Temporal change in urban fish biodiversity-Gains, losses, and drivers of change.

Our aim was to examine temporal change in alpha and beta diversity of freshwater fish communities in rivers that have urbanized over the same period to understand the influence of changes in land use and river connectivity on community change. We used biological (2001-2018), land use (2000-2015), and connectivity data (1987-2017) from Toronto, Ontario, Canada. We used linear mixed effects models to determine the strength of upstream land use, connectivity, and their changes over time to explain temporal change in alpha and beta diversity indices. We examined beta diversity using the temporal beta diversity index (TBI) to assess site-specific community change. The TBI was partitioned into gains and losses, and species-specific changes in abundance were assessed using paired t-tests. There were more gains than losses across the study sites as measured by TBI. We found little to no significant differences in species-specific abundances at aggregated spatial scales (study region, watershed, stream order). We found different relationships between landscape and connectivity variables with the biodiversity indices tested; however, almost all estimated confidence intervals overlapped with zero and had low goodness-of-fit. More fish biodiversity gains than losses were found across the study region, as measured by TBI. We found TBI to be a useful indicator of change as it identifies key sites to further investigate. We found two high value TBI sites gained non-native species, and one site shifted from a cool-water to warm-water species dominated community, both of which have management implications. Upstream catchment land use and connectivity had poor explanatory power for change in the measured biodiversity indices. Ultimately, such spatial-temporal datasets are invaluable and can reveal trends in biodiversity useful for environmental management when considering competing interests involved with urban sprawl in the ongoing "Decade on Restoration."

Unveiling functional linkages between habitats and organisms: Macroalgal habitats as influential factors of fish functional traits.

Understanding the relationship between the characteristics of habitats and their associated community is essential to comprehend the functioning of ecological systems and prevent their degradation. This is particularly relevant for in decline, habitat-forming species, such as macroalgae, which support diverse communities of fish in temperate rocky reefs. To understand the link between the functional habitats of macroalgae and the functional dimension of their associated fish communities, we used a standardized underwater visual census to quantify the macroalgal functional diversity, as well as the functional diversity, redundancy, and richness of fish communities in 400 sites scattered in three southern temperate marine realms. Our findings reveal that functional macroalgal habitats can be classified into three groups that shape the functional diversity, redundancy, and richness of fish when considering trait commonness. These results enhance our comprehension of the functional connections between the habitat and coexisting fish within marine ecosystems, providing valuable insights for the preservation of these habitats.

Characteristics of fish community structure and environmental driving factors in Taihu Lake during the first year of fishing ban.

Taihu Lake has officially implemented the full fishing ban policy since October 1, 2020. We investigated fish community of Taihu Lake in the four seasons of 2020. A total of 42 fish species were collected, belonging to 6 orders, 7 families, and 33 genera. The first five dominant species ranked by the index of relative importance were Coilia nasus, Toxabramis swinhonis, Hypophthalmichthys molitrix, Hypophthalmichthys nobilis, and Salangichthys tangkahkeii. The number of C. nasus accounted for 85.1% of the total number of catches. According to the distributional characteristics of cyanobacterial blooms and aquatic plants, Taihu Lake could be divided into the northern, central, and eastern regions. There was no significant difference in catch per unit effort (CPUE) among different lake regions, but Shannon diversity index and Pielou evenness index in the eastern region was greater than in the other two regions. The CPUE, Shannon diversity index, and Pielou evenness index were significantly different among the four seasons, with the lowest CPUE in autumn and higher diversity in autumn and winter than in spring and summer. Electrical conductivity, water depth, chloride, and transparency were the main environmental factors driving the seasonal variations of fish community in Taihu Lake, while electrical conductivity, dissolved oxygen, total alkalinity, and transparency were key variables driving the spatial patterns. The results could be used as the baseline data for fish community studies in Taihu Lake after the fishing ban.

Heterogeneity of Fish Taxonomic and Functional Diversity Evaluated by eDNA and Gillnet along a Mangrove-Seagrass-Coral Reef Continuum.

The effective and reliable monitoring of fish communities is important for the management and protection of marine ecosystems. Environmental DNA (eDNA) metabarcoding is a relatively new method that has been widely used in recent years, while traditional sampling via fish catching (i.e., gillnets) is one of the most common and reliable fish monitoring methods used to date. We compared the taxonomic and functional diversity of fish detected within a mangrove-seagrass-coral reef continuum using both survey methods. One liter seawater and gillnet samples were collected in August 2021 from mangrove forests, seagrass meadows and coral reef habitats (n = 3 each) in Hainan, China. Surveys using eDNA and gillnets identified 139 genera belonging to 66 families and 58 genera belonging to 42 families, respectively. Regardless of the survey method, fish detected in mangrove, seagrass and coral reef habitats were heterogeneous in their communities; however, the shared species between habitats suggest some degree of connectivity. There were no significant differences between habitats in terms of taxonomic and functional diversity, but a higher taxonomic diversity was detected using eDNA. Both methods were able to distinguish fish assemblages between different habitats; however, gillnet surveys performed better than eDNA surveys for distinguishing mangrove from seagrass assemblages. Therefore, the concurrent use of eDNA and gillnet survey methods provides a more comprehensive approach to understanding the heterogeneity of fish taxonomic and functional diversity along mangrove-seagrass-coral reef continuums.

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

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

Dynamics-based characterization and classification of biodiversity indicators.

Various biodiversity indicators, such as species richness, total abundance, and species diversity indices, have been developed to capture the state of ecological communities over space and time. As biodiversity is a multifaceted concept, it is important to understand the dimension of biodiversity reflected by each indicator for successful conservation and management. Here we utilized the responsiveness of biodiversity indicators' dynamics to environmental changes (i.e., environmental responsiveness) as a signature of the dimension of biodiversity. We present a method for characterizing and classifying biodiversity indicators according to environmental responsiveness and apply the methodology to monitoring data for a marine fish community under intermittent anthropogenic warm water discharge. Our analysis showed that 10 biodiversity indicators can be classified into three super-groups based on the dimension of biodiversity that is reflected. Group I (species richness and community mean of latitudinal center of distribution (cCOD)) showed the greatest robustness to temperature changes; Group II (species diversity and total abundance) showed an abrupt change in the middle of the monitoring period, presumably due to a change in temperature; Group III (species evenness) exhibited the highest sensitivity to environmental changes, including temperature. These results had several ecological implications. First, the responsiveness of species diversity and species evenness to temperature changes might be related to changes in the species abundance distribution. Second, the similar environmental responsiveness of species richness and cCOD implies that fish migration from lower latitudes is a major driver of species compositional changes. The study methodology may be useful in selecting appropriate indicators for efficient biodiversity monitoring.

Impacts of Strong ENSO Events on Fish Communities in an Overexploited Ecosystem in the South China Sea.

To better understand how fish communities respond to environmental changes under extreme climate events, we examine changes in fish communities in Beibu Gulf during strong El Niño and La Niña events. Strong La Niña and El Niño events affect the composition, abundance, and distribution of fish communities in Beibu Gulf. Fish community distribution and composition change before and after La Niña and El Niño events, and dominant species within them change with stable fishing intensity. The abundance and distribution of small pelagic fish such as Japanese jack mackerel (Trachurus japonicus) and Japanese scad (Decapterus maruadsi) are the most affected. Using a generalized additive model (GAM), we explore relationships between the abundance of T. japonicus and D. maruadsi and a suite of environmental variables. The GAM results revealed that sea surface salinity and sea surface temperature best explain changes in catch per unit effort of these two species during a La Niña event; depth, sea surface temperature, and mixed layer depth during an El Niño event. The results obtained in this study will offer support for implementing more-accurate, scientific fisheries management measures.

Exploring fish assemblage structure, feeding guild, and water quality in a typical river-reservoir interface of tropical large reservoir environment, Central India.

The present study aims to understand the spatio-temporal dynamics in habitat ecology and fish assemblage and determine the relationship of habitat transition and fish distribution in a large riverine-reservoir cascade system (Sardar Sarovar Reservoir part in Madhya Pradesh). This study was carried out along a 125-km riverine-reservoir interface (RRI) during 2018-2020. The study showed presence of a total of 110 fish species (104 spp. in upstream main Narmada River stretch excluding reservoirs, 56 in RRI, and 39 in Sardar Sarovar reservoir). We recorded 50 species common in upstream riverine stretch of Narmada and the RRI while RRI uniquely harbored 3 native species (Chitala chitala, Labeo boga, Salmostoma phulo) not previously reported from Narmada River stretch upstream. The similarity percentage (SIMPER) analysis showed presence of S. phulo causing 27.91%, Schistura dayi (3.71%), and Rita pavimentata (3.41%) of dissimilarity among Maheshwar (S1), Rajghat (S2), Koteshwar (S3) non-confluence zone, and Kakrana (S4)-confluence zone. The analysis of data indicated disappearance of some species like deccan peninsular carp Labeo fimbriatus, Mahseer Tor khudree which was earlier reported but was absent in recent years. The statistical correlation of environmental variables with observed abundances of fish feeding guilds showed significant positive correlation with specific conductivity and total dissolved solid content of the water. The canonical correspondence analysis (CCA) indicated association among omnivorous fishes of the reservoir with water temperature; total dissolved solids; specific conductivity; total alkalinity; chlorophyll; and NO3-N. The herbivore fishes were found to be more associated with magnesium, dissolved oxygen, and phosphorus content of the water while insectivorous fishes were more associated with the silicate and transparency of the water. The abundance of omnivores species indicated dominance of generalist fish species rather than specialists in the interface region of reservoir showing conservation and ecological importance of the ecosystem. The baseline information generated on fish assemblage and ecological perspectives of the river reservoir interface and science-based management recommendations formulated in the study are critical for sustaining fish diversity, promoting fisheries enhancement, and management planning of tropical large reservoirs.

Quantitative monitoring of diverse fish communities on a large scale combining eDNA metabarcoding and qPCR.

Environmental DNA (eDNA) metabarcoding is an effective method for studying fish communities but allows only an estimation of relative species abundance (density/biomass). Here, we combine metabarcoding with an estimation of the total abundance of eDNA amplified by our universal marker (teleo) using a quantitative (q)PCR approach to infer the absolute abundance of fish species. We carried out a 2850-km eDNA survey within the Danube catchment using a spatial integrative sampling protocol coupled with traditional electrofishing for fish biomass and density estimation. Total fish eDNA concentrations and total fish abundance were highly correlated. The correlation between eDNA concentrations per taxon and absolute specific abundance was of comparable strength when all sites were pooled and remained significant when the sites were considered separately. Furthermore, a nonlinear mixed model showed that species richness was underestimated when the amount of teleo-DNA extracted from a sample was below a threshold of 0.65 × 106 copies of eDNA. This result, combined with the decrease in teleo-DNA concentration by several orders of magnitude with river size, highlights the need to increase sampling effort in large rivers. Our results provide a comprehensive description of longitudinal changes in fish communities and underline our combined metabarcoding/qPCR approach for biomonitoring and bioassessment surveys when a rough estimate of absolute species abundance is sufficient.

Short-term hydromorphological and ecological responses of using woody structures for river restoration in a tailing-impacted tropical river.

Gualaxo do Norte River (GNR), in southeastern Brazil, was impacted by iron ore tailings from the Fundão Dam rupture (November 2015). The deposition of tailings on the riverbed has changed the hydrogeomorphological characteristics of the GNR, resulting in a decrease in the diversity of physical habitats and ecological biodiversity. As part of the process of restoration and management of this damaged ecosystem, the river restoration project ReNaturalize was implemented to restructure the geomorphological characteristics and the physical habitat and to enhance the reestablishment of biota, mainly for macroinvertebrates and fishes. For this goal, 203 wooden structures, such as tree trunks, branches, and grass were installed in two sections of GNR (T6R and T7R), totaling 1.8 km long. The effectiveness of the project was evaluated by an assessment that followed a before and after and control and impacted (BACI) design. Upstream of each Restored reach there is a Control and a Reference reach. Four campaigns were carried out, two before and two after the restoration process. After 14 months of the woody installation, an increase in hydraulic retention in the restored reaches was observed (T6R-20.2%; T7R-63.5%), when compared with the Control reaches, which favored the accumulation of sediments (T6R-388 metric tons; T7R-396 metric tons). This enhanced the formation of natural tailings barriers and promoted the enrichment of substrate types (T6R-39.2%; T7R-43%). The benthic macroinvertebrate community showed an increase in the total abundance (T6-110%), including the most sensitive groups (T6R-124%; T7R-124%). For fish, the increase was up to 81.38% with hand nets capture, indicating the recruitment of juveniles, and the abundance and the biomass of some species were also higher (up to 100%) than the Control reaches. The results indicated that the Restored reach is already qualitatively and quantitatively better than the Control reach and similar to the Reference reach, indicating the success of the study. Integr Environ Assess Manag 2023;19:648-662. © 2022 SETAC.

Effect of sampling design on estimation of phylogenetic diversity metrics of fish community.

Phylogenetic diversity has been widely used to explore diversity patterns and assess processes governing the species composition in community. The estimates of many metrics depend on high-quality data collected from well-designed sampling surveys. However, knowledge of impacts of sampling design on estimation of phylogenetic diversity metrics remains unclear. This study is aim to evaluate the influence of sampling design on phylogenetic diversity metrics estimation of fish community. Simple random sampling (SRS), systematic sampling (SS) and stratified random sampling (StRS) with different sampling intensities were chosen and mean pairwise distances (MPD), mean nearest taxon distance (MNTD), phylogenetic diversity (PD), phylogenetic species variability (PSV), phylogenetic species evenness (PSE) and phylogenetic species richness (PSR) were selected. SRS and StRS showed similar impact on phylogenetic diversity indices estimation and performed relatively well for collecting data to estimate phylogenetic diversity. The accuracy and precision of the estimation increased with sampling intensity under SRS and StRS except SS. MNTD was the only metric not underestimated in four seasons. Metrics strongly influenced by species richness were underestimated when sampling intensity was insufficient. MPD, PSV and PSE showed an obvious seasonal change, which was due to the seasonal differences in fish species composition. In cases where under-sampling is suspected or logistically unavoidable, phylogenetic diversity metrics that are relatively insensitive to sampling design (e.g., MPD and PSV) should be prioritized, especially for exploring the temporal variation in fish community. This study reveals it is indispensable to evaluate sampling design when estimating phylogenetic diversity metrics, especially those indices susceptible to species richness.

Distribution Pattern of Mangrove Fish Communities in China.

Mangroves are among the most productive marine and coastal ecosystems and play an important role in maintaining the stability and diversity of fish communities. To explore the structure of mangrove fish communities in China, we compiled previous studies, monographs, and two databases on 54 mangrove areas published in the past 30 years. Mangrove fish communities in China comprised Osteichthys (597 species) and Chondrichthyes (14 species), representing 611 species in 344 genera, 117 families, and 28 orders. Perciformes were the predominant taxon, with 350 species in 52 families, accounting for 57% of the total species richness. Reef fish accounted for 29.62%. With regard to feeding groups, there were 328 carnivorous species (53.68%), 214 omnivorous species (35.02%), 41 herbivorous species (6.71%), and 28 detritivores species (4.58%). Classified by body size, 57.61% were small-sized, 24.22% medium-sized, and 18.17% were large-sized fishes. A total of 5.23% (32 species) of these mangrove fish are currently on IUCN red lists, i.e., 2 species are critically endangered, 4 are endangered, 12 are vulnerable, and 14 are near threatened. Cluster analyses shows that Chinese mangroves fish were divided into two categories, i.e., coastal mangrove and island mangrove type. This is closely related to the distribution of reef fish. Moreover, the number of fish species showed a strong positive correlation with mangrove area, but not with latitude. The main reasons may be the subtropical and tropical geographic locations, as well as the characteristics of the South China Sea and the Taiwan Warm Current. The size and integrity of mangrove area are crucial to the local ecosystems; thus, protecting and restoring mangroves is of great significance to large-scale ecosystem-stability and local biodiversity.

[Spatio-temporal variations in species composition and diversity of fish communities in the adjacent waters of Changshan Islands, China]. / é•¿å±±åˆ—å²›é‚»è¿‘æµ·åŸŸé±¼ç±»ç¾¤è½ç§ç±»ç»„æˆå’Œå¤šæ ·æ€§æ—¶ç©ºå˜åŒ–.

In order to understand species composition and diversity of fish communities in the ecotone between the Yellow Sea and Bohai Sea, we examined species composition and temporal and spatial variations of fish species diversity using the relative importance index (IRI), species diversity index and k dominance curve based on bottom trawl survey data of fish resources in the adjacent waters of the Changshan Islands in October 2016, January, May and August 2017. The results showed that 77 fish species were captured, mainly temperate water fishes, demersal fishes and migratory fishes. The dominant species exhibited obvious seasonal variation. The dominant species in spring and winter were Lophius litulon, and those in summer were pelagic species such as Scomber japonicus and Engraulis japonicus. A total of 46 migratory fish species were found throughout the year. The seasonal species migration indices were all higher than 100, while the species migration index was the largest in autumn. The species diversity index showed high spatial and temporal dynamics, with the highest species richness in spring and the highest Shannon diversity and evenness in autumn. There was a significant negative correlation between species richness and sea surface temperature in summer, significant positive correlations between species richness and depth and bottom temperature in winter, and a significant positive correlation between Shannon diversity index and sea bottom temperature. In short, fish community showed high species diversity, rich migratory species and obvious temporal and spatial heterogeneity in the adjacent waters of the Changshan Islands, which is an ecotone between the Yellow Sea and the Bohai Sea.

Initial recovery of fish faunas following the implementation of pen-culture and fishing bans in floodplain lakes along the Yangtze River.

Given the decline of natural fish abundance and diversity, a ban on pen-culture and fishing has been imposed on floodplain lakes along the Yangtze River. In order to examine the recovery efficiency of fish faunas, we compared the changes in multidimensional (α and ß) diversity in the Shengjin Lake between pen-culture stage (PS) and recovery stage (RS). Our results demonstrated significant variations in fish community composition, with distinct populational restoration in wild species of high trophic level and river-lake migratory species. The higher abundance of wild and migratory species in RS implied the enhanced dispersal and exchange process of fish individuals with the elimination of net pens. Despite significant variations of community composition, the α and ß diversity indices exhibited non-significant change between PS and RS. However, our study still revealed the recovery of natural seasonal community dynamics, since there were significant variations of both α and ß diversity between high-water (HW) and low-water (LW) seasons in RS. The significant higher α diversity (S, d, H') in HW indicated flooding induced fish supplements in floodplain lakes, due to the well-developed breeding sites, nurseries and refuges provided by floodplain lakes. Meanwhile, the significant lower ßSOR and ßSIM in HW implied the homogenized communities during flooding seasons, which can be ascribed to better hydrological connectivity of various habitats and more even distribution of fish faunas triggered by flood pulses. The reappearance of natural seasonal variations in multidimensional (α and ß) diversity indicate the initial recovery of fish faunas. There is a pressing need for prolonged surveillance to explore the recovery mechanism of fish assemblage. Meanwhile, our results also highlight the importance of conserving the lacustrine connectivity and seasonal flooding for the recovery of fishery resources in the floodplain lakes.

Appraisal of different attributes of fish community in Andharmanik River of coastal Bangladesh and socio-economic conditions of fishermen.

The purpose of this study was to determine the fish species composition and appraise the status of fish diversity through sampling in six sample locations and to observe the socio economic conditions of the fishermen surrounding the river during the study period. There were 81 fish species found, classified into 13 orders, 40 families, and 69 genera. The most dominant order was Perciformes (55.42 %), followed by Clupeiformes (20.44 %), Cypriniformes (8.96 %), Siluriformes (8.13 %), and others (7.05%). To illustrate the species diversity, fish species richness and evenness in sampling areas, indices of fish community viz. Shannon-Wiener's Index (H), Simpson's Dominance Index (D), Simpson's Diversity Index (1-D), Margalef's Index (d) and Gibson's Evenness (€) were used and 3.29-3.48, 0.05-0.069, 0.93-0.95, 6.88-8.43 and 0.39-0.49 respectively were the overall values of the indices. S1 station is significantly differ in species richness from the rest of the five stations (P < 0.05). The analysis of similarity (ANOSIM) displayed significant (P-value < 0.05) variations in fish community among stations and months. In compliance with similarity percentage (SIMPER) analysis, 35.8% similarities were observed among the fish species from different stations, while 59.36% similarities were detected among the fish species from different months. One species is critically endangered (CR), three species are nearly threatened, eight species are endangered (EN), and eight species are vulnerable among the 81 fish species recorded at various sampling locations. The socioeconomic conditions of fishermen were determined on the basis of a personal interview and focus group discussion. Unfair fishing practices as well as environmental instabilities such as reduced water volume, increased sedimentation, water abstraction, and pollution have ravaged fish habitat and diminished fish diversity over time. As a result, fish preservation in the Andharmanik River has become imperative, and an integrated management plan should be designed and executed as soon as possible.

Responses of coastal fishery resources to rapid environmental changes.

Coastal systems experience strong impacts of ongoing environmental change, affecting fish communities and subsequently fishery yields. In the Baltic Sea, the combined effects of climate-induced changes and eutrophication-related pressures constitute major threats to its living resources. Although much work has been devoted to uncovering environmental impacts on the commercially most valuable fish stocks, only little is known about community-wide responses of fished species and how environmental change may affect their yield. In this study, the authors use a joint species distribution modelling framework to disentangle environmental impacts on species-specific fishery yields of 16 fished species along the coast of Finland over four decades. The authors show that environmental covariates substantially contributed to variations in fishery yields and are likely to have strong impacts on fished resources also in the future. Salinity and near-bottom oxygen concentration emerged as the strongest environmental drivers of yields at the community level, whereas temperature was particularly important for cod (Gadus morhua) and sprat (Sprattus sprattus) yields. The authors found shore density to be an important predictor for fisheries resources especially for freshwater fish. The results of this study suggest that the changes in environmental conditions during the past four decades had a positive effect on the yields of freshwater and warm-affinity species, whereas yields of marine cold-affinity species have been mainly negatively affected by contracting favourable habitats, becoming warmer and less saline.

[Spatiotemporal variations of fish feeding guilds in Yellow River basin]. / 黄河流域鱼类食性同资源种团的时空变化.

Conservation of fish resources is the key to ecological protection and high-quality development of Yellow River basin. From 1960 to 2019, Yellow River basin distributed 201 fish species, belonging to 16 orders, 35 families. The species number of Cypriniformes was the largest (accounting for 60.7%), followed by Perciformes (accounting for 10.0%). From 1960 to 1980, there were 182 fish species belonging to 15 orders, 28 families. During 1980-2019, there were 112 species, belonging to 10 orders, 23 families. The total number of fish species in source area, midstream and downstream decreased significantly, while that in the upper reaches increased slightly. Jaccard's similarity index of source area, upstream, midstream and downstream between two periods were 34.2%, 46.0%, 42.4% and 35.7%, respectively. Based on feeding preference characteristic, fish species could be divided into eight feeding guilds: phytobenthivores, herbivores, phytoplanktivores, zooplanktivores, omnivorous, insectivores, zoobenthivores, and piscivores. Compared with the period from 1960 to 1980, the proportion of insectivores decreased significantly in the Yellow River basin during 1980-2019, while that of phytobenthivores, herbivores, phytoplanktivores, omnivorous and piscivores increased significantly. From 1960 to 1980, the proportion of insectivores was higher than other reaches at source area and upstream, then began to decrease along the river continuum from reaches with elevation of 2000-3000 m; while the proportion of piscivores was lower than other reaches at source area and upstream, then began to increase along the river continuum from reaches with elevation of 2000-3000 m. From 1980 to 2019, the proportion of insectivores decreased along river continuum from source area, and that of piscivores increased from source area to midstream but decreased in downstream. Development of cascade hydropower, water pollution, insufficient water flow, overfishing and invasion of alien fish were important factors causing the spatiotemporal variations of fish feeding guilds in Yellow River basin.

Climate change linked to functional homogenization of a subtropical estuarine system.

Climate change causes marine species to shift and expand their distributions, often leading to changes in species diversity. While increased biodiversity is often assumed to confer positive benefits on ecosystem functioning, many examples have shown that the relationship is specific to the ecosystem and function studied and is often driven by functional composition and diversity. In the northwestern Gulf of Mexico, tropical species expansion was shown to have increased estuarine fish and invertebrate diversity; however, it is not yet known how those increases have affected functional diversity. To address this knowledge gap, two metrics of functional diversity, functional richness (FRic) and functional dispersion (FDis), were estimated in each year for a 38-year study period, for each of the eight major bays along the Texas coast. Then, the community-weighted mean (CWM) trait values for each of the functional traits are calculated to assess how functional composition has changed through time. Finally, principal component analysis (PCA) was used to identify species contributing most to changing functional diversity. We found significant increases in log-functional richness in both spring and fall, and significant decreases in functional dispersion in spring, suggesting that although new functional types are entering the bays, assemblages are becoming more dominated by similar functional types. Community-weighted trait means showed significant increases in the relative abundance of traits associated with large, long-lived, higher trophic level species, suggesting an increase in periodic and equilibrium life-history strategists within the bays. PCA identified mainly native sciaenid species as contributing most to functional diversity trends although several tropical species also show increasing trends through time. We conclude that the climate-driven species expansion in the northwestern Gulf of Mexico led to a decrease in functional dispersion due to increasing relative abundance of species with similar life-history characteristics, and thus the communities have become more functionally homogeneous.

Natural distinction of carbon and nitrogen isotopic niches in common fish species across marine biotopes in the Yellow River estuary.

Stable isotope analysis is a universally recognized and efficient method of indicating trophic relationships that is widely applied in research. However, variation in stable isotope ratios may lead to inaccuracies due to the effects of complex environmental conditions. This research compared the carbon and nitrogen isotopic niches of fish communities between diverse biotopes around the Yellow River estuary and adjacent sea areas, with the aim of revealing distinctions in stable isotopic niche metrics, trophic positions, and feeding preferences. Our analysis of the food source contribution indicated that allochthonous sources were considered major energy sources in estuarine areas directly affected by Yellow River-diluted water, while autochthonous benthic and pelagic producers dominated carbon input into the food web in Laizhou Bay and the open water. A significant variation in the fish δ15N characteristic was found within estuarine adjacent regions, so, together with the results from previous studies, we deemed the local high concentration of dissolved inorganic nitrogen as the original trigger of the abnormal δ15N characteristic in fishes via a transport process along food chains. These results provide a new perspective on the natural distinction of carbon and nitrogen isotopic niches. The detailed data reported here enhance our understanding of variations in fish communities in estuarine ecosystems.

Fish size spectra are affected by nutrient concentration and relative abundance of non-native species across streams of the NE Iberian Peninsula.

Aquatic ecosystems are strongly body-size structured with a decline of numerical abundance with increasing body size (hereafter, the size spectrum). Marine and lake fish studies have reported consistent variations of size spectra in relation to environmental conditions and biotic composition, but little is known about stream fishes. Accordingly, in this study we test several hypotheses about the effects of local water conditions, biotic introductions and cumulative pressures (measured as the IMPRESS index) on the fish size-spectrum slope (that is, the linear rate of decline of fish abundance as body size increase in a log-log scale) and the size-spectrum intercept (commonly used as proxy for carrying capacity) among 118 local fish assemblages in streams of the NE Iberian Peninsula. To our knowledge, this is the first time that an extensive river fish dataset is used in a dendritic network to cover systematic changes of size-spectrum parameters. We find that the slope and intercept of the fish size spectrum are negatively correlated with nutrient concentration (mainly total phosphorus), with a greater relative abundance of small fishes but a decline of overall carrying capacity. Moreover, fish assemblages with greater relative abundance of non-native species have flatter size-spectrum slopes. In contrast, the IMPRESS index and climate-related variables are poor predictors of the shape of the fish size spectra. This study contributes to better understanding of the main factors structuring fish assemblages in lotic environments of the Iberian Peninsula. We encourage more research on this line to further explore the use of fish size structure to evaluate the ecological health of riverine ecosystems.