Search Results (133)

Introduction: Climate change is reducing freshwater availability worldwide, making it essential to understand how freshwater inflow influences estuarine ecosystem functioning and marine fisheries productivity. In the Gulf of Cádiz (SW Spain), one of the most important fishing areas in Spain, the Guadalquivir Estuary serves as a key nursery habitat for commercially important fish and crustacean species. Objective: The aim of this study is to evaluate the effects of droughts and floods on estuarine functioning and coastal fisheries. Methodology: We analyzed 25 years of monthly data (1997–2022) from the Guadalquivir Long-Term Ecological Research Program (GUADALQUIVIR-LTER), using time-series analyses and dynamic structural equation modelling. Environmental variables, zooplankton and mysid biomass, and juvenile biomass of anchovy, sardine, and meagre were examined to assess trophic relationships and recruitment dynamics. Results: Our findings show that positive North Atlantic Oscillation (NAO) phases, associated with drought conditions in southern Europe, reduced freshwater inflow from the Alcalá del Río Dam into the estuary. Freshwater input increased organic matter and turbidity, which positively affected the mysid Rhopalophthalmus tartessicus, an important prey species for anchovy recruits. The mysid Mesopodopsis slabberi showed the strongest positive effect on anchovy recruitment (0.39). Although turbidity initially had a negative effect on M. slabberi, a significant positive effect appeared after monthly lag = 4. Conclusions: These findings demonstrate that spring freshwater inflow is essential for maintaining estuarine productivity, enhancing mysid abundance, and supporting anchovy recruitment, ultimately benefiting adult fish stocks after juveniles migrate from the estuary to coastal waters. Full article

Urban aquatic ecosystems are increasingly shaped by anthropogenic pressures that alter community structure and ecological functioning. This study investigates how the functional organization of zooplankton communities reflects ecosystem stability along an urbanization gradient in the Colentina River–Lake system (Romania). Zooplankton taxa were classified into trophic guilds and size-based functional groups, and functional diversity was quantified using the FEve, FDiv, FDis, and RaoQ indices, based on functional trait structure and distribution within communities. Ecosystem stability patterns were estimated through zooplankton community resilience (RSL) and resistance (RST), indices derived from Shannon diversity and Pielou evenness. Across the system, filter feeders dominated, and their density increased toward downstream, highly urbanized sectors. Also, small-sized organisms (SMC) were consistently prevalent, representing a zooplankton component commonly associated with stress tolerance and opportunism in disturbed aquatic environments. Functional diversity patterns showed low evenness but high divergence, suggesting that although few functional strategies dominate, communities maintain internal differentiation. While filter feeders remained dominant even in disturbed sectors, the uneven distribution of other groups, especially scrapers, may reflect greater sensitivity to anthropogenic conditions. These findings suggest that functional trait composition, in addition to diversity, plays an important role in shaping structural stability patterns. These findings indicate that functional trait composition, in addition to diversity, was associated with the observed stability patterns. The study reinforces the value of zooplankton as sensitive indicators of functional integrity in anthropogenically impacted freshwater systems and provides insights relevant for sustainable urban water management. Full article

Biological invasions and freshwater biodiversity loss are two of the most pressing global conservation challenges yet their interaction during the earliest stages of invasion remains poorly understood. Iberian freshwaters rank among Europe’s most biodiverse ecosystems, harbouring a remarkable assemblage of endemic fish species. This irreplaceable heritage is increasingly threatened by non-native piscivorous predators, to which endemic species often lack innate antipredator responses. The invasive European perch (Perca fluviatilis) was first detected in the Meimoa reservoir, within the Malcata Natural Reserve (Central Portugal), in 2023, and has since expanded exponentially in abundance while dispersing into adjacent stream networks. This emerging invasion provided a unique opportunity to assess the predation impacts of a novel piscivorous predator during the early stages of establishment and dispersion, across both lentic and lotic habitats. From 2022 to 2025, European perch were sampled in the invaded reservoir using gillnetting and in connected streams with electrofishing. Diet was assessed through stomach content analysis, and prey composition was analyzed in relation to site, season, year and ontogeny. European perch exhibited a clear ontogenetic diet shift as expected, from zooplankton and invertebrates to crayfish and fish, with minor variation in prey composition between systems. In the Meimoa reservoir, body size was the strongest driver of diet composition (PERMANOVA: R² = 0.134, p < 0.001), with 50% of the stomachs from individuals above 35 cm containing fish, with the Iberian nase, Pseudochondrostoma polylepis, being the dominant prey. Diet composition remained stable across years (R² = 0.007; p = 0.188), despite a 74% decline in nase catch per unit effort (CPUE) between 2022 and 2025. In streams, despite the absence of large perch, piscivory was recorded earlier and encompassing a broader range of native taxa. The sustained predation pressure on P. polylepis, a formerly dominant and culturally significant species, despite its steep population decline, suggests that European perch holds the potential to locally deplete native fish stocks. The advance of this predator into lotic habitats demands urgent conservation action, as it may critically threaten the long-term persistence of one of Portugal’s most vulnerable freshwater taxonomic groups. Full article

Water hyacinth (Pontederia crassipes Mart.) is native to the Amazon basin. It has spread to freshwater ecosystems in over 80 countries in tropical, subtropical, and warm temperate regions. Due to its invasive nature, water hyacinth is listed among the world’s 100 worst invasive alien species. Infestations of water hyacinth affect the abiotic components of these ecosystems, including water evaporation, flow, and quality; oxygen and nitrogen levels; sunlight transmission; and greenhouse gases. These changes reduce the abundance and diversity of primary producers in the food web, including phytoplankton and aquatic plants. Consequently, these alterations affect consumers in the food web, including zooplankton, invertebrates, fish, and birds. A negative correlation has often been observed between water hyacinth infestations and the abundance and diversity of these organisms, particularly native species. However, the abundance of some introduced species among these consumers has increased due to water hyacinth infestations. These changes alter the structure and function of natural ecosystems compared to what they were before infestations occurred. Infestations also negatively impact daily human activities and livelihoods, harming local communities and increasing disease transmission. Global warming and the eutrophication of freshwater ecosystems allow water hyacinth to spread into additional non-native areas in high latitudes, thereby increasing the threat it poses. Water hyacinth also contributes to global warming by increasing methane emissions. Over the past century, management strategies have shifted toward restoring the structure and function of ecosystems by progressively integrating various sectors. The infestation of water hyacinth is a complicated, site-specific process influenced by time, climate, existing biotic and abiotic factors, and ecosystem resilience. Therefore, long-term monitoring of environmental outcomes is essential for developing sustainable, site-specific strategies. Robust evaluation systems are necessary to track the efficacy of interventions and to understand the broader ecological ramifications of management strategies. Water hyacinth is still sold in some local markets for ornamental purposes. Raising public awareness of its invasive characteristics is necessary. 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

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

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

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

Many species within the family Moronidae possess biological traits that facilitate their success as invasive species in freshwater ecosystems. In Iowa, USA, non-native Yellow Bass (Morone mississippiensis) have expanded their range into at least 19 glacial natural lakes, yet their trophic interactions in these complex systems remain poorly understood. From 2018 to 2020, we evaluated the open-water diet composition of 1300 Yellow Bass across six Iowa natural lakes to quantify diet composition, feeding intensity, and ontogenetic dietary shifts. While zooplankton numerically dominated diets across most systems (>80% by number) biomass was driven primarily by benthic invertebrates and fish. Feeding intensity was not uniform, characterized by a distinct suppression of foraging during late spring followed by intense feeding in early summer. Overall, we found that Yellow Bass foraging is highly plastic but heavily constrained by spatial (lake identity, season, and year) and biological (ontogeny, age, and sex) filters. Spatial heterogeneity was the primary driver of diet composition ${(R}^2=0.407)$, with individual lakes explaining the largest portion of variance ${(R}^2=0.126)$. The interaction between lake size and population history ${(R}^2=0.054)$ was also significant, highlighting that the ecological impact of Yellow Bass is context-dependent, differing among established populations in small lakes versus recent invasions in large lakes. We identified distinct ontogenetic breakpoints at 114 mm and 252 mm; fish < 114 mm were obligate zooplanktivores, while significant piscivory was restricted to large adults (>252 mm). These results suggest that the successful colonization of Yellow Bass is supported by high dietary plasticity, which may lead to intensive resource competition with native juveniles. Our findings provide a critical baseline for fisheries managers to assess the ecological risks associated with Yellow Bass expansion and emphasize the importance of monitoring trophic shifts to preserve the integrity of native fish communities in the Midwest. Full article

In temperate freshwater ecosystems, zooplankton play a crucial role in the pelagic food web and act as sensitive indicators of environmental change. They respond to shifts in water temperature, hydrodynamic mixing, and short-term meteorological events. This study investigated the epilimnetic zooplankton fauna of Lake Karamurat (Bolu, Türkiye), a small tectonic temperate lake, with a specific focus on the influence of rainfall events and wind speed on community structure. The samples were taken seasonally and horizontally using a plankton net (55 µm mesh size) and were analyzed alongside in situ physico-chemical measurements and meteorological data. In total, 74 zooplankton taxa were identified, comprising 54 rotifer species and 20 crustacean species (16 Cladocera and 4 Copepoda). Testudinella greeni was recorded for the first time in Türkiye, representing a new addition to the Turkish Rotifera fauna. Multivariate analyses revealed that electrical conductivity, water temperature, dissolved oxygen, precipitation, and wind speed were key drivers shaping community composition. The findings suggest that wind-driven surface mixing and episodic rainfall events enhanced vertical redistribution, leading to dominance of rotifers and small-bodied cladocerans in the epilimnion. These findings underscore the critical role of sampling strategy in shallow lakes under dynamic conditions and provide new faunistic insights into the zooplankton diversity of Anatolian lakes. Full article

To characterize freshwater bivalve communities and their environmental drivers in the Caizi Lake water system following the 10-year fishing ban in Yangtze River, this study three rounds of standardized surveys across hydrological periods in 2024—May (normal-water), September (high-water), and November (low-water). The results recorded 22 freshwater bivalve species belonging to 15 genera and 4 families. Notably, Ptychorhynchus pfisteri and the second-class national key protected wild animals in China, Lamprotula leaii and Uninovaculina chinensis, were first recorded in the Caizi Lake water system. Community composition was partitioned into three subgroups: Group I—Dasha River, Guache River, Longmian River, and Kongcheng River; Group II—the lake area; and Group III—Chang River. Biomass, density, and dominant species exhibited pronounced spatial heterogeneity, and the assemblage reflected a state of moderate disturbance. Redundancy analysis indicated that the variables that contribute significantly to species richness in sequence are the bitterling and suitable host fish, phytoplankton, and zooplankton. The research results reveal for the first time the population status and distribution patterns of bivalve resources in the Caizi Lake water system following the fishing ban. They not only provide a decision-making basis for the conservation and protection management of bivalve resources in the Caizi Lake water system but also offer data support for the assessment of the fishing ban effect and the evaluation of biological integrity in key waters of Anhui Province. Full article

Understanding the mechanisms that maintain biodiversity is crucial for effective conservation in riverine ecosystems. However, the direct and indirect mechanisms by which land use patterns and water quality parameters influence plankton α- and β-diversity remain poorly elucidated. Here, we undertook a comprehensive survey of plankton communities across the Jialing River basin. Our results showed that Bacillariophyta and Chlorophyta were the dominant phytoplankton groups, whereas Protozoa and Copepoda predominated among zooplankton. Redundancy analysis identified dissolved oxygen and total phosphorus as key environmental factors shaping plankton community structure. Additionally, random forest models indicated that anthropogenic stressors exerted consistent effects on both α- and β-diversity of phytoplankton. Importantly, the decomposition of β-diversity revealed that species turnover constituted the major component, underscoring the importance of basin-scale management approaches. Structural equation modeling further demonstrated that land use practices predominantly affected phytoplankton β-diversity indirectly via water quality alterations, with a relatively weak direct effect. In contrast, neither the direct nor indirect effects of land use were significant for zooplankton communities. These findings suggest that phytoplankton may serve as more reliable bioindicators of anthropogenic disturbance than zooplankton in this freshwater system. Moreover, our findings highlight the central role of water quality in regulating phytoplankton diversity responses to environmental change. Consequently, we recommend that conservation strategies in the Jialing River basin focus on water quality monitoring and the mitigation of its ecological effects. Full article

Estuaries are vital coastal ecosystems that support fish during key life stages such as spawning, feeding, and early development. This study investigates ichthyoplankton composition and abundance in the Sanquianga Tapaje estuarine system, located in the southern Eastern Tropical Pacific (ETP) of Colombia. Zooplankton samples were collected using bongo nets at 11 stations across four river mouths (Tapaje, Amárales, Sanquianga, and Guascama), alongside measurements of oceanographic parameters at 1 and 10 m depths. A total of 357 fish larvae were identified, representing 23 species and 11 families, with Engraulidae, Gobiidae, and Carangidae dominating the assemblage. Water column conditions reflected typical tropical estuarine dynamics, influenced by tidal action and freshwater input. Spearman’s rank correlation revealed strong positive associations between larval abundance and surface salinity (r_s = 0.81, p = 0.003), as well as dissolved oxygen saturation and concentration (r_s > 0.68, p < 0.021). Diversity indices (Shannon, Pielou, Whittaker) indicated high species turnover in transitional zones, and larval hotspots were associated with outer estuarine zones. Salinity and dissolved oxygen emerged as key drivers of ichthyoplankton distribution. These findings underscore the ecological complexity and nursery function of tropical estuaries, offering baseline data to inform biodiversity conservation, ecosystem monitoring, and adaptive management in Colombia’s Pacific region and across the ETP. Full article