Patterns Of Fish Assemblages Research Articles

Navigating the scales of diversity in subtropical and coastal fish assemblages ascertained by eDNA and visual surveys

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.

Longitudinal patterns of fish assemblages in relation to environmental factors in the Anning River, China

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.

Variation in patterns of fish assemblage and their environmental correlates in a tropical river basin from the Gulf of Mexico slope

Abstract Understanding patterns of freshwater fish assemblage structure is key to protect them from ongoing human-induced threats to aquatic biodiversity. Yet, studies on associations between fish assemblages and habitat are lacking from many areas of high diversity in Middle America. We assessed fish assemblage structure and environmental associations from a portion of the Lacantún River sub-basin (Usumacinta River, Chiapas, Mexico). Based on environmental data and 17,462 individuals (56 species, 46 genera, and 22 families) captured from 13 sites sampled between 2017–2019, we found that stream order, distance to the Usumacinta, forest cover, temperature, and dissolved oxygen are key to explaining assemblage composition. Four clusters were found via multivariate regression tree analysis, with stream order and dissolved oxygen as defining variables. Our findings suggest that fish communities remain spatially structured even at small scales, in association to environmental gradients among habitats.

Influence of urbanization on stream fish assemblages in three microbasins in the Upper Paraná River Basin.

The colonization pattern of fish assemblages in streams is often studied in the context of environmental filters. On the other hand, when fish assemblages are subjected to anthropogenic effects, variables associated with environmental quality assume more importance. Therefore, this work evaluated the richness and composition of fish from streams sampled at different urbanization levels, aiming to determine any direct effects on the structure of fish assemblages. To accomplish this, samples were collected from 2003 to 2011 at 31 sites distributed among 3 microbasins in the Rio Ivinhema Basin, Alto Rio Paraná. Based on environmental variables, physicochemical of the water and analysis of the use and occupation of the soil, the microbasins were classified into different urbanization levels (low, medium and high). A total of 4,320 individuals were sampled, out of which 57 fish species were recorded. Sampled sites with medium urbanization level presented higher richness compared to sampled sites with high urbanization level which presented lower richness. Species richness in these sites was explained mainly by water temperature and water velocity. Results confirmed that urbanization does directly affect environmental integrity, which, in turn, can lead to the homogenization of stream assemblages.

Temporal patterns in coral reef fish assemblages with varying disturbance levels: A tale of two National Parks in Hawai´i

Long-term ecological monitoring of coral reefs can reveal the state of the reef communities and responses of different reef components to various pulse and press disturbance events. Here, we describe long-term monitoring of reef fish assemblages from two U.S. National Parks in Hawai‘i, Kaloko-Honokōhau National Historical Park (KAHO) and Kalaupapa National Historical Park (KALA) over the past decade. These two parks experience different anthropogenic disturbances as KAHO is highly accessible with multiple types of adjacent land use while KALA is relatively inaccessible, surrounded by large expanses of native forest, and known for having the highest documented fish biomass within the main Hawaiian Islands. The fish assemblages in KAHO were numerically dominated by small-bodied damselfish Chromis spp. and herbivorous surgeonfishes Acanthurus nigrofuscus, Ctenochaetus strigosus and Zebrasoma flavescens, while those in KALA were numerically dominated by Chromis vanderbilti, A. nigrofuscus, Thalassoma duperrey and Paracirrhites arcatus. Multivariate control charts detected anomalies in the fish assemblages in some years. In KAHO, gradual shifts in the assemblages were detected in recent years due to changes (both increases and decreases) in relative abundances of numerically dominant species including Chromis agilis, C. vanderbilti, A. nigrofuscus, C. strigosus and Z. flavescens. There was a documented reduction in live coral cover in KAHO due to a bleaching event in 2015, and potential delayed effects of the coral mortality on the fish assemblages were found particularly in the North and South regions of the park. In KALA, increases in the abundances of Acanthurus (A. blochii, A. leucopareius, A. nigrofuscus, A. thompsoni and A. triostegus) and C. strigosus were found in 2014, likely due to a large recruitment event that had not been well reported. As localized thermal stress events were detected in both KAHO and KALA in 2019, continuous monitoring of these two parks is critical to assess how the coral-reef ecosystems under two different human-use scenarios respond to repeated heating events and whether there are immediate as well as delayed effects on reef organisms resulting from losses of live coral tissue and a subsequent decrease in structural complexity provided by the coral.

Longitudinal Patterns in Fish Assemblages after Long-Term Ecological Rehabilitation in the Taizi River, Northeastern China

Fish assemblages inhabiting the Taizi River basin have been severely degraded by anthropogenic disturbances, which weaken the basin’s ecological function and limited revitalization of the northeast industrial base. Long-term ecological rehabilitation has been conducted to restore the fish fauna and improve habitat conditions. To explore fish distribution patterns and key factors after this ecological rehabilitation, a comprehensive and detailed survey of fish fauna was conducted twice in 2021 at 33 sampling sites in the Taizi River. A total of 50 fish species from 13 families were collected, and the dominant species were P. lagowskii, Z. platypus, C. auratus and P. parva. Compared to results reported over the last decade, the increasing trend in fish richness and the change in the longitudinal fish organization were detected. The abundance variation for P. lagowskii, Z. platypus, C. auratus, P. parva, R. ocellatus and H. leucisculus along the upstream to downstream axis contributed most to the fish distribution pattern. Species replacement and addition might have jointly caused the longitudinal changes in the fish fauna, but species replacement was the main underlying mechanism. The canonical correspondence analysis (CCA) results show that the fish structure pattern was mainly shaped by cultivated land coverage and urban land coverage. Our study provides reference sites for future fish-based bioassessment and implications for region-specific management in the Taizi River.

Fish Assemblage and In-Stream Habitat Variation in Relation to Dam Structures on the Withlacoochee River, Florida, with Notes on Historical Records

The Withlacoochee River in central Florida is a large blackwater river lacking substantive data on fish assemblage and has undergone extensive hydrological modification since the early 1900s. We compared fish assemblages in river segments above and below 2 major dams by conducting electrofishing surveys between April 2016 and June 2018. We also compiled historical records to assess temporal changes in species occurrence. We found that fish assemblages were significantly different in the lower segment than in the middle and upper segments. The lower segment had the lowest total catch-per-unit-distance and freshwater-fish species richness. Fish assemblage patterns were most highly correlated with Secchi depth, specific conductance, and percent of non-vegetative habitat cover. Much of the variation in fish assemblages among segments was consistent with that observed in undammed coastal rivers, but the lack of estuarine species in upper reaches of our study area suggests that the Inglis Dam may restrict upstream dispersal of these taxa. Comparison of species composition with historical records did not reveal any potential extirpations since 1931, but we recorded 8 marine species and 3 non-native species that were not present in historical records.

Regional patterns in demersal fish assemblages among subsea pipelines and natural habitats across north-west Australia

Regional patterns of fish diversity, abundance, distribution, and assemblage composition are driven by a combination of biotic and abiotic conditions in the marine environment, but these conditions can be altered through anthropogenic activities, such as those associated with oil and gas extraction. The present study utilises data on fish relative abundance and diversity obtained from 1546 baited remote underwater video deployments conducted between 2004 – 2019 in depths of 9 – 170 m across 2000 km of coastline in north-west Australia on natural habitats and subsea pipelines to understand the influence of oil and gas infrastructure on fish assemblages. A total of 450 fish taxa from 56 families was observed, with populations dominated by generalist and invertebrate carnivore taxa. At the regional scale, subsea pipelines had lower diversity (lower taxonomic richness) than natural environments, but possessed a higher abundance of piscivorous and herbivorous fish taxa. Clear patterns in fish assemblage composition were observed in multivariate analyses, reflecting the proximity of oceanic shoals and banks, depth, and to a lesser extent, oil and gas infrastructure. Shallow-water and close to shoals assemblages were characterised by a diversity of site-attached (e.g., wrasses, tuskfish), reef-associated taxa (e.g., emperors). Mesophotic fish assemblages were characterised by commercially important (e.g., goldband snapper), wide-ranging (e.g., sharks) and sand-affiliated (e.g., toadfish, threadfin bream) taxa. Proximity to pipelines and platforms ranked low as predictors in the multivariate analyses suggesting a negligible regional influence of these structures on fish communities in comparison to depth and shoal habitats. Local-scale influences of subsea infrastructure, however, may be important for some fish species (infrastructure vs. immediate surrounds). Our study highlights the influence of abiotic factors on regional-scale patterns in fish assemblage structure across north-west Australia.

Spatio-temporal dynamics of fish assemblage in the Datong and Xiaotong rivers, karst tributaries in the upper Yangtze River drainage: Implications for ecological adaptation and conservation of fish in rivers

The Datong and Xiaotong rivers are karst tributaries in the upper Yangtze River drainage and represent considerable habitat diversity that contributes to high fish diversity and rich fishery resources in the two rivers. During the few decades, fish resources have abruptly declined due to overfishing, water pollution and habitat degradation. In order to further strengthen conservation and restoration of fish resources and provide scientific support for fishery management in these rivers, the temporal and spatial dynamics of fish assemblage in the Datong and Xiaotong rivers were investigated in the present study. A total of 45 species were captured at 30 sample sites during four surveys conducted from March 2016 to January 2017. Species diversity and richness both increased from upstream to downstream in the two rivers. The fish assemblages significantly differed between river reaches, while did not differ in significantly between 4 months. The spatial variations in the abundance of Rhynchocypris oxycephalus, Zacco platypus, Triplophysa bleekeri, Sinogastromyzon szechuanensis, Platysmacheilus nudiventris, Sinibrama taeniatus, Saurogobio gymnocheilus, Pseudorasbora parva, Pseudobagrus truncates and Opsariichthys bidens were considered to contribute most to the spatial pattern of fish assemblages. The lack of a temporal pattern of the fish assemblage in the rivers might be attributed to ecological habits of short-distance migration and diversified mesohabitats with riffles and pools for fish spawning, feeding or overwintering within a very short river range. Our results suggest the spatio-temporal dynamics of fish assemblages is highly adapted to the habitat characteristics in the two karst rivers. We recommend that fish conservation of these tributaries be focused on the mesohabitats, particularly the many pools and riffles.

Temporal and spatial patterns of demersal fish assemblages in the coastal water of Sierra Leone

Information on the temporal and spatial patterns of fish community is key to further understand the functioning of marine ecosystem and protect marine organism resources efficiently. 6 demersal trawl surveys were carried out in the coast water of Sierra Leone during Sep 2019∼May 2021. Obvious temporal and spatial heterogeneity of oceanographic condition were observed in the survey area, the water temperature and salinity were usually higher in dry season and lower in rainy season. A total of 195 species belong to 79 families were identified. Offshore Sciaenid sub-community and Inshore sparid sub-community were the 2 common and major groups identified from 6 surveys, but the composition of dominant species may have changed. Less abundant of some traditional economic species (P. Typ, P. qui, Epinephelus, Arius and Lutjanus) and more abundant of T. myo were caught The Offshore sciaenid sub-community distributed mainly in southeast part or closed to shoreline in north part of survey area. The Inshore sparid sub-community distributed mainly in northwest part. Bottom sediment type (Btype) and depth were the common significant factors for the special pattern of fish community in all surveys. Offshore sciaenid sub-community was always associated with mud substrate and shallow water; Inshore sparid sub-community was associated with sand substrate and most of sites distributed in deeper water. The significant effect of sea surface salinity (SSS) were only observed in Oct, Dec, Jan and May. SSS was filtered as significant environment parameter, may not just base on the effect of salinity on fish community, but SSS was also a better characteristic parameter for monthly fluctuation of oceanographic condition. The increasing fishing activities maybe the one of major disturbance factors to the structure change of fish community. In order to promote the biodiversity conservation, strengthen fishery management based on ecosystem approach and developing sustainable fishery should be advocated.

Taxonomic and functional diversity patterns of stream fish assemblages from Brazilian Atlantic Rain Forest

Disentangling the hierarchical structure of river systems and multi-scale environmental effects is essential for understanding freshwater fish community structure and function. We sampled 70 stream stretches to investigate how the taxonomic and functional composition and diversity of fish assemblages responded to the environment considering a hierarchical organisation of streams in three Brazilian watersheds (Upper Sorocaba, Upper Paranapanema and Upper Ribeira de Iguape). Functional diversity indicated that stream fish community function was independent of the watershed. The most critical environmental variable was substrate gradient. In streams with a consolidated substrate, equitability and functional dispersion were low due to invertivores occurring in this type of substrate. Our results highlight the importance of local environmental filters for shaping streams fish assemblages across different basins. This shaping was more evident when functional descriptors of assemblages were analysed, thereby reinforcing the importance of an approach based on traits as a tool to elucidate local community assembly processes at broader spatial scales.

Structure‐from‐motion photogrammetry demonstrates that fine‐scale seascape heterogeneity is essential in shaping mesophotic fish assemblages

AbstractBenthic components of tropical mesophotic coral ecosystems (MCEs) are home to diverse fish assemblages, but the effect of multiscale spatial benthic characteristics on MCE fish is not well understood. To investigate the influence of fine‐scale benthic seascape structure and broad‐scale environmental characteristics on MCE fish, we surveyed fish assemblages in Seychelles at 30, 60 and 120 m depth using submersible video transects. Spatial pattern metrics from seascape ecology were applied to quantify fine‐scale benthic seascape composition, configuration and terrain morphology from structure‐from‐motion photogrammetry and multibeam echosounder bathymetry and to explore seascape–fish associations. Hierarchical clustering using fish abundance and biomass data identified four distinct assemblages separated by the depth and geographic location, but also significantly influenced by variations in fine‐scale seascape structure. Results further revealed variable responses of assemblage characteristics (fish biomass, abundance, trophic group richness, Shannon diversity) to seascape heterogeneity at different depths. Sites with steep slopes and high terrain complexity hosted higher fish abundance and biomass, with shallower fish assemblages (30–60 m) positively associated with aggregated patch mixtures of coral, rubble, sediment and macroalgae with variable patch shapes. Deeper fish assemblages (120 m) were positively associated with relief and structural complexity and local variability in the substratum and benthic cover. Our study demonstrates the potential of spatial pattern metrics quantifying benthic composition, configuration and terrain structure to delineate mesophotic fish–habitat associations. Furthermore, incorporating a finer‐scale perspective proved valuable to explain the compositional patterns of MCE fish assemblages. As developments in marine surveying and monitoring of MCEs continue, we suggest that future studies incorporating spatial pattern metrics with multiscale remotely sensed data can provide insights will that are both ecologically meaningful to fish and operationally relevant to conservation strategies.

Integration of ABC curve, three dimensions of alpha diversity indices, and spatial patterns of fish assemblages into the health assessment of the Chishui River basin, China.

Index of biotic integrity (IBI) based on fish has been applied globally. However, few have considered that fish assemblages change among different aggregate ecoregions when conducted their health assessment. Indeed, some comprehensive indices, such as functional and phylogenetic diversity indices and ABC curve, can be used to identify aspects that are not captured by traditional metrics. Consequently, we try to integrate comprehensive indices and spatial patterns of fish assemblages to develop IBI systems and then verified their effectiveness and accuracy for assessing the environmental health of the Chishui River basin. The comprehensive disturbance index (CDI), based on 11 water quality parameters and 4 human land use, was set to distinguish reference sites and impaired sites. According to the spatial patterns of fish assemblages, the 40 sites were finally divided into 2 aggregate ecoregions, include wadeable streams and nonwadeable rivers. 97 candidate metrics were selected to develop our IBI systems based on the systematic screening method. The result also showed that our IBI systems performed well in discriminating anthropogenic disturbances at both aggregate ecoregions, which suggests that our systems could provide a reliable evaluation. The mean IBI score of the Chishui River basin was 72.09 ± 16.58, and was classified as good status. However, S1 (Chishuiyuan Town), Baisha River, Tongzi River, and Xishui River were disturbed by various human activities. We conclude that the spatial patterns of fish assemblages should be combined with more comprehensive indices to assess river health. On the other hand, we do believe that the process of developing and verifying our IBI systems could be regarded as a reference for biomonitoring in more mountain river systems.

Nearshore fish assemblage dynamics in southern Lake Michigan: 1984–2016

Many coastal ecosystems, including those of the Laurentian Great Lakes, suffer from various natural and anthropogenic stressors. Given that multiple stressors often concomitantly impact ecosystems, it may be difficult to disentangle which stressors are most influential. Upper trophic level communities, such as fish assemblages, can provide insights to the influence of diverse stressors as they may integrate cumulative effects over the long-term and also reflect responses of lower trophic levels. We used multivariate analyses and assemblage indices to investigate long-term (1984–2016) patterns in a nearshore fish assemblage indexed via annual trawling in the Indiana waters of southern Lake Michigan. Based on observations from other regions of the Great Lakes, we expected that oligotrophication, due to reduced nutrient loading and filtering by invasive mussels, would have a strong influence on the fish assemblage. However, we were unsure if the very nearshore fish assemblage would track observed decreased production patterns in offshore Lake Michigan or if observed increased primary production in the very nearshore would affect the fish assemblage. Consistent with the former expectation, overall abundance and richness of the assemblage declined over time. However, contrary to observations in other regions there was no overall evidence of species tolerant to more eutrophic conditions being replaced by more sensitive species. Moreover, there was limited evidence of the fish assemblage shifting towards species more tolerant of warm water, as might be expected with climate change. While increased numbers of invasive species added species to the system, overall species richness and native species richness declined.

Spatial Patterns of Larval and Juvenile Fish Assemblages in an Eddy Area in the Western South China Sea

The objective of this study was to investigate influence of meso-scale eddies in the western South China Sea on species composition and spatial patterns of fish larvae and juveniles based on the data collected during summer and autumn in 2012. Nintyeight species belonging to 38 families were collected, including 78 species in summer and 41 species in autumn. The dominant species in summer were Vinciguerria sp. (39.70%), Stephanolepis cirrhifer (11.21%), Caranx sp. (5.45%) and Benthosema pterotum (1.97%). The dominant species in autumn were Gobiidae sp. (15.32%), Ceratoscopelus townsendi (7.26%), Diaphus sp. (6.45%), Astronesthes sp. (5.65%) and Callionymidae sp. (4.03%). Abundance of fish larvae and juveniles in summer was higher than that found in autumn. Similarity cluster analysis results indicated that larval fish assemblages in summer can be divided into two communities: (1) larval fish in the cyclonic eddy; (2) larval fish in the anticyclonic eddies. While in autumn, the larval fish assemblages can be divided into three communities: (1) larval fish without influence of the cyclonic eddy; (2) larval fish influenced slightly by the cyclonic eddy; (3) larval fish gathered near the center of the cyclonic eddy. The variations of abundance and assemblage of larval fish might be attributed to sea surface temperature (SST), sea surface salinity (SSS) and sea level anomaly (SLA).

Taxonomic and functional assemblage structure of coral reef fishes from Jardines de la Reina (Caribbean Sea, Cuba)

The Jardines de la Reina (JR) archipelago includes one of the largest marine protected areas (MPAs) in the Caribbean Sea. However, there is limited understanding about the assemblage structure of its coral reef fishes. We aim to (1) describe the spatial patterns of fish assemblages and their potential drivers along the reef system and (2) compare several metrics of assemblages inside and outside the MPA. We surveyed the ichthyofauna at 12 sites (inside and outside the MPA) along ~200 km of reef tract using a diver-operated stereo-video system. We identified 31323 fishes, represented by 95 species and 24 functional groups, including large rare and threatened species of parrotfishes and groupers. The biomass of fishes from the Lutjanidae, Serranidae, and Scaridae families was higher than that in other Caribbean reefs. Site and depth explained the larger fraction of variance in most of the evaluated metrics, suggesting the importance of local environmental heterogeneity. Fish assemblages did not show a significant gradient along the JR tract from the center of the MPA to the periphery. Distance to the center of the MPA explained some of the variability in the abundance, functional richness, and multivariate structure of assemblages. Our results do not show that fish assemblages inside the MPA are healthier than those outside. Instead, the ichthyofauna is abundant and both taxonomically and functionally diverse both inside and outside the MPA probably as a result of a spillover effect. The successful combination of natural and management-associated features likely results in an overall good ecological status of fish assemblages in JR.

Longitudinal patterns in riverine ecology within and among seven Pacific Northwest rivers: Implications for river research, monitoring and management

AbstractRivers vary because of their different geographic settings and their differing levels of anthropogenic disturbances. Relative to wadeable streams, boatable or raftable rivers are much less studied because they require more expensive gear and are more dangerous to sample. Because of the importance of Pacific Northwest rivers for water supply, recreation, and endangered fish species, we selected seven rivers of interest to state, tribal, or federal agencies. Our objectives were to determine the degree to which fish and macroinvertebrate assemblages varied with water quality, habitat structure, and distance along each river, as well as the degree to which each river differed from the others. We sampled the rivers by inflatable rafts and assessed spatial patterns in fish and macroinvertebrate assemblages as well as water quality and physical habitat structure at 20 sites spread out longitudinally along each river. By analyzing site‐to‐site similarity matrices for fish, macroinvertebrates, chemistry, habitat, and river distance, we found that water quality‐river distance relationships were relatively strong, but habitat structure‐distance relationships were usually weak or absent. Also, site‐to‐site similarity in water quality was unrelated to the site‐to‐site similarity in habitat structure. Among‐river variability was much greater than within‐river variability for both fish and macroinvertebrate assemblages. We observed very different patterns among the seven rivers regarding the importance of distance, water quality, and physical habitat similarities relative to fish and macroinvertebrate assemblage similarities. The best set of environmental variables for distinguishing biotic assemblage similarities varied widely among rivers, and among the two assemblage types. We conclude that the riverscape concept is valuable for river monitoring, research, and management, as well as the value of rigorously sampling both water quality and physical habitat as well as both fish and macroinvertebrate assemblages.

Characterizing the spatial signal of environmental DNA in river systems using a community ecology approach.

Environmental DNA (eDNA) is gaining a growing popularity among scientists but its applicability to biodiversity research and management remains limited in river systems by the lack of knowledge about the spatial extent of the downstream transport of eDNA. Here, we assessed the ability of eDNA inventories to retrieve spatial patterns of fish assemblages along two large and species-rich Neotropical rivers. We first examined overall community variation with distance through the distance decay of similarity and compared this pattern to capture-based samples. We then considered previous knowledge on individual species distributions, and compared it to the eDNA inventories for a set of 53species. eDNA collected from 28sites in the Maroni and 25sites in the Oyapock rivers permitted to retrieve a decline of species similarity with increasing distance between sites. The distance decay of similarity derived from eDNA was similar and even more pronounced than that obtained with capture-based methods (gill-nets). In addition, the species upstream-downstream distribution range derived from eDNA matched to the known distribution of most species. Our results demonstrate that environmental DNA does not represent an integrative measure of biodiversity across the whole upstream river basin but provides a relevant picture of local fish assemblages. Importantly, the spatial signal gathered from eDNA was therefore comparable to that gathered with local capture-based methods, which describes fish fauna over a few hundred metres.

Longitudinal drifting pattern of larval assemblages in the lower reach of the Yangtze River: Impact of the floodplain lakes and conservation implementation

AbstractFloodplain lakes are significant lateral habitats that play an important role in structuring larval fish assemblages in large river–floodplain ecosystems. The abundance of floodplain lakes, including both naturally connected and main stem‐isolated lakes, declines in a downstream direction in the lower reach of the Yangtze River, forming a longitudinal reduction gradient. We investigated whether this longitudinal reduction gradient of floodplain lakes is an essential driver of the larval fish assemblage patterns in the river. Drifting larval fish were investigated weekly during the prevailing spawning season both in 2014 and 2015 among three locations at Wangjiang (WJ), Zhenjiang (ZJ) and Nantong (NT). Thirty‐four species belonging to 28 genera and eight families were identified. The number and abundances of collected species, the reproduction duration for dominant species and the niche breadth of dominant species all exhibit a longitudinal decrease (WJ > ZJ > NT) in the downstream direction. Additionally, the bloom of larval fish tended to occur earlier at WJ than at ZJ and NT. We suggest that these results reflect the crucial effect of floodplain lake distribution in shaping the longitudinal distribution pattern of larval assemblages. Both natural connected lakes and isolated lakes (with irregular connectivity patterns) play a crucial role in recruitment success of freshwater fish in the system. Hence, conservation and management approaches for fish resources should be concentrated on restoring and maintaining river–lake connectivity in the upstream sections of the lower reach of the Yangtze River.

Marine fish assemblages of Eastern Brazil: An update after the world's largest mining disaster and suggestions of functional groups for biomonitoring long-lasting effects

When the Fundão dam collapsed in Brazil, 50 million m3 of iron ore tailings were released into the Doce river, resulting in the world's largest mining disaster. The contaminated mud was transported 668 km downstream of the Doce river and reached the Atlantic Ocean 17 days after the collapse. Seven months later, there was evidence that the tailings had reached the largest and richest coral reef formation in the South Atlantic Ocean. This study provides the first description of species composition, abundance, and diversity patterns of fish assemblages in estuaries, coastal areas, and coral reefs affected by the rupture of the mining dam in the Doce river. A linear mixed model (GLMM) was used to evaluate the influence of salinity on fish abundance across estuarine and coastal ecosystems. In addition, based on functional traits related to habitat use and feeding habits, this study identified fish species suitable as bioindicators of the long-lasting effects of this major mining disaster. Bottom trawls were used to sample five estuaries and their respective coastal areas, and a visual census was employed to sample five reef areas, representing an impact gradient. A total of 269 species were recorded in all three habitats, but only seven were shared among them. The results showed lower similarity in assemblages among estuarine areas compared to the coastal and reef areas. Species composition among estuaries and reef ecosystems was more heterogeneous. In contrast, coastal habitats exhibited high homogeneity. Salinity had no statistically significant effect on fish abundance either in estuaries (p = 0.22) and along the coast (p = 0.14). Twelve fish species were identified as suitable bioindicators for evaluating the long-lasting effects of resuspension of contaminated sediments. These species are commonly found in the ecosystems under the influence of the disaster inhabiting potentially contaminated substrates and substrate-associated benthic preys.