Macroinvertebrate community structure in relation to environmental variables in a Swiss glacial stream

1. Benthic macroinvertebrate distribution was examined in relation to channel characteristics (including stability), substratum, hydraulic variables, primary production (chlorophyll a ) and coarse particular organic matter (CPOM) in an alpine glacial stream, the Mutt (Upper Rhône valley, Switzerland). Co-inertia analysis and canonical correspondence analysis were used to identify the major environmental gradients influencing community variations.
2. The Mutt (length: 3.6 km, altitudinal range: 1800–3099 m a.s.l.) exhibited typical characteristics of a kryal stream. Average summer temperature remained below 2 °C immediately downstream from the snout but was on average 5 °C higher 1700 m downstream. Seasonal variations in water sources were evidenced by the high late-summer (September) contribution of groundwater with increased conductivity.
3. Sixty-six taxa were recorded from the five reaches sampled at three periods (snowmelt, ice melt and low water in late summer) in 1996 and 1997, of which 29 were Chironomidae. Three taxa of Diamesinae were the first colonizers of the stream below the glacier, but 16 taxa, including Ephemeroptera, Plecoptera and Trichoptera, were already recorded 200 m downstream. Water depth, channel slope and Pfankuch's Index of channel stability were strongly correlated with the longitudinal faunal gradient. Maximum temperature, current velocity and water conductivity were also correlated, but to a lesser extent.
4. The rapid incorporation of non-chironomid taxa into the stream community represented a departure from Milner & Petts's (1994) conceptual model of invertebrate succession downstream of glacial margins. The results confirmed that glacial stream communities are primarily driven by physical determinants.     

Biological traits of stream macroinvertebrates from a semi-arid catchment: patterns along complex environmental gradients

1. The relationships between biological traits of macroinvertebrates and environmental characteristics were investigated in streams with contrasting physical, chemical or landscape level attributes. We used an ordination technique, RLQ analysis, which links an environmental table (R) with traits table (Q) through an abundance table (L) to investigate the relationship between habitat characteristics and biological traits.
2. A major environmental axis explaining the distribution of species and their distinctive biological features was obtained. This axis included variables of anthropogenic pressure (agricultural and urban uses) and natural variability (climatic and geologic) that are strongly intercorrelated in the study area, with a clear spatial component.
3. The attributes of species from frequently disturbed systems (small size, multivoltinism, diapause, ovoviviparity, etc.) were associated with semi-arid areas whereas traits common in more stable and favourable environments (large body size, semi-voltinism, isolated eggs, etc.) were found in upland forested areas.
4. The natural climatic variation was proposed as a disturbance axis of a theoretical habitat templet (driven by the intense hydrological disturbances typical of semi-arid streams), while anthropogenic pressure (mainly intensive agriculture) and high salinity, a natural consequence of geology, was proposed as an adversity axis. Different life-histories associated with contrasting environmental features were superimposed in this habitat templet.
5. The ecological–evolutionary scenario in which stream macroinvertebrates have evolved and by which their communities are organized, is closely linked to disturbance, environmental harshness and human pressure.     

Gradients in stream fish assemblages across a Mediterranean landscape: contributions of environmental factors and spatial structure

1. Despite wide recognition that fish assemblages are influenced by factors operating over a range of spatial scales, little effort has been devoted to quantifying large‐scale variation and the multiscale dependencies of assemblage patterns and processes. This is particularly true for Mediterranean streams, where seasonally predictable drying‐up may lead to a strong association between assemblage attributes and large‐scale factors affecting the distribution of population sources and extinction likelihood. 2. The contribution of large‐scale factors to stream fish assemblage variation was quantified across a Mediterranean landscape, in south‐west Portugal. Fish abundance and species composition were estimated at 166 sites across third‐ to sixth‐order streams, in March–July 1998. Variance partitioning by redundancy analyses was used to analyse assemblage variation against three sets of predictor variables: environmental (catchment position, and geomorphic and hydrological factors), large‐scale spatial trends and neighbourhood effects. 3. Environmental variables and spatial trends accounted for 34.6% of the assemblage variation across the entire region, and for 36.6 and 57.8% within the two largest catchments (Mira and Seixe). Neighbourhood effects were analysed at the catchment scale, increasing the explained variation to 56.1% (Mira) and 70.7% (Seixe). 4. A prevailing environmental gradient was reflected in an increase in the abundance of all species and size‐classes in relation to catchment position, with more fish present in larger streams and in downstream reaches. Variables describing geomorphic and hydrological settings were less important in explaining assemblage variation. 5. Spatial trends always accounted for the smallest fraction of assemblage variation, and they were probably associated with historical barriers to fish dispersal. The strong neighbourhood effects may be related to spatially autocorrelated habitat conditions, but they are also a likely consequence of fish emigration/extinction and colonisation processes. 6. These results emphasise that a substantial proportion of fish assemblage variation in Mediterranean streams may be explained by large‐scale factors, irrespective of microhabitats and local biotic interactions. It is suggested that this pattern results to a large extent from the seasonal drying‐up, with the summer shortage of surface water limiting fish occurrence in headwaters, and consequently the key core areas for fish concentrating in larger streams and tributaries adjacent to large streams because of neighbourhood effects.     

Environmental and spatial controls of taxonomic versus trait composition of stream biota

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Implications of community concordance for assessing stream integrity at three nested spatial scales in Minnesota,U.S.A.

1. Fish and invertebrate assemblage data collected from 670 stream sites in Minnesota (U.S.A.) were used to calculate concordance across three nested spatial scales (statewide, ecoregion and catchment). Predictive taxa richness models, calibrated using the same data, were used to evaluate whether concordant communities exhibited similar trends in human‐induced taxa loss across all three scales. Finally, we evaluated the strength of the relationship between selected environmental variables and the composition of both assemblages at all three spatial scales. 2. Significant concordance between fish and invertebrate communities occurred at the statewide scale as well as in six of seven ecoregions and 17 of the 21 major catchments. However, concordance was not consistently indicative of significant relationships between rates of fish and invertebrate taxa loss at those same scales. 3. Fish and invertebrate communities were largely associated with different environmental variables, although the composition of both communities was strongly correlated with stream size across all three scales. 4. Predictive taxa‐loss models for fish assemblages were less sensitive and precise than models for invertebrate assemblages, likely because of the relatively low number of common fish taxa in our data set. Both models, however, distinguished reference from non‐reference sites. 5. The importance of concordance, geographic context and scale are discussed in relation to the design and interpretation of stream integrity indicators. In particular, our findings suggest that community concordance should not be viewed as a substitute for an evaluation of how assemblages respond to environmental stressors.     

Diel activity patterns of the fish community in a temperate stream

The diel activity patterns of fishes in a temperate New Brunswick stream were studied during the summer over 5 years. Young‐of‐the year Atlantic salmon Salmo salar and blacknose dace Rhinichthys atratulus were more active during the day than at night, whereas lake chub Couesius plumbeus, brook trout Salvelinus fontinalis and adult white suckers Catostomus commersonii were more active at night than during the day. Because fishes were as likely to be nocturnal as diurnal, the data suggest that more night‐time sampling is needed to provide an unbiased view of fish community structure in temperate streams.     

Relationships between stream acidity and bacteria,macroinvertebrates, and fish: a comparison of north temperate and south temperate mountain streams,USA

A comparative study of relationships between stream acidity and bacteria, macroinvertebrates, and fish in the Adirondack Mountains of upper New York state and in the Southern Blue Ridge Mountains of eastern Tennessee, USA, was conducted. Although the study sites in both regions spanned a pH range from approximately 4.5 to 6.4, considerably greater seasonal variability in pH and higher monomeric Al concentrations characterized the Adirondack sites. Relationships between several biological characteristics and stream water acidity were similar in both regions, including lower production of epilithic bacteria and bacteria on decomposing leaves, lower leaf decomposition rates, lower density and generic richness of scraper/grazer macroinvertebrates, particularly Ephemeroptera, and lower fish abundance and survival in more acidic streams. Densities of total macroinvertebrates and densities of macroinvertebrates and bacteria inhabiting or closely associated with stream sediments were generally not related to stream water acidity.Regional differences occur in some of the relationships between biological characteristics and stream water acidity. Negative correlations between bacterial production on rocks and pH, between bacterial production on decomposing leaves and pH, and between densities of Ephemeroptera and scrapers and pH were stronger in the Adirondacks than in the Southern Blue Ridge. Higher Al concentrations in the Adirondacks may be responsible for the stronger relationships with pH there. The steeper slopes of the relationships between Ephemeroptera density and all forms of Al in the Adirondacks compared with the Southern Blue Ridge suggests that there may be some adaptation among a few acid/aluminum-tolerant species in the seasonally more constant acidic Southern Blue Ridge streams. Fish bioassays indicated longer survival times in acidic streams in the Adirondacks compared with the Southern Blue Ridge, but these results may be an artifact associated with the use in the Southern Blue Ridge of rainbow trout as the test species which is known to be more acid sensitive compared with brook trout, the test species used in the Adirondacks.     

Effects of sediment releases from a reservoir on stream macroinvertebrates

Effects of sediment release from Guernsey Reservoir on macroinvertebrates of the North Platte River, Wyoming, were investigated during summer 1981. Suspended solids concentrations during sediment release increased from <20 mg l^–1 to >300 mg l^–1. Because fine particulates remained in suspension, mean particle size of substrates was unaltered. Densities of chironomids decreased 90% + during sediment release but recovered to initial levels in 3 weeks after the release ended. Densities of mayflies and oligochaetes increased. Changes in benthic populations were highly correlated with increases in suspended solids.     

An analysis of changes in the invertebrate community along a southern New Zealand montane stream

Changes in benthic community structure at four sites along a flood-prone montane stream continuum in the South Island of New Zealand were analysed using rank correlation (Kendall's Tau and Spearman's r_s) and a community similarity index (S_c) developed initially for stream pollution assessment. Species richness was highest in a forested headwater stream, which is attributed to its relatively greater physical stability and habitat heterogeneity. Community similarity decreased with distance apart, and pairs of open and forested sites showed the greatest similarity. Species composition and relative abundance along the continuum changed least in the numerically dominant Ephemeroptera and Plecoptera, groups in which several species had broad habitat requirements. In contrast, a number of dipteran and trichopteran species had more restricted distributions. The more specialised niche requirements of some species in these orders are attributed to their generally small size, their ability to spin silk, and their holometabolous development. Physical rather than biological factors appeared to limit the distributions of most invertebrates, and there was little evidence of ecological segregation by either food resource partitioning or differences in life history patterns amongst many closely related species. Theories that stream communities are well ordered entities maximising the efficiency of energy utilisation cannot realistically be applied to such unstable stream systems.     

Ecology of a cyanobacterial mat community in a Korean thermal wastewater stream

Cyanobacterial mats along a small stream receiving thermal wastewater from an artificial hot spring in the mid-upper part of the Mankyeong River system, Korea, were studied during the winter of 1995-1996. In the cyanobacterium, Oscillatoria terebriformiscomprised >95% of total biomass. Ash-free dry-weight (AFDW) and chlorophyll a in the cyanobacterial mats decreased significantly (r²= 0.78 and 0.83, respectively) with distance downstream from the thermal water outlet, while primary productivity increased slightly. The concentrations of the majority of ions sharply decreased with distance downstream, although they were not markedly related with spatial changes in AFDW, Chl a and primary productivity. O. terebriformis appeared to have a tremendous potential in wastewater treatment because of its marked ability to glean ions.     

Dynamics of dissolved and particulate organic carbon in a saline and semiarid stream of southeast Spain (Chicamo stream)

Annual variations in the concentration of dissolved (DOC) and particulate organic carbon (CPOC = Coarse; FPOC = Fine; UPOC = Ultrafine) were studied in a 100 m-reach of the Chicamo stream, an intermittent saline stream in southeast Spain. DOC represented the most important fraction of organic carbon flowing in the Chicamo stream (>98%), with concentrations of about 1.7 mgC l^–1 during most of the year, reaching 2.5 mgC l^–1 in summer. One high flow episode during a rain storm in winter was characterized by a considerably increased concentration of DOC (9.4 mgC l^–1). CPOC was the dominant POC fraction. Positive and significant correlations were found for DOC and discharge, which support the idea of allochthonous inputs due to floods. There was no significant correlation between POC and discharge. No significant correlations were found for DOC or POC with the physico-chemical parameters measured, while a negative significant correlation was found between DOC and temperature. The export of total organic carbon from the drainage basin of the Chicamo stream was low (6.2 × 10^–4 gC m^–2 yr^–1) and typical of streams in arid and semi-arid regions. The results of a Principal Component Analysis defined three different phases. The first consisted of short periods, during which floods provide pulses of allochthonous organic carbon and nutrients, the second a dry phase (summer), defined by biotic interactions, during which the stream could acts as a `sink' of organic matter, and the third and final phase which is characterised by hydrological stability.     

Responses of taxonomic distinctness and species diversity indices to anthropogenic impacts and natural environmental gradients in stream macroinvertebrates

1. Many studies have shown traditional species diversity indices to perform poorly in discriminating anthropogenic influences on biodiversity. By contrast, in marine systems, taxonomic distinctness indices that take into account the taxonomic relatedness of species have been shown to discriminate anthropogenic effects. However, few studies have examined the performance of taxonomic distinctness indices in freshwater systems. 2. We studied the performance of four species diversity indices and four taxonomic distinctness indices for detecting anthropogenic effects on stream macroinvertebrate assemblages. Further, we examined the effects of catchment type and area, as well as two variables (pH and total phosphorus) potentially describing anthropogenic perturbation on biodiversity. 3. We found no indications of degraded biodiversity at the putatively disturbed sites. However, species density, rarefied species richness, Shannon's diversity and taxonomic diversity showed higher index values in streams draining mineral as opposed to peatland catchments. 4. Of the major environmental gradients analysed, biodiversity indices showed the strongest relationships with catchment area, lending further support to the importance of stream size for macroinvertebrate biodiversity. Some of the indices also showed weak linear and quadratic relationships to pH and total phosphorus, and residuals from the biodiversity index‐catchment area regressions (i.e. area effect standardized) were more weakly related to pH and total phosphorus than the original index values. 5. There are a number of reasons why the biodiversity indices did not respond to anthropogenic perturbation. First, some natural environmental gradients may mask the effects of perturbation on biodiversity. Secondly, perturbations of riverine ecosystems in our study area may not be strong enough to cause drastic changes in biodiversity. Thirdly, multiple anthropogenic stressors may either increase or decrease biodiversity, and thus the coarse division of sites into reference and altered streams may be an oversimplification. 6. Although neither species diversity nor taxonomic distinctness indices revealed anthropogenic degradation of macroinvertebrate assemblages in this study, the traditional species diversity and taxonomic distinctness indices were very weakly correlated. Therefore, we urge that biodiversity assessment and conservation planning should utilize a number of different indices, as they may provide complementary information about biotic assemblages.     

Application of universally amplifying plastid primers to environmental sampling of a stream periphyton community

To demonstrate the utility of universal plastid primers for probing of environmental samples, we extracted DNA from a tropical stream periphyton community and created two environmental clone libraries. We demonstrate the recovery of DNA sequences corresponding to the major groups of algae observed microscopically in the sample, illustrating the utility of these primers for analysis of environmental samples. Using a touchdown polymerase chain reaction technique, almost 99% of recovered sequences correspond to plastid-containing or cyanobacterial taxa, which allows algae to be targeted to the almost complete exclusion of noncyanobacterial prokaryotes and nonplastid-containing eukaryotes.     

The influence of scale and geography on relationships between stream community composition and landscape variables: description and prediction

SUMMARY 1. We analysed an existing database of macroinvertebrates and fish in the context of a newly established geographical information system (GIS) of physical features to determine the relationships between stream community composition and physical factors measured at three landscape scales – catchment, reach and bedform. Both an exploratory (concordance analysis) and a predictive ( ausrivas ) approach were used.
2. The environmental variables that most successfully accounted for variation in macroinvertebrate assemblages were mainly 'natural' and at the catchment-scale (relief ratio, basin diameter, etc.) but the human-induced physical setting of percentage of pasture in the riparian zone was also influential. For fish, 'natural' variables were also dominant, but these were mostly at the bedform or reach scales and land use featured strongly.
3. Geographic location accounted for some of the variation in invertebrate assemblages, partly because geography and influential conditions/resources are correlated but also because different species may have evolved in different places and have not colonised every 'ecologically appropriate' location. Geographic location was not influential in accounting for variation in assemblages of strongly flying invertebrates, supporting the hypothesis that organisms having high dispersal potential can be expected to break down geographic barriers more readily than those with poor dispersal powers. In accord with what is known about the local evolution and restricted distributions of native and exotic species, history (reflected in geography) appeared to account for some variation in fish assemblages.
4. Given their different mathematical bases, the fact that exploratory and predictive analyses yielded similar results provides added confidence to our conclusions.     

Diel foraging in relation to available prey in an Adirondack Mountain stream fish community

The diets of the fish community of Trucka Brook, a small stream located in the central Adirondack Mountains in northern New York, were examined in relation to the bottom fauna and invertebrate drift. Measures of overlap were calculated between the diets of each fish species examined, brook trout (Salvelinus fontinalis), blacknose dace (Rhinichthys atratulus), creek chub (Semotilus atromaculatus) and pearl dace (Semotilus margarita). Overlap was also examined between the fish diets and bottom and drift samples. Blacknose dace, pearl dace and brook trout had the most similar diets which were closely associated with the benthos. Creek chub had the most distinctive diets which did not compare well with any other fish species during either diurnal or nocturnal periods. The mayfly nymph Litobranchia recurvata was the most abundant bottom invertebrate and was the major prey of benthic feeding fishes. The invertebrate drift did not compare favorably with any of the fishes' diets because of the predominance of large cased limnephilid larvae (primarily Psychoglypha sp.) which were not readily consumed by fish.     

Composition and trophic structure of a fish community of a clear water Atlantic rainforest stream in southeastern Brazil

As part of a larger project that aimed to determine the factors that regulate fish productivity in a clear water river of the Atlantic rainforest, São Paulo State, Brazil, composition and the trophic structure of the fish community of the middle course of the river were studied from January 1995 to May 1996. Of the 17 species collected, Mimagoniates microlepis, Schizolecis guentheri, Phalloceros caudimaculatus and Kronichthys heylandi accounted for 83.2% of the total fish abundance. Most of the species were insectivorous (35.7%), followed by detritivores (21.4%), benthivores (14.2%), omnivores (14.2%), herbivores (7.1%), and piscivores (7.1%). Results of food overlap analysis as calculated by the Index of Morisita showed that 17.5% of the species pairs overlapped. Habitat segregation, however was observed among most of the species, suggesting some degree of food partitioning. Despite the characteristics of this escarpment river, which produces spates year round, no seasonal variation in diet was observed, suggesting that although food abundance may fluctuate throughout the year, most items are in constant supply. The importance of allochthonous food was considered and it appears that, though only a few species feed on this source (including detritivores), they make up 87.2% of the total fish abundance. The low abundance of most of the fishes, the high number of endemic species and the strong dependence of the species on a few food resources suggest that these systems are sensitive to anthropogenic impacts and require future studies.     

Temporal variation in foraging group structure of a size-structured stream fish community

Temporal variation in foraging group structure of a fish assemblage was examined in a flood-prone stream in southern Hokkaido, Japan. Foraging behaviour was observed underwater for four species which inhabit the water column: ayu, Plecoglossus altivelis, white-spotted charr, Salvelinus leucomaenis, masu salmon, Oncorhynchus masou, and Japanese dace, Tribolodon hakonensis, with each species being categorized into five size classes (species-size group; SSG). Based on foraging behaviour, each SSG of the fish assemblage was classified into one of four foraging groups: algae grazers, drift foragers, benthos-drift foragers, and omnivores, defined as SSG exhibiting similar foraging behaviour. All size classes of ayu, and of charr and salmon were categorized as algae grazers and drift foragers, respectively, throughout the study period. In contrast, size classes of dace were categorized as drift foragers, benthos-drift foragers, or omnivores with the same size classes often assigned to different foraging groups from month to month. Digestive tract contents of the fishes in the four foraging groups reflected their observed foraging behaviour, and foraging groups were therefore regarded as representing trophic groups. Abundance and membership of each foraging group varied in accordance with changes in abundance of SSG due to their growth, immigration, emigration, and/or mortality. Moreover, due to numerical dominance within the assemblage, plasticity in foraging behaviour of small- and medium-sized dace also played a key role in determining variability in the foraging group structure. Relative frequencies of two types of foraging behaviour, algae nipping and benthos foraging, of the small-sized dace were significantly correlated with the level of each resource, whereas no significant relationship was detected between foraging frequencies of the medium-sized dace and either resource. Fluctuations in foraging group structure within this assemblage occurred through niche shifts of some component members and by changes in SSG composition.     

On the importance of trait interrelationships for understanding environmental responses of stream macroinvertebrates

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