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Comprehending fish diversity through multiple dimensions is a crucial aspect in advancing our understanding of fish populations and promoting sustainable fisheries as well as diversity conservation. Traditional research on fish diversity has been limited to non-genetic methods. The advent of environmental DNA (eDNA) technology enables simultaneous examination of both non-genetic and genetic aspects of fish diversity. In this study, we evaluated the ability of eDNA to capture multidimensional fish diversity in the northern South China Sea, with emphasis on phylogenetic diversity. The effect of environmental change and geographical location on multidimensional fish diversity across different seasons was also investigated. The analysis of species accumulation curves revealed that the observed species richness approached an asymptote, achieving 94.7% and 89.5% of the predicted values during the summer and winter, respectively. Alpha diversity of taxonomic (species, 225 vs. species, 102), functional (FRic, 0.51 vs. FRic, 0.19), and phylogenetic (PD, 26.27 vs. PD, 15.81) dimensions were found to be higher in summer compared to winter, with environmental factors significantly influencing these diversities across seasons. Regarding the three dimensions of beta diversity, replacement made a greater relative contribution to total taxonomic, functional, and phylogenetic beta diversity than richness difference. These effects were primarily influenced by water environment factors (e.g., NO2−, SiO32−, surface temperature) during the summer and geographical factors (e.g., longitude and latitude) during the winter. This study provides evidence supporting the feasibility of utilizing eDNA techniques to uncover fish diversity in multiple dimensions, with a specific emphasis on its intrinsic genetic characteristics, which hold substantial value for the protection of diversity and the scientific administration of fishery resources.

Dams as crucial metrics for characterizing aquatic species diversity and river ecosystem have significant effects on river longitudinal connectivity (RLC). Specially, the reduction of RLC can lead to the degradation of suitable habitats and loss of migration opportunities for freshwater fish. However, the assessment of RLC in cascade dams is still limited, particularly in relation to fish species and habitats. Therefore, this paper analyzed the influence mechanism of cascade dams on aquatic ecosystems by simulating the flow field using the Delft3D model. Additionally, a novel index-based method associated with five fish-related indices has been developed to evaluate the RLC. Considering that numerous large dams posed serious threats to the aquatic ecosystem in Southwest China, the Yalong River was chosen as a study case to illustrate the application of this new framework. The results showed that the reservoir area exhibited the most stable flow field, with the lowest values of flow velocity (v), Reynolds number (Re) and Froude number (Fr); and the highest hydrodynamic parameters were observed at the reservoir head. The v from upstream to downstream of the five studied reservoirs (Jinping I, Jinping II, Guandi, Ertan and Tongzilin) showed a decreasing trend, characterized by turbulent flow (Re greater than 500) and sluggish flow (Fr less than 1). These changes in flow regime had a profound impact on fish diversity and habitats due to the construction of cascade dams. Based on the novel index-based method, the RLC was determined to be moderate, with a value of 12.90. Notably, the lowest score occurred in the Tongzilin reservoir, indicating its largest contribution to the reduction of RLC. The different impacts of the five studied dams on RLC were attributed to multiple factors, including their geographical location, distribution, distance, reservoir operations and regulations, as well as the cumulative effects of cascade dams. The results can provide references for decision-making in dam projects and river management, and the framework can be applied to evaluate RLC of other rivers worldwide.

Environmental DNA (eDNA) technology has emerged as a widely used method in resource monitoring. The purpose of this study was to assess the effectiveness of the eDNA approach in determining fish composition in the marine ranching of the Bailong Pearl Bay National Marine Ranching Demonstration Zone. Samples were collected from 12 sites in four different zones within Bailong Pearl Bay of the Beibu Gulf, and species diversity was analyzed through 12S rRNA gene amplicon sequencing. The results showed the collection of a total of 75 fish species, with Setipinna taty, Hypoatherina valenciennei, Trachurus japonicus, and Scatophagus argus identified as the dominant species based on the eDNA survey. Alpha and beta diversity index analyses revealed significant differences in composition and abundance of the different fish groups in Bailong Pearly Bay in July 2021. Furthermore, it was found that the artificial reef area and the natural sea area outside Bailong Bay harbored a more diverse fish population, which can be attributed to the positive effects of marine ranching construction. Mantel test correlation analysis demonstrated that phycoerythrin, salinity, and dissolved oxygen were the primary environmental factors influencing the structure of fish assemblages in different zones. The results indicated that eDNA can detect a greater number of species and uncover taxa that are rarely observed visually, thereby providing a comprehensive picture of fish diversity in the sample. This survey offers important technical support for the Bailong Pearl Bay National Marine Ranching Demonstration Zone, and the research findings provide valuable data for the development of marine ranching.

In order to explore the spatial layout of fish assemblages and their related environmental factors, a survey of species composition was conducted in the Anning River. From 2018 to 2021, 28 sites at 987–2,077 m in altitude were surveyed, gathering 64 species in total, of which 60 were native and 4 were exotic. Fifteen of the species sampled were indigenous to the upper Yangtze River, and two were classified as critically endangered or endangered. Fish communities displayed significant upstream-to-downstream variation. There are two site-groups, one covering upstream and tributaries and the other covering midstream and downstream. The upstream-tributary fish assemblages had a dominance of Nemacheilidae and Schizothoracinae, which are plateau species with habitat preferences for boulders and fast-flowing water. Conversely, the mid-downstream fish assemblages had a dominance of Gobioninae, Cyprininae, Bagridae and Siluridae, which are common river species that prefer slow-flowing water. The spatial patterns of these fish communities were chiefly affected by altitude and substratum composition. The fish assemblage pattern was consistent with the zonation concept because the fish communities changed abruptly and clearly along the upstream–downstream axis. The findings of this study offer a crucial research foundation for comprehending the fish assemblages of mountainous rivers, which will be conducive to biodiversity management and habitat preservation of aquatic species.

Marine ecosystems are a primary conservation concern because of the separate and synergistic effects of overfishing and climate change on their productivity and biodiversity. For the purpose of implementing ecosystem-based fisheries management, it is essential to understand how fish stocks respond to climate change in marine ecosystems, especially those that have been overexploited. The Beibu Gulf in the northwestern part of the South China Sea has long been one of China’s major fishing grounds. After the collapse of the demersal ecosystem in 1990 s, small pelagic fishes, including Japanese jack mackerel (Trachurus japonicus) and Japanese scad (Decapterus maruadsi), have occupied a more-important ecological niche in this gulf. However, insufficient research on how small pelagic fish respond to climate change creates great uncertainty for implementing the current management measures. This study used fish data of trawl surveys and environmental data to investigate possible mechanisms leading to dramatic fluctuations in small pelagic fish populations and their possible effects on the Beibu Gulf marine ecosystem. Abnormal blooms of small pelagic fish, especially T. japonicus and D. maruadsi, occurred following four La Niña events (in 2007/2008, 2010/2011, 2011/2012, and 2020/2021). Moreover, the dominant fish species shifted observably and regularly, Shannon–Wiener diversity and Pielou’s evenness decreased significantly in the northeastern coastal waters of the gulf, and the spatial pattern of the fish community was reorganized in this ecosystem. The small pelagic fish blooms in summers probably resulted from a combination of climate change, overfishing, and a summer fishing moratorium, which thereby caused a series of responses in the marine ecosystem. Fluctuations in the small pelagic fish populations after La Niña events seemed more dramatic after the collapse of demersal fish stocks. Therefore, we emphasize the need for implementing ecosystem-based, preventive, and adaptive fisheries management.

With the decrease in biodiversity in freshwater ecosystems, the monitoring of fish has become a current research hotspot. The eDNA-based method has been applied to a variety of single-type water systems (i.e., rivers, lakes, or oceans), but it has not been applied to river–lake-connected systems. We collected eDNA from water samples from the Changjiang River–Shijiu Lake connected system (including the lake area, river channel, and river section) and discussed the fish diversity characteristics of the connected system. A total of 180 samples were collected, and the fish community was analyzed using eDNA metabarcoding of the mitochondrial 12 s region. We finally identified 66 taxa of fish, including one at the order level, two at the family level, 9 at the subfamily level, 20 at the genus level, and 34 annotated to the species level. The number of fish species in the river–lake connected system was greater than that in a single-type water system. The lake area, river channel, and river section had a high degree of overlap in fish composition, and the maximum number of fish was in the river section. There was no significant difference in α diversity index among the three types of waters, but there were significant differences in fish relative abundance, which was dominated by different species. The distribution of three migratory fish (Elopichthys bambusa, Ctenopharyngodon idella, and Hypophthalmichthyinae sp.) accorded with the unique life history migration strategy in the middle and lower reaches of the Changjiang River. Our results provide detailed data on fish diversity and have important implications for the long-term management and conservation of river–lake connected systems in the lower reaches of the Changjiang River. Our research further proves that eDNA can be used to monitor the biodiversity of river–lake connected systems and reflect their spatial characteristics. As a continuously explored method, eDNA shows great potential in the study of fish diversity in river–lake systems.

• The roles of different functional traits and diversity indicators were compared. • Dominant traits rather than diversity drive the changes in community productivity. • The trait of locomotion and the diversity of feeding modes are crucial. • The mass ratio hypothesis was supported in the marine fish community. The biodiversity-ecosystem functioning (BEF) relationship is a critical topic in ecological research, as it guides the maintenance of ecosystem functioning in the face of climate change and human disturbance. However, the BEF relationship is complicated by the fact that biodiversity has multiple dimensions, and in particular functional diversity may be strongly correlated with community productivity. But the understanding is still lacking about how different functional traits determine community productivity. The present study tested the relationship between biodiversity and community productivity empirically in a demersal fish community, based on continuous bottom trawl surveys in Haizhou Bay, China from 2013 to 2022. Structural equation modeling (SEM) with composite variables was used to evaluate the relationships among environmental factors, species diversity (SD), functional diversity (FD), community weighted mean traits (CWM), and community productivity (CP), and the roles of different aspects of functional traits were further compared. The results showed that there were considerable heterogeneities in the temporal and spatial distributions of CP , and PCA revealed that the CP was weakly correlated with both species and functional diversity. SEM showed that CWM had the greatest influences on CP (r = 0.63), followed by SD (r = 0.52), and FD had the least impact (r = -0.42). This finding supported the mass ratio hypothesis, indicating that functional traits of dominant species determined community productivity. Environmental factors showed no direct impacts on CP but had indirect effects through biodiversity. Regarding the role of different functional traits, the trait of locomotion was the most important driver of CP in terms of CWM , while the food acquisition was more important than other components in terms of FD. Our study can contribute to an improved comprehension of the BEF linkages in marine fish communities, and serve as a guideline for fisheries management and biodiversity protection in the face of climate changes. [ABSTRACT FROM AUTHOR]

• The δ13C and δ15N values of fish communities were different between nearshore and offshore islands. • The food chain length of fish communities in nearshore islands was longer than that in offshore islands. • Fish communities located on nearshore islands had more abundant food sources, more diverse trophic levels, and higher trophic diversity than offshore fish communities. • The fisheries of the Wanshan Islands mainly feed on zooplankton, and may gradually transition to detritus feeding species. The Wanshan Archipelago, situated in the Pearl River Estuary, stood as a key fishing ground in China, boasting abundant fishery resources. To investigate variations in trophic niches and food sources among different islands within the Wanshan Archipelago, and to advance research on fish food webs and energy flow in the Pearl River Estuary, this study conducted a survey of fish communities in nearshore islands (Guishan Island, Dongao Island) and offshore islands (Wailingding Island, Wanshan Island) using triple gill nets during the autumn of 2021. The trophic niche characteristics of fishery organisms in these islands were analyzed utilizing carbon and nitrogen stable isotope technology. The results indicated that trophic niche width and biodiversity of fish communities in the nearshore islands surpassed those in the offshore islands, and the food chain length exhibited a trend of Guishan Island (4.04) > Dongao Island (3.98) > Wanshan Island (3.91) > Wailingding Island (3.86). The trophic niche indexes (CR, NR, CD, and SEAc) of fish communities in nearshore islands were higher compared to those on offshore islands, while MNND and SDNND suggested that fish communities in offshore islands were at a lower trophic level. Zooplankton emerged as the primary food source for fishery organisms in the Wanshan Archipelago. Feeding rates on zooplankton were 68.8 % and 70.4 % in Guishan Island and Dongao Island, and 53.7 % and 58.0 % in Wailingding Island and Wanshan Island, respectively. The proportion of benthic organisms fed near offshore islands was higher than nearshore islands. This study speculated that the fish in nearshore islands may shift from zooplankton food chain to benthic food chain. In addition, this study compared the trophic niche differences among the four islands in the Pearl River Estuary, clarified the diversity of feeding sources and trophic structure within fish communities, and revealed significant distinctions in fish food webs between the islands inside and outside the Pearl River Estuary. It will provide new information on the trophic interactions of fish in the Pearl River Estuary, and help to promote the ecological development and sustainable use of fishery resources. [ABSTRACT FROM AUTHOR]

[Display omitted] • Higher fish TD α , FD α and PD α were detected in summer in the nSCS. • TD β , FD β and PD β of fish community significantly increased in winter. • Species replacement predominantly drove fish beta diversity in the nSCS. • Water environmental factors mainly influenced TD β , FD β , PD β in summer. Comprehending fish diversity through multiple dimensions is a crucial aspect in advancing our understanding of fish populations and promoting sustainable fisheries as well as diversity conservation. Traditional research on fish diversity has been limited to non-genetic methods. The advent of environmental DNA (eDNA) technology enables simultaneous examination of both non-genetic and genetic aspects of fish diversity. In this study, we evaluated the ability of eDNA to capture multidimensional fish diversity in the northern South China Sea, with emphasis on phylogenetic diversity. The effect of environmental change and geographical location on multidimensional fish diversity across different seasons was also investigated. The analysis of species accumulation curves revealed that the observed species richness approached an asymptote, achieving 94.7% and 89.5% of the predicted values during the summer and winter, respectively. Alpha diversity of taxonomic (species, 225 vs. species, 102), functional (FRic, 0.51 vs. FRic, 0.19), and phylogenetic (PD, 26.27 vs. PD, 15.81) dimensions were found to be higher in summer compared to winter, with environmental factors significantly influencing these diversities across seasons. Regarding the three dimensions of beta diversity, replacement made a greater relative contribution to total taxonomic, functional, and phylogenetic beta diversity than richness difference. These effects were primarily influenced by water environment factors (e.g., NO 2 −, SiO 3 2−, surface temperature) during the summer and geographical factors (e.g., longitude and latitude) during the winter. This study provides evidence supporting the feasibility of utilizing eDNA techniques to uncover fish diversity in multiple dimensions, with a specific emphasis on its intrinsic genetic characteristics, which hold substantial value for the protection of diversity and the scientific administration of fishery resources. [ABSTRACT FROM AUTHOR]

• ML models recognize complex salmon habitat-abundance relationship, using small data. • Regression models struggle with intricate relationships in habitat data. • Models with substrates, shades, and vegetation variables offer higher accuracy. • Support vector classification excels in modeling accuracy. • The study highlights ML challenges in salmon habitat-abundance modeling. Climate change and anthropogenic activities have impacts on fish habitat suitability, demanding more accurate modeling of species abundance for effective conservation and management. In this study, we applied Machine Learning techniques to model the habitat-abundance relationship of juvenile Atlantic salmon (Salmo salar) in the Teno catchment in Finland and Norway. To capture the complexity and nonlinearity of the habitat-abundance relationship, we employed Support Vector Regression (SVR), Random Forest (RF), Gradient Boosting (GB), and Support Vector Classification (SVC) and compared their performances. Among the regression models considered, those incorporating input variables such as substrate, shade, and vegetation demonstrate higher performance. Support Vector Regression yields the highest mean cross-validation score (R2 = 0.58), and Gradient Boosting produces the highest test score (R2 = 0.6) among the regression techniques. The mean cross-validation and test scores obtained for the classification models are notably higher compared to the regression models across all scenarios. A comparison between regression and classification results highlights the challenges of accurately modeling the habitat-abundance relationship. This study provides insights into the challenges and potential of machine learning techniques for juvenile Atlantic salmon habitat-abundance modeling in complex riverine habitat environments. The findings emphasize the importance of considering the limitations of machine learning models, particularly in ecological contexts, and the need for further research to address temporal variations and improve the precision of habitat-abundance modeling. [ABSTRACT FROM AUTHOR]

• eDNA metabarcoding could reconstruct the phylogenetic diversity of fishes and uncover hidden endemic species. • Key endemic species made the greatest contribution to maintain community stability. • The robustness, vulnerability and competition of fish communities in mainstem and tributary were obviously different. Monitoring and evaluating river ecosystems are of paramount importance in addressing ecological and environmental challenges. While eDNA (environmental deoxyribonucleic acid)-based method has emerged as a valuable tool for understanding these issues, its application in assessing phylogenetic diversity, community stability, and the identification of key species within river systems has been limited. In this study, we conducted eDNA metabarcoding to assess fish community phylogenetic diversity, species composition, assembly variations, and their relationship with hydrologic characteristics. We also explored ecological stability and the roles of key species in a river system comprising a mainstem (MS) and a tributary (TB) with distinct hydrologic features. Our findings uncovered previously unknown endemic fish species diversity, exemplified by the discovery of Triplophysa. We identified disparities in diversity, community composition, and assembly between the MS and TB. Furthermore, we established significant associations between water-level variations, water flow, and changes in community composition. Triplophysa , with its high diversity, played a pivotal role in the ecological network, contributing significantly to community stability. The loss of Triplophysa increased fragility in co-occurrence patterns. Comparing the ecological network of fish communities between the MS and TB, we found that the MS displayed greater robustness and lower vulnerability, with increased species competition likely promoting network stability. Overall, this study highlights the potential of integrating eDNA metabarcoding data for monitoring phylogenetic diversity, community structure, and variations in stability within fish communities. [ABSTRACT FROM AUTHOR]

[Display omitted] • We utilized eDNA to study riverine fish communities across the Qinghai-Tibet Plateau. • A total of 90 fish species were detected, belonging to 34 families and 79 genera. • Fish communities were directly affected by watershed characteristics. • This study implied potential species invasion on the Qinghai-Tibet Plateau. The Qinghai-Tibet Plateau (QTP) serves as the source of many large rivers in Asia, and also serves as a natural habitat for rare wildlife and a genetic reservoir for plateau species. The exceptional ecological environment of the QTP has fostered diverse fish species. However, due to climate change and human activities, fish species in this area are facing serious threats, while large spatial scale investigation is a big challenge. Environmental DNA (eDNA) metabarcoding, as an innovative monitoring technology, offers a simple, fast, and environmentally friendly approach to explore fish communities on the QTP. This study utilized eDNA technology to assess the diversity, composition, and potential environmental influences of riverine fish communities across the QTP. A total of 90 fish species were identified belonging to 79 genera, 34 families, and 18 orders. The dominant species were Schizothorax chongi , Gymnocypris przewalskii , Carassius carassius , and Botia striata. PCoA and ADONIS indicated significant differences among fish community in different river basins of the Qinghai-Tibet Plateau. Canonical correspondence analysis (CCA) revealed that the ratio of SRP to TP, average NDVI, average elevation, and proportion of bare land significantly influenced the distribution of fish community. This study provided a novel monitoring method and insight for fish communities and implied potential species invasion on the QTP. [ABSTRACT FROM AUTHOR]

• Coupling morphology with eDNA to investigate fish diversity. • Stochastic processes dominate fish assembly in Taizi River Basin. • Main environmental filtration factors to fish are total phosphorus, biological oxygen demand and temperature. The loss of freshwater biodiversity has drawn greater attention to fish diversity and community assembly patterns. However, traditional survey methods, such as ground cages and electrofishing, may cause damage to fish communities and have become increasingly unsuitable for frequent and large-scale fish diversity surveys. In this study, environmental DNA (eDNA) metabarcoding and morphological data were both used to investigate the distribution and diversity of fish communities in the Taizi River basin, a temperate river in Northeast China, and the fish diversity and assembly patterns were investigated by using the null model. The results showed that a total of 7 orders, 17 families, 49 genera and 56 species were detected by the eDNA metabarcoding (6 orders, 15 families, 40 genera and 45 species) and morphological method (6 orders, 10 families, 31 genera and 34 species), and the eDNA method had a higher detection probability. Cypriniformes was detected most frequently, followed by Perciformes. Principal coordinate analysis revealed that fish communities in the Taizi River exhibited different spatial structures between the upper and lower reaches, with fish sensitive to environmental changes mostly found in the upper reaches and higher fish richness in the same area. The beta diversity in the upper reaches was higher than that in the lower reaches. The null model results showed the main factor that affected the distribution of fish in the Taizi River is the stochastic processes. Among the deterministic processes, the main environmental filter factors affecting fish community structure include total phosphorus, biochemical oxygen demand and temperature. We also confirm that eDNA metabarcoding has a higher detection rate compared to traditional survey methods, so it is feasible for freshwater ecosystem and fish resource monitoring. Therefore, the utilization of eDNA metabarcoding can effectively enhance monitoring efficiency and minimize interference with water bodies. [ABSTRACT FROM AUTHOR]

• Observed drastic declines in the abundance of kingfishers during 2010–2020 in wetlands in southwest India. • Shifts in environmental variables influenced abundance of kingfisher population. • Declining kingfishers indicate deteriorating wetland habitats. • Development and implementation of tailored conservation plans are imperative. Fragile wetland habitats are susceptible to multiple threats from anthropogenic activities. Direct waste deposition, habitat modification and overexploitation of fish have caused alternations in food webs in wetlands. Kingfishers are ecological indicators with the potential ability to respond to the minute changes in their microenvironment. Their abundance and distribution at wetland habitats are affected by multiple environmental factors. We studied the kingfisher assemblages in India to determine proximate and ultimate causes of their decline. We recorded the abundance of five species of kingfishers across five wetland habitats from 2011 to 2020 in Kerala, southwest coast of India. Kingfishers were counted twice in a month between 6.00 and 12.00 hrs. Air temperature, water temperature, humidity and turbidity were recorded. We measured fish diversity and abundance and organic waste as an additional explanatory variable. One-way ANOVA, Autoregressive Integrated Moving Average model and structural equation modelling were used to determine which explanatory variables affected kingfisher populations. Air temperature, water temperature and turbidity increased significantly during the study and had negative effects on the abundance of kingfishers. Humidity decreased significantly but had no effect on the kingfisher abundance. Fish abundance declined and had a strong positive effect on the abundance of kingfishers. The analysis of incidence of wastes across the study areas revealed that, all the sites were severely polluted. We also observed drastic decline in the abundance of all the species of kingfishers studied across the sites with a rapid decline in Pied Kingfisher and slower decline in White-throated Kingfisher. Black-capped Kingfisher is a local migrant to the study areas and is already red listed and categorized as Vulnerable (VU). This study suggests that kingfisher assemblages are declining along with the health status of the habitat. Urgent action is needed to help in designing and implementing effective management strategies for the sustainability of wetlands in the region. [ABSTRACT FROM AUTHOR]

• Fish communities show a distance-decay pattern at low water, not high water. • Water quality and levels are key factors shaping fish community compositions. • Stochastic processes dominate and drive fish community assembly in the TGR. • Growth-limiting index (GLI) is first proposed to intuitively predict fish fate. The Three Gorges Dam is the largest water conservancy project in the world, and the Three Gorges Reservoir Area (TGRA) possesses precious fish resources. Currently, due to the lack of efficient biodiversity monitoring tools, the precise evaluation of fish community composition in a riverine reservoir has been restricted. Here, we investigated fish resources using 12S-rDNA barcoding in the TGRA before and after 175 m water level during the first year of a 10-year Yangtze fishing ban. Our results showed that the fish composition exhibited obvious seasonal differences. The environmental water levels, land use, and spatial characteristics less influenced the development of fish communities. Based on Infer Community Assembly Mechanisms (iCAMP) by phylogenetic bin-based null model analysis, 66.12 % of unexplained variables were driven by stochastic processes of community assembly and unmeasured key factors. We developed a growth-limiting index (GLI) and firstly applied it to inferring fish environmental adaptability, revealing the growth adaption response of reservoir fish species to environmental pressure. Compared to the downstream from the dam, fish population growth at the low- or high-water levels was partly inhibited. However, seven species of tiny or medium-sized fish showed strong adaptability in the reservoir region at both water levels. Taken together, this study clarified the patterns of fish community assembly in the TGRA and provided unique insights for chronic monitoring of fish diversities in a reservoir. [ABSTRACT FROM AUTHOR]

• A complete eDNA workflow was established for the Marine Ranching Demonstration area. • The artificial reef marine ranch demonstration area in Beibu Gulf has achieved remarkable results. • Environmental factors have different effects on fish in different habitats. • Fish diversity distribution in the different four areas was different and the overall fish community is changing to smaller species. Environmental DNA (eDNA) technology has emerged as a widely used method in resource monitoring. The purpose of this study was to assess the effectiveness of the eDNA approach in determining fish composition in the marine ranching of the Bailong Pearl Bay National Marine Ranching Demonstration Zone. Samples were collected from 12 sites in four different zones within Bailong Pearl Bay of the Beibu Gulf, and species diversity was analyzed through 12S rRNA gene amplicon sequencing. The results showed the collection of a total of 75 fish species, with Setipinna taty , Hypoatherina valenciennei , Trachurus japonicus , and Scatophagus argus identified as the dominant species based on the eDNA survey. Alpha and beta diversity index analyses revealed significant differences in composition and abundance of the different fish groups in Bailong Pearly Bay in July 2021. Furthermore, it was found that the artificial reef area and the natural sea area outside Bailong Bay harbored a more diverse fish population, which can be attributed to the positive effects of marine ranching construction. Mantel test correlation analysis demonstrated that phycoerythrin, salinity, and dissolved oxygen were the primary environmental factors influencing the structure of fish assemblages in different zones. The results indicated that eDNA can detect a greater number of species and uncover taxa that are rarely observed visually, thereby providing a comprehensive picture of fish diversity in the sample. This survey offers important technical support for the Bailong Pearl Bay National Marine Ranching Demonstration Zone, and the research findings provide valuable data for the development of marine ranching. [ABSTRACT FROM AUTHOR]

• An index-based method associated with aquatic ecosystem was proposed to evaluate RLC. • The changes of flow regime in cascade dams impacted the migratory and endemic fish. • The downstream Tongzilin reservoir had the largest contribution to the loss of RLC. • RLC was impacted by multiple factors especially cumulative effects in cascade dams. Dams as crucial metrics for characterizing aquatic species diversity and river ecosystem have significant effects on river longitudinal connectivity (RLC). Specially, the reduction of RLC can lead to the degradation of suitable habitats and loss of migration opportunities for freshwater fish. However, the assessment of RLC in cascade dams is still limited, particularly in relation to fish species and habitats. Therefore, this paper analyzed the influence mechanism of cascade dams on aquatic ecosystems by simulating the flow field using the Delft3D model. Additionally, a novel index-based method associated with five fish-related indices has been developed to evaluate the RLC. Considering that numerous large dams posed serious threats to the aquatic ecosystem in Southwest China, the Yalong River was chosen as a study case to illustrate the application of this new framework. The results showed that the reservoir area exhibited the most stable flow field, with the lowest values of flow velocity (v), Reynolds number (Re) and Froude number (Fr); and the highest hydrodynamic parameters were observed at the reservoir head. The v from upstream to downstream of the five studied reservoirs (Jinping I, Jinping II, Guandi, Ertan and Tongzilin) showed a decreasing trend, characterized by turbulent flow (Re greater than 500) and sluggish flow (Fr less than 1). These changes in flow regime had a profound impact on fish diversity and habitats due to the construction of cascade dams. Based on the novel index-based method, the RLC was determined to be moderate, with a value of 12.90. Notably, the lowest score occurred in the Tongzilin reservoir, indicating its largest contribution to the reduction of RLC. The different impacts of the five studied dams on RLC were attributed to multiple factors, including their geographical location, distribution, distance, reservoir operations and regulations, as well as the cumulative effects of cascade dams. The results can provide references for decision-making in dam projects and river management, and the framework can be applied to evaluate RLC of other rivers worldwide. [ABSTRACT FROM AUTHOR]

Highlights • Effects of invasions and extirpations on phylogenetic diversity are little known. • We assessed impacts of extirpations and invasions on fish phylogenetic diversity. • Phylogenetic alpha diversity increased, but the phylogenetic dissimilarity declined. • Measuring phylogenetic diversity provides complementary information to taxonomy. Abstract Human-mediated introductions of exotic species and extirpations of native species have modified the composition of biotic communities throughout the world, but the consequences of introductions and extirpations on local phylogenetic diversity (alpha-diversity) and on phylogenetic distinctiveness between sites (beta-diversity) remains poorly investigated. Here we analyze the long-term impacts of extirpations and invasions on both phylogenetic and taxonomic alpha and beta diversity of fish assemblages in Chinese isolated lakes. Data of fish assemblages in 15 lakes were grouped into three periods spanning the last 75 years: historical, intermediate and current periods. We partitioned phylogenetic beta diversity into turnover and nestedness component, and examined how introductions and extirpations led to temporal changes in alpha and beta diversity using linear regression and multiple regression models on distance matrices, respectively. Introductions and extirpations caused an increase of phylogenetic diversity (Δ+) and phylogenetic unevenness (Λ+) within the lakes, but the phylogenetic dissimilarity between lakes declined. Such trend, resulting from 60 years introductions and extirpations, was mainly due to a decline of the phylogenetic turnover, indicating that the replacement of native endemic species by widespread exotic species was the main driver of the observed phylogenetic homogenization. Temporal changes in phylogenetic and taxonomic dissimilarities were positively correlated, and taxonomic homogenization causes phylogenetic homogenization in ca. 60% of the lake pairs. Nevertheless, taxonomic homogenization turns to phylogenetic differentiation in one third of lake pairs due to the extirpation of the closely-related species and the introduction of distinct exotic species belonging to different lineages among lakes. Therefore, measuring phylogenetic diversity changes provides complementary information to taxonomy, and gives support to the Darwin's naturalization hypothesis stipulating that species distantly related to natives easily establish in their introduction range. Our results demonstrate that half a century of anthropogenic disturbance was sufficient to blur the phylogenetic distinctiveness among lakes that resulted from the last 5 million years evolutionary history of the Yun-Gui plateau. [ABSTRACT FROM AUTHOR]

[Display omitted] • Patterns and driving factors of fish biodiversity in metacommunities were quantified. • Almost all indices of alpha and beta diversity decreased during the 1980 s-2010 s. • Land use contributed more to biodiversity decline than other stressors. Understanding patterns and driving factors of freshwater fish biodiversity in metacommunities is essential for biological conservation but rarely studied in regions experiencing rapid land use changes. We examined changes of both alpha and beta fish diversities in taxonomic, functional, and phylogenetic facets during the 1980 s to 2010 s, and quantified contributions from natural and human drivers in lakes located in China's fastest economic development region. Results showed that almost all indices of alpha and beta diversity decreased through time. For alpha diversity, taxonomic and functional richness declined by 13 to 15%. Rheophilic and piscivorous fish species declined by 50 and 36%, respectively. For beta diversity, the decline of overall functional (-31%) diversity was greater than taxonomic (-17%) and phylogenetic (-19%) diversity. The decline of multiple facets of beta diversity indicated that fish communities in these lakes have homogenized through time. Land use (i.e., increased urban land and aquaculture ponds), hydrology (i.e., increased water level), climate (i.e., increased air temperature), and fishing (i.e., increased lake fishery catch) factors all made significant contributions to both alpha and beta fish diversity decline in multiple facets. The overall contribution from land use to the decline of multidimensional fish diversity was greater than those of other stressors. While attention should be given to both local human disturbance and regional climate factors, in regions experiencing rapid economic development and land use changes, local disturbances should be considered as a priority in biodiversity management plans. [ABSTRACT FROM AUTHOR]

Human-induced impact on the biocoenoses in small water bodies within field landscape, aquatic ecosystems undergoing habitat loss, is not only restricted to trophic increase. Ponds are often used for amateur fish production, mainly carp and crucian carp. In addition, in order to limit the growth of aquatic vegetation alien fish species to native fauna, grass carp, are frequently introduced. Only temporary ponds remain entirely free of such manipulations. Therefore, changes in diversity and the occurrence of specific species can be expected in ponds representing different scenarios of fish predation FP and water regime WR. In order to establish conditions responsible for zooplankton occurrence in field ponds subjected to FP (three categories of ponds: fish-free; low fish stocking; high fish stocking) and WR (two categories of ponds: permanent vs. temporary), material was collected from the open water of six neighbouring ponds, thirteen times in 2009, covering the spring, summer and autumn. A total of 134 zooplankton taxa was recorded with rotifers (94 taxa) prevailing taxonomically over cladocerans (24) and copepods (16). A tendency of certain taxa and species diversity to group along a gradient of WR and FP was observed. Higher species diversity was attributed to fish-free ponds, partly depending on the higher contribution of macrophyte-dominated areas, which are known to support a high variation of organisms. Two groups from among the most frequent species that indicated temporary ponds were: 1/littoral-associated (e.g. Lepadella ovalis , Chydorus sphaericus ) in fish-free ponds and 2/large-bodied mainly pelagic (e.g. Eudiaptomus gracilis ) in low-fish ponds. Fish ponds that were of permanent character, however, had lower species richness, with a high frequency of typically eutrophic taxa such as Brachionus angularis , Keratella cochlearis f. tecta or Trichocerca pusilla . However, they were also a source of rare species such as Brachionus falcatus , Lecane tenuiseta , Ceriodaphnia dubia that occurred exclusively in these ponds compared to natural fish-free ponds, which were remnants of lost species richness. This in turn increased overall zooplankton richness in the regional aspect. Thus, the co-occurrence of temporary ponds along with fish-production targeted permanent ponds may lead to a rise in zooplankton biodiversity on a local scale. We assume therefore that not only patterns of zooplankton biodiversity but also the occurrence of particular species can be treated as a useful indicator of FP and WR in small water bodies and are crucial for conservation purposes and management of aquatic systems at regional and landscape levels. [ABSTRACT FROM AUTHOR]

The estimation of biodiversity is complex in remote areas like Andean-Amazon piedmont where the lack of knowledge is noticeable and most species have not yet been identified. An alternative to the taxonomical approach to assess biodiversity and community structure is to study the body size structure of the community. The present study aimed to identify systematic changes of the size structure of fish communities along the altitudinal gradient of pristine Andean streams. At the same time, we assessed if size structure of fish communities could be an alternative or complementary approach to traditional taxonomic metrics of ecological assessment. This study was conducted along two rivers of eastern Andean piedmont: Hacha River and Alto Madre de Dios basin. Our analysis showed lower values of total size range, maximum length and number of size classes in the highest places and increasing in lower reaches of the rivers. Concerning abundance size spectra, we found flatter slopes (indicating higher relative abundance of large fish) and lower coefficient of determination (i.e. less linear size spectra) and intercept at y-axis on upstream reaches. On the other hand, fish abundance, species richness and species diversity increasing from upstream to downstream. These systematic changes on size-related variables were similar using both basins together or independently and may be used in future studies as management reference conditions when assessing the effect of perturbations in freshwater ecosystems, while bypassing the error associated with the lack of taxonomic information. [ABSTRACT FROM AUTHOR]

The Mekong, Sekong, Sesan, and Srepok (Mekong-3S) river system, a Ramsar wetlands of international importance and critical fish migration routes, is altered by dams that distort the seasonal flow dynamics, structuring dispersal and reproduction success of fishes. Here, we investigate the temporal responses of local fish beta diversity to hydrologic modification by the upstream functioning dams in five sites of the Mekong-3S system. The sampling design adopted (two sites on the Mekong River displaying relatively undisturbed flow and three sites in the 3S displaying a gradient in flow perturbation) allows us to focus on the effect of flow alteration on local fish assemblage compositions. By analysing 7-year daily fish monitoring data (06/2007–05/2014), we found that there have been overall declining trends in local species richness and abundance, with strong temporal variability in local beta diversity. Undisturbed sites are characterized by seasonal assemblage variability, while disturbed sites are characterized by aseasonal assemblage changes. Temporal shifts in assemblage composition suggest that dams alter seasonal flow patterns and favour generalist species. This study contributes to a better understanding of the temporal changes of tropical freshwater fish beta diversity in regulated and unregulated rivers. It is thus relevant for fisheries planning and conservation. [ABSTRACT FROM AUTHOR]

The member states of the European Union use multi-metric macrobenthos indicators to monitor the ecological status of their marine waters in relation to the Water Framework and Marine Strategy Framework Directives. The indicators translate the general descriptors of ecological quality in the directives into a single value of ecological status by combining indices of species diversity, species sensitivity and density. Studies and inter-calibration exercises have shown that the indicators respond to chemical pollution and organic enrichment, but little is known about their response to bottom trawling. We use linear mixed effects models to analyze how bottom trawling intensity affects the indicators used in the Danish (Danish Quality Index, DKI) and Swedish (Benthic Quality Index, BQI) environmental monitoring programs in the Kattegat, the sea area between Sweden and Denmark. Using year and station as random variables and trawling intensity, habitat type, salinity and depth as fixed variables we find a significant negative relationship between the BQI indicator and bottom trawling, while the DKI is related significantly to salinity, but not to trawling intensity. Among the indicator components, the species diversity and sensitivity indices used in the DKI are not significantly linked to trawling, and trawling only affects the BQI when species sensitivities are derived from rarefied samples. Because the number of species recorded per sample (species density) is limited by the number of individuals per sample (density), we expect species density and density to be positively correlated. This correlation was confirmed by a simulation model and by statistical analysis of the bottom samples in which log species density was highly significantly related to log density (r = 0.75, df = 144, p < 0.001). Without accounting for the effect of density on species density, indicators based on species density will be affected by temporal and spatial variations in density linked e.g. to variable recruitment success. When this variation is accounted for by random year and station effects we find log trawling intensity to explain more of the variation in log density than in the indicators currently used to monitor Good Ecological and Environmental Status in the Kattegat. Disregarding random effects and the relationship between density and species density, the impacts of bottom trawling are likely to be lost in the translation of ecological quality into macrobenthos indicators. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fish richness from eDNA or visual surveys was compared at various spatial scales. • eDNA captures the highest richness at α and γ scales; visual surveys underestimated it. • All methods reveal the same spatial patterns of β -diversity. • None are exhaustive in getting α richness, but visual surveys best reflect benthos. • Questions motivate methods; the risk of combining them should be fully considered. Environmental DNA (eDNA) metabarcoding emerges as a powerful method, allowing a more exhaustive investigation of fish fauna than any other methods. Yet, the general use of eDNA as a replacement of traditional methods such as visual surveys or physical sampling remains debatable. Therefore, a prior understanding of eDNA's spatial resolution is necessary. This study aimed to compare the assessments of fish diversity at three spatial scales by eDNA, underwater visual census (UVC), and diver-operated video (DOV) surveys across 21 reef sites in northern Taiwan. The specific objectives were to explore the regional species pool (γ-diversity), reveal spatial patterns of fish assemblages (β-diversity), and disentangle the relationships between fish assemblages and benthic composition (α-diversity). At the γ-diversity level, a total of 438 marine fish species were detected across methods. eDNA exhibits an extraordinary power to explore the regional species pool given sufficient replication, a power which is unachievable by DOV and UVC. At the β-diversity level, all the methods successfully revealed the same spatial patterns of beta diversity and the distance decay of similarity in fish assemblages. At the α-diversity level, none of the methods is capable of investigating the entire resident fish fauna, but visual surveys are more suitable for scrutinizing interactions between fish and benthos. Instead of undiscriminatingly recommending a combination of eDNA with traditional survey methods, we suggest implementing specific surveys in accordance with the ecological questions of interest. [ABSTRACT FROM AUTHOR]

[Display omitted] • eDNA metabarcoding was gradually applied to investigating estuarine fish diversity. • 156 fish taxa were detected by eDNA metabarcoding and gillnetting. • Significant/highly significant seasonal differences were found for both methods. • More species obtained by eDNA than gillnetting, with significant differences. Non-destructive and cost-effective fish diversity monitoring approaches are needed for the management and protection of estuarine ecosystems. Environmental DNA (eDNA) technology is a promising, environmentally friendly technology that has been applied in fish diversity studies in estuarine ecosystems. In this study, we investigated the seasonal composition, diversity, and structure of fish community in the Pearl River Estuary (PRE) using eDNA technology and gillnetting. We identified 156 fish in the PRE, including 26 orders, 58 families, 93 genera, and 115 species according to eDNA technology. And eDNA technology provided more taxonomic composition information in the PRE than did gillnetting. Significant or highly significant seasonal differences in fish community composition and structure were detected between the wet and dry seasons. Fifteen and eight genus-level indicator taxa differed significantly between the two seasons according to eDNA technology and gillnetting, respectively. However, the significant differences detected in this study suggest that some taxa did not overlap between the two approaches. Therefore, fish diversity monitoring in the PRE should include a combination of eDNA technology and gillnetting for comprehensive fish community data analysis. Our findings have important implications for fish community monitoring and estuarine ecosystem management. [ABSTRACT FROM AUTHOR]

• Two site-groups were classified, corresponding to upstream-tributaries and mid-downstream. • Altitude and the proportion of substrate composition were major environmental variables influencing the spatial patterns of fish assemblages. • Compared with natural riverine conditions, reservoirs and dams seemed to affect fish communities to a small extent. • To protect the fish diversity of Anning River, construction of hydropower stations and sand extraction activities should be managed. In order to explore the spatial layout of fish assemblages and their related environmental factors, a survey of species composition was conducted in the Anning River. From 2018 to 2021, 28 sites at 987–2,077 m in altitude were surveyed, gathering 64 species in total, of which 60 were native and 4 were exotic. Fifteen of the species sampled were indigenous to the upper Yangtze River, and two were classified as critically endangered or endangered. Fish communities displayed significant upstream-to-downstream variation. There are two site-groups, one covering upstream and tributaries and the other covering midstream and downstream. The upstream-tributary fish assemblages had a dominance of Nemacheilidae and Schizothoracinae, which are plateau species with habitat preferences for boulders and fast-flowing water. Conversely, the mid-downstream fish assemblages had a dominance of Gobioninae, Cyprininae, Bagridae and Siluridae, which are common river species that prefer slow-flowing water. The spatial patterns of these fish communities were chiefly affected by altitude and substratum composition. The fish assemblage pattern was consistent with the zonation concept because the fish communities changed abruptly and clearly along the upstream–downstream axis. The findings of this study offer a crucial research foundation for comprehending the fish assemblages of mountainous rivers, which will be conducive to biodiversity management and habitat preservation of aquatic species. [ABSTRACT FROM AUTHOR]

• Ecological uniqueness is jointly shaped by species sorting and dispersal limitation. • Ecological uniqueness can be explained by species richness and functional features of single site. • Species with intermediate occupancy, high abundance and low niche position contribute more to β diversity. • Ecological uniqueness could be useful in guiding biodiversity conservation and management. Understanding the patterns and ecological determinants of β diversity in freshwater ecosystems is fundamental to biogeography, conservation biology, and environmental management. It has been proposed that β diversity can be divided into contributions of individual sites (LCBD) or species (SCBD) to total β diversity. However, the patterns and underlying mechanisms of LCBD and SCBD remain understudied in freshwater fish. Here, using fish assemblages sampled from the Chishui River basin, we analysed β diversity based on both abundance and presence-absence data. We also examined the relationships between LCBD and SCBD with site (i.e., community abundance, species richness, functional diversity indices, environmental factors, and spatial variables) and species (i.e., occupancy, total abundance, niche position and breadth, and functional traits) characteristics, respectively. Our results revealed that fish LCBD in the Chishui River basin was well explained by both environmental and spatial factors. Fish LCBD was negatively related to species richness and community abundance, showing that sites with high ecological uniqueness generally supported low fish richness and abundance. Furthermore, functional features of fish assemblages were also significantly associated with LCBD, with high LCBD associated with high functional specialization, originality, and uniqueness, but low functional richness, divergence, and dispersion. Abundance-based SCBD showed positive relationships with both occupancy and total abundance, whereas there were hump-shaped relationships between presence-absence SCBD and occupancy and total abundance. Niche position was negatively correlated with SCBD, whereas niche breadth and functional traits were not significant correlates of SCBD. Overall, this study suggests that understanding contributions of sites and species to β diversity is key to understanding biodiversity variation and its applied repercussions. Our results advocate the importance of environmental conditions and between-site connectivity for effective conservation of riverine fish diversity. Moreover, a simultaneous application of LCBD, species richness, SCBD, and rare species would be the most suitable approach for biodiversity conservation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Small pelagic fish blooms in Beibu Gulf occurred in summers of La Niña years. • Japanese jack mackerel and Japanese scad contributed to the blooms. • Higher densities, smaller body sizes, and later spawning times followed La Niña events. • The blooms affected abundance, diversity, and spatial pattern of the fish community. Marine ecosystems are a primary conservation concern because of the separate and synergistic effects of overfishing and climate change on their productivity and biodiversity. For the purpose of implementing ecosystem-based fisheries management, it is essential to understand how fish stocks respond to climate change in marine ecosystems, especially those that have been overexploited. The Beibu Gulf in the northwestern part of the South China Sea has long been one of China's major fishing grounds. After the collapse of the demersal ecosystem in 1990 s, small pelagic fishes, including Japanese jack mackerel (Trachurus japonicus) and Japanese scad (Decapterus maruadsi), have occupied a more-important ecological niche in this gulf. However, insufficient research on how small pelagic fish respond to climate change creates great uncertainty for implementing the current management measures. This study used fish data of trawl surveys and environmental data to investigate possible mechanisms leading to dramatic fluctuations in small pelagic fish populations and their possible effects on the Beibu Gulf marine ecosystem. Abnormal blooms of small pelagic fish, especially T. japonicus and D. maruadsi , occurred following four La Niña events (in 2007/2008, 2010/2011, 2011/2012, and 2020/2021). Moreover, the dominant fish species shifted observably and regularly, Shannon–Wiener diversity and Pielou's evenness decreased significantly in the northeastern coastal waters of the gulf, and the spatial pattern of the fish community was reorganized in this ecosystem. The small pelagic fish blooms in summers probably resulted from a combination of climate change, overfishing, and a summer fishing moratorium, which thereby caused a series of responses in the marine ecosystem. Fluctuations in the small pelagic fish populations after La Niña events seemed more dramatic after the collapse of demersal fish stocks. Therefore, we emphasize the need for implementing ecosystem-based, preventive, and adaptive fisheries management. [ABSTRACT FROM AUTHOR]

• Upland streams of New England frequently experience low pH, high inorganic Al conditions. • Acid-Al conditions are related to season, site buffer conditions and elevation. • Fish diversity and abundance is reduced at sites with high acid-Al. • Salmonid gill Al accumulation is significantly increased at sites with high acid-Al. • Elevated acid-Al impairs osmoregulatory proteins of Atlantic salmon. In spite of overall improvements in air and water quality, biological stress from low pH and high concentrations of inorganic aluminum continue to impact fish and fish habitat in northeastern North America, with independent and interactive effects on individuals, populations and communities. Integrative indicators can therefore be useful in monitoring both impact and recovery across multiple scales. Using coupled water chemistry (pH, conductivity, and base cation and inorganic aluminum concentration), geographic (site elevation and watershed area) and biological (fish diversity, fish abundance, gill aluminum concentration and gill physiology) data, we developed an integrated indicator of acid-aluminum stress across the White and Green mountains in central New England, USA. As has been established in a number of previous studies, preliminary analysis clearly indicated that across all sites, inorganic aluminum concentration was consistently greatest during the spring season. Structural Equation modeling (SEM) revealed that toxic conditions (concurrent low pH and high concentrations of inorganic aluminum) were well summarized with an integrated toxicity score, related to both base cation concentrations and elevation, with sites at higher elevations more likely to experience toxic conditions as well as low base cation concentrations. Fish diversity and abundance generally trended negatively with toxicity score, with fewer cyprinids and sculpins at high toxicity score sites. In spite of considerable variation among individuals, gill aluminum was positively related to toxicity score for both Atlantic salmon and brook trout. Observed elevated gill aluminum levels associated with reduced gill metabolic activity in Atlantic salmon smolts from impacted systems likely result in impaired osmoregulatory function and seawater tolerance. Overall, our results suggest that the integrated toxicity score metric is associated with a syndrome of acute physiological stress, reduced abundance, and low species diversity for sensitive stream fishes in New England, and can likely serve as a reliable indicator of continued impairment or recovery of acid-aluminum vulnerable systems in this ecoregion. [ABSTRACT FROM AUTHOR]

• Urbanization is one of the critical factors affecting fish assemblages. • Native invasive species are also critical to affecting biodiversity. • Changes in functional diversity were related to the urbanization indicators. Understanding human-induced changes in biodiversity and the environment can provide important references for managing and conservating freshwater fish. To date, most studies on the influence of urbanization on fish assemblage diversity have focused on large rivers, estuaries, and urban ponds; the process and mechanism of urbanization driving diversity changes in fish assemblages in headwater streams are unclear. We assessed the effects of urbanization on the taxonomic and functional alpha and beta diversity of fish assemblages in the headwater streams of the Xin'an River in China. Our results showed that compared with natural segments, urban segments had higher species richness and lower functional richness, which resulted from the gain of native invasive species and the loss of endemic species; fish assemblages also became taxonomically differentiated but functionally homogenized. In addition, ΔFD (difference value in functional beta diversity between urban and natural segments) was significantly positively correlated with ΔTD (difference value in taxonomic beta diversity between urban and natural segments), whereas only ΔFD was significantly negatively related to the urbanization indicators (e.g. urban land use and ammonia nitrogen concentration). Thus, a combination of taxonomic and functional diversity indices better reveals how fish biodiversity responds to urbanization. Our study provides evidence of urbanization-induced changes in fish assemblages as well as early warning signs for urban-disturbed ecosystems, both of which will benefit fish conservation in headwater streams. [ABSTRACT FROM AUTHOR]

Multimeric index based on fish composition was used to assess integrity of shallow and wadeable streams of lower Himalayas in temperate and subtropical ecoregions. Streams were surveyed for biotic and abiotic sampling during base flow periods in pre and post monsoon seasons in 2007 and 2008. Twenty three metrics were computed based on taxonomic richness, trophic composition, habitat preferences, abundance, stress tolerance and species origin attributes of 19 fish species. Candidate metrics were analyzed for efficiency to discriminate degraded sites from non-degraded and redundancy analysis, which sorted 71% of omnivore individuals (excluding intolerant species), 40% of intolerant individuals, 44% of herbivore individuals (excluding benthic species), abundance and 44.5% of non-native individuals as potential metrics. IBI values at forest, agriculture and urban zones were ranged between (max–min) 9.9–3.22, 6.18–2.49 and 4.43–0.69 respectively. Results suggested that poor ecological conditions in streams were generally related to drainage of urban sewage and habitat fragmentation while agriculture land use seems to have moderate impact on ecological integrity of the streams. Less urbanized upstream with grasslands and forests as land use, showed excellent to good ecological integrity of the streams. Proposed index was able to distinguish varying degrees of human impact on ecological integrity of streams and thus index could be used as valuable tool for bioassessment of regional flowing water resources. [ABSTRACT FROM AUTHOR]

IndiSeas (“Indicators for the Seas”) is a collaborative international working group that was established in 2005 to evaluate the status of exploited marine ecosystems using a suite of indicators in a comparative framework. An initial shortlist of seven ecological indicators was selected to quantify the effects of fishing on the broader ecosystem using several criteria (i.e., ecological meaning, sensitivity to fishing, data availability, management objectives and public awareness). The suite comprised: (i) the inverse coefficient of variation of total biomass of surveyed species, (ii) mean fish length in the surveyed community, (iii) mean maximum life span of surveyed fish species, (iv) proportion of predatory fish in the surveyed community, (v) proportion of under and moderately exploited stocks, (vi) total biomass of surveyed species, and (vii) mean trophic level of the landed catch. In line with the Nagoya Strategic Plan of the Convention on Biological Diversity (2011–2020), we extended this suite to emphasize the broader biodiversity and conservation risks in exploited marine ecosystems. We selected a subset of indicators from a list of empirically based candidate biodiversity indicators initially established based on ecological significance to complement the original IndiSeas indicators. The additional selected indicators were: (viii) mean intrinsic vulnerability index of the fish landed catch, (ix) proportion of non-declining exploited species in the surveyed community, (x) catch-based marine trophic index, and (xi) mean trophic level of the surveyed community. Despite the lack of data in some ecosystems, we also selected (xii) mean trophic level of the modelled community, and (xiii) proportion of discards in the fishery as extra indicators. These additional indicators were examined, along with the initial set of IndiSeas ecological indicators, to evaluate whether adding new biodiversity indicators provided useful additional information to refine our understanding of the status evaluation of 29 exploited marine ecosystems. We used state and trend analyses, and we performed correlation, redundancy and multivariate tests. Existing developments in ecosystem-based fisheries management have largely focused on exploited species. Our study, using mostly fisheries independent survey-based indicators, highlights that biodiversity and conservation-based indicators are complementary to ecological indicators of fishing pressure. Thus, they should be used to provide additional information to evaluate the overall impact of fishing on exploited marine ecosystems. [ABSTRACT FROM AUTHOR]

The influence of variations in sampling unit dimensions on the assessment of fish species structuring has been widely documented. However, this issue has been restricted to a very limited range of community and population indices (mainly species richness and density). Here, we have investigated this issue through the analysis of 13 diversity indices related to 3 diversity components (number of species, evenness and functional diversity). We analyzed a large set of 257 standardized underwater visual census (UVC) transects dealing with 254 coral fish species. The sensitivity of the indices to the variation in sampling unit dimensions was studied by comparing a range of 55 couples of transect length and width representing 34 sampling surfaces. We found that the extent and profile of the sensitivity to changes in transect dimensions strongly varied both from one index to another and from one dimension to another (length and width). The most sensitive indices were more strongly impacted by variation in length than width. We also showed that for a fixed transect surface, the couple of chosen length and width may alter the assessment of indices related to each of the three main diversity components studied. Some widely used diversity indices, such as species richness and Shannon index, appeared to be very sensitive to changes in transect length and width. In contrast, while still very little used in coral fish studies, two functional diversity indices (FDiv, FEve), and to a lesser extent an evenness index (Berger–Parker), remained robust in the face of change in sampling dimensions. By showing that the variation in sampling dimensions (length, width and surface) may impact diversity indices in a contrasting manner, we stress the need to take into account the sensitivity of the indices to this criterion in the process of selection of the indices to be analyzed in diversity studies. Finally, we found that 30 m long*5 m wide transects might be a suitable compromise size for assessing the patterns of each of the three major complementary components of coral fish diversity. [ABSTRACT FROM AUTHOR]

Changes in land use have manifold effects on stream ecosystems. Consequently, the degradation of watersheds can cause extreme responses if the resilience of the stream is exceeded, triggering changes in fish communities and a reorganization of the ecosystem. Fish community surveys are frequently used to evaluate the impact of anthropogenic pressures on freshwater streams. Dynamic indices such as individual growth are also interesting because they integrate the effects of environmental conditions through time, providing an assessment in the long term. In this study we have investigated the ecological implications of watershed land use cover on fish diversity and growth of the generalist species Umbra limi (central mudminnow) in six streams in Southern Ontario (Canada). In detail, the growth of U. limi has been explored using a Dynamic Energy Budget (DEB) model, which pursues a mechanistic explanation of the bioenergetics of an individual under different environmental conditions. Given the mechanistic approach, the outcomes of the DEB model can provide a solid foundation for extrapolating the conclusions of this study to a broader spatial scale. The results of this study reveal that the proportion of modified land use of the watershed (agricultural and urban land) can reach a tipping point beyond which the functioning of the stream abruptly changes. Consequently, land use cover may be used as a precautionary indicator for watershed management. The results also demonstrate that U. limi could be used as a sentinel species to identify potential impacts on fish diversity and size-at-age as a cost-effective indicator for stream monitoring programs. [ABSTRACT FROM AUTHOR]

Lake Malawi is one of the African Great Lakes and is well known for its fish biodiversity which is the greatest in the world for freshwaters. The lake basin is a valuable resource to the riparian countries. Activities associated with the derivation of the values offered by the lake basin, however, result in the generation of wastes and pollutants that also impact on the lake basin. Such anthropogenic activities within the lake basin place considerable strain on the lake system and may lead to the degradation of the lake basin. Proper application of technology can effectively supplement command-and-control measures and economic instruments for better lake basin management. Currently, no comprehensive framework exists to assess the management of the lake basin. Such a framework is necessary to guide managers and policy-makers in the formulation of management plans and strategies for the sustainable management and utilization of the lake basin. We propose an indicator framework for assessing the technology aspect of Integrated Lake Basin Management (ILBM) in the context of the Lake Malawi Basin. We further demonstrate applicability of the proposed framework through a study conducted in the Malawian side of the basin. We applied a five point Likert-type scale in our indicator assessment. Overall, our results show that the technology aspect of the management of the lake basin is weak to moderate. This threatens the sustainability of the lake especially in the areas of solid waste management, sanitation services, pollution control and protection of wetlands and lagoons which performed from very low to moderate. The major challenges are weak institutional capacity, weak regulation enforcement, and insufficient resources. [ABSTRACT FROM AUTHOR]

• Taxonomic families have high potential as surrogates of stream fish diversity. • Cichlidae and Lebiasinidae are potential diversity surrogates in six Amazon basins. • Crenuchidae and Hypopomidae were good diversity surrogates in floodplain basins. • Characidae, Gymnotidae, Rivulidae were good diversity surrogates in upland basins. The reliable identification of the fish species found in Amazonian streams requires a considerable investment of both time and resources, which often hampers the biodiversity pattern mapping and conservation planning. This problem can be overcome using biological surrogates such taxonomic families, this would reduce the number of fish to be identified and thus facilitate the development of studies. The present study analyzes the potential of families as surrogates of the fish diversity of Amazonian streams. For this, we verified the degree of congruence between the distribution of species organized by family and the composition of the assemblage in two different spatial scenarios. At the biome scale, we verified the degree of congruence in the fish faunas of 54 streams located within six drainage basins in Brazilian Amazonia. At the regional scale, we compared the data from the basins located on the lowland floodplain and those at higher altitudes. The Cichlidae and Lebiasinidae were identified as potential biological surrogates at both spatial scenarios, demonstrating more than 80% similarity with species matrix in all the analytical approaches. The families Crenuchidae and Hypopomidae were the most congruent with the fish from the floodplain basins, both were more than 80% congruent with the species matrix. In upland basins, Characidae, Gymnotidae and Rivulidae were highly similar to the species matrix, in particular Gymnotidae and Rivulidae with more than 90% similarity. Overall, we can conclude that the biological surrogacy approach is a potentially valuable alternative for species diversity evaluation of Amazonian streams ecosystems, considering the accelerated loss of the diversity of these systems. [ABSTRACT FROM AUTHOR]

The lower Ebro River (Catalonia, Spain) has a fish community dominated by alien species in both richness (55%) and abundance (78%). This river stretch is regulated by many dams and its flow was severely reduced by increasing water uses. We found strong evidence that the success of establishment and dispersal of alien fish species in this Mediterranean large river is enhanced by flow reduction through decreased water flow velocity in the littoral zone. Results show that when water flow is below 0.40 m/s, the probability that a fish community is dominated by alien species is higher than 50%, according to a logistic regression model that achieved 91% of well classified cases when predicting alien species dominance over natives. This relationship was used to perform an ecologically-based validation (biological validation) of 12 environmental flows proposed by several authors using different hydrologically-based methods. An HEC-RAS model previously developed and validated by the Catalan Water Agency (ACA) was used to simulate water velocity in the littoral zone. Results show that most of the proposed environmental flows (i.e., 89, 100 and 122 m3/s mean annual flow) favor a fish community structure dominated by alien species. The only biologically-validated environmental flows (227, 302 and 398 m3/s for dry, medium and wet years, respectively) were those based on data from the Sacramento model and calculated with the RVANGPRP method. [ABSTRACT FROM AUTHOR]

• eDNA could be applied to studying fish diversity in river–lake connected system. • The results of eDNA reflect the spatial variation of fish diversity. • eDNA enhances the ability to monitor fish diversity in waters. • Composition overlapped but there are significant differences in relative abundance. • Hydrological connectivity helps maintain stable fish diversity. With the decrease in biodiversity in freshwater ecosystems, the monitoring of fish has become a current research hotspot. The eDNA-based method has been applied to a variety of single-type water systems (i.e., rivers, lakes, or oceans), but it has not been applied to river–lake-connected systems. We collected eDNA from water samples from the Changjiang River–Shijiu Lake connected system (including the lake area, river channel, and river section) and discussed the fish diversity characteristics of the connected system. A total of 180 samples were collected, and the fish community was analyzed using eDNA metabarcoding of the mitochondrial 12 s region. We finally identified 66 taxa of fish, including one at the order level, two at the family level, 9 at the subfamily level, 20 at the genus level, and 34 annotated to the species level. The number of fish species in the river–lake connected system was greater than that in a single-type water system. The lake area, river channel, and river section had a high degree of overlap in fish composition, and the maximum number of fish was in the river section. There was no significant difference in α diversity index among the three types of waters, but there were significant differences in fish relative abundance, which was dominated by different species. The distribution of three migratory fish (Elopichthys bambusa , Ctenopharyngodon idella , and Hypophthalmichthyinae sp.) accorded with the unique life history migration strategy in the middle and lower reaches of the Changjiang River. Our results provide detailed data on fish diversity and have important implications for the long-term management and conservation of river–lake connected systems in the lower reaches of the Changjiang River. Our research further proves that eDNA can be used to monitor the biodiversity of river–lake connected systems and reflect their spatial characteristics. As a continuously explored method, eDNA shows great potential in the study of fish diversity in river–lake systems. [ABSTRACT FROM AUTHOR]

• eDNA can be transported on several kilometers in lotic environments. • Dilution and dispersion show effect on eDNA relative abundance after 100 m. • eDNA metabarcoding can locally document community composition in large rivers. Protection of freshwater fish diversity is a global conservation priority in face of its alarming decline in the last decades. A crucial step to protect freshwater fish diversity is the production of prompt and precise evaluation of community composition and spatial distribution. Metabarcoding of environmental DNA (eDNA metabarcoding) generally surpasses traditional methods for documenting diversity and community composition in aquatic environments. Nevertheless, empirical evidence evaluating how eDNA transportation in water affect community composition and structure via eDNA metabarcoding data remains scarce. Using a brown trout (Salmo trutta) cage transplant experiment in the St. Lawrence River (Canada), a large fluvial system, we tested the detection and relative abundance of species' eDNA along 15 sampling locations. We detected brown trout eDNA in five localities up to 5,000 m from the cage, but only one sampling location situated 10 m downstream and in the direct line of the cage was affected at the community composition level. This locality showed a relative abundance of brown trout eDNA of 13.1%, while the four others showed a relative abundance under 1.0%. K-means cluster analysis confirmed the impact of brown trout eDNA on community composition by separating this locality from all others. Based on species loading of a redundancy analysis, we showed that this different k-means group was associated with the high relative abundance of brown trout. No evidence of transport effect of brown trout eDNA on fish community composition was observed in any other sampling locations. Together, our results support the view that eDNA metabarcoding can be both a conveyor belt of biodiversity information and a precise tool to study the composition and structure of fish communities in river. [ABSTRACT FROM AUTHOR]

Abstract: We developed an approach to quantify early life history diversity for Chinook salmon (Oncorhynchus tshawytscha). Early life history diversity (ELHD) is the variation in morphological and behavioral traits expressed within and among populations by individual juvenile salmon during downstream migration. A standard quantitative method does not exist for this prominent concept in salmon biology. For Chinook salmon, ELHD reflects the multitude of possible strategies undertaken during the juvenile (fry through smolt) phases of their life cycle, where a life history strategy (or pattern) describes the combination of traits exhibited by an organism throughout its life cycle. Increasing life history diversity to improve resilience and aid recovery of diminished salmon and steelhead populations is a common objective in fish population recovery efforts. In this paper, we characterized early life history traits and prioritize timing and fish size as two appropriate, measurable dimensions for an ELHD index. We studied diversity index literature, identified an indexing approach based on the effective number of time-size trait combinations, and tested several candidate indices for performance and usefulness in case studies using juvenile salmon catch data from the lower Columbia River and estuary. The recommended ELHD index is diversity expressed as the effective number of time-size trait combinations for the Shannon Index, modified to include an adjustment for missing time-size trait combinations and a sample coverage factor. This index applies to multiple life history strategies of juvenile salmonids; incorporates fish abundance, richness, and evenness; and produces readily interpretable values. The ELHD index can support comparisons across like locales and examinations of trends through time at a given locale. It has application as a high-level indicator to track trends in the status of the recovery of salmon and steelhead populations in the Columbia River basin and elsewhere where salmon recovery efforts are under way. [Copyright &y& Elsevier]

[Display omitted] • Spatial and temporal distribution change of 21 fish species were modeled using MaxEnt. • Fish habitats would move poleward with a projected mean distance of 110–206.5 km. • Species richness may decrease in the south and increase in the north in the seas of China. • Species turnover is the main component that will promote species community change. • Yangtze River Estuary is probably a geographical barrier for species migration. Long-term habitat shifts in marine fishes under climate change have been discussed over the last few decades. However, there is still a limited understanding of how fish distribution and biodiversity patterns will change in the offshore areas of China over time. In the present study, the potential distributions of 21 important marine fishes under current conditions and two climate change scenarios up to the 2050 s were projected using the maximum entropy (MaxEnt) model. The predicted habitat shifts were further used to observe how future environmental changes would affect communities. By the 2050 s, nine out of 21 fish species may have reduced habitats, which were considered as potential loser species in adapting to climate change, while the other 12 fish species were considered as winner species. The habitats of 20 species were predicted to move northward, with a mean habitat centroid shifting distance from 110 to 206.5 km. A novel discovery is that the Yangtze River Estuary is probably a geographical barrier for the northward migration of some species. An asymmetry in the habitat range shift was observed within the study region, wherein the leading edge moved 1° faster than the trailing edge. The Beibu Gulf, Pearl River Estuary, Southwest Taiwan Strait, and Yangtze River Estuary were identified as fish refuges, indicating that large river estuaries and upwelling systems may have positive effects on reducing the vulnerability of biological communities to climate change. At the community level, species richness would be reduced at lower latitudes, while it would be increased at higher latitudes, and species turnover was the main component of temporal beta diversity. Our study provides an informative outlook on the impact of climate change on the distribution and biodiversity of marine fish species in China, supporting the adaptive conservation and management of fish habitats. [ABSTRACT FROM AUTHOR]

Abstract: River obstacles are recognised as being among the serious ecological concerns, having negative effects on biodiversity and ecosystem functions. They have been shown to affect fish community structure, which represents a fundamental component of the biological integrity of riverine ecosystems. However, a general quantitative relationship that links the response of fish community structure to river obstacles across larger spatial scales is lacking. We assessed young of the year (YOY) fish (27,596 specimens and 35 species) from a total of 54 study sites distributed across three international river basins. The YOY fish community structure was expressed as the probability of habitat-related guild dominance. We also examined the indicative value and responsiveness of two large spatial-scale, fish-based indices of biological integrity (IBI), the European Fish Index (EFI) and the Czech multi-metric index (CZI). We analysed two types of obstacles (1118 weirs and 28 dams for a total of 2126 obstacles) for which numerical and distance-related descriptors were derived using a geographic information system (GIS). All the obstacles considered together were found to be the most relevant predictor of YOY fish community structure response. The negative impact on YOY fish (a loss of rheophilic species and low IBIs values) increased with the increasing number of obstacles and the decreasing relative distance between two consecutive obstacles, indicating the habitat quality and availability and the poor connectivity of particular watersheds. This investigation allowed us to identify the functional and numerical responses of the YOY fish community structure to river obstacles across hydrological networks. Our results contribute an important prerequisite to river restoration efforts, identifying where in the hydrological networks either ecological studies or restoration actions would produce the most effective results. [Copyright &y& Elsevier]

• Functional diversity of freshwater fish assemblages in Chile varies across latitude. • Exotic freshwater fish species modify the functional diversity on Chilean watersheds. • Changes in functional diversity components in fish assemblages are decoupled. In the freshwater basins of central Chile, 28 exotic species have been introduced, which have contributed to increase taxonomic diversity. Nevertheless, how these species have modified the components of functional diversity in these assemblages, a key aspect in learning about their present and future stability within an ecosystem, is unknown. In this study, we analyzed how the introduction of exotic species affects the functional diversity components of richness (FRic), divergence (FDiv), specialization (FSpe), and functional originality (FOri). Additionally, we simulated the effect of the loss (extinction/extirpation) of threatened native species. To do so, we gathered information on the distribution and functional characters of native and exotic species. Through Principal Coordinates Analysis (PCo), we obtained three independent axes (PCoA1, PCoA2, and PCoA3), which allowed us to define a multidimensional space and then to calculate FRic, FDiv, FSpe, and FOri. Our results indicate that richness and functional originality have increased significantly with the introduction of exotic species (263% and 32%, respectively). In contrast, functional divergence and specialization have remained the same. The possible extinction of threatened native species may promote increases in functional originality, decreases in functional richness and divergence, and unchanged functional specialization. On the other hand, a subset of exotic species presents novel features, while another shows redundant features with native ichthyofauna. We emphasize that the possible extinction of native species currently classified as threatened may lead to the disappearance of unique functional groups, which puts at risk the persistence and stability of these assemblages. [ABSTRACT FROM AUTHOR]

[Display omitted] • Predictive powers of four statistical modelling methods were compared. • Artificial neural networks best modeled relations between species and environment. • Artificial neural networks and mixed models are equally good predictors of diversity. • Feature selection is an important step for building predictive models. Over the past several decades, ecologists have been striving to develop models that accurately describe species-habitat relationships across ecological communities. Statistical models that explain ecological dynamics need to consider the nuances of the complex interactions between communities and ecological factors. Here, we used multiple linear mixed models (LMM), generalized additive models (GAM), multivariate adaptive regression splines (MARS), and artificial neural networks (ANN) to model species richness and diversity of freshwater fishes in eastern and central India. The models were based on fish abundance and associated ecological data over three years across the study regions. We developed global models using all predictors after removing highly correlated variables (Pearson's r > 0.7). Results revealed conductivity, water temperature, and water velocity as the most important predictive factors of both species richness and diversity. We, then, built two subsets of selected factors to build predictive models for diversity and richness- one variable set containing common significant factors as revealed from the four different modeling methods used and the second, using an automatic feature selection technique. Amongst the modeling methods used in our study, ANN was found to create the best fit models for explaining nonlinearities between response variables and predictors. The importance of variable selection is highlighted, given that subset 1 (common consensual factors) creates more homogeneity in predictions compared to using subset 2 (automated feature selection). Contrary to similar studies in recent years, which show machine learning (ML) methods to typically outperform conventional methods, our results revealed that ANN performed at par with other methods in terms of predictive power. Our findings underline the need for a judicious choice of modeling techniques based on the availability of the data and the ecological communities being studied. [ABSTRACT FROM AUTHOR]

• Forage fishes constitute key species in marine food webs and their biomass largely fluctuates between years. • The Magellanic penguin is a conspicuous top predator of the Southwest Atlantic Ocean that feeds upon forage fish. • Magellanic penguin isotopic niche size increases with decreasing abundance of forage fish. • Magellanic penguin trophic preferences indicate the abundance of forage fish. As marine ecosystems are harvested or modified by anthropogenic or natural factors, there is an increasing demand for indicators of trophic web health or status. The Magellanic Penguin (Spheniscus magellanicus) is a widely distributed species that forages in the Patagonian Shelf. During breeding, this species is a central-place forager that feeds mainly on schooling fish, with Argentine anchovy (Engraulis anchoita) being the dominant prey in the north and Fuegian sprat (Sprattus fuegensis) in the south of the Argentine Patagonian distribution (40–55°S). Like most forage fish, both prey species display large natural interannual recruitment fluctuations. We used stable isotope analysis of adult Magellanic penguin blood obtained at twelve colonies along its Patagonian latitudinal range to assess changes in isotopic niche and in trophic level as a response to interannual changes in abundance and spatial segregation of forage fish size classes, respectively. Magellanic penguins showed large isotopic niche fluctuations among breeding seasons, explained by the contribution of forage fish in their diet. Furthermore, the size of the isotopic niche negatively correlated with forage fish biomass estimated from acoustic surveys and with their contribution in penguin diet. We defined an isotopic niche size threshold that indicates low abundance of forage fish in nearby feeding grounds. In addition, the trophic level of Magellanic penguins increased with latitude, which corresponds to the size-distribution of both main forage fish species, showing that penguins from different colonies target different size classes of their main prey. We present here a simple and easy to implement indicator to monitor the status of the base of the food web in one of the most productive marine areas in the world, which constitutes the feeding ground of a diverse group of high trophic level predators and sustains large-scale fisheries. [ABSTRACT FROM AUTHOR]

• Introduces ensemble modelling framework combining generalized linear models (GLM), Bayesian modelling, and Bayesian structural equation modeling (SEM) to assess impacts of ecological disturbances. • Explores the response of the sport fish and forage fish communities to a non-toxic brown algal bloom resulting in a fish kill. • Strong positive correlation exists between sport fish and forage fish abundance during the bloom. • Following the fish kill, the forage and sport fish communities were less strongly linked as compared to non-disturbed years. Ecological disturbances may result in mortality events that alter biotic communities and ecosystems. In many coastal zones disturbances are increasing, including algal blooms and fish kills. These two disturbances are often related, with blooms releasing toxins or depleting oxygen, ultimately killing fish. Depending on the intensity, duration, and geographic extent of an algal bloom, the fish community can take days to years to recover from disturbances. To explore the relationship among environmental disturbances, sport fish, and forage fish communities, this study examines a non-toxic brown algal bloom (Aureoumbra lagunensis) occurring from December 2015 through March 2016. Using an ensemble modelling framework combining generalized linear models (GLM), Bayesian modelling, and Bayesian structural equation modeling (SEM), this complementary framework helped elucidate complex relationships among environmental variables and the fish community following a disturbance. The algal bloom crashed over a three-day period in March 2016 and resulted in a fish kill when dissolved oxygen concentrations dropped below hypoxic levels (DO < 2 mg/L). The bloom and subsequent fish kill led to shifts in both forage and sport fish communities, and their relationships, when compared to non-disturbed years. Both sport fish and forage fish abundances decreased following the bloom, but the response of the forage fish community was more rapid. When looking at direct correlations between individual sport fish and forage fish community metrics during the bloom, a large amount of variation in sport fish abundance was explained by forage fish abundance (R2 = 0.34). Also, the variation in forage fish abundance was explained well by pH (R2 = 0.72). Forage fish community dynamics were more closely related to water quality metrics than sport fish communities during non-disturbed periods. However, during this algal bloom, sport fish community dynamics were more closely associated with water quality metrics than forage fish community dynamics. Furthermore, sport fish community dynamics were strongly related to bloom dynamics during the three months prior to the fish kill. In the three months following the kill, the forage and sport fish communities were less strongly linked than in non-disturbed years. These large shifts in community dynamics and relationships following a disturbance suggest both forage and sport fish communities, food webs, and trophic dynamics may be at increasing risk of crossing ecological thresholds as algal blooms become more common in coastal ecosystems. [ABSTRACT FROM AUTHOR]

[Display omitted] • We studied recent littoral and subfossil diatoms in a high mountain lake (Alps). • The sensitive low-profile life-form decreased after fish introduction. • Species more competitive under higher nutrient levels increased. • Some of these effects could as well have been caused by grazing and global warming. • We acknowledge the typical complex-interaction pattern among different stressors. We investigated modern-littoral and subfossil sediment-core diatoms in the shallow (max depth 6.4 m) high-mountain Lake Balma in the Orsiera Rocciavrè Nature Park (Italian Western Alps). Our study provided evidence that might be related to the response of diatom assemblages to fish introduction, in particular the decreasing of the nutrient-enrichment sensitive low-profile life-form/ecological guild and the increase in species known to react positively to the augmented nutrient availability due to fish excretions (e.g., Fragilaria nanana , Pseudostaurosira brevistriata , Staurosirella neopinnata). We are, however, aware that some of these effects could as well have been caused by pastures and cattle watering, and by increased temperatures due to global warming, and we acknowledge the typical complex-interaction pattern among different stressors. High-mountain lakes are "early warning systems" for the whole alpine system and can contribute valuable information also on the interactions between environmental global changes and anthropogenic impacts. Benthic diatoms, in particular, can provide useful indications on the deleterious effects of non-native fish introduction, cattle grazing, and global warming, and thus support an adaptive and sustainable management of high-mountain lakes for the sake of nature conservation. [ABSTRACT FROM AUTHOR]

• This study firstly reported fish species divresity in the middle and lower Yarlung Zangbo River. • A total of 35 species, including four new species, 14 endemic and five endangered species was collected. • The structure of fish assemblages changed significantly along the longitudinal gradient. • Altitude, channel width and macroinvertebrates density were the main environmental factors determining the fish assemblages. The Yarlung Zangbo River is the largest river on the Tibetan Plateau, which is considered a hotspot of biodiversity conservation efforts. In this study, the fish fauna of the middle and lower Yarlung Zangbo River was investigated, to explore the species composition and spatial patterns of fish assemblages as well as the associated environmental factors. Thirty-four sites across an elevation of 589 to 3410 m were sampled in 2015 and 2016. A total of 35 species—28 native and seven exotic—was collected. Of these species, four were described for the first time, 14 were endemic to the Yarlung Zangbo-Brahmaputra River drainage and five are considered endangered. Cluster analysis revealed significant spatial changes in fish assemblages along the longitudinal gradient. Two site-groups separated by the Yarlung Zangbo Grand Canyon were identified, corresponding to midstream and downstream. In the midstream, fish assemblages were characterized by typical plateau fish species (e.g., Schizopygopsis younghusbandi , Schizothorax oconnori , Triplophysa stenura , Triplophysa brevicauda , Schizothorax macropogon , Triplophysa tibetana and Ptychobarbus dipogon), while in the downstream fish assemblages were characterized jointly by plateau species (e.g., Schizothorax curilabiatus and Schizothorax molesworthi) and oriental species (e.g., Garra tibetana , Psilorhynchus homaloptera , Pseudecheneis sulcata , Exostoma tenuicaudata , Parachiloglanis hodgarti , Neolissochilus hexagonolepis and Garra yajiangensis). Canonical correspondence analysis (CCA) showed that altitude, channel width and the density of macroinvertebrates were the main environmental factors determining the spatial distribution of fish assemblages. This study is an important step towards understanding fish assemblages in the middle and lower Yarlung Zangbo River and will help with future efforts to protect aquatic communities and their habitats. [ABSTRACT FROM AUTHOR]

• Human-caused stressors influence fish species richness and assemblage composition. • Richness and composition expectations vary naturally between different lake types. • Four fish IBIs describe ecological condition in a broad suite of Minnesota lakes. • Ecologically meaningful thresholds identify impaired and exceptional lakes. • Fish IBI scores are strongly correlated with lake eutrophication. Indices of biological integrity (IBIs) have been developed for a wide variety of locales and ecological systems to describe their biological condition. Due to variability in geophysical and chemical conditions, IBIs are often developed regionally and applied to similar ecological systems. Researchers in Minnesota previously developed a fish IBI (FIBI) for lakes; however, its application was limited to lakes 40–200 ha surface area and located in central Minnesota. The objectives of this study were to develop FIBIs and ecologically meaningful thresholds for application to a broader suite of Minnesota lakes with surface areas 40–4,050 ha. Fish communities in 419 lakes throughout Minnesota were sampled using gill nets, trap nets, backpack electrofishers, and beach seines between mid-June and early-September 2005–2013. Fish species were assigned to functional groups based on family, tolerance, primary feeding niche, special habitat use, and whether they were native to Minnesota. Lakes were classified into seven groups based on their geophysical and chemical attributes, and four groups were ultimately used in FIBI development. A suite of potential metrics was evaluated for each of the four FIBIs based on their relationships to measures of human-induced watershed and in-lake stressors and 8–15 were retained for each FIBI. Metrics that were retained were summed, and composite scores were scaled 0–100. Biological Condition Gradient (BCG) models were developed for each FIBI. The BCG models established thresholds for impairment and exceptional condition. The FIBIs and thresholds are being used to guide clean water planning, restoration, and protection efforts and to complement pollutant-based water quality sampling efforts in lakes during the Minnesota watershed assessment process. [ABSTRACT FROM AUTHOR]

• No single method of those 5 examined adequately quantified indicators of fish assemblages. • Trawling detected within canopy species, stationary video favoured supra-canopy species. • UVC detected small fish whereas BRUVs favoured larger individuals. • A combination of two methods including trawling and stationary stereo video was optimal. • Power to detect change in diversity indicators was greatest for trawling and BRUVs. Seagrass fishes perform key ecological roles and are a critical component of many of the world's fisheries. A sound understanding of seagrass fish communities, based on robust methods, is therefore integral for their successful environmental management and conservation. Here we quantitatively compare taxa and size class of seagrass fish assemblages collected using; baited and unbaited remote underwater video (BRUV, URUV), diver operated video (DOV), underwater visual census (UVC) and trawling. We assess comparisons of these methods in terms of biodiversity indicators and power to detect change. All five methods were deployed in coastal embayments dominated by Posidonia spp. and within three marine parks along the south-western coast of Western Australia. Fish assemblages recorded using the different methods separated into two distinct groups; those dominated by smaller and less motile species, that are typically present beneath the canopy among seagrass leaves; and those dominated by larger, faster swimming species present above the seagrass canopy. Trawling provided the most effective method for assessing species within the canopy, including those of conservation concern. Conversely, BRUV followed by URUV recorded the greatest number of individuals, successfully detecting the larger supra-canopy and highly motile species typically omitted by trawling. Both trawl and BRUV methods had a higher power to detect change in species richness of seagrass fishes compared to other methods, even though each method recorded different components of the fish assemblage. Fish assemblages recorded using UVC detected both inter and supra-canopy species, but fish abundances recorded by this method were low compared to trawl and BRUV surveys, resulting in reduced power to detect change in richness. DOV was a comparatively less effective method, recording few fish, as well as low richness and diversity values. The combination of trawling and stationary video techniques, particularly BRUV, provided a two-method combination able to holistically measure commonly used indicators of fish assemblage composition in seagrass habitat. These results demonstrate that careful consideration of the methodology is essential when assessing ichthyofauna in seagrass habitat, particularly when only a single method can be employed. As the extent of methodological influence on recording fish assemblages also varied among the three survey areas, geographical differences in the structure of fish and seagrass communities should be considered when selecting an appropriate sampling method. [ABSTRACT FROM AUTHOR]