Stream Fish Research Articles

Elements of fish metacommunity structure in Neotropical freshwater streams.

The identification of the mechanisms underlying patterns of species co‐occurrence is a way to identify which process(es) (niche, neutral, or both) structure metacommunities. The current paper had the goal of identifying patterns of co‐occurrence in Neotropical stream fish and determining which processes structure the fish metacommunity, and identifying any gradients underlying this structure. Results indicated that the metacommunity formed by the species pool was structured by a pattern of nested co‐occurrence (hyperdispersed species loss) and a mass‐effect mechanism. However, a set of core species, displaying a Clementsian pattern, was structured by a species‐sorting mechanism. Both, hyperdispersed species loss and the Clementsian patterns point to a discrete set of communities within the metacommunity. These communities could be isolated by the water physicochemical conditions or morphological characteristics of the stream channel.

Multispecies models reveal that eDNA metabarcoding is more sensitive than backpack electrofishing for conducting fish surveys in freshwater streams.

Environmental DNA (eDNA) sampling can provide accurate, cost-effective, landscape-level data on species distributions. Previous studies have compared the sensitivity of eDNA sampling to traditional sampling methods for single species, but similar comparative studies on multispecies eDNA metabarcoding are rare. Using hierarchical site occupancy detection models, we examined whether key choices associated with eDNA metabarcoding (primer selection, low-abundance read filtering and the number of positive water samples used to classify a species as present at a site) affect the sensitivity of metabarcoding, relative to backpack electrofishing for fish in freshwater streams. Under all scenarios (teleostei and vertebrate primers; 0%, 0.1% and 1% read filtering thresholds; one or two positive samples required to classify species as present), we found that eDNA metabarcoding is, on average, more sensitive than electrofishing. Combining vertebrate and teleostei markers resulted in higher detection probabilities relative to the use of either marker in isolation. Increasing the threshold used to filter low-abundance reads decreased species detection probabilities but did not change our overall finding that eDNA metabarcoding was more sensitive than electrofishing. Using a threshold of two positive water samples (out of five) to classify a species as present typically had negligible effects on detection probabilities compared to using one positive water sample. Our findings demonstrate that eDNA metabarcoding is generally more sensitive than electrofishing for conducting fish surveys in freshwater streams, and that this outcome is not sensitive to methodological decisions associated with metabarcoding.

Визначний дослідник іхтіофауни України Анатолій Щербуха (1935–2020)

A brief overview of the biography and scientific achievements of Anatoliy Shcherbukha — a prominent Ukrainian zoologist, museologist, collector, fish expert, developer of the Ukrainian fish nomenclature, and promoter of science. Biographical information reconstructed from a personal file found in the archives of the National Museum of Natural History NAS of Ukraine (NMNH), as well as some scientific works of the researcher are presented. An overview of his works, both articles and monographs, including reference books, scientific monographs, popular science publications, catalogues, textbooks, and identification keys is given. The entire creative path of the researcher was connected with the academic Zoological Museum, which was alternately part of the Institute of Zoology and the Central Museum of Natural History, NAS of Ukraine. The researcher went from a scientist who studied the fish fauna of a small river Psel to a prominent expert of the fish fauna of all types of water bodies of Ukraine, both natural and artificial, fresh and marine waters, aboriginal and alien components of fauna, rare and industrial fish species. The researcher's achievements in the development and approval of the Ukrainian nomenclature of fishes are also significant, including the definition of the central role of genus names, from which the names of both species and families and other taxa are formed. The zoological collection of the NMNH contains more than 2,000 fish specimens of 59 species collected by A. Shcherbukha. The researcher paid much attention to the promotion of scientific knowledge and authored two popular publications on fishes, each of which was republished. The five most cited works of the researcher are the monograph "Percomorpha" in the series "Fauna of Ukraine" (1982), the catalogue of NMNH collections "Lampreys and Fishes" (2003), the popular science book "Fishes of Our Waters" (1987), the scientific article “Fish fauna of Ukraine in retrospective and modern problems of its diversity conservation” (2004), and the reference book “The Ukrainian Nomenclature of Fishes of Ukraine” (2003). The last work of the researcher was "Key to Fishes of Continental Waters and Streams of Ukraine" written in collaboration with colleagues from other institutions (2020).

Conserving stream fishes with changing climate: Assessing fish responses to changes in habitat over a large region

Changes in climate are known to alter air temperature and precipitation and their associated thermal and hydrological regimes of freshwater systems, and such alterations in habitat are anticipated to modify fish composition in fluvial systems. Despite these expected changes, assessing climate change effects on habitat and fish over large regions has proven challenging. The goal of this study is to describe an approach to assess and identify stream reaches within a large region that are susceptible to climate changes based on responses of multiple fish species to changes in thermal and hydrological habitats occurring with changes in climate. We present a six-step approach to connect climate, habitat, and fish responses, demonstrated through an example to assess effects of climate change on fishes for all stream reaches in a large U.S. ecoregion (955,029 km2). Step 1 identified measures of air temperature and precipitation expected to change substantially in the future. Step 2 identified the climatic measures strongly associated with stream thermal and hydrologic metrics calculated from measured data from a subset of streams. Step 3 linked thermal and hydrologic metrics identified in Step 2 with abundances of fish species from the same stream reaches, and these fishes were combined into groups based on similar associations with specific thermal or hydrologic metrics. Step 4 used the linkages between fish groups and climatic measures and their associated thermal and hydrologic metrics to classify stream reaches. Step 5 assigned all stream reaches into classes based on the established classification under current climate measures and then re-assigned all stream reaches using projected climatic measures for three future time windows. Step 6 assessed changes in classes of stream reaches between current and future climate conditions. Stream reaches projected to change in stream classes were considered “vulnerable” to future climate change, as they would no longer support the same fish composition. The projected vulnerable streams for the years 2040, 2060, and 2090 were mapped and summarized to identify temporal patterns and identify their spatial distribution, along with underlying mechanisms leading to changes. Our results showed that 45.7% of the 320,000 reaches and 49.3% of the overall 650,000 km stream length in the study region were expected to change stream class by the year 2090, with spatially-explicit changes including streams' responding to changing air temperature or precipitation. This study provides critical guidance for integrating climate projections, landscape factors, stream habitat data, and fish data into a meaningful approach for understanding linkage. Outcomes greatly improve our ability to describe habitat changes at a stream reach scale throughout large regions, and they can aid in prioritizing management strategies to adapt to climate change at local and regional scales.

Consistent but secondary influence of hydropeaking on stream fish assemblages in space and time

Hydropeaking corresponds to rapid artificial discharge variations, designed to address sub-daily peaks in electricity demand. It generates rapid changes in physical habitat (e.g., flow velocity and water depth) with potential impacts on stream assemblages. For assessing the generality of hydropeaking effects on fish assemblages, we present an original combination of spatial (among 45 reaches, including six groups of nearby reaches) and temporal (over 3-17 years) analyses of these effects. Our analyses involved descriptions of natural and artificial hydraulic variations in reaches, obtained after translating hourly discharge data into hydraulics. We found that the influence of hydropeaking was secondary compared to well-known spatial variations in fish assemblage structure along longitudinal gradients, and negative influences of floods on annual densities. However, the spatial and temporal analyses consistently suggested that hydropeaking may disfavour fish species typical of medium-sized streams relative to species of headwater streams (Salmo trutta, Phoxinus phoxinus, Cottus gobio). The magnitude of hydropeaking effects observed here, as well as an apparent weaker effect of ramping rates than the frequency of hydropeaks, may be due to lower ramping rates in our data set than in other studies.

How modified landscapes filter rare species and modulate the regional pool of ecological traits?

Common and rare species differ in their level of dispersal ability and habitat specialization, and thus should respond to distinct assembly rules. Rare species are much more spatially restricted and usually show higher habitat specialization, so they can be much more vulnerable to landscape changes than common species. We simulated three species-loss scenarios to assess how different groups of stream fish species respond to environmental and spatial variables and how potential extinctions affected regional functional richness and the average functional distinctiveness. Rare and common species contribute similarly to the global functional richness, but the loss of common species led to a marked decrease in local redundancy. Whilst intermediate and rare species are regulated by dispersal, dominant species respond to niche processes and are more affected by land-use changes. Therefore, common and rare species are under distinct assembly rules and may exhibit distinct responses in the face of environmental anthropization. Addressing rare species is often overlooked, despite constant claims regarding their importance and their frequently concerning conservation status. Accounting for their rarity can offer a more refined look at the responses of species to human modifications, providing valuable information on how to tackle biodiversity loss.

Importance of local and landscape variables on multiple facets of stream fish biodiversity in a Neotropical agroecosystem

Few studies have considered the effects of environmental variables at different spatial scales on Neotropical stream biodiversity. Furthermore, scale-related studies mostly include only one facet of biodiversity. To determine the contribution of local and landscape variables to the variation in the taxonomic, functional and phylogenetic α-diversity of stream fish assemblages, we sampled 85 streams in the Upper Parana River basin, Brazil. Local variables explained a substantial fraction of the variance in almost all biodiversity facets. Landscape variables (i.e., land-use and spatial variables) contributed little to the variation in the α-component of biodiversity. Our results thus highlight the importance of local features for maintaining stream fish biodiversity in agroecosystems. Probably, land-use were not significant because the study area was in a relatively homogeneous landscape severely impacted by anthropogenic activities. It is possible that insignificant effects of spatial structuring occurred because the ichthyofauna has already gone through a homogenization process and/or due to the spatial scale of our study. We suggest that even though local-scale restoration actions would influence biodiversity, we should not neglect landscape restoration because substantial improvements in the ecological integrity of streams are more likely to be accomplished with large-scale actions (e.g., re-establishment of the native riparian forest).

Assessing the legacy of land use trajectories on stream fish communities of southern Brazil

Loss of native vegetation cover in the watershed is known to affect stream fish communities. However, community response may not occur immediately after land cover change, and may become apparent only years later. In this study, we investigated how a c.a. 30-year (1985–2017) historical trajectory of native vegetation loss affected fish communities in 47 streams of southern Brazilian grasslands. We tested whether current species richness and composition would be more related to past or to recent natural vegetation cover. We then defined trajectories of vegetation loss and tested whether different attributes (frequency, magnitude and duration of disturbance) affected particular species and functional groups. We found that current species richness and composition were more related to past than to current vegetation cover. However, we also observed that responses of particular species and functional groups were dependent on specific trajectory attributes. We concluded that present fish community characteristics may respond not only to past watershed conditions but also to how watershed conditions have changed over the time. Exploring land use trajectories seems a promising approach for improving our understanding of landscape effects on stream ecosystems, as well as the predictability of present landscape management and planning on freshwater communities.

Resource pulses increase the diversity of successful competitors in a multi‐species stream fish assemblage

AbstractFood resources are often patchily distributed through space and time and are classified as resource pulses when hyperabundant. Resource pulses can benefit growth, reproduction, and abundance of various consumers. Yet, it is relatively unknown how such resources are partitioned among competing consumers and how this is influenced by the magnitude of the pulse. Here, we examined how the magnitude of a pulsed resource influences resource partitioning among diverse sizes and species of consumers in a natural setting over small spatial and temporal scales. We focused on salmon egg subsidies to stream fish consumers. We experimentally added different quantities of pink salmon eggs to five meter long experimental stream sections. Egg additions spanned three orders of magnitude from 6 to 3575 eggs. Stream fish (egg consumers) were captured and gastric lavaged at each experimental section to determine how many eggs each individual fish consumed. We modeled taxon‐specific individual egg consumption as a function of egg availability, individual mass, community composition, number of competitors, and stream velocity using hurdle models in a Bayesian framework. We found that there were diminishing returns for increasing egg abundance increasing egg consumption (i.e., type II functional response) for individual size classes of fish, but that higher egg numbers were needed to benefit diverse consumers. Top models indicated that egg availability and individual fish characteristics (size and taxon) drove egg consumption, while community characteristics (species composition and number of competitors) were not supported. Our results suggest that resource pulses can provide rare opportunities for less dominant sizes and species of fish to consume abundant resources. The current paradigm in the stream fish literature suggests that stream fish communities are structured by dominance hierarchies; however, dominance hierarchies may be less influential where pulsed resources comprise a large portion of the resource base.

Do body mass and habitat factors predict trophic position in temperate stream fishes?

In animals with indeterminate growth, such as predatory fishes, mouth size is related to, and increases with, body mass of the organism. As fishes grow in body size, they can consume larger-bodied prey items at potentially-higher trophic levels. Therefore, body size should predict trophic position. Trophic position (TP) is useful for describing energy flow between biota, giving a more comprehensive picture of aquatic food webs, but the factors that influence the body-size–TP relationship are unclear. Additionally, stable isotope-derived TP and body-size relationships are untested for temperate freshwater fishes. Using linear mixed-effects models, we tested fish body mass as a predictor of TP across 6 species of temperate freshwater fish (n = 921 total individuals) sampled from 110 stream reaches in New Zealand, and we evaluated habitat factors (flood disturbance and stream size) likely to affect trophic structure of stream fish assemblages. Supporting ecological theory, but contrasting with some previous findings in marine and tropical environments, we found that TP was positively associated with body size across all species. Habitat factors did not affect fish TP. However, stream network spatial factors included in models as random effects explained the majority of variance in TP across species. Thus, while our study shows that New Zealand temperate freshwater fish body size is positively associated with stable isotope-derived TP, researchers will need to account for catchment-specific spatial factors to make accurate inferences about TP based on body size.

Conservation of fish communities: Extending the ‘research life cycle’ by achieving practical effects

Abstract This article highlights the practical impact of our 2018 Aquatic Conservation: Marine and Freshwater Ecosystems publication, ‘Importance of peripheral basins: Implications for the conservation of fish assemblages’, which described fish communities in a Polish river. Data on the fish assemblages of the Dniester River (Black Sea basin) are scarce; however, evidence indicates that the assemblages have declined. In our 2018 study, we hypothesized that the peripheral basin (the small basin on the edge) of the larger Upper Dniester River basin (the Strwiąż River) could maintain good ecological status and contained unique fish assemblages. To examine the influence of historical factors and assess the role of peripheral basins on fish conservation, data from the Strwiąż basin were compared with the adjacent but unconnected Wiar basin (the Vistula basin; Baltic Sea basin). The Strwiąż River fish assemblages featured higher species richness and a greater number of native Ponto–Caspian species that function near the edge of their ranges. This article focuses on four impacts of the 2018 publication: increasing awareness by various groups and organizations of the unique character of the surveyed river basin; highlighting important issues in assessing the ecological status of European rivers; driving the red‐listing of species and the development of stream fish conservation strategies; and identifying possible future impacts. Our 2018 publication demonstrated the value of studying peripheral basins, which may affect conservation strategy development and encourage study of the importance of other peripheral basins and their role in aquatic resources conservation. Our article influenced the interpretation of fish‐based biotic indices and the conduct of monitoring work and its evaluation. It also strongly emphasized the native origin of the racer goby (Babka gymnotrachelus) in the Strwiąż River, which was important for subsequent works seeking to change the legal status of the species in Poland.

Description of a new species of cryptic snubnose darter (Percidae: Etheostomatinae) endemic to north-central Mississippi.

Many subclades within the large North American freshwater fish genus Etheostoma (Percidae) show brilliant male nuptial coloration during the spring spawning season. Traditionally, perceived differences in color were often used to diagnose closely related species. More recently, perceived differences in male nuptial color have prompted further investigation of potential biodiversity using genetic tools. However, cryptic diversity among Etheostoma darters renders male nuptial color as unreliable for detecting and describing diversity, which is foundational for research and conservation efforts of this group of stream fishes. Etheostoma raneyi (Yazoo Darter) is an imperiled, range-limited fish endemic to north-central Mississippi. Existing genetic evidence indicates cryptic diversity between disjunctly distributed E. raneyi from the Little Tallahatchie and Yocona river watersheds despite no obvious differences in male color between the two drainages. Analysis of morphological truss and geometric measurements and meristic and male color characters yielded quantitative differences in E. raneyi from the two drainages consistent with genetic evidence. Morphological divergence is best explained by differences in stream gradients between the two drainages. Etheostoma faulkneri, the Yoknapatawpha Darter, is described as a species under the unified species concept. The discovery of cryptic diversity within E. raneyi would likely not have occurred without genetic tools. Cryptic diversity among Etheostoma darters and other stream fishes is common, but an overreliance on traditional methods of species delimitation (e.g., identification of a readily observable physical character to diagnose a species) impedes a full accounting of the diversity in freshwater fishes in the southeastern United States.

Mercury bioaccumulation in stream fish from an agriculturally-dominated watershed

Bioaccumulation of mercury in freshwater fish is a complex process driven by environmental and biological factors. In this study, we assessed mercury in fish from four tributaries to the Red Deer River, Alberta, Canada, which are characterized by high surface water mercury concentrations. We used carbon (δ13C) and nitrogen (δ15N) stable isotopes to examine relationships between fish total mercury (THg) concentrations, food web dynamics and patterns in unfiltered THg and methylmercury (MeHg) concentrations. We found that THg concentrations exceeded the tissue residue quality guideline for the protection of wildlife consumers in 99.7% of fish sampled. However, while the surface water THg concentration was highest in Michichi Creek and the MeHg concentration was consistent across streams, patterns of fish THg concentrations varied depending on species. Furthermore, body size and trophic level were only correlated with THg concentrations in white sucker (Catostomus commersoni) and Prussian carp (Carrasius gibelio). The results of this study suggest that mercury poses a risk to the health of piscivorous wildlife in the Red Deer River watershed. Despite high THg concentrations in these streams, mercury bioaccumulation is not driven by environmental inorganic mercury concentrations. Additionally, commonly cited factors associated with mercury concentrations in fish, such as body size and trophic level, may not strongly influence bioaccumulation in these stream ecosystems.

Social behaviour of European grayling before and after flow peaks in restored and unrestored habitats

AbstractCost‐effective implementation of fish‐friendly hydropower flow operation and habitat restoration measures require an understanding of their effects on fitness‐related behaviours of stream fish. Here, we investigated how changes in flow and bottom structure influence the social behaviour of European grayling, using large experimental flumes (700 L s−1), with and without added boulders (i.e., restored and unrestored habitat). Grayling increased their distance to nearest neighbour at the start of flow ramping up and after a flow peak compared to stable base flow. At the start of ramping up the flow, grayling made less position changes (movements >1 m) than at stable base flow and after a flow peak. In the unrestored habitat, the proportion of time grayling spent actively swimming was lower before a flow peak than it was both at the start of ramping up the flow and after the peak, an effect not found in the restored habitat. In addition, we compared two static flows, and habitat restoration mediated their effect on distance to nearest neighbour. Grayling in the restored habitat were positioned closer to each other in the low (~10 cm s−1) than in the intermediate static flow (~40 cm s−1), whereas in the unrestored habitat, grayling showed the opposite pattern. Moreover, grayling reduced their number of position changes in the intermediate static flow, which was reflected by a reduction in active swimming. Stomach analysis after the trials revealed that foraging success was higher in variable than in the stable flow treatment. These results show that flow magnitude, flow changes and instream structure play important roles in the behaviour of stream fishes.

Multiple stressor effects on alpha, beta and zeta diversity of riverine fish

We examined the effects of regional scale land use and local scale environmental and biotic stressors on alpha, beta and zeta diversities of native fish communities in wadeable streams and non-wadeable rivers in the Danube basin, Hungary. Relationships among land use and local scale environmental and biotic stressors were weak both in streams and rivers, suggesting that these stressors act relatively independently. Alpha diversity decreased strongly with increasing local scale environmental stressor intensity in rivers. On the contrary, its response to stressors was more obscure in streams, where the best-fit statistical model indicated the importance of the interaction between land use, local scale environmental and biotic stressors, while the secondly ranked model highlighted the negative impact of local scale environmental stressors. Analysis of variance using distance matrices provided evidence that stressors alone and in interactions explained compositional differences of pairs of study sites (beta diversity). Considering the degree of overall degradation, both local (alpha) and among-site (beta and zeta) diversity indices responded to increasing stressor intensity, generally negatively. Riverine fish communities showed higher degrees of similarity (lower beta and higher zeta) than stream fish communities. They also showed increasing similarity (i.e. homogenization) with increasing overall stressor intensity, unlike stream fish communities, which showed no relationship with overall stressor intensity. Our results suggest that the relationships between land use and local scale environmental and biotic stressors can be complex and so do their effects on biodiversity. While stressor specific indices can provide information on the role of specific stressors in some cases, the examination of overall stressor effects is needed to assess realistically the effects of anthropogenic disturbances on native fish diversity. Diversity indices that quantify among-site changes in species composition, such as measures of beta and zeta diversity, can be fruitful for better understanding the role of multiple stressors in structuring ecological communities.

Hotspots of species loss do not vary across future climate scenarios in a drought-prone river basin.

Climate change is expected to alter the distributions of species around the world, but estimates of species’ outcomes vary widely among competing climate scenarios. Where should conservation resources be directed to maximize expected conservation benefits given future climate uncertainty? Here, we explore this question by quantifying variation in fish species’ distributions across future climate scenarios in the Red River basin south‐central United States. We modeled historical and future stream fish distributions using a suite of environmental covariates derived from high‐resolution hydrologic and climatic modeling of the basin. We quantified variation in outcomes for individual species across climate scenarios and across space, and identified hotspots of species loss by summing changes in probability of occurrence across species. Under all climate scenarios, we find that the distribution of most fish species in the Red River Basin will contract by 2050. However, the variability across climate scenarios was more than 10 times higher for some species than for others. Despite this uncertainty in outcomes for individual species, hotspots of species loss tended to occur in the same portions of the basin across all climate scenarios. We also find that the most common species are projected to experience the greatest range contractions, underscoring the need for directing conservation resources toward both common and rare species. Our results suggest that while it may be difficult to predict which species will be most impacted by climate change, it may nevertheless be possible to identify spatial priorities for climate mitigation actions that are robust to future climate uncertainty. These findings are likely to be generalizable to other ecosystems around the world where future climate conditions follow prevailing historical patterns of key environmental covariates.

Unravelling patterns of taxonomic and functional diversity of Amazon stream fish

Environmental filtering and dispersal limitation are essential processes affecting the variability of ecological communities. However, their relative contributions are highly debated and remain largely unknown in several systems, such as the hyperdiverse Amazon Basin. We determined the relative role of local, catchment, spatial, and biogeographical variables on the taxonomic and functional alpha and beta diversity of stream fish. We sampled 54 streams across six river basins in the Amazon. For each stream, we obtained 35 local habitat variables and 11 climate-catchment variables. Watercourse distances and basin identity were converted into spatial and biogeographical variables, respectively. We found that taxonomic alpha diversity responds both to spatial and local predictors, whereas its functional counterpart was mainly associated with local variables. Biogeography was the main factor structuring taxonomic and functional beta diversity, with a secondary contribution of catchment and local variables. Locally, substrate type and isolation determined the number and relative abundance of species and traits. The shared variation between biogeographical and environmental variables, especially altitude and slope, were strongly associated with beta diversity patterns, indicating a joint role of habitat filtering and dispersal limitation. Our results show the need to include both spatial and environmental variables in studies of stream communities at large spatial scales, as they are related to distinct processes that regulate community structure. We also encourage future studies to account for the responses of multiple facets of biodiversity to different drivers, as they provide essential and complementary information for community ecology and biogeography.

Testing the diversity–biomass relationship in riverine fish communities

AbstractAimWe examined the diversity–biomass relationship in stream fish communities and quantified direct and indirect effects of abiotic variables on this relationship.LocationFrance.Time period1992–2012.Major taxa studiedStream fishes.MethodsWe analysed the relationship between biodiversity (species richness and functional diversity) and fish community biomass at 1,357 stream sites distributed throughout France. We used piecewise path analysis to quantify effects of abiotic and biodiversity variables on biomass and assess relative contributions of native and non‐native species on the diversity–biomass relationship.ResultsBiodiversity showed a direct positive relationship with biomass after controlling for sampling effort, and direct effects of biodiversity variables on community biomass exceeded those of climate and physical habitat variables. Our analysis indicates that positive effects of species richness on biomass exceeded those of functional diversity. Indirect effects of abiotic variables mediated by biodiversity metrics indicated that biomass increased in warmer, lowland habitats. Human impact had no effect on native biodiversity but had a positive effect on non‐native biodiversity.Main conclusionsWe provide evidence that direct effects of biodiversity on community biomass outweigh those of abiotic variables in riverine fish communities, but resource partitioning alone is unlikely to drive the effects of biodiversity on biomass in this system. Quantification of the relative roles of anthropogenic impacts, biodiversity and environmental context in the regulation of ecosystem functioning will be necessary to understand the potential consequences of ongoing global change.

Gradients of flow regulation shape community structures of stream fishes and insects within a catchment subject to typhoon events

Alterations in natural flow regimes caused by dams can significantly alter the aquatic habitats of stream organisms. However, few studies have characterized flow regulation to assess its impacts on stream fauna in the context of interannually variable extreme floods. This study aims to understand the variation in stream animals along flow regulation gradients due to hydropower dams in a catchment experiencing typhoons. We observed freshwater fishes and stream insects at fully regulated sites (receiving residual flow), moderately regulated sites (receiving hydropower outflow), and nonregulated site (tributary) in the Mimi River catchment in southern Japan, in summer and winter from 2010 to 2018. We computed indicators of hydrologic alteration (IHA) in each calendar/water (July to June) year from 2007 to 2017 and selected subsets of IHA based on principal component analysis (PCA) and variance inflation factor. The largest variance was mainly explained by minimum discharge levels (e.g., 30-day annual minimum) and flow variability among IHAs, distinguishing the moderately regulated and nonregulated sites from fully regulated sites because of residual flow and suppressed high pulses in the fully regulated sites. Generalized additive models revealed that annual maxima of specific discharge were most significant predictors of fish and insect metrics while its effects were generally inconsistent between summer and winter. Non-metric multidimensional scaling revealed that insect communities were clustered into the regulation extents in both seasons. The differences in winter fauna between the regulated and nonregulated sites, characterized by Ephemeroptera-Plecoptera-Trichoptera abundance, were associated with maximum discharge and high pulse numbers. Fish community variation did not correspond to flow regime gradients. Our findings on mechanistic ecohydrological consequences of various flow regulations, supported by long-term observations, will be useful for river managers attempting to compensate for alterations in flow regime and ecological integrity.

Metabolic adjustment of Pyrrhulina aff. brevis exposed to different climate change scenarios.

The increases in CO2 concentrations and, consequently, temperature due to climate change are predicted to intensify. Understanding the physiological responses of Pyrrhulina aff. brevis to the climatic scenarios proposed by the IPCC (2014) for the next 100 years is of fundamental importance to determine its susceptibility. Thus, the present study aimed to evaluate the effects of the predicted climatic scenarios for the year 2100 on the metabolic adjustments of P. aff. brevis . Specifically, the rate of oxygen uptake, electron transport system capacity, glycogen and lactate content and the role of Na+K+-ATPases and H+-ATPase were evaluated. P. aff. brevis individuals were exposed for 15 days to the simulated climatic scenarios in climate scenario rooms, where temperature and CO2 in the air were controlled. Two rooms were used to simulate the climatic scenarios predicted by the IPCC (2014): moderate (RCP 6; 2.5°C and 400μatm CO2 above current levels) and extreme (RCP 8.5; 4.5°C and 900μatm CO2 above current levels), in addition to the "control room" that represents the current scenario. There was an increase in the metabolic rate (MO2) in the animals acclimated to the climate change scenarios (RCP 6 and RCP 8.5) compared to the current scenario. These responses showed a typical effect of temperature on energy demand in relation to the increase in temperature and CO2. Our data showed an increase in O2 consumption (MO2), lactate levels and H+-ATPase activity of the animals acclimated to the moderate and extreme climate change scenarios. Such adjustments presented a clear metabolic imbalance, an alteration that may imply challenges for survival, growth, distribution and reproduction in the face of the expected environmental changes for the year 2100.