The Significance of Meander Restoration for the Hydrogeomorphology and Recovery of Wetland Organisms in the Kushiro River,a Lowland River in Japan

The meanders and floodplains of the Kushiro River were restored in March 2011. A 1.6‐km stretch of the straightened main channel was remeandered by reconnecting the cutoff former channel and backfilling the straightened reach, and a 2.4‐km meander channel was restored. Additionally, flood levees were removed to promote river–floodplain interactions. There were four objectives of this restoration project: to restore the in‐stream habitat for native fish and invertebrates; to restore floodplain vegetation by increasing flooding frequency and raising the groundwater table; to reduce sediment and nutrient loads in the core wetland areas; to restore a river–floodplain landscape typical to naturally meandering rivers. In this project, not only the natural landscape of a meandering river but also its function was successfully restored. The monitoring results indicated that these goals were likely achieved in the short term after the restoration. The abundance and species richness of fish and invertebrate species increased, most likely because the lentic species that formerly inhabited the cutoff channel remained in the backwater and deep pools created in the restored reach. In addition, lotic species immigrated from neighboring reaches. The removal of flood levees and backfilling of the formerly straightened reach were very effective in increasing the frequency of flooding over the floodplains and raising the water table. The wetland vegetation recovered rapidly 1 year after the completion of the meander restoration. Sediment‐laden floodwater spread over the floodplain, and approximately 80–90% of the fine sediment carried by the water was filtered out by the wetland vegetation.     

Fish assemblage changes over half a century in the Yellow River,China

Riverine environments have been threatened by anthropogenic perturbations worldwide, whereby their fish assemblages have been modified by habitat changes and nonendemic species invasions. We assessed changes in fish assemblages by comparing the species presence in historical and contemporary fish data in the Yellow River from 1965 to 2015. The temporal change in species assemblages was found with increased nonendemic species and fewer natives. Fish species richness of the river declined 35.4% over the past fifty years. Moreover, the decreased mean Bray–Curtis dissimilarity among reaches suggested that the fish assemblages of different reaches in the Yellow River were becoming more similar over time. However, temporal patterns of fish assemblages varied among reaches. In the upper Yellow River, higher species richness and more invasive species were found than those in the historical record, while the lower reaches experienced significant species loss. Dam constructions, exotic fish invasions, and flow reductions played the vital role in structuring the temporal fish assemblages in the Yellow River. It is suggested that river basins which experienced different types and levels of stressors by anthropogenic perturbations can produce varied effects on their temporal trends of species assemblages.     

Determinants of fine‐scale homogenization and differentiation of native freshwater fish faunas in a Mediterranean Basin: implications for conservation

Aim Increasing threats to freshwater biodiversity are rapidly changing the distinctiveness of regional species pools and local assemblages. Biotic homogenization/differentiation processes are threatening the integrity and persistence of native biodiversity patterns at a range of spatial scales and pose a challenge for effective conservation planning. Here, we evaluate the extent and determinants of fine‐scale alteration in native freshwater fish assemblages among stream reaches throughout a large river basin and consider the implications of these changes for the long‐term conservation of native fishes. Location Guadiana River basin (South‐Western Iberian Peninsula). Methods We quantified the magnitude of change in compositional similarity between observed and reference assemblages and its potential effect on natural patterns of compositional distinctiveness. Reference assemblages were defined as the native species expected to occur naturally (in absence of anthropogenic alterations) and were reconstructed using a multivariate adaptive regression splines predictive model. We also evaluated the role of habitat degradation and introduced species as determinants of biotic homogenization/differentiation. Results We found a significant trend towards homogenization for native fish assemblages. Changes in native fish distributions led to the loss of distinctiveness patterns along natural environmental gradients. Introduced species were the most important factor explaining the homogenization process. Homogenization of native assemblages was stronger in areas close to reservoirs and in lowland reaches where introduced species were more abundant. Main conclusions The implementation of efficient conservation for the maintenance of native fish diversity is seriously threatened by the homogenization processes. The identification of priority areas for conservation is hindered by the fact that the most diverse communities are vanishing, which would require the selection of broader areas to adequately protect all the species. Given the principal role that introduced species play in the homogenization process and their relation with reservoirs, special attention must be paid to mitigating or preventing these threats.     

Spatial and temporal variation in fish assemblages of drying stream pools: The role of abiotic and biotic factors

Droughts and summer drying create unusual temporary aquatic habitats in the form of isolated pools in many small streams around the world. To examine spatial and temporal variation in fish community structure of drying stream pools, their relation to abiotic environmental variables, and associations among species, fish were sampled during summer 1995 and 1996 from pools of four streams in the Ozark mountains, Arkansas, USA. Redundancy analysis of physical-chemical variables showed significant differences among stream sites, but no significant difference between years or stream site by year interaction. Stream sites separated consistently along axes one (habitat heterogeneity) and two (temperature/canopy cover) in both years. Redundancy analysis of fish species-size class densities showed a significant stream site by year interaction. Groupings of stream sites based on fish assemblages were not well explained by physical-chemical variables measured at the pool scale, but were related to location within the drainage basin, and these groupings differed between years. There were 27 (15.8%) and 10 (5.8%) significant associations found among fish species-size classes in 1995 and 1996, respectively, and all but two significant associations in 1995 were positive. Pool depth, habitat heterogeneity, pool size and dissolved oxygen/canopy cover were important local abiotic factors depending on response variables examined. In both years, large fish total density, large central stoneroller density (80 mm TL), and small sunfish (<80 mm TL) density were positively related to pool depth. Otherwise, there was no consistent relationship between physical-chemical variables and dependent variables (fish density and species richness) within a year or between years for a given dependent variable. These results support the hypothesis that local abiotic factors are important in structuring fish assemblages in harsh environments, but the importance of those factors varies temporally, and regional influences appear to override local abiotic conditions as factors structuring fish assemblages in drying stream pools. Predation by terrestrial vertebrates may also be an important factor structuring these fish assemblages that has been largely overlooked.     

BIODIVERSITY RESEARCH: Native and introduced fish species richness in Mediterranean streams: the role of multiple landscape influences

Aim To examine the role of multiple landscape factors on the species richness patterns of native and introduced freshwater fish. Location Mediterranean streams, south‐western Iberian Peninsula, Europe (c. 87,000 km²). Methods We used a dataset of fish occurrences from 436 stream sites. We quantified the incremental explanatory power of multiple landscape factors in native, introduced, and overall local species richness using regression analysis. First, we related variation in local species richness across river basins to regional species richness (here, the basin species pool), area and factors of climate and topography. Second, we related within‐river basin local species richness to site’s climate and topography, and spatial structure derived from Principal Coordinates of Neighbour Matrices approach, after testing for species richness spatial autocorrelation; predicted local richness was mapped. Results Patterns of local species richness across river basins were strongly associated with regional species richness for overall, native and introduced species; annual rainfall showed a significant incremental contribution to variation in introduced species richness only. Within river basins, environmental factors were associated with local richness for the three species groups, though their contributions to the total explained variation were inferior to those of spatial factors; rainfall seasonality and stream slope were the most consistent environmental correlates for all species groups, while the influence of spatial factors was most prevalent for native species. Main conclusions Landscape factors operating among and within river basins seem to play a relevant role in shaping local species richness of both native and introduced species, and may be contingent on basin‐specific contexts. Nevertheless, local factors, such as habitat characteristics and biotic interactions and human‐induced disturbances may also be at play. Multiscale approaches incorporating a multitude of factors are strongly encouraged to facilitate a deeper understanding of the biodiversity patterns of Mediterranean streams, and to promote more effective conservation and management strategies.     

Factors influencing fish distribution and community structure in a small coastal river in southwestern Costa Rica

We evaluated the relative importance of habitat size and diversity and distance from the ocean in explaining longitudinal patterns of fish distribution and community structure (species richness, evenness, and diversity) in the lower 5 km of the Rio Claro. The Rio Claro is a small coastal river in Corcovado National Park, southwestern Costa Rica, with a depauperate freshwater fish fauna. We observed 22 species in pools, 19 of which occured during quantitative sampling. Most of these species probably spent part of their lives in the Pacific Ocean. We observed no species in riffles, although these habitats were common and several taxa (e.g., Gobiesocidae, Gobiidae) were adapted for life in fast turbulent water. Fish abundance, and species richness, evenness, and diversity were highest near the ocean, where high tides influenced river levels and salinity. Eight species were not observed further than 2900 m from the ocean, whereas 6 species were not encountered in samples nearest the ocean; the remaining 8 species were present throughout the study area. Distance from the ocean was a better predictor of fish abundance and community structure than were pool width, pool depth, pool surface area, pool volume, amount of cover present, substrate diversity, or depth diversity. Based in qualitative comparisons of our data with previously published data from 1980–1986, the fish assemblage of the Rio Claro is persistent in both species composition and relative abundance.     

Fish species richness and incidence patterns in isolated and connected stream pools: effects of pool volume and spatial position

I tested the effects of pool size and spatial position (upstream or downstream) on fish assemblage attributes in isolated and connected pools in an upland Oklahoma stream, United States. I hypothesized that there would be fundamental differences between assemblages in these two pool types due to the presence or absence of colonization opportunities. Analyses were carried out at three ecological scales: (1) the species richness of pool assemblages, (2) the species composition of pool assemblages, and (3) the responses of individual species. There were significant species-volume relationships for isolated and connected pools. However, the relationship was weaker and there were fewer species, on average, in isolated pools. For both pool types, species incidences were significantly nested such that species-poor pools tended to be subsets of species-rich pools, a common pattern that ultimately results from species-specific differences in colonization ability and/or extinction susceptibility. To examine the potential importance of these two processes in nestedness patterns in both pool types, I made the following two assumptions: (1) probability of extinction should decline with increasing pool size, and (2) probability of immigration should decline in an upstream direction (increasing isolation). When ordered by pool volume, only isolated pools were significantly nested suggesting that these assemblages were extinction-driven. When ordered by spatial position, only connected pools were significantly nested (more species downstream) suggesting that differences in species-specific dispersal abilities were important in structuring these assemblages. At the individual-species level, volume was a significant predictor of occurrence for three species in isolated pools. In connected pools, two species showed significant position effects, one species showed a pool volume effect, and one species showed pool volume and position effects. These results demonstrate that pool size and position within a watershed are important determinants of fish species assemblage structure, but their importance varies with the colonization potential of the pools. Isolated pool assemblages are similar to the presumed relaxed faunas of montane forest fragments and land bridge islands, but at much smaller space and time scales. Received: 6 December 1996 / Accepted: 10 December 1996     

Spatial and temporal patterns in the fish assemblages of individual pools in a midwestern stream (U.S.A.)

Synopsis The composition and consistency of fish assemblages in 14 adjacent pools (6–120 m long) of a clear-water, limestone and gravel creek in midwestern U.S.A. were quantified in eight snorkeling surveys over 19 months, to establish a baseline of natural variation in the system at this scale. The fauna of the stream was dominated numerically by minnows (Cyprinidae), sunfish and black bass (Centrarchidae), and topminnows (Fundulidae). The pool fish fauna of the total 1 km reach (including all 14 pools) was highly consistent throughout the study, despite two major floods. Assemblages in individual pools generally were consistent, but there was more variation within pools than at the scale of the entire reach. Throughout the study, most individual pools remained within discrete subsets of the total occupied multivariate space in a principal components analysis based on fish species abundances. Sunfishes (Lepomis spp.) and bass (Micropterus spp.) were more consistent in their distribution among pools than were minnows (Cyprinidae) or a topminnow (Fundulus). There were 25 significant correlations in occurrence of species pairs among stream pools, out of 91 possible comparisons of the 14 most abundant taxa in the reach. Many pools contained assemblages either dominated by large centrarchids or by abundant cyprinids and juvenile centrarchids, but intermediate assemblages also were observed. The dynamics of distribution of fish species and fish assemblages among individual stream pools are likely influenced by a combination of species-specific behaviors and habitat selection, predator constraints on use of individual pools by small fishes, riffles as size-selective barriers to fish movements between pools, dispersal of young-of-the-year fishes, and abiotic phenomena like floods. Individual stream pools appear to be discrete habitat units for fishes, and do represent an appropriate scale for biologically meaningful studies of fish assemblages or their effects on streams.Department of Zoology, University of Oklahoma     

A Large-scale, Hierarchical Approach for Assessing Habitat Associations of Fish Assemblages in Large Dryland Rivers

Multiple-scale assessments of fish-habitat associations are limited despite the fact that riverine fish assemblages are influenced by factors operating over a range of spatial scales. A method for assessing fish-habitat assemblages at multiple scales is proposed and tested in a large Australian dryland river, the Barwon–Darling River. Six discrete mesohabitat types (large wood, smooth bank, irregular bank, matted bank, mid-channel and deep pool) nested within 10 km long river reaches were sampled. Individual reaches were, in turn, nested within four larger geomorphological zones, previously identified along the river. Fish assemblages varied significantly between mesohabitat types and at different spatial scales. Golden perch (Macquaria ambigua), Murray cod (Maccullochella peelii peelii) and common carp (Cyprinus carpio) were strongly associated with large wood, but golden perch and Murray cod exhibited higher habitat specificity than carp. Bony herring (Nematalosa erebi) were more common in shallow edgewater habitats. At the river-scale, regional differences in the fish assemblage occurred at scales closely corresponding to geomorphological zones and these differences were associated with changes in the relative abundance of species rather than the addition or replacement of species. The proposed hierarchical framework improves the efficiency of fish surveys in large rivers by viewing meso-scale fish-habitat associations in the context of larger-scale geomorphological processes.     

Species richness of resident and transient coral-dwelling fish responds differentially to regional diversity

Aim To determine whether the diversity of resident and transient coral‐dwelling fish responds differentially to gradients in regional species richness. Location Three regions in the Indo‐Pacific (Red Sea, western Indian Ocean, Great Barrier Reef) which contain increasingly larger regional diversities of reef fish. Methods I surveyed fish residing within branching coral species. Fish species were a priori categorized as resident or transient based on the degree of affiliation between the fish and live coral. To compare among regions that differ in coral diversity I used a modified species–volume relationship (SVR). Each point in the SVR represents the total number of fish species, resident or transient, found within the cumulative volume of a specific coral species. Empirical SVRs were further compared with random‐placement null models. Results For transient species, I found that the observed SVRs did not differ consistently from those expected from random samples drawn from the corresponding regional species pools. In addition, for a given volume of coral, more fish species were found in richer regions, indicating strong regional influences on local diversity. In contrast, resident richness was lower than that expected from random samples of the species pool, and richness in rich regions was reduced comparably more than in poor regions. The SVRs of resident species were similar among regions with different regional diversities. Main conclusion These results suggest that, within coral species, transient fish richness is mostly influenced by stochastic allocation of species from the regional pool. Conversely, richness of resident species within a coral species is limited, making it independent of regional diversity. Since higher regional diversity of resident fish was not accompanied by higher richness per coral species or by decreased niche breadth, higher regional diversity of resident fish species must be rooted in higher coral richness. Consequently, ecological interactions between functional groups (coral and fish) can be powerful drivers of regional biodiversity.     

Spatial patterns of the biological traits of freshwater fish communities in south‐west France

Spatial patterns in the combinations of biological traits of fish communities were studied in the Garonne River system (57 000 km², south‐west France). Fish species assemblages were recorded at 554 sampling sites, and the biological traits of species were described using a fuzzy‐coding method. A co‐inertia analysis of species distributions and biological traits identified some spatial patterns of species trait combinations. Fish species richness progressively increased from up‐ to downstream sections, and the longitudinal patterns of fish assemblages partitioned the river into clear biogeographic areas, such as the brown trout Salmo trutta (headwater streams), the grayling Thymallus thymallus , the barbel Barbus barbus and the bream Abramis brama zones (most downstream sections), which fitted with Huet's well‐known zonation for western European rivers. Only a few biological traits, chiefly related to life‐history attributes, significantly influenced the observed fish distributions. Fecundity, potential size, maximum age and reproductive factor increased from headwater to plain reaches. As a theoretical framework for assessing and predicting the functional organization of stream fish communities, spatial variations in species traits can be related to habitat conditions, thus providing explicit spatial schemes that may be useful to the design of both scientific studies and river management.     

Environmental DNA reveals a mismatch between diversity facets of Amazonian fishes in response to contrasting geographical,environmental and anthropogenic effects

Freshwater ecosystems are among the most endangered ecosystem in the world. Understanding how human activities affect these ecosystems requires disentangling and quantifying the contribution of the factors driving community assembly. While it has been largely studied in temperate freshwaters, tropical ecosystems remain challenging to study due to the high species richness and the lack of knowledge on species distribution. Here, the use of eDNA-based fish inventories combined to a community-level modelling approach allowed depicting of assembly rules and quantifying the relative contribution of geographic, environmental and anthropic factors to fish assembly. We then used the model predictions to map spatial biodiversity and assess the representativity of sites surveyed in French Guiana within the EU Water Framework Directive (WFD) and highlighted areas that should host unique freshwater fish assemblages. We demonstrated a mismatch between the taxonomic and functional diversity. Taxonomic assemblages between but also within basins were mainly the results of dispersal limitation resulting from basin isolation and natural river barriers. Contrastingly, functional assemblages were ruled by environmental and anthropic factors. The regional mapping of fish diversity indicated that the sites surveyed within the EU WFD had a better representativity of the regional functional diversity than taxonomic diversity. Importantly, we also showed that the assemblages expected to be the most altered by anthropic factors were the most poorly represented in terms of functional diversity in the surveyed sites. The predictions of unique functional and taxonomic assemblages could, therefore, guide the establishment of new survey sites to increase fish diversity representativity and improve this monitoring program.     

Modelling Stream-Fish Functional Traits in Reference Conditions: Regional and Local Environmental Correlates

Identifying the environmental gradients that control the functional structure of biological assemblages in reference conditions is fundamental to help river management and predict the consequences of anthropogenic stressors. Fish metrics (density of ecological guilds, and species richness) from 117 least disturbed stream reaches in several western Iberia river basins were modelled with generalized linear models in order to investigate the importance of regional- and local-scale abiotic gradients to variation in functional structure of fish assemblages. Functional patterns were primarily associated with regional features, such as catchment elevation and slope, rainfall, and drainage area. Spatial variations of fish guilds were thus associated with broad geographic gradients, showing (1) pronounced latitudinal patterns, affected mainly by climatic factors and topography, or (2) at the basin level, strong upstream-downstream patterns related to stream position in the longitudinal gradient. Maximum native species richness was observed in midsize streams in accordance with the river continuum concept. The findings of our study emphasized the need to use a multi-scale approach in order to fully assess the factors that govern the functional organization of biotic assemblages in ‘natural’ streams, as well as to improve biomonitoring and restoration of fluvial ecosystems.     

Scale, environment, and trophic status: the context dependency of community saturation in rocky intertidal communities

Our understanding of the relative influence of different ecological drivers on the number of species in a place remains limited. Assessing the relative influence of local ecological interactions versus regional species pools on local species richness should help bridge this conceptual gap. Plots of local species richness versus regional species pools have been used to address this question, yet after an active quarter-century of research on the relative influence of local interactions versus regional species pools, consensus remains elusive. We propose a conceptual framework that incorporates spatial scale and ecological interaction strength to reconcile current disparities. We then test this framework using a survey of marine rocky intertidal algal and invertebrate communities from the northeast Pacific. We reach two main conclusions. First, these data show that the power of regional species pools to predict local richness disintegrates at small spatial scales coincident with the scale of biological interactions, when studying ecologically interactive groups of species, and in generally more abiotically stressful habitats (e.g., the high intertidal). Second, conclusions of past studies asserting that the regional species pool is the primary driver of local species richness may be artifacts of large spatial scales or ecologically noninteractive groups of species.     

Characterization of an Atlantic salmon Salmo salar stream at the southern limit of its eastern Atlantic distribution

Ten reaches of an Atlantic stream located in north‐west Spain were sampled intensively during one summer to characterize the conditions where Atlantic salmon Salmo salar have been re‐introduced along the stream. Fish species richness and diversity showed a downstream increase, which was mainly attributed to the higher number of cyprinid species found in the lower reaches. Moreover, except for brown trout Salmo trutta that appeared to be the most ubiquitous species, the densities of the other species was higher in the lower than in the upper stream reaches. Redundancy analysis showed that the pattern of fish assemblages observed along the studied stream was mainly related to the expected gradient observed in the levels of dissolved oxygen, discharge and mean current speed. There was a significant differentiation between midstream and downstream reaches, both in terms of the composition of their fish assemblages and the freshwater habitat. This study emphasizes the importance of describing the variations in fish assemblages and habitat characteristics along a river to explore its relation to potential changes in the survival of fish populations. In particular, the development of habitat–fish relationships may be a useful tool for water managers to assess the effects of development and restoration projects on the habitat of S. salar.     

Valley‐scale hydrogeomorphology drives river fish assemblage variation in Mongolia

River hydrogeomorphology is a major driver shaping biodiversity and community composition. Here, we examine how hydrogeomorphic heterogeneity expressed by Functional Process Zones (FPZs) in river networks is associated with fish assemblage variation. We examined this association in two distinct ecoregions in Mongolia expected to display different gradients of river network hydrogeomorphic heterogeneity. We delineated FPZs by extracting valley‐scale hydrogeomorphic variables at 10 km sample intervals in forest steppe (FS) and in grassland (G) river networks. We sampled fish assemblages and examined variation associated with changes in gradients of hydrogeomorphology as expressed by the FPZs. Thus, we examined assemblage variation as patterns of occurrence‐ and abundance‐based beta diversities for the taxonomic composition of assemblages and as functional beta diversity. Overall, we delineated 5 and 6 FPZs in river networks of the FS and G, respectively. Eight fish species were found in the FS river network and seventeen in the G, four of them common to both ecoregions. Functional richness was correspondingly higher in the G river network. Variation in the taxonomic composition of assemblages was driven by species turnover and was only significant in the G river network. Abundance‐based taxonomic variation was significant in river networks of both ecoregions, while the functional beta diversity results were inconclusive. We show that valley‐scale hydrogeomorphology is a significant driver of variation in fish assemblages at a macrosystem scale. Both changes in the composition of fish assemblages and the carrying capacity of the river network were driven by valley‐scale hydrogeomorphic variables. River network hydrogeomorphology as accounted for in the study has, therefore, the potential to inform macrosystem scale community ecology research and conservation efforts.     

水坝拆除对黑水河鱼类群落结构和空间分布的影响

水坝拆除引起河流连通性、水动力、河流地貌等一系列变化,直接影响了鱼类群落结构和空间分布。黑水河为金沙江左岸一级支流,其上共建四级电站,出于支流生境恢复需求,第四级水坝老木河水坝于2018年12月实行拆除。为探明低水头坝拆除对鱼类群落的影响,结合2018年6月和2019年6月黑水河下游60.4km河段10个点位的渔获物调查,对拆坝前后鱼类群落结构和生态类型变化、优势物种与单位捕捞努力量以及不同河段间的群落相似性进行了分析。结果表明,水坝拆除半年后优势物种仍以鲤科和鳅科为主,但物种数和丰度整体上增加;生态类型上以杂食、喜急流和产微粘性卵鱼为主;拆坝后鱼类群落空间分布变化明显,靠近河口的自然河段鱼类上溯洄游到原坝址的上下游,部分长江上游特有鱼类在原坝址附近发生定殖行为,且拆坝后各河段的鱼类组成结构有同质化趋势。总体上,老木河水坝的拆除对黑水河下游的鱼类群落结构和空间分布产生了积极的影响。