Biogeography,ecoregions, and geomorphology affect fish species composition in streams of eastern Oklahoma,USA

Stream fish assemblages are structured by biogeographical, physical and biological factors acting on different spatial scales. We determined how physical factors, geomorphology and stream habitat, influenced fish species composition (presence–absence) in eastern Oklahoma, USA relative to the ecoregion and biogeographic effects previously reported. We sampled fish assemblages and surveyed geomorphology and habitat at 107 stream sites in the Boston Mountains, Ouachita Mountains, and Ozark Highlands ecoregions in eastern Oklahoma. Partial canonical correspondence analyses (pCCAs) and variance partitioning showed that patterns of endemism related to drainage basins and ecoregions explained important variation in fish species composition in all streams, but stream size and local channel morphology explained more variation overall. Stream size effects were most important in explaining variability in fish species composition in both northeastern and southeastern Oklahoma streams. Local channel morphology and substrate characteristics were secondarily important. Variables typically considered important as fish habitat (aquatic vegetation, etc.) had little effect on fish species composition.     

Ichthyofauna of two streams (silted and reference) in the Upper Paraná river basin, Southeastern Brazil.

In this study the fish assemblages of the silted Aguas Claras stream (AC) was compared with that of a reference, the S?o Carlos stream (SC), so as to identify potential fish indicators of integrity or degradation. Both streams, located about 5 km from one another, are part of the Upper Paraná river basin, Brazil, and present similar physiographical features. Twenty-one species were collected in AC (1,271 specimens) and 18 in SC (940 specimens). In AC, dominant species e.g., Corydoras aeneus (sandy pools), Serrapinnus notomelas, and Pyrrhulina australis (warm marginal shallow pools) were those favored by new microhabitats linked to siltation and removal of the riparian vegetation. Changes in the composition of the marginal vegetation resulted in dominance of species such as Hisonotus francirochai (marginal grasses). In SC the dominant species was Phalloceros caudimacultus, abundant in marginal shallow pools, and Trichomycterus diabolus. and Hypostomus nigromaculatus, exclusively riffle-dwelling species, which were absent in AC. Fish assemblage monitoring is recommended for use in riparian management programs in order to evaluate negative instream sedimentation effects.     

Inter and intraspecific variation in fish body size constrains microhabitat use in a subtropical drainage

Microhabitat characteristics are expected to influence the distribution of stream fish species at fine spatial scales (e.g., within riffle segments). Body size is probably the most important trait that constrains microhabitat occupation by fish, but the effect of intraspecific variation has been understudied. We investigated how physical microhabitat characteristics affect species and body size distribution of fish within a stream riffle segment in a coastal subtropical drainage of Brazil. Fishes were sampled by electrofishing 56 riffle plots along a 730-m long stream segment. Species composition was significantly related to four microhabitat characteristics: substrate size, flow velocity, distance to margin and depth. In addition, mean body size increased with increasing substrate size and depth of microhabitat sampling plots. However, when including species identity in linear mixed-effects models (LMM), we observed a different relationship between body size and microhabitat characteristics, but most of the variation was explained by species identity. Thus, we fitted LMMs separately for each species and found species-specific relations between intraspecific variation in body size and microhabitat characteristics. The low variation explained in the models suggests that other fine scale factors, such as biotic interactions and dispersal from adjacent habitat patches, should be incorporated in modeling microhabitat use by stream fish. Our findings suggest that body size is important by itself, but intraspecific variation in body size also constrains microhabitat use differently for each species, which may depend on other species-specific traits, such as morphology, behavior and life history.     

Quantifying the direct and indirect effects of flow‐related disturbance on stream fish assemblages

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Revealing the pathways by which agricultural land‐use affects stream fish communities in South Brazilian grasslands

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Concordance among stream assemblages and spatial autocorrelation along a fragmented gradient

Patterns of spatial autocorrelation of biota and distributional similarity (concordance) between assemblages of different organism groups have important implications in both theoretical ecology and biodiversity conservation. Here we report environmental gradients and spatial distribution patterns of taxonomic composition among stream fish, benthic macroinvertebrate, and diatom assemblages along a fragmented stream in south‐western France. We quantified spatial patterns of lotic assemblage structure along this stream, and we tested for concordance in distribution patterns among the three taxonomic groups. Our results showed that both environmental characteristics and stream assemblages were spatially autocorrelated. For stream fish and diatom assemblages, these patterns reflected assemblage changes along the longitudinal stream gradient, whereas environmental variables and benthic macroinvertebrates exhibited a more patchy spatial pattern. Cross‐taxa concordance was significant between stream fish and diatoms, and between stream fish and benthic macroinvertebrates. The assemblage concordance between stream fish and diatoms could be attributed to similar responses along the longitudinal gradient, whereas those between stream fish and benthic macroinvertebrates may result from biotic interactions. Based on potential dispersal capacities of taxa, our results validated the hypotheses that weakly dispersing taxa exhibit greater concordance than highly dispersing ones and that dispersal capacities affect how taxonomic groups respond to their local environment. Both diatoms and highly dispersing stream fish were affected by stream fragmentation (i.e. the number of dams between sites), while the effect of fragmentation was not significant for invertebrates that fly well in their adult stage, thus emphasizing the importance of the way of dispersal. These results suggest that addressing the effects of dispersal capacity on stream assemblage patterns is crucial to identifying mechanisms behind patterns and to better understanding the determinants of stream biodiversity.     

Effect of siltation on stream fish communities

Synopsis The effect of siltation on stream fish in northeast Missouri was evaluated using community structural measurements and a functional approach that emphasized feeding and reproductive guilds. As the percentage of fine substrate increased, the distinction among riffle, run, and pool communities decreased, primarily because the number of individuals of typical riffle species decreased. Within the riffle communities the abundance of fish of two feeding guilds — benthic insectivores and herbivores — was reduced as the percent of fine substrate increased. The abundance of fish in other feeding guilds was not affected. The only reproductive guild to be similarly affected was the simple and lithophilous, whose members require a clean gravel substrate for spawning. Species within each guild affected by siltation had significantly similar trends in abundance. The guild analysis indicated that species with similar ecological requirements had a common response to habitat degradation by siltation.     

Relationship between genotoxicity,mutagenicity, and fish community structure in a contaminated stream

Genotoxic responses (chromosomal damage, DNA strandbreakage) of redbreast sunfish (Lepomis auritis)populations exposed to industrial effluent andmutagenicity of the associated sediments weredetermined in order to compare them to changes incommunity structure. Data were collected from areference stream and East Fork Poplar Creek (EFPC), afirst-order stream which originates on the grounds ofthe Department of Energy Y-12 Plant at Oak Ridge, TN. This stream is contaminated with mercury, PCBs, andnumerous other compounds. Previous studies have shownthat sediment contaminant concentrations, as well asphysiological biomarker responses of the local fishpopulations, are highest at the headwaters of EFPC anddecrease with increasing distance from the DOEfacility as contaminant loading decreases. Chromosomal damage was measured by flow cytometry – asreflected by variation in cellular DNA content – andstrand breakage was determined by agarose gelelectrophoresis using blood as the source of DNA. Mutagenicity was determined by theSalmonella/microsome assay using organic solventextracts of sediment surface samples. Community levelresponses included community diversity and percentpollution-tolerant species. Biomarker responses andmutagenicity were found to be highest at theheadwaters of EFPC, and tended to decrease withincreasing distance from the effluent. In general,biomarker responses appeared to be correlated withmutagenicity of the sediment, and both of theserelated to fish community disturbance and level ofstream contamination. Because responses at severallevels of biological organization show similarpatterns of downstream effects, this suggests thatthere may be a causal relationship betweencontamination and biological effects.     

Use of terrestrial arthropod prey by a stream-dwelling cyprinid fish

Synopsis The spatio-temporal availability to, and use of terrestrial (allochthonous) prey by, a subset of the fish assemblage of a Virginia piedmont stream were investigated during spring and summer. Terrestrial invertebrates were most abundant in drift nets, but least common in fish stomachs, during April. In contrast, during August, terrestrial prey dominated the diet of the major cyprinid fish,Notropis ardens, even though terrestrial prey availability in the stream declined by an order of magnitude. Several other co-occurring fishes only rarely consumed prey of terrestrial origin. Drifting terrestrial invertebrates, were concentrated at the surface near the thalweg, compared to stream margin or substrate locations. This study suggests that morphologial and behavioral constraints of individual fish taxa, including predator avoidance responses, regulate the use of terrestrial prey within a given fish assemblage.     

Functional redundancy of stream macroconsumers despite differences in catchment land use

1. The conversion of forested landscapes to agriculture and, increasingly, to suburban and urban development significantly affects the structure and function of both terrestrial and aquatic ecosystems. While a growing body of research is examining how biotic communities change in response to human alteration of landscapes, less is known about how these changes in community structure affect biotic interactions. 2. The objective of this study was to examine top‐down control by macroconsumers (fish and crayfish) across a human‐impacted landscape. We predicted that changes in stream macroconsumers and physicochemical characteristics associated with increased catchment development (e.g. decreased abundance of fish that are obligate benthic invertivores, increased sedimentation) would diminish top‐down control of benthic insects. We expected that effects on algal assemblages would be more variable, with increased top‐down control at sites dominated by algivorous fish and diminished control elsewhere. To test these predictions, we experimentally excluded fish and crayfish from areas of the bed of five streams whose catchments ranged from 100% to <50% forested, and examined the effects of exclusion on benthic insects and algae. 3. Despite cross‐site differences in physical, chemical and biological characteristics, the outcome of our experiments was consistent across five sites representing a range of catchment development. Across all sites, macroconsumers reduced total insect biomass, largely due to decreases in Chironomidae and Hydropsychidae larvae. Macroconsumers also affected algal assemblages, reducing chlorophyll‐a and the proportion of upright and filamentous diatoms (e.g. Melosira, Cymbella) but increasing the proportion of adnate diatoms (e.g. Achnanthes) across all sites. 4. We expected that differences in factors such as macroconsumer assemblage composition, nutrient and light availability and sedimentation would result in variable responses to macroconsumer exclusion in the five streams. Contrary to these expectations, only one response variable (ash‐free dry mass) showed a statistically significant interaction (i.e. site × exclusion) effect. Most responses to exclusion were relatively consistent, suggesting functional redundancy in assemblages of macroconsumers among the sites despite differences in catchment land use.     

Identification of key microhabitats for fish assemblages in tropical Brazilian savanna streams

The habitat use by stream fish can provide an understanding of this important component of species niches, and the changes in the availability of certain structures of instream habitats have a strong influence on the occurrence and abundance of fish species. In this study, we identified the interaction networks between fish and microhabitats in 19 streams of three watersheds from the Brazilian savanna, known as the “Cerrado”. We also investigated whether the connectance between fish species and microhabitats depends on either the species abundance or availability of microhabitats and verified whether the use of stream microhabitats vary among watersheds. The data for the fish were obtained using standardized fish collections and underwater (snorkeling) observations to record the association of fish species with 11 stream microhabitats. We used the incidence data to calculate the connectance of species with different microhabitats, a Spearman correlation analysis to test the dependence of the connectance to the species abundance and microhabitat availability, and an Analysis of Similarity to test whether the use of stream microhabitats by fish can vary among watersheds. In all of the watersheds, the tetras of the family Characidae used the largest number of microhabitats. The most‐used microhabitats by the fish watersheds were the lateral surface, column surface, and unconsolidated substrate, which were differentially used by the fish in each watershed, indicating the variable importance of microhabitats. Despite this observation, the fish occurred more frequently in the lateral microhabitats. When the data for all of the streams were combined, the species connectance was correlated with the species abundance. We also discuss the consequences of the elimination of certain bottom structures in the context of siltation, which is the main issue in the studied region. The results of our study allowed the detection of key microhabitat structures and can be used for the aquatic ecosystems restoration. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A quarter century of change in the fish communities of three small streams modified by anthropogenic activities

Anthropogenic modification of small stream habitats insouthern Ontario has occurred with little concern forindigenous, non-game fish communities. The combinedeffects of urbanization, impoundment, and agricultureon the fish communities of three small streams, fromheadwaters to near-confluence locations, wereevaluated by comparing current fish communitystructure to historical records (species lists)collected over the last quarter century. Comparisonsusing cluster analysis showed that spatial andtemporal shifts in fish community composition did notoccur immediately after stream modifications but tookup to 10 years. Replacement of common species byformerly rare or absent species was evident in twostreams subjected to urbanization and impoundment;stream sections subjected to primarily agriculture land usedemonstrated minimal change during this study period. Urban zones and sections downstream of impoundmentswere dominated by species tolerant of controlledflows, siltation, channelization, homogenous spawningsubstrates, and elevated temperatures. Barrier-freeheadwater and agriculture zones with abundant riparianvegetation supported communities that were intolerantof controlled flows, dependent on lower summer watertemperatures, and require high dissolved oxygenlevels. Greater understanding of the causative forcesshaping fish communities can be used to facilitateintegration of greater biological realism into anyfuture conservation or restoration programs inanthropogenically-modified streams.     

Nematomorph parasites indirectly alter the food web and ecosystem function of streams through behavioural manipulation of their cricket hosts

Nematomorph parasites manipulate crickets to enter streams where the parasites reproduce. These manipulated crickets become a substantial food subsidy for stream fishes. We used a field experiment to investigate how this subsidy affects the stream community and ecosystem function. When crickets were available, predatory fish ate fewer benthic invertebrates. The resulting release of the benthic invertebrate community from fish predation indirectly decreased the biomass of benthic algae and slightly increased leaf break-down rate. This is the first experimental demonstration that host manipulation by a parasite can reorganise a community and alter ecosystem function. Nematomorphs are common, and many other parasites have dramatic effects on host phenotypes, suggesting that similar effects of parasites on ecosystems might be widespread.     

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     

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.     

Effects of fine sediment addition and removal on stream invertebrates and fish: a reach‐scale experiment

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Induction of heat shock proteins, changes in liver ultrastructure, and alterations of fish behavior: are these biomarkers related and are they useful to reflect the state of pollution in the field?

Heat shock protein (hsp70) expression, changes inliver ultrastructure, and alterations of swimmingbehavior were simultaneously investigated in browntrout (Salmo trutta f. fario) exposed towater from test streams in southern Germany undersemi-field conditions during 1995 and 1996. Chemicalanalyses revealed different levels of contamination ofthe two streams by pesticides, PAHs, PCBs, and heavymetals, whereas stream pollution was only partlyreflected by body burdens of contaminants in fish.Biomarker responses were compared after differenttimes of exposure and with respect to differenttemperature conditions. Differences in pollutionstates of the streams were reflected by differentbiomarker responses of the trout. In the highlycontaminated stream, the biomarker responses were morecoincident with one another than in the moderatelypolluted stream in which the biomarkers showed littlerelation to one another. This is primarily due to thedifferential capacities of the biomarkers to integratestress responses over time. Understanding the dynamicsof the stress response curves and the effects oftemperature on biomarker responses is essential forevaluating the effects of environmental stressors suchas contaminants on the health of organisms.     

Relating fish biomass to habitat and chemistry in headwater streams of the northeastern United States

Stream pH and stream habitat have both been identified as important environmental features influencing total fish biomass in streams, but few studies have evaluated the relative influence of habitat and pH together. We measured total fish biomass, stream habitat, and stream pH in sixteen sites from three tributary systems in the northeastern United States. The habitat metrics included total pool area, a cover score, large wood frequency, and stream temperature. We created and compared nine linear models relating total fish biomass in summer to stream pH and stream habitat using Akaike’s Information Criterion (AIC) analysis. The best (most parsimonious) models included pool area and stream pH. These results and a separate comparison of three regressions (low-flow pH, pool area, and these two metrics together versus total fish biomass) suggest that both habitat and stream buffering capacity affect the total biomass of fish in northeastern US headwater streams. When stream pH is adequate (low-flow pH greater than at least 5.7), physical habitat is likely to be more important, but under lower pH conditions, habitat is likely to be less effective in accounting for the total biomass of fish in these streams. This work demonstrates the continued effects of stream acidification in the northeastern US and more generally, it illustrates the importance of considering both physical and chemical conditions of a stream when evaluating the factors influencing fish communities.     

Downstream fish assemblage response to river impoundment varies with degree of hydrologic alteration

River impoundments can fundamentally restructure downstream fish assemblages by altering flow regimes. However, the degree of alteration and associated ecological change may depend on pre-existing hydrologic regimes. We used long-term datasets to compare downstream hydrological and fish assemblage responses to impoundment in two catchments classified as having intermittent and perennial-flashy natural hydrologic regimes. We observed significant shifts in fish assemblage structure at both sites after stream impoundment. The historically intermittent stream shifted to a stable perennial flow regime. Changes in fish assemblage structure covaried with changes in five different components of the flow regime; most species that increased in abundance require fluvial habitats and likely benefited from increased flows during historically low flow seasons. Shifts in fish assemblage structure were also observed in the perennial stream, despite minimal flow alteration after impoundment; however, most species shifts were associated with lentic environments, and were more likely related to proximity of reservoirs in the drainage system rather than changes in stream flow. Findings from this study confirm that downstream fish assemblage response to river impoundment can be associated with high levels of hydrologic alteration, but other factors including expansion of lentic species into lotic environments also influence shifts in assemblage structure.