Changes in taxonomic and functional diversity of fish communities after catastrophic habitat alteration caused by construction of Three Gorges Dam

Impacts of Belo Monte dam on fish co-occurrence and artisanal fishing

The operation of large hydroelectric dams, such as Belo Monte in the Brazilian Amazon, significantly disrupts local freshwater ecosystems, impacting the socio-economic fabric and food security of dependent communities. To investigate and simulate future dam-induced impacts on fish species crucial for subsistence and artisanal fishing, this study leveraged subsistence fishing data from four areas of the Xingu River: the reservoir, upstream, the de-watered reach, and downstream. Using network analysis and graph theory, we examined the temporal and spatial variations in fish species composition, focusing on species that co-occur in fishing catches and their ecological roles within the network. Results showed a 34 % reduction in total biomass, from 8442.51 kg (2012-2015) to 5537.42 kg (2016-2020). The analysis revealed marked changes in species diversity and catch composition, with substantial shifts in heavily altered regions. For instance, in the de-watered reach, traditional species such as curimatã (Prochilodontidae) were replaced by others like pacu (Serrasalmidae), reflecting ecological shifts and the replacement of a detritivorous species by an omnivorous one. Directed simulations projected the dynamics of species loss, revealing significant alterations in co-occurrence patterns and network centrality, particularly in the de-watered reach. These simulations demonstrated that species such as pacu, pescada (Sciaenidae), and tucunaré (Cichlidae) remained central to the network despite ongoing ecological transformations. While this study provides valuable insights into environmental shifts, the absence of direct socio-economic data highlights the need for future research to understand the broader impacts on artisanal fisheries better. These results underscore the profound transformations in fish diversity and emphasize the critical need for adaptive management strategies to mitigate these impacts, ensuring the resilience of local fishing communities. While our findings offer valuable ecological insights, the absence of direct socio-economic data highlights the need for future research to better understand the broader impacts of hydroelectric dams on artisanal fisheries.

Environmental pressures on Mekong fish: Insights from temporal functional diversity dynamics

The Mekong River faces increasing environmental threats. To understand fish community responses to these threats, we explored the links between functional diversity (FD) dynamics and environmental changes across four sites using trait-based methods and fish monitoring data for 347 species. We assessed functional richness (FRic) and divergence (FDiv) using standardized effect sizes to investigate the main assembly rules structuring fish communities and used generalized additive models to identify key environmental drivers. After dam construction, all four sites experienced significant changes in environmental conditions. Deterministic processes, particularly environmental filtering, dominated in structuring fish communities. The upstream Lao People's Democratic Republic site (LPB) influenced by deterministic and stochastic processes. The Cambodia sites in Stung Treng province (CST) and Tonle Sap (TLS) Lake primarily driven by deterministic process with a decline in FRic and FDiv. Conversely, the Viet Nam site (VCM) seemed primarily influenced by stochastic process with more subtle environmental effects, evidenced by an increase in FRic and FDiv over time. The upper sites (LPB, CST, and TLS) displayed a distinct seasonal pattern in FD indices, with values decreasing during the dry season and increasing during the wet season. Conversely, the lower site (VCM) exhibited the opposite. Water level emerged as the key driver across all sites, with temperature and total nitrogen as secondary drivers. Dam impacts and other anthropogenic factors not included in our analyses (e.g., unsustainable fishing and habitat degradation) probably contributed to the observed changes in FD at specific sites. These findings highlight potential strategies for conservation, offering national and regional practitioners an opportunity to develop and refine river management plans.

The "Blue" Habitat of Urban & Suburban Areas and approaches for its biodiversity research: A scoping review

This article explores recent research initially driven by interest in studying the "Blue" Habitat of Urban and Suburban Areas (BHUS), focusing on water-related ecosystems. BHUS, encompassing a wide range of aquatic habitats, is crucial to ecosystem health but is increasingly threatened by biodiversity loss resulting from climate change, land-use expansion, and unsustainable practices. Through a scoping review of 93 peer-reviewed studies, this article establishes a framework to classify BHUS types, identify target species, and analyze diverse and latest techniques in water system research. The main themes for studying biodiversity and environmental aspects of these blue habitats are highlighted, along with the urgent need to address BHUS in urban biodiversity conservation. Findings reveal that water systems are biologically rich but present unique research challenges due to their variability and dynamic, interconnected nature. While there is growing recognition of the need to consider human influence, many studies overlook the complex, adaptive nature of BHUS as an integrated system. The article gives insight into establishing a comprehensive framework and integrating diverse methodologies and technologies for specialized research of the BHUS biodiversity, emphasizing the role of advancing technologies and interdisciplinary collaboration between urbanism and ecology. These approaches are essential to support sustainable development that addresses conservation needs and mitigates urbanization's impacts on BHUS. Further research should explore how spatial planning and strategies can more effectively integrate blue habitats to strengthen biodiversity conservation within the global urbanization context.

Numerical Simulation Study on Fish Habitats in the Downstream Section of Yangqu Hydropower Station

To promote the coordinated and sustainable development of hydropower exploitation and ecological environment in the upper reaches of the Yellow River, a fine simulation of the downstream riverway of Yangqu Hydropower Station was carried out to analyze the impact of the changes in water depth and flow velocity on fish habitats after the impoundment of Yangqu Hydropower Station. In this paper, Gymnocypris eckloni was selected as the target fish species. The fish habitat model was constructed using MIKE21. The habitat quality of the target fish species was graded by the fuzzy logic method with suitable flow velocity and water depth as conditions. The Weighted Usable Area (WUA)-flow response relationship of fish habitats under different qualities was studied, and the ecological flow required by the target fish species was obtained. The results indicated that the suitable ecological flow range, derived from the relationship between the weighted total area of habitats of different qualities and flow variations, ranged from 350 to 1100 m3/s. Furthermore, the suitable flow range determined through the proportion of WUA of habitats of different qualities was between 600 and 1150 m3/s. After a comprehensive analysis, the final suitable ecological flow range was determined to be 600 to 1150 m3/s. The proportion of high-quality habitat WUA ranged from 0.26 to 0.50, As the traffic increased, it first increased and then decreased, and was most affected by changes in traffic, the proportion of medium-quality habitat WUA fluctuated between 0.40 and 0.55, showing an overall upward trend. Meanwhile, the proportion of low-quality habitat WUA increased from 0.11 to 0.21, indicating the smallest impact from flow variations. The research results could provide a certain reference for the ecological scheduling of hydropower stations in the upper reaches of the Yellow River.

Biogeographic patterns of meio- and micro-eukaryotic communities in dam-induced river-reservoir systems

Although the Three Gorges Dam (TGD) is the world's largest hydroelectric dam, little is known about the spatial-temporal patterns and community assembly mechanisms of meio- and micro-eukaryotes and its two subtaxa (zooplankton and zoobenthos). This knowledge gap is particularly evident across various habitats and during different water-level periods, primarily arising from the annual regular dam regulation. To address this inquiry, we employed mitochondrial cytochrome c oxidase I (COI) gene-based environmental DNA (eDNA) metabarcoding technology to systematically analyze the biogeographic pattern of the three communities within the Three Gorges Reservoir (TGR). Our findings reveal distinct spatiotemporal characteristics and complementary patterns in the distribution of meio- and micro-eukaryotes. The three communities showed similar biogeographic patterns and assembly processes. Notably, the diversity of these three taxa gradually decreased along the river. Their communities were less shaped by stochastic processes, which gradually decreased along the longitudinal riverine-transition-lacustrine gradient. Hence, deterministic factors, such as seasonality, environmental, and spatial variables, along with species interactions, likely play a pivotal role in shaping these communities. Environmental factors primarily drive seasonal variations in these communities, while hydrological conditions, represented as spatial distance, predominantly influence spatial variations. These three communities followed the distance-decay pattern. In winter, compared to summer, both the decay and species interrelationships are more pronounced. Taken together, this study offers fresh insights into the composition and diversity patterns of meio- and micro-eukaryotes at the spatial-temporal level. It also uncovers the mechanisms behind community assembly in various environmental niches within the dam-induced river-reservoir systems. KEY POINTS: • Distribution and diversity of meio- and micro-eukaryotes exhibit distinct spatiotemporal patterns in the TGR. • Contribution of stochastic processes in community assembly gradually decreases along the river. • Deterministic factors and species interactions shape meio- and micro-eukaryotic community.

Early impacts of the largest Amazonian hydropower project on fish communities

Hydropower is a threat to freshwater fishes. Despite a recent boom in dam construction, few studies have assessed their impact on mega-diverse tropical rivers. Using a before-after study design, we investigated the early impacts of the Belo Monte hydroelectric complex, the third-largest hydropower project in the world, on fishes of the Xingu River, a major clear-water tributary of the lower Amazon. We explored impacts across different river sectors (upstream, reservoir, reduced flow sector, and downstream) and spatial scales (individual sectors vs. all sectors combined) using joint species distribution models and different facets of diversity (taxonomic, functional, and phylogenetic). After 5 years of the Belo Monte operation, species richness declined ~12% in lentic and ~16% in lotic environments. Changes in abundance were of less magnitude (<4%). Effects were particularly negative for species of the families Serrasalmidae (mainly pacus), Anostomidae (headstanders), Auchenipteridae, and Pimelodidae (catfishes), whereas no taxonomic group consistently increased in richness or abundance. The reservoir and downstream sectors were the most impacted, with declines of ~24-29% in fish species richness, overall reductions in fish body size and trophic level, and a change in average body shape. Richness and abundance also declined in the reduced river flow, and changes in size, shape, and position of fins were observed. Relatively minor changes were found in the upstream sector. Variation in functional and phylogenetic diversity following river impoundment was subtle; however, across sectors, we found a reduction in functional divergence, indicating a decline in the abundance of species located near the extremities of community functional space. This may be the first sign of an environmental filtering process reducing functional diversity in the region. Greater changes in flow and habitats are expected as hydropower operations ramp up, and continued monitoring is warranted to understand the full scope and magnitude of ecological impacts.

Multifaceted fish diversities respond differently to impounding age and longitudinal location along a reservoir cascade

Damming usually modifies riverine habitats, which affects various aspects of fish diversity, especially in a reservoir cascade. Their influence on fish assemblage has been studied widely, but a lack of data from the diversity perspective remains. The Gezhouba Reservoir and Three Gorges Reservoir are two of the largest cascaded reservoirs located on the upper Yangtze River. In this study, we investigated the current fish assemblages in 2020∼2021 and retrieved 22 previous investigations in different sections of this cascade system to analyze how fish taxonomic, functional, and phylogenetic alpha- and beta-diversity change with the distance from the dams and the impounding age during 1998∼2021, and all sampling sites are located in the upper section of the dams. The total species richness and phylogenetic diversity increased significantly with the distance from the dams, but the functional diversity did not change substantially. No significant difference was found in the influence of impounding age on the three aspects of fish diversity. We observed a noticeable increase in non-indigenous fish species richness, functional diversity, and phylogenetic diversity over time, these effects were similar in areas at different distances from the dams. The species richness and phylogenetic diversity of lotic fish decreased from the lotic to lentic zones, whereas the functional and phylogenetic diversities decreased significantly with impounding age. The taxonomic beta-diversity was remarkably higher than the functional and phylogenetic beta-diversities. The differences among the three facets of beta-diversity were driven by a lower functional turnover than the taxonomic and phylogenetic turnovers, and their nestedness components were low without exception. The present study suggests that trade-offs should be considered when designing policies to protect fish diversity based on different objectives.

Possible consequences of climate change on global water resources stored in dam reservoirs

Construction of dams and transformation of rivers, not only affects river-related and adjacent habitats, but also establishes new threats to surface freshwater resources globally. Predicted climate changes and increase of mean annual temperature will affect thermal regimes of dam reservoir ecosystems, severely altering their functioning. Analyzing three projections of representative concentration pathway (RCP 4.5, 6.0 and 8.5) for period of 2061-2080, we found that mean annual temperature at dam reservoir locations will increase by 3.06 °C to 4.74 °C from present. The highest projected increase of temperature was identified for dam reservoirs located in high latitudes of Northern Hemisphere, and therefore dam reservoirs located there will be most significantly affected. Numerous consequences of temperature increase are already recorded. Further increase will amplify unfavorable effects on numerous ecosystems, including dam reservoirs which are built on the purpose of the human population development. Our study indicates a threat for artificially stored water globally, with special attention to high latitudes in northern hemisphere and latitudes close to 20⁰S meridian in southern hemisphere.

Regime shifts in a shallow lake over 12 years: consequences for taxonomic and functional diversity, and ecosystem multifunctionality

Under increasing nutrient loading, shallow lakes may shift from a state of clear water dominated by submerged macrophytes to a turbid state dominated by phytoplankton or a shaded state dominated by floating macrophytes. How such regime shifts mediate the relationship between taxonomic and functional diversity and lake multifunctionality is poorly understood. We employed a detailed database describing a shallow lake over a 12-year period during which the lake has displayed all the three states (clear, turbid, and shaded) to investigate how species richness, functional diversity of fish and zooplankton, ecosystem multifunctionality, and five individual ecosystem functions (nitrogen and phosphorus concentrations, standing fish biomass, algae production, and light availability) differ among states. We also evaluated how the relationship between biodiversity (species richness and functional diversity) and multifunctionality is affected by regime shifts. We showed that species richness and the functional diversity of fish and zooplankton were highest during the clear state. The clear state also maintained the highest values of multifunctionality as well as standing fish biomass production, algae biomass, and light availability, whereas the turbid and shaded states had higher nutrient concentrations. Functional diversity was the best predictor of multifunctionality. The relationship between functional diversity and multifunctionality was strongly positive during the clear state, but such relationship became flatter after the shift to the turbid or shaded state. Our findings illustrate that focusing on functional traits may provide a more mechanistic understanding of how regime shifts affect biodiversity and the consequences for ecosystem functioning. Regime shifts towards a turbid or shaded state negatively affect the taxonomic and functional diversity of fish and zooplankton, which in turn impairs the multifunctionality of shallow lakes.

A cascade of dams affects fish spatial distributions and functional groups of local assemblages in a subtropical river

Abstract Dams reduce the longitudinal connectivity of rivers and thereby disrupt fish migration and the spatial distribution of species, impacts that remain poorly studied for some Neotropical rivers from mega-diverse basins. We investigated the spatial distribution of fish species with different trophic and movement/reproductive/size characteristics to assess how functional groups have responded to a cascade of dams on the Uruguai River in southern Brazil. Fish abundance, biomass, and species composition were evaluated at eight locations along the longitudinal gradient. The fish assemblage in the upper stretch was mainly characterized by small and medium-sized species at higher trophic levels, whereas the sites located furthest downstream displayed more medium and large-sized species, including many carnivorous species. Species with high fecundity, seasonal migrants, and catfishes with internal fertilization were common in the river´s middle and lower reaches. Detritivorous species dominated areas distant from the dams. Overall, functional diversity of local fish assemblages was greater in lower reaches. The cascade of dams has impacted the distribution of functional groups of local fish assemblages of Uruguai River. The alteration of functional groups in upper reaches of the river has potential consequences for ecosystem processes and services, such as nutrient cycling and fisheries.