retain, modify, and transfer dietary fatty acids to higher consumers. Finally, the capacity of freshwater fish larvae to synthesize and regulate long-chain PUFAs through key metabolic enzymes is examined, along with the influence of diet and environmental conditions on these processes. By integrating information from molecular, biochemical, physiological, and ecological studies, this review provides an overview of the mechanisms underlying PUFA production and trophic transfer in freshwater aquaculture food webs. Full article

Lake Balkhash is a large endorheic lake experiencing ongoing hydrological and climatic variability. This study aimed to evaluate the species composition and structure of the forage base across three trophic levels—phytoplankton, zooplankton, and zoobenthos—and to analyze trophic interactions of fish communities, including non-native species, in order to assess the functioning of the food web in the western and eastern basins of the lake. A 2025 assessment revealed a structurally reorganized yet relatively stable ecosystem. Phytoplankton showed an increase in taxonomic richness, while zooplankton and zoobenthos demonstrated compositional restructuring with a greater representation of ecologically tolerant taxa. The presence of certain invertebrate taxa in both Lake Balkhash basins indicates persistent spatial heterogeneity of the ecosystem. Despite moderate ecological resilience, biodiversity has not yet returned to historically recorded peak levels. Trophic analysis of fish communities showed generally moderate niche overlap among benthivorous species with localized differentiation of resource use. Predatory fishes also exhibited moderate overlap: pikeperch (Sander lucioperca) maintained stable dietary patterns with partial overlap with Volga pikeperch (Sander volgensis), whereas snakehead (Channa argus) and asp (Aspius aspius) demonstrated clearer trophic segregation. Non-native species displayed relatively narrow trophic niches (Bi < 0.30), indicating summer feeding specialization. Full article