Diatom Assemblages and their Associations with Environmental Variables in Oregon Coast Range Streams, USA

The Oregon Coast Range, rich in natural resources, is under increasing pressure from rapid development. The purpose of this study was to examine diatom species patterns in relation to environmental variables in streams of this region. Diatoms, water quality, physical habitat and watershed characteristics were assessed for 33 randomly selected stream sites. Watershed size, elevation, geology, vegetation and stream morphology varied substantially among sites. Streams were characterized by dilute water chemistry and a low percent of fine substrate. A total of 80 diatom taxa were identified. Taxa richness was low throughout the region (median 15, range 10–26). Assemblages were dominated by two adnate species, Achnanthidium minutissimum and Achnanthes pyrenaicum. Diatoms sensitive to organic pollution dominated the assemblages at all sites (median 85%). Non-metric multidimensional scaling (NMDS) and correlational analysis showed quantitative relationships between diatom assemblages and environmental variables. NMDS axes were significantly correlated with watershed area, watershed geology, conductivity, total nitrogen, total solids and stream width. Diatom-based site classification (Two-way Indicators Species Analysis, (TWINSPAN)) yielded 4 discrete groups that displayed weak correlations with environmental variables. When stream sites were classified by dominant watershed geology, overall diatom assemblages between groups were significantly different (Analysis of Similarity (ANOSIM) global R = 0.19, p < 0.05). Our results suggest that streams in the coastal region are in relatively good condition. High natural variability in stream conditions in the Oregon Coast Range ecoregion may obscure quantitative relationships between environmental variables and diatom assemblages. A bioassessment protocol that classifies sites by major landscape variables and selects streams along the major human disturbance gradient might allow for detection of early signs of human disturbance in environmentally heterogeneous regions, such as the Pacific Northwest.     

Dissimilarity of stream insect assemblages: effects of multiple scales and spatial distances

In addition to the effects of environmental conditions, biotic assemblages may exhibit spatial structure depending on the scale of study. We tested whether the dissimilarity of stream insect assemblages is related to two types of spatial distances (stream corridor and overland distance), and evaluated the relative importance of diversity components at multiple spatial scales. Field data included assemblages of Ephemeroptera, Plecoptera, and Trichoptera found in 16 streams in four microbasins. We evaluated the relationship of the dissimilarity of assemblages with the distance types, using Mantel tests. In addition, we evaluated the relationships among the diversity components at multiple spatial scales, using additive partitioning analysis. The biological dissimilarities were correlated only with the geographical distances. Additive partitioning showed that the values of richness observed in the β1 (among Surber), β2 (among riffles), β3 (among streams), and β4 (among microbasins) were higher than those expected. The highest variation of the richness was found in β3 (30.6%). We conclude that stream faunas are distributed in patches all over the studied spatial extent, causing a weak relationship of biological dissimilarity with distance but important beta components when compared to a completely homogenous distribution of the fauna.     

Niche partitioning and the effect of interspecific competition on microhabitat use by two sympatric galaxiid stream fishes

1. Numerous interacting abiotic and biotic factors influence niche use and assemblage structure of freshwater fishes, but the strength of each factor changes with spatial scale. Few studies have examined the role of interspecific competition in structuring stream fish assemblages across spatial scales. We used field and laboratory approaches to examine microhabitat partitioning and the effect of interspecific competition on microhabitat use in two sympatric stream fishes (Galaxias‘southern’ and Galaxias gollumoides) at large (among streams and among sites within streams) and small (within artificial stream channels) spatial scales. 2. Diurnal microhabitat partitioning and interspecific competition at large spatial scales were analysed among three sympatry streams (streams with allotopic and syntopic sites; three separate catchments) and four allopatry streams (streams with only allotopic sites; two separate catchments). Electro‐fishing was used to sample habitat use of fishes at 30 random points within each site by quantifying four variables for each individual: water velocity, depth, distance to nearest cover and substratum size. Habitat availability was then quantified for each site by measuring those variables at each of 50 random points. Diet and stable isotope partitioning was analysed from syntopic sites only. Diel cycles of microhabitat use and interspecific competition at small spatial scales were examined by monitoring water velocity use over 48 h in artificial stream channels for three treatments: (i) allopatric G. ‘southern’ (10 G. ‘southern’); (ii) allopatric G. gollumoides (10 G. gollumoides) and (iii) sympatry (five individuals of each species). 3. One hundred and ninety‐four G. ‘southern’ and 239 G. gollumoides were sampled across all seven streams, and habitat availability between the two species was similar among all sites. Galaxias‘southern’ utilised faster water velocities than G. gollumoides in both the field and in channel experiments. Both species utilised faster water velocities in channels at night than during the day. Diet differences were observed and were supported by isotopic differences (two of three sites). No interspecific differences were observed for the other three microhabitat variables in the field, and multivariate habitat selection did not differ between species. Interspecific competition had no effect on microhabitat use of either species against any variable either in the field (large scale) or in channels (small scale). 4. The results suggest that niche partitioning occurs along a subset of microhabitat variables (water velocity use and diet). Interspecific competition does not appear to be a major biotic factor controlling microhabitat use by these sympatric taxa at any spatial scale. The results further suggest that stream fish assemblages are not primarily structured by biotic factors, reinforcing other studies de‐emphasising interspecific competition.     

Spatial population genetic structure reveals strong natal site fidelity in Echinocladius martini (Diptera: Chironomidae) in northeast Queensland,Australia

1. A diverse array of patterns has been reported regarding the spatial extent of population genetic structure and effective dispersal in freshwater macroinvertebrates. In river systems, the movements of many taxa can be restricted to varying degrees by the natural stream channel hierarchy. 2. In this study, we sampled populations of the non‐biting freshwater midge Echinocladius martini in the Paluma bioregion of tropical northeast Queensland to investigate fine scale patterns of within‐ and among‐stream dispersal and gene flow within a purported historical refuge. We amplified a 639‐bp fragment of mitochondrial cytochrome c oxidase subunit I and analysed genetic structure using pairwise Φ_ST, hierarchical amova , Mantel tests and a parsimony network. Genetic variation was partitioned among stream sections, using Streamtree , to investigate the effect of potential instream dispersal barriers. 3. The data revealed strong natal site fidelity and significant differentiation among neighbouring, geographically proximate streams. We found evidence for only episodic adult flight among sites on separate stream reaches. Overall, however, our data suggested that both larval and adult dispersal was largely limited to within a stream channel. 4. This may arise from a combination of the high density of riparian vegetation physically restricting dispersal and from the joint effects of habitat stability and large population sizes. Together these latter may make it more likely that upstream populations will persist, even in the absence of regular compensatory upstream flight, and will thus reduce the adaptive value of dispersal among streams. Taken together, these data suggest that dispersal of E. martini is highly restricted, to the scale of only a few kilometres, and hence occurs predominantly within the natal stream.     

Characterizing fish–habitat associations in streams as the first step in ecological restoration

Abstract Habitat availability is often regarded as the primary factor that limits population and community recovery in degraded ecosystems, and physical habitat is thus often targeted in restoration. The identification of which habitat(s) to attempt to restore is a critical step in the restoration process, but one for which there is often a paucity of useful information. Here we examine the distribution of fish in three lowland streams in Victoria, Australia, that have been degraded by severe sedimentation. We aim to identify habitats that are associated with high abundances of native fish, and that thus might be appropriate to target in habitat restoration. Associations between native fish abundances and physical habitat characteristics were examined at three spatial scales (among streams, among sites and within sites) to determine the types of habitat to which fish respond, and the scales over which these responses occur. Of the four species of native fish found in the streams, three (Galaxias olidus Günther, Gadopsis marmoratus (Richardson) and Nanoperca australis Günther) showed significant habitat associations at small spatial scales (i.e. within sites). In particular, these species were generally found in deeper water, and in close proximity to cover (typically either coarse or fine woody debris or vegetation). Differences in habitat availability among sites and streams were less influential, except in the case of G. marmoratus, which was completely absent from both the ephemeral streams. Although our results suggest that these species collectively respond to habitat at several spatial scales, fish distributions were allied to the presence of habitat structure at the scale of metres, the smallest spatial scale examined. We hypothesize that fish abundances are currently limited by the low availability of habitat at these small spatial scales. It may therefore be possible to increase fish abundances in these creeks by augmenting the amount of available habitat via stream restoration.     

Phylogenetic and morphometric analyses reveal ecophenotypic plasticity in freshwater mussels Obovaria jacksoniana and Villosa arkansasensis (Bivalvia: Unionidae)

Freshwater mollusk shell morphology exhibits clinal variation along a stream continuum that has been termed the Law of Stream Distribution. We analyzed phylogenetic relationships and morphological similarity of two freshwater mussels (Bivalvia: Unionidae), Obovaria jacksoniana and Villosa arkansasensis, throughout their ranges. The objectives were to investigate phylogenetic structure and evolutionary divergence of O. jacksoniana and V. arkansasensis and morphological similarity between the two species. Our analyses were the first explicit tests of phenotypic plasticity in shell morphologies using a combination of genetics and morphometrics. We conducted phylogenetic analyses of mitochondrial DNA (1416 bp; two genes) and morphometric analyses for 135 individuals of O. jacksoniana and V. arkansasensis from 12 streams. We examined correlations among genetic, morphological, and spatial distances using Mantel tests. Molecular phylogenetic analyses revealed a monophyletic relationship between O. jacksoniana and V. arkansasensis. Within this O. jacksoniana/V. arkansasensis complex, five distinct clades corresponding to drainage patterns showed high genetic divergence. Morphometric analysis revealed relative differences in shell morphologies between the two currently recognized species. We conclude that morphological differences between the two species are caused by ecophenotypic plasticity. A series of Mantel tests showed regional and local genetic isolation by distance. We observed clear positive correlations between morphological and geographic distances within a single drainage. We did not observe correlations between genetic and morphological distances. Phylogenetic analyses suggest O. jacksoniana and V. arkansasensis are synonomous and most closely related to a clade composed of O. retusa, O. subrotunda, and O. unicolor. Therefore, the synonomous O. jacksoniana and V. arkansasensis should be recognized as Obovaria arkansasensis (Lea 1862) n. comb. Phylogenetic analyses also showed relative genetic isolation among drainages, suggesting no current gene flow. Further investigation of in‐progress speciation and/or cryptic species within O. arkansasensis is warranted followed by appropriate revision of conservation management designations.     

Assessment of an index of biological integrity (IBI) to quantify the quality of two tributaries of river Chenab,Sialkot, Pakistan

Nullah Aik and Nullah Palkhu, two tributaries of river Chenab, were investigated for the assessment of fish habitat degradation as indicator of stream health. Fish abundance data were collected from 18 sites from September 2004 to April 2006 to develop multimetric indices for fish assemblage integrity and to detect the intensity of habitat degradation. A total of 12 metrics were calculated on the basis of taxonomic richness, habitat preference, trophic guild, stress tolerance and origin of species to develop stepped and continuous index of biological integrity (IBI) criteria. Cluster analysis (CA) classified sites based on species composition into three groups, viz., reference, moderately impaired and impaired groups. Non-metric multidimensional scaling (NMDS) was applied to identify underlying ecological gradient to highlight the habitat degradation. NMDS segregated two sites as less impaired, five sites as moderately impaired and eleven sites as impaired groups. Axes 1 and 2 explained a total variation of 53.3%. First axis explained the level of habitat impairment, whereas axis 2 indicated species richness along longitudinal gradient of streams. Sites located upstream of Nullah Aik showed higher IBI scores which dropped to its lowest in downstream sites near Sialkot city. Lowest values of IBI of sites in close proximity of city indicated the role of anthropogenic activities in catchment areas. The results indicated that variability in water chemistry can be related as a function of stream sites impairments (i.e., unimpaired, moderately impaired, and severely impaired). Water quality parameters showed strong correlation with IBI scores. Significantly negative correlation of IBI scores with COD, TDS, turbidity, Fe, Cr, Zn and positive correlation with DO and pH was found. The results can be used for restoration and future management of small streams passing through urban areas of Pakistan. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: J. A. Cambray     

Beta diversity of stream diatoms at two hierarchical spatial scales: implications for biomonitoring

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The spatial structure of variation in salamander survival,body condition and morphology in a headwater stream network

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A fish-based biotic integrity index for assessment of lowland streams in southeastern Brazil

This study was carried out to develop and apply a fish-based biotic integrity index to assess lowland streams in a highly deforested region of the Upper Paraná River basin. Fifty-six first-order segments were randomly selected for environmental and fish evaluation. Because previous analysis had identified the main type of effect on the streams of the region as physical habitat degradation, 22 qualitatively biological attributes were selected and tested over a physical condition gradient between reference and degraded sites. Sensitivity and redundancy of each attribute revealed that five metrics were adequate for discriminating higher quality from degraded sites. Of the fifty-six streams assessed, one (2%) was classified as good, four (7%) as fair, ten (18%) as poor, and forty-one (73%) as very poor, indicating that, on a regional scale, many aspects of biological integrity are altered, indicative of serious degradation. Considering that first-order segments amount to 11,000 km in total, it is noticeable that 10,000 km of the stream segments have no more than half of the expected conditions, indicative of poor or very poor biotic integrity conditions. Possible strategies of mitigating this scenario are discussed. Handling editor: S. M. Thomaz