Human impacts on global freshwater fish biodiversity

Impacts of multi-environmental stresses on different facets of riverine phytoplankton beta diversity in a large-scale semi-arid basin

Rivers are among the most threatened ecosystems worldwide, with their biodiversity facing pressures from both natural variability and human activities. Compared to river ecosystems in humid regions, those in semi-arid regions are more fragile and susceptible to environmental stresses. However, the impacts of diverse environmental stresses on multiple facets of riverine phytoplankton beta diversity in semi-arid basins remain understudied. Here, we examined the responses of taxonomic (Tβ), functional (Fβ), and phylogenetic (Pβ) beta diversity of riverine phytoplankton communities to land use, water quality, bioclimate, and spatial structure in the middle reaches of the Yellow River Basin in Northwest China. Field surveys were conducted across 33 rivers in three distinct geomorphic regions during autumn (2022) and spring (2023), respectively. We identified a total of 367 phytoplankton taxa representing 127 genera and 7 phyla in samples collected from the Loess Plateau (LP, north), Guanzhong Plain (GZ, middle), and Qinling Mountains (QL, south). Bacillariophyta (40 %) and Chlorophyta (30 %) were dominant across regions during both seasons. Phytoplankton richness and density were higher in spring than in autumn and increased from QL to GZ and LP. Tβ (79.8 %) and Pβ (62.8 %) were mainly driven by turnover, with Fβ (72.6 %) dominated by nestedness. Fβ trended downward from south to north across the QL, GZ and LP regions. The major ecological processes influencing phytoplankton beta diversity displayed seasonal variation, represented by dispersal limitation in autumn and environmental filtering in spring. These findings present a holistic picture of riverine phytoplankton beta diversity within a large-scale semi-arid basin, and recommendations are proposed for the management and conservation of aquatic ecosystems.

Discriminating spatiotemporal heterogeneity and environmental drivers of fish assemblages using environmental DNA metabarcoding in mosaic habitat ecosystems

Surveys of fish diversity in complex heterogeneous environments are highly challenging to perform using traditional survey methods. Although environmental DNA (eDNA) metabarcoding has been effectively used to evaluate fish diversity, studies exploring the spatial and temporal variability of fish communities in mosaic habitats and their connection to water quality after ecological project implementation are still scarce. Here, we evaluated the changes in water quality and fish assembles using the traditional method and environmental DNA (eDNA) metabarcoding after Ecological water replenishment (EWR) and the links between fish communities and water quality were established in the Baiyangdian (BYD) ecosystem in the North China Plain. All water quality variables including TN, NH3-N, CODMn and TP showed a conspicuous improvement pattern, and the number of fish species increased notably after EWR. In addition, 6 more introduced fish species were recorded when compared with the historical data before the implementation of the EWR project. Furthermore, the species richness showed a highly significant difference among the four habitats in the summer 2020 and spring 2021 (spring: P = 0.000; summer: P = 0.002), and obvious discrimination of fish communities across two seasons was observed (P = 0.001) with eDNA metabarcoding. The water quality variables driving the changes of fish communities during the same period varied significantly across different habitats, while not all showed noticeable discrepancy in driving cross-seasonal fish community changes. Thus, our study highlights that the continuous EWR improves the water quality and fish richness but potential ecological issues associated with introduced species should be carefully considered after EWR. Our results also confirm that eDNA is a reliable tool for assessing fish diversity and distinguishing spatiotemporal variability of fish communities in mosaic habitat ecosystems.

Exposure to malathion impairs learning and memory of zebrafish by disrupting cholinergic signal transmission, undermining synaptic plasticity, and aggravating neuronal apoptosis

The prevalence of organophosphorus pesticides, such as malathion, in water environments poses a severe threat to aquatic organisms. Although the brain is a potential target for malathion, little is known about its effect on cognitive functions in fish. In this study, we evaluated the effect of 4-week malathion exposure on the learning and memory of zebrafish using T-maze tasks. In addition to verifying the accumulation of malathion in the brain and its deleterious effects on blood-brain barrier integrity, the impacts of malathion on cholinergic signal transmission, synaptic plasticity, apoptosis, and oxidative stress were determined. Our results demonstrated that a 4-week malathion exposure resulted in typical learning and memory-deficit-like behaviors. Apart from inhibiting cholinergic signal transmission, synaptic plasticity was severely undermined by malathion (as evidenced by the disruption of BDNF/PI3K/AKT/CREB pathway, suppression of synaptophysins, and activation of microglia). Moreover, significantly higher levels of TUNEL fluorescence signals as well as apoptotic enzymes and genes probably induced by oxidative stress were detected in the brains of malathion-exposed zebrafish. Collectively, our results suggested that malathion at environmentally realistic levels can significantly undermine learning and memory of zebrafish by disrupting cholinergic signal transmission, impairing synaptic plasticity, and aggravating neuronal apoptosis via inducing oxidative stress.

Urgent Conservation Actions Are Needed for Qinling Lenok Brachymystax lenok tsinlingensis Li, 1966: Enlightenment From Model Simulations

The Qinling lenok Brachymystax lenok tsinlingensis Li, 1966, an endemic to China and South Korea, is a rare protected species. Its unique requirements to habitat have made this fish extraordinarily fragile when faced with human pressures and global warming. Hence, predicting and understanding the potential influence of human pressures and global warming on this fish's spatial distribution is quite critical for the conservation and management of the species. To do so, based on its occurrence records and current as well as future environmental dataset, this study constructed a Maximum Entropy (MaxEnt) model for the species to analyze how its potential suitable areas (PSAs) would respond to global warming and human pressures (3 Global Climate Models ×2 Shared Socioeconomic Pathways ×3 future time nodes). The results showed that: (1) the MaxEnt model had strong generalization or transferability ability (AUC > 0.90), was highly reliable to predicting the current and future PSAs of the species; (2) Mean Temperature of Driest Quarter (BIO9), Human Population Density (Pop), Elevation (Elev), and Mean Temperature of Wettest Quarter (BIO8) were the salient environmental factors (given in descending order by significance); (3) the present PSAs for this fish were mainly distributed in Europe, Asia, and North America, and with the intensification of global changes, these areas in all continents would shrink on a large scale, and their distribution centroids would move towards northwest. Based on the above, a series of proposals for conservation and management of the fish were put forward so as to alleviate the loss of this relict species' habitats in the future.

Human land use and non-native fish species erode ecosystem services by changing community size structure

Organism body size influences ecosystem services, and human pressures alter the size structure of ecological communities. However, our understanding of how different human-induced pressures (such as land use and biotic invasion) interact to drive community size structure and ecosystem services remains limited. Combining 21 years of fish size spectrum data and fishery potential (fishery monetary value in the Upper Paraná River Floodplain, Brazil), we demonstrate that the size spectrum exponent of native species has become more negative over time, indicating a relative decrease in the biomass of large versus small individuals. Conversely, the size spectrum exponent of non-native species has become less negative over time owing to the increased abundance of large species. Overall, fishery potential declined by more than 50% over time. Human land use replaced the coverage of natural environments, indirectly reducing native richness. This scenario decreased the exponent of the native size spectrum, indirectly reducing fishery potential. Our study illustrates how intensification of human land use alters the size structure of communities, favouring non-native individuals and suppressing ecosystem services.

Global Patterns and Drivers of Freshwater Fish Extinctions: Can We Learn From Our Losses?

Nearly one-third of extant freshwater fish species, which account for over 50% of global fish diversity, are at risk of extinction. Despite their crucial ecological and socioeconomic importance, the extinction of freshwater fishes remains under-researched on a global scale. This is a comprehensive assessment of taxonomic, spatial, and temporal patterns of freshwater fish extinctions while identifying key extinction drivers and driver synergies. Using data from the International Union for Conservation of Nature Red List, 89 extinct freshwater fish and 11 extinct in the wild were analyzed. Taxonomic statistical analysis revealed the disproportionate impact on Cyprinidae, Leuciscidae, and Salmonidae. Estimated globally for the period 1851-2016, the modern extinction rate for freshwater fishes stands at 33.47 extinctions per million species-years (E/MSY), more than 100 times greater than the natural background extinction rate of 0.33 E/MSY. Extinction rates, when calculated per continent using the number of extinct species and the total number of species per continent, indicated that North America has the highest extinction rate (225.60 E/MSY), followed by Europe (220.26 E/MSY) and Asia (34.62 E/MSY). Although Africa is less affected, it still shows a 42-fold increase over the background rate. Bayesian modeling, reflecting cumulative species extinctions, indicated a strong association of North America and Asia with species loss (37 and 34 extinctions, respectively), a moderate one for Europe (20 extinctions) and a weak association of Africa (eight extinctions). Natural system modification, pollution, and invasive species emerged as the primary extinction drivers, often acting synergistically. Temporal trends indicate an acceleration in extinctions since the mid-20th century. This study highlights that, despite recent increases in conservation efforts, freshwater fish extinctions continue to rise, indicating the urgent need for integrated conservation strategies. Without immediate action, many species currently at risk may soon follow the same trajectory of extinction as the 100 extinct freshwater fishes of this study.

Invasive Fish Reshape Biodiversity Patterns in China's Freshwater Lakes

Globalization has dramatically accelerated the spread of non-native species, intensifying threats to freshwater ecosystems. While China ranks among the most heavily invaded countries, the role of non-native species as key drivers of biodiversity changes is often overlooked in research on anthropogenic impacts. This oversight hampers the development of effective conservation and management strategies by limiting a full understanding of what shapes biodiversity patterns. To bridge this gap, an extensive dataset from 131 lakes across China was compiled and analyzed using a novel composite diversity index that integrates species richness with functional and phylogenetic uniqueness, allowing for a more precise identification of fish multidimensional diversity hotspots. Additionally, gradient forest models were employed to elucidate the impacts of non-native species, geography, climate, and physicochemical factors on these patterns. Our findings revealed significant taxonomic and functional homogenization in non-native hotspots within the overall fish community, coupled with phylogenetic diversification. Notably, non-native fish diversity emerged as the primary factor shaping overall and native fish multidimensional diversity patterns. While the establishment of non-native species may provide an immediate enhancement to overall diversity, it often leads to the extirpation/extinction of native species, ultimately resulting in biodiversity loss at local and potentially the regional scale. This study highlights the importance of examining multiple dimensions to characterize the intricate dynamics between native and non-native species, which is essential for understanding their true impact on biodiversity and for achieving global conservation goals.

The global human impact on biodiversity

Human activities drive a wide range of environmental pressures, including habitat change, pollution and climate change, resulting in unprecedented effects on biodiversity1,2. However, despite decades of research, generalizations on the dimensions and extent of human impacts on biodiversity remain ambiguous. Mixed views persist on the trajectory of biodiversity at the local scale3 and even more so on the biotic homogenization of biodiversity across space4,5. We compiled 2,133 publications covering 97,783 impacted and reference sites, creating an unparallelled dataset of 3,667 independent comparisons of biodiversity impacts across all main organismal groups, habitats and the five most predominant human pressures1,6. For all comparisons, we quantified three key measures of biodiversity to assess how these human pressures drive homogenization and shifts in composition of biological communities across space and changes in local diversity, respectively. We show that human pressures distinctly shift community composition and decrease local diversity across terrestrial, freshwater and marine ecosystems. Yet, contrary to long-standing expectations, there is no clear general homogenization of communities. Critically, the direction and magnitude of biodiversity changes vary across pressures, organisms and scales at which they are studied. Our exhaustive global analysis reveals the general impact and key mediating factors of human pressures on biodiversity and can benchmark conservation strategies.

Anthropogenic influences reshape lentic fish diversity: Patterns of homogenization and differentiation across a Mediterranean biodiversity hotspot

Freshwater ecosystems are increasingly impacted by human activities, resulting in species invasions and extinctions, disrupting biodiversity and ecosystem functions. This study investigates the patterns of taxonomic and functional homogenization and differentiation in fish assemblages within 103 lentic ecosystems across a Mediterranean biodiversity hotspot (Greece). We focus on how non-native species have altered the taxonomic and functional diversity at both national and ecoregional levels while exploring the drivers and pathways behind these changes. Our analysis combined historical and current species data, evaluating the effects of species introductions and local extinctions on biodiversity of distinct freshwater ecoregions. We calculated taxonomic and functional similarities using Jaccard and Gower dissimilarity indices and employed generalized linear models (GLMs) to assess the significance of changes over time. Results reveal significant taxonomic homogenization across lentic ecosystems, primarily driven by the introduction of widespread alien and translocated fish species. In contrast, functional homogenization was less pronounced, with some regions exhibiting differentiation, including increases in species richness due to the introduction of species with distinct ecological traits. Non-native species introduced through angling, ornamental trade, and unintentional pathways were the primary contributors to homogenization. The findings highlight prominent regional differences and vulnerabilities: mainland ecoregions experienced stronger homogenization, while insular ecoregions have experienced taxonomic differentiation. Additionally, the study reveals a decoupling of taxonomic and functional changes, emphasizing the need to consider both in biodiversity assessments and conservation management. This research contributes to the broader understanding of how species invasions reshape biodiversity patterns and ecosystem functions in freshwater systems. Our approach provides a useful framework for assessing biotic homogenization and differentiation, with implications for conservation and management strategies worldwide.

Response of Montane Fish Biodiversity to Landscape and Anthropogenic Activity Under Potential Water Quality Pathways

Mountain river ecosystems, globally recognized biodiversity hotspots shaped by pronounced landscape heterogeneity, are facing intensifying anthropogenic pressures. However, interactions between landscape and anthropogenic activity on montane fish biodiversity remain poorly quantified. Taking the Yuan River (Yunnan, China) as a model system, environmental DNA (eDNA) and partial least squares structural equation modeling (PLS-SEM) were coupled to disentangle responses of fish biodiversity facets (taxonomic, functional and genetic diversity) to elevation and human footprint gradients. First, eDNA-derived taxonomic composition (R = 0.97 against catch data) demonstrated Cypriniformes and Perciformes dominance. Second, downstream areas exhibited enhanced taxonomic (R = 0.32) and functional diversity (R = 0.49), contrasting with upstream genetic diversity maxima (R = -0.47). Third, elevation gradients and human footprint exerted stronger direct effects on taxonomic diversity than on functional or genetic metrics, independent of spatial autocorrelation. Crucially, PLS-SEM identified water quality (i.e., total phosphorus (TP), total nitrogen (TN), biochemical oxygen demand (BOD5), and total organic carbon (TOC)) as a pivotal mediator linking elevation and human footprint to biodiversity outcomes. Overall, the present study establishes a mechanistic framework for disentangling landscape and anthropogenic drivers of biodiversity change, offering a scalable reference for conservation prioritization in montane freshwater ecosystems.

Longitudinal reconfiguration of multifaceted fish α and β diversity triggered by non-native species invasion in tropic rivers of Hainan Island

Human-mediated fish invasions have reconfigured the native fish faunas throughout the freshwater ecosystems worldwide. Beyond the well-documented homogenization reported in temperate basins, our knowledge on how multifaceted biodiversity response to fish invasions in tropic rivers remains poorly understood. It is also hanged in doubt that how fish invasions modify the longitudinal patterns of fish faunas under the concept of river continuum. Here, we applied one-way permutational multivariate analysis of variance to test how fish invasion influenced the longitudinal patterns of multifaceted α and β diversity of fish assemblages in three largest rivers of Hainan Island, China. Meanwhile, we employed multiple regression analysis to examine the relationships between the invasion degree and multiple α diversity indices as well as functional traits of native fishes. We found non-significant longitudinal variations for all multifaceted α diversity for native fish assemblages. However, our results demonstrated significantly longitudinal variations for multifaceted overall β diversity and its turnover components to the upstream-downstream gradient. Considering the consequence of non-native species invasion, we recorded tough homogenization in all the multifaceted aspects, as all the overall β diversity and its turnover components were concurrently significantly decreased after invasions. In comparation with upper reaches, the middle-lower reaches exhibited more significant homogeneous patterns incurred by invasions. In terms of biotic acceptance/resistance hypothesis, we found native fish faunas with higher richness, evenness and trophic level tented to resistant invaders, whereas with even phylogenetic compositions and late maturation showed acceptance to invasions.

Identifying Critical Land Use Thresholds for Biodiversity Conservation in China's Lake Ecosystems

Aquatic biodiversity loss, particularly in rapidly developing nations, continues to raise concerns, prompting urgent debates on reconciling economic growth with environmental preservation through land use planning. While spatial variations in aquatic communities along land use gradients are well-documented, precise ecological thresholds for land use impacts on freshwater lakes remain elusive, hindering sustainable development efforts. This study investigated six representative freshwater lakes in China between 2019 and 2020, all significantly impacted by anthropogenic activities. We utilized macroinvertebrate communities as bioindicators and employed four categories of aquatic ecological metrics─taxonomic diversity, functional diversity, pollution tolerance, and water quality─to assess their responses to local land use patterns. Macroinvertebrate community composition varied significantly among the studied lakes, with pollution-tolerant taxa predominating in highly urbanized and eutrophic systems. Notably, benthic communities exhibited greater sensitivity to urban land use (ecological thresholds: 2-10%) compared to agricultural land use (thresholds: 15-40%). The most pronounced responses were observed within 1-5 km of the lakeshore, with circular buffers yielding more significant effects than fan-shaped buffers, excluding water areas. A novel land use intensity indicator─the ratio of nonecological to ecological land (NEL/EL = area of nonecological land/area of ecological land)─proved effective in predicting ecological shifts. Smaller or heavily urbanized lakes showed marked changes at NEL/EL ratios between 0 and 0.6, while larger or river-connected lakes exhibited shifts at ratios exceeding 1.5. These findings underscore the profound ecological footprint of human activities on lake ecosystems with urban land cover emerging as the most deleterious factor.

No attenuation of fish and mammal biodiversity declines in the Guiana Shield

Real-time biodiversity monitoring should provide more resolved data to quantify shifts in ecological communities progressively altered by anthropogenic disturbances. Identifying biodiversity trends requires a rapid and efficient inventory method that enables the collection and delivery of high-resolution data within short intervals. Using aquatic environmental DNA (eDNA), we investigated spatiotemporal changes in fish and mammal communities along the Maroni River in French Guiana. We compared spatial biodiversity trends between two years, separated by a four-year interval, during which an increase in anthropogenic disturbances was observed. To evaluate biodiversity changes, we examined the impact of these disturbances on both taxonomic and functional diversity. Our findings revealed that, while the increase in disturbances did not result in major biodiversity decline, it continued to drive alterations in community taxonomic and functional richness. Communities underwent changes in their functional structure, with mammal communities experiencing a decline in extreme functional traits, while fish communities lost functional redundancy in generalist functions and experienced a reduction in extreme functional strategies. In a context of small-scale anthropogenic disturbances, these changes highlight the necessity of long-term, short-interval monitoring to capture rapid reorganisation of ecological communities under stress.

Environmental DNA metabarcoding: Current applications and future prospects for freshwater fish monitoring

Fish, as the top predators in freshwater, greatly contribute to maintain ecosystem stability. There has been a sharp decline in freshwater fish stocks due to multiple factors, both natural and anthropogenic. Effective and accurate monitoring of freshwater fish is necessary to inform on ecosystem health and guide environmental management practices. Traditional survey methods are gradually unable to meet the growing monitoring needs. Environmental DNA (eDNA) metabarcoding provides a high sensitivity, fast and affordable approach for surveying and monitoring of aquatic biology. However, due to the limitations of incomplete databases and non-standardized procedures, the use of eDNA techniques for monitoring freshwater fish remains less mature compared to traditional fish monitoring methods. To systematically review the current applications and future prospects of the eDNA metabarcoding for freshwater fish monitoring, this article: (i) summarizes relevant researches on freshwater fish monitoring using eDNA technology (e.g., methodologies, resource surveys, habitat assessments, etc.) over the past decade. (ii) outlines the methodology of eDNA metabarcoding in freshwater fish monitoring, proposes a standardized process for eDNA methods, and suggests ways to eliminate detection errors. (iii) analyzes the current challenges of the eDNA metabarcoding application in resource surveys and ecological quality assessments of freshwater fish. The eDNA technology can be used as a better alternative or supplement to traditional survey methods for monitoring the diversity, biomass, population distribution, and spawning behaviors of freshwater fish, in particular, it has a prominent advantage in monitoring endangered and rare fish species. (iv) investigates the application of eDNA technology in investigating the impact of human activities and invasive species on freshwater fish, and emphasizes the eDNA's potential in assessing the impacts of water projects (e.g., dam construction or removal, water diversion project) on fish habitats, and the effectiveness of fish passage and invasive fish control efforts. (v) discusses the future prospects of eDNA-based freshwater fish monitoring, both in terms of technology and application. This review provides a guidance for the future development and application of eDNA technology in freshwater fish monitoring and ecological quality assessments.

Resistance and propulsion trade-offs induced by different morphologies: Insights for fish conservation

Understanding the adaptive relationships between fish morphology and water flow and leveraging this knowledge to shape water flow conditions beneficial for the conservation of rare fish are critical for their protection. This study integrates a high-precision fish model with a wave equation motion framework to accurately analyze and visualize the forces acting on various parts of fish bodies during swimming. The results quantitatively reveal the trade-offs in resistance and propulsion between two fish morphologies. For Carassius auratus, a propulsive force advantage is observed within a velocity range of 0-0.6 m/s, while Schizothorax prenanti demonstrates a staged propulsive advantage as velocity increases. Specifically, S. prenanti achieves maximum propulsion more rapidly at 0.4 m/s, maintains higher propulsion values at 0.6 m/s, and demonstrates adaptability to water velocities of 1 m/s, which prove insurmountable for C. auratus. Furthermore, a detailed analysis uncovers a strong correlation between fish morphology and biomechanical performance. The long-term adaptation of S. prenanti to flowing water environments is driven by its low-resistance morphology, enabling it to dominate despite generating less propulsion than C. auratus. Conversely, C. auratus, adapted to low-flow environments, prioritizes strong propulsion at the cost of heightened resistance in high-flow conditions. This study establishes a morphology-biomechanics-flow environment framework, enabling researchers to design flow conditions that align with the mechanical advantages of target fish species. Such an approach offers a novel perspective for fish habitat management and conservation.

Restoration of river connectivity enables long-distance spawning migrations in a potamodromous fish

Rivers across the world are increasingly fragmented due to anthropogenic barriers, with the restoration of connectivity often using fish passes. Fish passes are, however, usually designed for anadromous species, despite ecologically important non-anadromous species being present in the communities impacted by fragmentation. To assess the outcomes for non-anadromous fishes of the installation of multiple fish passes and weir modifications, the movements of the potamodromous European barbel Barbus barbus were evaluated in the lower River Severn basin, western Britain, which was fragmented by six weirs (two on a tributary, four on the Severn mainstem). Movements of individual fish were measured using long-life acoustic transmitters, with stable isotope analysis assisting the assessment of individual variability in movements. The movements of three tagging groups were measured: barbel tagged in 2015 (n = 19; no fish passes/modifications), 2018 (n = 19; tributary weirs modified), and 2020/21 (n = 20; all Severn mainstem weirs fitted with fish passes). No fish in the 2015 group passed the weirs on the Severn mainstem, despite approaches, and only one fish in the 2018 group passed the most downstream weir during high water conditions in winter. Following the opening of all fish passes in early 2021, individuals in the 2020/21 group moved above all the weirs via the fish passes between April and June (the spawning season). These fish then moved upstream for up to 110 km, and some were detected returning downstream. These spawning migrations potentially have high ecological and evolutionary significance, indicating that reconnection schemes designed for anadromous fishes also benefit potamodromous fishes.

Dynamic Impacts of Stock Enhancement on Kaluga Sturgeon (Huso dauricus): Novel Conservation Strategy Insights from the Gut Microbe Composition and Gene Expression Mode

The sturgeon population has experienced strict threats due to inordinate human activities in the last decade and has been classified into the Red List of Threatened Species in recent years. Stock enhancement is one effective practice for the conservation of wild sturgeons. However, the survival conditions for sturgeon were not satisfactory after they were directly restocked into their natural habitat. Huso dauricus is an important protected sturgeon species, and finding an appropriate conservation strategy for the wild population is urgent. To clarify the dynamic adaptability of Huso dauricus to its wild environment, 1000 individuals were released into a natural river. On the 0th, 7th, 14th, and 30th days, five recaptured individuals were used to evaluate the dynamic trends in biochemical biomarkers, intestinal histomorphology, gut microbe taxon composition, and transcription profile over 30 days of stock enhancement. Our results indicated that Huso dauricus individuals still had a physiological stress status on the seventh day and then gradually adapted to the wild habitat 14 days after reintroduction based on the serum cortisol level. Meanwhile, the feeding habitat, organ function indicators, and growth performance showed similar dynamic changes within 30 days. Interestingly, their gut bacterial diversity and taxon structure also fluctuated over the 30 days after restocking, and they were accompanied by dynamic changes in intestinal pathological injury and tight junction protein expression in this period. The transcriptome analysis revealed the dynamic adaptability of Huso dauricus to wild habitats associated with the expression modes of genes related to the FoxO family, immune system, cytochrome family, and ATP metabolism. Taken together, the findings of the present research demonstrated that artificial reintroduction had dynamic impacts on the health condition of Huso dauricus and that 14 days of wilderness training might be essential for sturgeon restocking practices. Our study revealed the adaption mechanism of Huso dauricus at the molecular level during the restocking period and shed light on the theoretical guidelines for wild sturgeon conservation.

Meta-analysis reveals global variations in plant diversity effects on productivity

Positive effects of plant diversity on productivity have been globally demonstrated and explained by two main effects: complementarity effects and selection effects1-4. However, plant diversity experiments have shown substantial variation in these effects, with driving factors poorly understood4-6. On the basis of a meta-analysis of 452 experiments across the globe, we show that productivity increases on average by 15.2% from monocultures to species mixtures with an average species richness of 2.6; net biodiversity effects are stronger in grassland and forest experiments and weaker in container, cropland and aquatic ecosystems. Of the net biodiversity effects, complementarity effects and selection effects contribute 65.6% and 34.4%, respectively. Complementarity effects increase with phylogenetic diversity, the mixing of nitrogen-fixing and non-nitrogen-fixing species and the functional diversity of leaf nitrogen contents, which indicate the key roles of niche partitioning, biotic feedback and abiotic facilitation in complementarity effects. More positive selection effects occur with higher species biomass inequality in their monocultures. Complementarity effects increase over time, whereas selection effects decrease over time, and they remain consistent across global variations in climates. Our results provide key insights into understanding global variations in plant diversity effects on productivity and underscore the importance of integrating both complementarity and selection effects into strategies for biodiversity conservation and ecological restoration.

Genomes reveal pervasive distant hybridization in nature among cyprinid fishes

BACKGROUND

Genomic data have unveiled a fascinating aspect of the evolutionary past, showing that the mingling of different species through hybridization has left its mark on the histories of numerous life forms. However, the relationship between hybridization events and the origins of cyprinid fishes remains unclear.

RESULTS

In this study, we generated de novo assembled genomes of 8 cyprinid fishes and conducted phylogenetic analyses on 24 species. Widespread allele sharing across species boundaries was observed within 7 subfamilies of cyprinid fishes. Based on a systematic analysis of multiple tissues, we found that the testis exhibited a conserved pattern of divergence between the herbivorous Megalobrama amblycephala and the carnivorous Culter alburnus, suggesting a potential link to incomplete reproductive isolation. Significant differences in the expression of 4 genes (dpp2, ctrl, psb7, and ppce) in the liver and intestine, accompanied by variations in enzyme activities, indicated swift divergence in digestive enzyme secretion. Moreover, we identified introgressed genes linked to organ development in sympatric fishes with analogous feeding habits within the Cultrinae and Leuciscinae subfamilies.

CONCLUSIONS

Our findings highlight the significant role played by incomplete reproductive isolation and frequent gene flow events, particularly those associated with the development of digestive organs, in driving speciation among cyprinid fishes in diverse freshwater ecosystems.

Spatial and temporal variability of physicochemical characteristics in Lancang River sediments amid hydropower development

The construction of river dams disrupts river continuity and sediment transport, altering the riverbed between sediment "sources" and "sinks" and changing the sediment characteristics of the river. In this study, 256 sediment samples from 54 major control cross-sections of the Lancang River (LCR) were analyzed to examine the spatial and temporal distribution of clay and non-clay minerals in the sediment and their relationship with the environmental changes caused by the construction 11 hydropower plants. The results indicate that the construction of terrace dams on the LCR interrupted the downstream refinement trend of sediments, which reappeared once the terrace reservoirs stabilized. Additionally, the interception of the dam increased the accumulation of clay mineral in sediments. From 2011 to 2023, the relative abundance of clay mineral in the regulated reaches (RRs) increased by 2.4 %, the quartz content decreased by 26.2 %, and the contents of calcite, mica, kaolinite, and chlorite increased, respectively. Consequently, the main non-clay mineral assemblage in the sediments shifted from quartz+feldspar to quartz+feldspar+mica. Furthermore, the clay mineral content was higher upstream the main dams (15.3 %) than downstream (14.8 %), with the sediment quartz and calcite contents being higher downstream, and mica and chlorite contents being higher upstream. The feldspar content showed a minimal change. However, the mineral composition of the sediments in individual reservoirs varied significantly, owing to the specific environmental conditions of each reservoir. The distribution of sediment clay also differed between the dry and rainy seasons. This study provides a scientific basis for managing reservoir sediment scheduling and regulating the ecological and environmental safety in watersheds.

Change in sediment transport regime of the Keelung River in Taiwan induced by the operation of Yuanshantze flood diversion tunnel

The impact of flood diversion channels on river sediment transport has been rarely reported. This study uses the Yuanshantze flood diversion tunnel (YFDT), which was commissioned in July 2005 in Taiwan, as an example. This study calculates the sediment transport in the Keelung River from 1997 to 2018 by using seasonal rating curves, in the form of aQb. Changes in rating curve coefficients are also analyzed to understand the impact of YFDT on sediment transport regime. The results show that after the construction of YFDT, the annual sediment transport dropped from 0.59 ± 0.47 [Mt y-1] to 0.17 ± 0.09 [Mt y-1], leading to dampened inter- and intra-annual variation. Before flood diversion, the Keelung River requires ~1% cumulative time to export 50% cumulated sediment loads, but it takes ~4.5% cumulative time after flood diversion. Exponent b decreased from 1.23±0.18 to 1.15±0.13, and log a decreased from 0.71±0.15 to 0.51±0.11, suggesting that the Keelung River is akin to a different river in terms of sediment transport regime. While the design of the diversion tunnel mainly considered its impact on flow, its impact on sediment transport is far greater than its impact on flow and should not be overlooked. Whether this new normality will affect the downstream river continuum requires continuous attention.

Freshwater fish in mid and northern German rivers - Long-term trends and associated species traits

To understand biodiversity change and support conservation decision-making, estimates of species' long-term population trends at regional and national scales are essential. However, such estimates are missing for many freshwater taxa, despite the diverse range of threats that they face. For this study, we mobilised monitoring data on riverine freshwater fish abundance collected across different regions of Germany. We applied generalized mixed effect models to estimate the population trends for 55 native species and 11 non-native species between 2004 and 2020. In addition, we used boosted regression trees to identify trait-based predictors of species trends and assessed their predictive ability. We found evidence of increasing abundance trends for 14 species and decreasing trends for 15 species; while the remaining species were mostly stable (26 species). Native species were more typically decreasing than increasing (14 vs 10 species); while non-native species were more often increasing (4 vs 1 species). Important traits associated with trends were maximum length, spawning temperature, and water quality tolerance, with small species, those spawning at high temperatures, and those preferring unpolluted waters, being most likely to have positive trends. Despite these associations, overall trait-based models showed limited power to predict trends in terms of direction as well as magnitude. Our results highlight the ongoing change in riverine fish communities and the importance of on-going species-level monitoring. The trait-based associations also indicate climate change and invasive species as important drivers of change in European freshwater rivers.

Hydrology and water quality drive multiple biological indicators in a dam-modified large river

Freshwater biodiversity is increasingly threatened by dams and many other anthropogenic stressors, yet our understanding of the complex responses of different biotas and their multiple facets remains limited. Here, we present a multi-faceted and integrated-indices approach to assess the differential responses of freshwater biodiversity to multiple stressors in the Yangtze River, the third longest and most dam-densely river in the world. By combining individual biodiversity indices of phytoplankton, zooplankton, periphyton, macroinvertebrates, and fish with a novel integrated aquatic biodiversity index (IABI), we disentangled the effects of hydrology, water quality, land use, and natural factors on both α and β diversity facets in taxonomic, functional, and phylogenetic dimensions. Our results revealed that phytoplankton and fish species and functional richness increased longitudinally, while fish taxonomic and phylogenetic β diversity increased but phytoplankton and macroinvertebrate β diversity remained unchanged. Hydrology and water quality emerged as the key drivers of all individual biodiversity indices, followed by land use and natural factors, with fish and phytoplankton showed the strongest responses. Importantly, we found that natural, land use, and hydrological factors indirectly affected biodiversity by altering water quality, which in turn directly influenced taxonomic and phylogenetic IABIs. Our findings highlight the complex interplay of multiple stressors in shaping freshwater biodiversity and underscore the importance of considering both individual and integrated indices for effective conservation and management. We propose that our multi-faceted and integrated-indices approach can be applied to other large, dam-modified river basins globally.

Investigation on the Distribution of Bangana Tungting in Yuanshui Unique Fish Species National Aquatic Germplasm Resources Reserve Using Environmental DNA Technology

Freshwater ecosystems face unprecedented challenges as the cumulative impact of human activities intensifies. While protected areas and species-specific conservation policies are widely implemented, their effectiveness remains difficult to gauge using traditional catch-based surveys. This research employed environmental DNA (eDNA) technology to assess the distribution of the endangered fish, Bangana tungting, within the Yuanshui Unique Fish Species National Aquatic Germplasm Resources Reserve (YUFRR) in Hunan, China. Over a 2-year period, we conducted comprehensive eDNA survey multiple sites within the YUFRR, confirming the species' continued existence in the area. In September 2022, B. tungting eDNA was detected at 8 of 60 sampling locations, while a follow-up survey in May 2023 identified its presence at 4 of 44 sites. Further analysis revealed critical environmental factors influencing B. tungting distribution, primarily dissolved oxygen concentration and the presence of physical barriers such as hydroelectric stations. Our data suggest a minimum dissolved oxygen tolerance threshold of 4 mg/L for this species. Moreover, we observed an inverse relationship between B. tungting detection rates and both the number of hydroelectric stations and their distance to sampling sites. This case study demonstrates the effectiveness of eDNA technology in mapping the distribution of endangered fish species like B. tungting and guiding conservation strategies. Our findings emphasize the crucial need to enhance environmental conditions, particularly water quality and habitat suitability, to ensure the effective conservation of B. tungting within the YUFRR.

eDNA metabarcoding reveals differences in fish diversity and community structure in Danjiang River

Fish diversity, an important indicator of aquatic ecosystem health, is declining due to water pollution, overfishing, climate change, and invasive species. Effective surveying and monitoring are required to protect fish diversity. Here, a high-sensitivity environmental DNA (eDNA) metabarcoding technique was used to investigate fish diversity in the Danjiang River, Shaanxi Province, China. In total, 59 species were identified in eight orders, 19 families, and 40 genera. Cypriniformes and Perciformes were the main groups in the survey area, while Cyprinidae accounted for 50.85% of the total fish species. Rhinogobius similis (19%), Hemibarbus umbrifer (11%), Gnathopogon herzensteini (10%), Triplophysa stewarti (8%), and Zacco platypus (7%) were the dominant species. Eight rare and two exotic fish species were identified. Combined with analysis of historical data, the richness of fish identified using eDNA metabarcoding was significantly higher than that of fish captured in ground cages. Temperature, pH, and oxidation-reduction potential are the main environmental factors that affect the spatial distribution of fish communities. These results suggest that eDNA metabarcoding could be a new tool with broad application prospects; however, local databases must be improved. This study provides theoretical data and a methodological reference for protecting and managing fish diversity in the Qinling Mountains.

Interbasin trade worsens the state of freshwater fish biodiversity in China

Human economic activities severely threaten freshwater fish biodiversity in different river basins. Trade makes the impact more mysterious and complex and confounds local efforts to protect freshwater biodiversity. To investigate the relationship between trade and freshwater fishes, we developed a river-basin economic transaction model that is applied to mainland China, home to 9% of the world's freshwater fish species. Here, we show that interbasin trade induced by final demand contributes 74% of the threats to China's freshwater fish biodiversity. Economically developed river basins (e.g., the Huaihe River) are the main beneficiaries of interbasin trade at the cost of biodiversity deterioration in economically underdeveloped river basins (e.g., the upper Pearl River), especially when trade occurs between distant basins. Our findings highlight the significance of the shift in governance from administrative divisions to river basins and control measures in different stages of economic supply chains to mitigate freshwater fish biodiversity threats.

The impact of anthropogenic pressures on microbial diversity and river multifunctionality relationships on a global scale

Conserving biodiversity is crucial for maintaining essential ecosystem functions, as indicated by the positive relationships between biodiversity and ecosystem functioning. However, the impacts of declining biodiversity on ecosystem functions in response to mounting human pressures remain uncertain. This uncertainty arises from the complexity of trade-offs among human activities, climate change, river properties, and biodiversity, which have not been comprehensively addressed collectively. Here, we provide evidence that river biodiversity was significantly and positively associated with multifunctionality and contributed to key ecosystem functions such as microbially driven water purification, leaf litter decomposition and pathogen control. However, human pressure led to abrupt changes in microbial diversity and river multifunctionality relationships at a human pressure value of 0.5. In approximately 30 % (N = 58) of countries globally, the ratio of area above this threshold exceeded the global average (∼11 %), especially in Europe. Results show that human pressure affected ecosystem functions through direct effects and interactive effects. We provide more direct evidence that the nonadditive effects triggered by prevailing human pressure impact the multifunctionality of rivers globally. Under high levels of human stress, the beneficial effects of biodiversity on nutrient cycling, carbon storage, gross primary productivity, leaf litter decomposition, and pathogen control tend to diminish. Our findings highlight that considering interactions between human pressure and local abiotic and biotic factors is key for understanding the fate of river ecosystems under climate change and increasing human pressure.

Comparison Between Environmental DNA Metabarcoding and Traditional Survey Method to Identify Community Composition and Assembly of Stream Fish

Environmental DNA (eDNA) metabarcoding has been widely used in freshwater systems, contributing to the advancements in the monitoring of fish diversity and community species composition. Nevertheless, the accuracy and reliability of eDNA metabarcoding in assessing functional structures and revealing the mechanisms underlying fish community assembly remain unclear. In this study, we combined a traditional survey method (electrofishing) and eDNA metabarcoding to conduct fish stock monitoring in the upper reaches of the Huishui stream. We assessed taxonomic and functional structures, as well as community assembly mechanisms, during dry and wet seasons. The results revealed that, compared with electrofishing surveys, eDNA metabarcoding detected a greater number of species and higher functional richness in both seasons. Despite significant differences in fish taxonomic composition between the seasons, both eDNA and traditional methods indicated that environmental filtering dominated the process of fish community assembly in both dry and wet seasons. We showed that eDNA metabarcoding is comparable to the electrofishing method in monitoring the community composition of stream fish and can accurately and reliably determine fish community assembly mechanisms. Combining functional traits and eDNA is a robust approach for monitoring stream fish community compared to taxonomic uncertainty.

Genomic and Epigenomic Influences on Resilience across Scales: Lessons from the Responses of Fish to Environmental Stressors

Understanding the factors that influence the resilience of biological systems to environmental change is a pressing concern in the face of increasing human impacts on ecosystems and the organisms that inhabit them. However, most considerations of biological resilience have focused at the community and ecosystem levels, whereas here we discuss how including consideration of processes occurring at lower levels of biological organization may provide insights into factors that influence resilience at higher levels. Specifically, we explore how processes at the genomic and epigenomic levels may cascade up to influence resilience at higher levels. We ask how the concepts of "resistance," or the capacity of a system to minimize change in response to a disturbance, and "recovery," or the ability of a system to return to its original state following a disturbance and avoid tipping points and resulting regime shifts, map to these lower levels of biological organization. Overall, we suggest that substantial changes at these lower levels may be required to support resilience at higher levels, using selected examples of genomic and epigenomic responses of fish to climate-change-related stressors such as high temperature and hypoxia at the levels of the genome, epigenome, and organism.

Application of Synchronous Evaluation-Diagnosis Model with Quantitative Stressor-Response Analysis (SED-QSR) to Urban Lake Ecological Status: A Proposed Multiple-Level System

Ecological integrity assessment and degradation diagnosis are used globally to evaluate the health of water bodies and pinpoint critical stressors. However, current studies mainly focus on separate evaluation or diagnosis, leading to an inadequate exploration of the relationship between stressors and responses. Here, based on multiple data sets in an urban lake system, a synchronous evaluation-diagnosis model with quantitative stressor-response analysis was advanced, aiming to improve the accuracy of evaluation and diagnosis. The weights for key physicochemical stressors were quantitatively determined in the sequence of NDAVIadj > CODMn > TP > NH4+-N by the combination of generalized additive model and structural equation modeling, clarifying the most significant effects of aquatic vegetation on the degradation of fish assemblages. Then, sensitive biological metrics were screened by considering the distinct contributions of four key stressors to alleviate the possible deviation caused by common methods. Finally, ecological integrity was evaluated by summing the key physicochemical stressors and sensitive biological metrics according to the model-deduced weights instead of empirical weights. Our system's diagnosis and evaluation results achieved an accuracy of over 80% when predicting anthropogenic stress and biological status, which highlights the great potential of our multiple-level system for ecosystem management.

Human activities strengthen the influence of deterministic processes in the mechanisms of fish community assembly in tropical rivers of Yunnan, China

Human-induced global alterations have worsened the severe decrease in fish biodiversity in rivers. To successfully reduce the pace of reduction in fish diversity, it is crucial to prioritize the understanding of how human activities impact the processes that shape and maintain fish diversity. Traditional fish survey methods are based on catch collection and morphological identification, which is often time-consuming and ineffective. Hence, these methods are inadequate for conducting thorough and detailed large-scale surveys of fish ecology. The rapid progress in molecular biology techniques has transformed environmental DNA (eDNA) technique into a highly promising method for studying fish ecology. In this work, we conducted the first systematic study of fish diversity and its formation and maintenance mechanism in the Xishuangbanna section of the Lancang River using eDNA metabarcoding. The eDNA metabarcoding detected a total of 159 species of freshwater fishes spanning 13 orders, 34 families, and 99 genera. The fishes in the order cypriniformes were shown to be overwhelmingly dominant. At different intensities of anthropogenic activity, we found differences in fish community composition and assembly. The analysis of the Sloan's neutral community model fitting revealed that stochastic processes were the dominant factor in the shaping of fish communities in the Xishuangbanna section of the Lancang River. We have further confirmed this result by using the phylogenetic normalized stochasticity ratio. Furthermore, our findings indicate that as human activities get more intense, the influence of stochastic processes on the shaping of fish communities decreases, while the influence of deterministic processes eventually becomes more prominent. Finally, we discovered that salinity positively correlated with fish community changes in the high-intensity anthropogenic sample sites, but all environmental factors had little effect on fish community changes in the low-intensity and moderate-intensity anthropogenic sample sites. Our study not only validated the potential application of eDNA metabarcoding for monitoring fish diversity in tropical rivers, but also revealed how fish communities respond to human activities. This knowledge will serve as a solid foundation for the protection of fish resources in tropical rivers.

Pathways linking watershed development and riparian quality to stream water quality and fish communities: Insights from 233 subbasins of the Great Lakes region

Anthropogenic stressors such as urban development, agricultural runoff, and riparian zone degradation impair stream water quality and biodiversity. However, the intricate pathways that connect these stressors at watershed and riparian scales to stream ecosystems-and their interplay with climate and hydrology-remain understudied. In this study, we used Partial Least Squares (PLS) path modeling to examine these pathways and their collective impacts on stream water quality and fish community structures across 233 watersheds in the Great Lakes region. Our study suggests that moderate levels of watershed development enhance overall fish richness, potentially due to increased water temperature and nutrient availability, but reduces both the percentages and richness of cold water and intolerant taxa. Riparian quality exerts indirect effects on water quality with climate and stream order serving as key mediators. Complementing our SEM analysis, we also used Multiple Linear Regression (MLR) models and identified a significant positive relationship between the proportion of clay and agricultural land with TN concentrations. However, TP concentrations are influenced by a more complex set of interactions involving developed areas, soil, and slope. These findings emphasize the necessity of adopting integrated management strategies to preserve the health and integrity of freshwater ecosystems in the Great Lakes region. These strategies should integrate watershed and riparian protection measures while also taking into account the effects of climate change and specific local conditions.

Using DNA barcoding to identify high-priority taxa (Hymenoptera: Ichneumonidae) from Great Smoky Mountains National Park

The All Taxa Biodiversity Inventory (ATBI) in Great Smoky Mountains National Park (GSMNP) seeks to document every species of living thing in the park. The ATBI is decades in progress, yet some taxa remain virtually untouched by taxonomists. Such "high priority" taxa include the hyper-diverse parasitoid wasp family Ichneumonidae. Despite the positive and multifaceted effects ichneumonids have on their environment, only a small percentage of those collected in the park have been identified as species, mostly to their complex morphology and overwhelming diversity. Recently, DNA barcoding has transformed biodiversity inventories, streamlining the process to be more rapid and efficient. To test the effectiveness of barcoding 20 + year-old specimens of Ichneumonidae and catalog new records for GSMNP, COI was amplified from 95 ichneumonid morphospecies collected from Andrew's Bald, NC. Species identifications were confirmed morphologically. Eighty-one ichneumonids generated sequence data, representing 16 subfamilies and 44 genera. The subfamily Oxytorinae is newly recorded from GSMNP, along with 10 newly recorded genera and 23 newly recorded species across Ichneumonidae. These results contribute significantly to the ATBI by adding new park records for a high-priority taxon and demonstrate the effectiveness of applying DNA barcoding to samples in long-term storage or those lacking immediate taxonomic expertise.

Climate change vulnerability of Arctic char across Scandinavia

Climate change is anticipated to cause species to shift their ranges upward and poleward, yet space for tracking suitable habitat conditions may be limited for range-restricted species at the highest elevations and latitudes of the globe. Consequently, range-restricted species inhabiting Arctic freshwater ecosystems, where global warming is most pronounced, face the challenge of coping with changing abiotic and biotic conditions or risk extinction. Here, we use an extensive fish community and environmental dataset for 1762 lakes sampled across Scandinavia (mid-1990s) to evaluate the climate vulnerability of Arctic char (Salvelinus alpinus), the world's most cold-adapted and northernly distributed freshwater fish. Machine learning models show that abiotic and biotic factors strongly predict the occurrence of Arctic char across the region with an overall accuracy of 89 percent. Arctic char is less likely to occur in lakes with warm summer temperatures, high dissolved organic carbon levels (i.e., browning), and presence of northern pike (Esox lucius). Importantly, climate warming impacts are moderated by habitat (i.e., lake area) and amplified by the presence of competitors and/or predators (i.e., northern pike). Climate warming projections under the RCP8.5 emission scenario indicate that 81% of extant populations are at high risk of extirpation by 2080. Highly vulnerable populations occur across their range, particularly near the southern range limit and at lower elevations, with potential refugia found in some mountainous and coastal regions. Our findings highlight that range shifts may give way to range contractions for this cold-water specialist, indicating the need for pro-active conservation and mitigation efforts to avoid the loss of Arctic freshwater biodiversity.

Local environment and fragmentation by drought and damming shape different components of native and non-native fish beta diversity across pool refuges

Pool refuges are critical for maintaining stream fish diversity in increasingly intermittent streams. Yet, the patterns and drivers of beta diversity of native and non-native fish in pool refuges remain poorly known. Focusing on Mediterranean streams, we decomposed beta diversity of native and non-native fish into richness difference (RichDiff) and species replacement (Repl), and local (LCBD, LCBDRichDiff and LCBDRepl) and species (SCBD) contributions. We assessed the influence of environmental and spatial factors associated with drought and damming fragmentations on beta diversity components and LCBDs, and of local species richness and occupancy on LCBDs and SCBD, respectively. Overall, non-native species showed a more limited occupancy of pool refuges than native fish. RichDiff dominated beta diversity, though it was influenced by drought and damming fragmentations for native fish and local environment for non-native fish. Repl for native fish was slightly influenced by local environment, but for non-native fish was largely driven by drought and damming, albeit with a contribution of local environment as well. LCBD and LCBDRichDiff increased in pools in low order streams for native fish and at low elevations for non-native fish, and with high or low species richness. SCBD was higher for native species with intermediated pool occupancy, but for non-native species with low occupancy. Our results suggest that stream fragmentation may drive native species loss and non-native species replacement in pool refuges, and that environmental filtering may shape non-native species loss. Pools in lower order streams harbouring unique species-rich or species-poor assemblages should be prioritize for conservation and restoration, respectively, and pools at low elevation with unique non-native assemblages should deserve control efforts. We encourage the partitioning of beta diversity and individual analysis of native and non-native fish in intermittent streams, which may be key in stressing the importance of pool refuges in safeguarding native fish diversity.

A systematic toxicologic study of polycyclic aromatic hydrocarbons on aquatic organisms via food-web bioaccumulation

Pollution-induced declines in fishery resources restrict the sustainable development of fishery. As a kind of typical environmental pollutant, the mechanism of polycyclic aromatic hydrocarbons (PAHs) facilitating fishery resources declines needs to be fully illustrated. To determine how PAHs have led to declines in fishery resources, a systematic toxicologic analysis of the effects of PAHs on aquatic organisms via food-web bioaccumulation was performed in the Pearl River and its estuary. Overall, PAH bioaccumulation in aquatic organisms was correlated with the trophic levels along food-web, exhibiting as significant positive correlations were observed between PAHs concentration and the trophic levels of fishes in the Pearl River Estuary. Additionally, waterborne PAHs exerted significant direct effects on dietary organisms (P < 0.05), and diet-borne PAHs subsequently exhibited significant direct effects on fish (P < 0.05). However, an apparent block effect was found in dietary organisms (e.g., zooplankton) where 33.49 % of the total system throughput (TST) was retained at trophic level II, exhibiting as the highest PAHs concentration, bioaccumulation factor (BAF), and biomagnification factor (BMF) of ∑15PAHs in zooplankton were at least eight-fold greater than those in fishes in both the Pearl River and its estuary, thereby waterborne PAHs exerted either direct or indirect effects on fishes that ultimately led to food-web simplification. Regardless of the block effect of dietary organisms, a general toxic effect of PAHs on aquatic organisms was observed, e.g., Phe and BaP exerted lethal effects on phytoplankton Chlorella pyrenoidosa and zooplankton Daphnia magna, and decreased reproduction in fishes Danio rerio and Megalobrama hoffmanni via activating the NOD-like receptors (NLRs) signaling pathway. Consequently, an assembled aggregate exposure pathway for PAHs revealed that increases in waterborne PAHs led to bioaccumulation of PAHs in aquatic organisms along food-web, and this in turn decreased the reproductive ability of fishes, thus causing decline in fishery resources.

How the Water-Sediment Regulation Scheme in the Yellow River affected the estuary ecosystem in the last 10 years?

The Yellow River, renowned as the most sediment-laden river globally, grapples with sediment deposition issues compromising reservoir functionality and elevating downstream riverbeds, posing threats to human life and property safety. In response, the Water-Sediment Regulation Scheme (WSRS) has been innovatively implemented to address these challenges. While effectively mitigating sediment deposition, WSRS has concurrently disrupted the equilibrium of the estuarine ecosystem. This paper addresses the understudied but crucial topic of the interannual impact of WSRS on the estuarine ecosystem. Drawing upon physical, chemical, and biological data gathered through field surveys conducted before, during, and after WSRS from 2011 to 2022, the analysis delves into the interannual changes in the estuarine environment, fish eggs and larvae abundance, and species diversity under the influence of WSRS. The findings reveal an interannual decreasing trend in terrestrial material input due to WSRS, juxtaposed with an interannual increasing trend in fish eggs and larvae around the estuary, as well as the species diversity index. Notably, these trends became more pronounced post-2014. Compared to pre-2014, nutrient concentrations experienced a ~20 % decrease, chlorophyll-a concentration increased by 44 %, fish eggs proliferated approximately 1 time, and the species diversity index transitioned from a declining trend to an ascending trajectory. After 12 years of continuous WSRS implementation, the impact on the estuarine ecosystem has demonstrably diminished. This research aims to furnish reference experience and scientific basis for water and sediment regulation in major rivers around the world in terms of estuarine ecology.

Water quality drives the reconfiguration of riverine planktonic microbial food webs

The food web is a cycle of matter and energy within river ecosystems. River environmental changes resulting from human activities are increasingly threatening the composition and diversity of global aquatic organisms and the multi-trophic networks. How multiple environmental factors influence food web patterns among multi-trophic microbial communities in rivers remains largely unknown. Using water quality evaluation and meta-omics techniques, we investigated the composition, structure and interaction characteristics, and drivers of food webs of microorganisms (archaea, bacteria, fungi, protists, metazoa, viridiplantae and viruses) at multiple trophic levels in different water quality environments (Classes II, III, and IV). First, water quality deterioration led to significant changes in the composition of the microbial community at multiple trophic levels, which were represented by the enrichment of Euryarchaeota in the archaeal community, the increase of r-strategists in the bacterial community, and the increase of the proportion of predators in the protist community. Second, deteriorating water quality resulted in a significant reduction in the dissimilarity of community structure (homogenization of community structure in Class III and IV waters). Of the symbiotic, parasitic, and predatory networks, the community networks in Class II water all showed the most stable symbiotic, parasitic, and predatory correlations (higher levels of modularity in the networks). In Class III and IV waters, nutrient inputs have led to increased reciprocal symbiosis and decreased competition between communities, which may have the risk of a positive feedback loop driving a system collapse. Finally, inputs of phosphorus and organic matter could be the main drivers of changes in the planktonic microbial food web in the Fen River. Overall, the results indicated the potential ecological risks of exogenous nutrient inputs, which were important for aquatic ecosystem conservation.

Conservation units alone are insufficient to protect Brazilian Amazonian chelonians

The creation of protected areas (PAs) is not always based on science; consequently, some aquatic species may not receive the same level of protection as terrestrial ones. The objective of this study was to identify priority areas for the conservation of chelonians in the Brazilian Amazon basin and assess the contribution of PAs, distinguishing between Full Protection Areas, Sustainable Use Areas, and Indigenous Lands for group protection. The entire species modeling procedure was carried out using Species Distribution Models. Location records were obtained from platforms such as SpeciesLink, GBIF, the Hydroatlas database, and WorldClim for bioclimatic variables adjusted with algorithms like Maximum Entropy, Random Forest, Support Vector Machine, and Gaussian-Bayesian. Indigenous lands cover more than 50% of the distribution areas of chelonian species in the Brazilian Amazon. Protected areas with higher conservation importance (Full Protection Areas and Sustainable Use Areas) hold less than 15% of the combined species distribution. Researchers face significant challenges when making decisions with models, especially in conservation efforts involving diverse taxa that differ significantly from one another within a group of individuals.

Global conservation status of the jawed vertebrate Tree of Life

Human-driven extinction threatens entire lineages across the Tree of Life. Here we assess the conservation status of jawed vertebrate evolutionary history, using three policy-relevant approaches. First, we calculate an index of threat to overall evolutionary history, showing that we expect to lose 86-150 billion years (11-19%) of jawed vertebrate evolutionary history over the next 50-500 years. Second, we rank jawed vertebrate species by their EDGE scores to identify the highest priorities for species-focused conservation of evolutionary history, finding that chondrichthyans, ray-finned fish and testudines rank highest of all jawed vertebrates. Third, we assess the conservation status of jawed vertebrate families. We found that species within monotypic families are more likely to be threatened and more likely to be in decline than other species. We provide a baseline for the status of families at risk of extinction to catalyse conservation action. This work continues a trend of highlighting neglected groups-such as testudines, crocodylians, amphibians and chondrichthyans-as conservation priorities from a phylogenetic perspective.

Global freshwater fish invasion linked to the presence of closely related species

In the Anthropocene, non-native freshwater fish introductions and translocations have occurred extensively worldwide. However, their global distribution patterns and the factors influencing their establishment remain poorly understood. We analyze a comprehensive database of 14953 freshwater fish species across 3119 river basins and identify global hotspots for exotic and translocated non-native fishes. We show that both types of non-native fishes are more likely to occur when closely related to native fishes. This finding is consistent across measures of phylogenetic relatedness, biogeographical realms, and highly invaded countries, even after accounting for the influence of native diversity. This contradicts Darwin's naturalization hypothesis, suggesting that the presence of close relatives more often signifies suitable habitats than intensified competition, predicting the establishment of non-native fish species. Our study provides a comprehensive assessment of global non-native freshwater fish patterns and their phylogenetic correlates, laying the groundwork for understanding and predicting future fish invasions in freshwater ecosystems.

An experimental sound exposure study at sea: No spatial deterrence of free-ranging pelagic fisha)

Acoustic deterrent devices are used to guide aquatic animals from danger or toward migration paths. At sea, moderate sounds can potentially be used to deter fish to prevent injury or death due to acoustic overexposure. In sound exposure studies, acoustic features can be compared to improve deterrence efficacy. In this study, we played 200-1600 Hz pulse trains from a drifting vessel and investigated changes in pelagic fish abundance and behavior by utilizing echosounders and hydrophones mounted to a transect of bottom-moored frames. We monitored fish presence and tracked individual fish. This revealed no changes in fish abundance or behavior, including swimming speed and direction of individuals, in response to the sound exposure. We did find significant changes in swimming depth of individually tracked fish, but this could not be linked to the sound exposures. Overall, the results clearly show that pelagic fish did not flee from the current sound exposures, and we found no clear changes in behavior due to the sound exposure. We cannot rule out that different sounds at higher levels elicit a deterrence response; however, it may be that pelagic fish are just more likely to respond to sound with (short-lasting) changes in school formation.

Contrasting impacts of non-native and threatened species on morphological, life history, and phylogenetic diversity in bird assemblages

Human activities have altered the species composition of assemblages through introductions and extinctions, but it remains unclear how those changes can affect the different facets of biodiversity. Here we assessed the impact of changes in species composition on taxonomic, functional, and phylogenetic diversity across 281 bird assemblages worldwide. To provide a more nuanced understanding of functional diversity, we distinguished morphological from life-history traits. We showed that shifts in species composition could trigger a global decline in avian biodiversity due to the high number of potential extinctions. Moreover, these extinctions were not random but unique in terms of function and phylogeny at the regional level. Our findings demonstrated that non-native species cannot compensate for these losses, as they are both morphologically and phylogenetically close to the native fauna. In the context of the ongoing biodiversity crisis, such alterations in the functional and phylogenetic structure of bird assemblages could heighten ecosystem vulnerability.

Risk of introduction and establishment of alien vertebrate species in transboundary neighboring areas

Cross-border neighboring areas could be particularly vulnerable to biological invasions due to short geographic distances and frequent interactions, although the invasion risk remains unevaluated worldwide. Here, based on global datasets of distributions of established alien vertebrates as well as vectors of introduction and establishment, we show that more than one-third of the world's transboundary neighboring areas are facing high invasion risk of alien vertebrates, especially in Europe, North America, South Asia, and Southeast Asia. The most important predictors of high introduction and establishment risk are bilateral trade, habitat disturbance and the richness of established alien vertebrates. Interestingly, we found that border fences may have limited effects in reducing the risk, as only 7.9% of border fences spatially overlap with hotspots of biological invasion even in the Eurasia areas (13.7% overlap) where physical border barriers are mainly located. We therefore recommend the implementation of immediate and proactive prevention and control measures to cope with cross-border invasions in response to continued globalization.

Environmental DNA biomonitoring reveals the human impacts on native and non-native fish communities in subtropical river systems

Subtropical rivers are one of the hotspots of global biodiversity, facing increased risks of fish diversity changes and species extinction. However, until now, human impacts on native and non-native fish communities in subtropical rivers still lack sufficient effort. Here, we used the environmental DNA (eDNA) approach to investigate fish communities in the Dongjiang River of southeast China, a typical subtropical river, and explored the effects of regional land use and local water pollution on fish taxonomic and functional diversity. Our data showed that 90 species or genera of native fish and 15 species or genera of non-native fish were detected by the eDNA approach, and there was over 85% overlap between eDNA datasets and historical records. The taxonomic and functional diversity of all, native and non-native fish communities showed consistent spatial patterns, that is, the upstream of the tributary was significantly higher than that of the mainstream and downstream. Land use and water pollution such as COD and TP were the determinants in shaping the spatial structure of fish communities, and water pollution explained 31.56%, 29.88%, and 27.80% of the structural variation in all, native and non-native fish communities, respectively. The Shannon diversity and functional richness of native fish showed a significant downward trend driven by COD (pShannon = 0.0374; pfunctional = 0.0215) and land use (pShannon = 0.0159; pfunctional = 0.0441), but they did not have significant impacts on non-native fish communities. Overall, this study emphasizes the inconsistent response of native and non-native fish communities to human impacts in subtropical rivers, and managers need to develop strategies tailored to specific fish species to effectively protect water security and rivers.

Reconnoitre on ichthyofauna of Mahanadi River of India: shifting diversity down the river continuum and linking ecological traits with patterns in biodiversity

Anthropogenic alterations have paramount impacts on the alpha and beta diversity of aquatic resources, and fishes are predominantly susceptible to such impacts. Mahanadi River, one of the major peninsular rivers of India, has abundant fish resources, which play a significant role in supporting the fishers' livelihoods. The exploratory study in the river conducted for three consecutive years recorded 148 species under 53 families. Cyprinids dominated the fish diversity with 41 species, followed by Bagrids (9) and Sciaenids (7). One hundred-one species under 29 families were reported from the freshwater stretch. With a total of 111 species reported under 48 families, the estuarine and tidal freshwater stretch was more speciose, due to marine migrant species which advent the estuarine and tidal freshwaters stretch for breeding and feeding purposes. Tikarpara, a conserved site within a sanctuary, was the most species-diverse as well as a species-even site. The study also recorded the extension of the distributional range of 3 fish species and also 4 exotic species from the river. The seasonal variations in diversity indicated that the deviations were not prominent in freshwater sites, whereas in tidal brackish water sites, species richness was relatively higher in post-monsoon, and species evenness was higher during monsoon. Taxonomic distinctness test showed that the average taxonomic distinctness was high for tidal estuarine locations as they harbour taxonomically distant fishes. The hierarchical clustering of sites showed the inordinate effect of river gradient and fragmentation on the fish community structure. Analyzing the key drivers of the assemblage structure of the entire river, salinity was the major deterministic factor, and within the freshwater stretch, the major influences were depth, transparency, and specific conductivity. The study concluded that, despite all of its ecological stresses, Mahanadi still supports rich fish diversity, yet there is a notable shift in the fish community structure. There is a need for integrating molecular and morphological tools for the taxonomic revision of many genera and species for proper in situ and ex situ conservation measures and to formulate future biodiversity management plans addressing to reduce the impacts of the ecological threats.

Environmental DNA unveiling the fish community structure and diversity features in the Yangtze River basin

Fish, as top predators in aquatic ecosystems, play an important role in maintaining the structure and functioning of these ecosystems, making their diversity a topic of great interest. This study focused on the Yangtze River Basin to investigate the fish community structure and diversity using environmental DNA (eDNA) technology. The results showed that a total of 71616 fish operational taxonomic units (OTUs) and 90 fish belonging to 23 families were detected, with the Cyprinidae family being the dominant group, followed by the Cobitidae, Amblycipitidae, etc. Compared to historical traditional morphological fish surveys, the quantity of fish detected using eDNA was relatively low, but the overall distribution pattern of fish communities was generally consistent. The highest fish Shannon-Wiener diversity index in the Yangtze River Basin sites reaches 2.60 with an average value of 1.25. The fish diversity index was higher in the downstream compared to the middle and upstream regions, and there were significant differences among different sampling sites. Significant environmental factors influencing α-diversity included chlorophyll-a, chemical oxygen demand, dissolved oxygen, total nitrogen, and elevation. Non-metric multidimensional scaling (NMDS) analysis revealed significant differences in fish community composition between the upstream and middle/lower reaches of the Yangtze River, while the composition of fish communities in the middle and lower reaches was more similar. Redundancy analysis (RDA) indicated that total organic carbon (TOC) was positively correlated with fish community distribution in the upstream, while water temperature and NO3-N were negatively correlated with fish distribution in the upstream. NH3-N and CODMn were negatively correlated with fish distribution in the middle and downstream regions, indicating a relatively severe water pollution in these areas. Additionally, fish communities in the Yangtze River displayed a typical distance decay pattern.

Species range shifts of notorious invasive fish species in China under global changes: Insights and implications for management

Due to global changes, e.g., climate change and trade globalization, China is facing an increasingly severe threat from invasive freshwater fish species, which have the potential to cause negative impacts across various aspects and pose significant challenges for their eradication once established. Therefore, prioritizing the understanding of invasive species' potential ranges and their determinants is vital for developing more targeted management strategies. Moreover, it is equally essential to consider the transitory range dynamics of invasive species that reflect changes in habitat availability and accessibility. Here, we used species distribution models (the maximum entropy algorithm) to assess the potential distributions of six notorious invasive fish species (i.e., Coptodon zillii, Cyprinus carpio, Gambusia affinis, Hemiculter leucisculus, Oreochromis mossambicus, and Oreochromis niloticus) in current and future (i.e., the 2030s, 2050s, and 2070s) periods along with their determinants, under two Shared Socio-economic Pathways scenarios (SSP1-2.6 and SSP5-8.5; global climate model: MRI-ESM2-0). Our results showed that the habitat suitability for the six species substantially benefited from temperature conditions (i.e., annual mean temperature or maximum temperature of warmest month). Throughout the given time periods, dramatic range expansions would occur for C. zillii, G. affinis, O. mossambicus, and O. niloticus, ranging from 38.61% to 291.90%. In contrast, the range of C. carpio would change slightly and irregularly, while H. leucisculus would contract marginally, with losses ranging from 1.06% to 12.60%. By the 2070s, species richness of these species would be relatively high in South, Central, and East China and parts of Southwest China. Furthermore, transitory fluctuations in the species ranges for all six species were observed throughout the entire time period (the 2030s-2070s). Given the range shifts for each species during different time periods, as well as time costs and budgets, adaptation strategies should be developed and implemented in the areas where they are most needed in each time period.