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Few studies consider spatio‐temporal variation in egg‐laying for benthic insects in streams. However, such variation can have lasting effects on the numbers and distribution of offspring and subsquent life‐cycle stages. For species that require specific egg‐laying habitats, such as rocks that protrude from the water surface (emergent rocks, ER), densities of egg‐laying habitat can affect densities of benthic eggs and even larvae for some species. For such species, changes in water levels alter the spatio‐temporal distribution of ER and can affect densities of eggs and, potentially, larvae. Below dams, modified flow regimes may alter the temporal availability of ER. In this study we tested whether river regulation altered the availability of oviposition habitat and changed the phenology of oviposition compared to unregulated rivers.At multiple sites in two regulated (Murrumbidgee, Tumut) and three unregulated (Goobarragandra, Goodradigbee, Micalong) rivers (south‐east Australia), we surveyed densities of ER and egg masses of five species of caddisflies (family Hydrobiosidae) seasonally over 3 years (2019–2021). Samples of adults also were collected during two seasons using light traps.High flows in both regulated rivers submerged all rocks during spring and summer and low‐flow releases stranded rocks above the waterline at all (Murrumbidgee River) or most (Tumut River) sites during autumn and winter. No ER or egg masses were observed on any date in the Murrumbidgee River, despite relatively large catches of adults. On the Tumut River, low densities of ER and egg masses were twice observed at one site, during seasons (winter, autumn) when oviposition was low in the unregulated rivers.In unregulated rivers, ER and egg masses (five species, four genera) were present at all sites but with lower densities in winter than in other seasons. During peak oviposition periods, densities of egg masses per site were not strongly related to densities of ER. In summer 2019, ER in two unregulated rivers were blanketed by sheets of algae and sediment that appeared to prevent oviposition because no egg masses were observed at this time.In regulated rivers, aseasonal flows precluded egg‐laying by submerging (summer, autumn) or stranding (winter, spring) all or most ER. In contrast, ER were available all year in the unregulated rivers and egg‐laying occurred all year, except when ER were blanketed by algae and sediment. Within seasons, local densities of egg masses may be limited by numbers of gravid females, rather than numbers of ER, which differs from previous research.Identifying impediments to reproduction is critical to understanding variability in population numbers in natural and altered systems. Our observations of oviposition failure downstream of dams present a new hypothesis for why some insect species are absent from channels where flows are regulated for irrigation. Blankets of algae may similarly preclude reproduction in rivers with low‐flow conditions, but this remains untested. [ABSTRACT FROM AUTHOR]

Environmental change and growing anthropogenic pressure on water resources is increasing the duration and intensity of drying events in streams in many geographical locations. Favourable sediment characteristics (e.g. high porosity and low fine sediment load within the substrate matrix) may facilitate benthic macroinvertebrate use of subsurface sediments in response to drying. However, the influence of sedimentary characteristics on the use and subsequent recovery of macroinvertebrates from initial vertical migration into, survival during unfavourable conditions within, and subsequent re‐emergence from subsurface sediments have not been directly observed.Transparent mesocosm tanks were used to directly observe the vertical movement and subsequent re‐emergence of Gammarus pulex from subsurface sediments in response to increasing dry period (1, 7, or 21 days) and fine sediment load (0.5–1 mm particle diameter used for light and heavy sediment treatment) and following rehydration and resumption of flowing conditions.Increasing volumes of fine sediment addition limited the ability of G. pulex to access subsurface sediment in response to drying and re‐emerge following rehydration. The longest dry period (21 days) reduced the ability of G. pulex to re‐emerge from the subsurface sediments following rehydration and flow resumption.Increasing fine sediment load negatively affects taxa using subsurface sediments as a refuge. Increased fine sediment deposition has the potential to reduce both access to the sub‐surface and re‐emergence once surface flow resumes.As many rivers are beginning to dry out, or are showing prolonged drying due to global warming, it is increasingly important that river management reduces the input of fine sediment into rivers and increase sediment porosity of riverbeds to facilitate access into the subsurface refuge by benthic fauna. [ABSTRACT FROM AUTHOR]

The impact of global warming on mountain ecosystems is predicted to be high, and particularly in the tropical region. Geothermal streams have provided comprehensive evidence about how aquatic biodiversity changes across natural thermal gradients, but current knowledge is restricted to arctic and temperate zones. Thermal tolerances are different in tropical biological communities, resulting in high thermal sensitivity and low capacity to endure change in their thermal environments. This feature can change the response of aquatic organisms to warming, yet there is little empirical evidence to support this assumption.In this study, we address this issue by evaluating how water temperature affects biodiversity, and the structure of primary and secondary producers of a high‐elevation geothermal stream system (4,500 m above sea level) in the Bolivian Andes. We analysed multi‐taxa responses to increased water temperature using benthic macroinvertebrate families, benthic algae and cyanobacteria, fishes, and macrophytes as study organisms. Different models were run to assess the response of aquatic biota to temperature. In addition, threshold indicator taxa analysis (TITAN) was used to identify changes in macroinvertebrate taxa distributions along the thermal gradient.We found that macroinvertebrate richness decreased at 24–25°C due to the different taxon‐specific responses to temperature. Threshold indicator taxa analysis identified 17 temperature thresholds for each family of macroinvertebrates. Changes in macroinvertebrate community composition were significantly associated with changes in water temperature. Similarly, changes in macrophytes were associated with temperature differences, and high macrophyte richness was found at 19–20°C. Chlorophyll‐a concentration of green algae and diatoms was higher at intermediate temperatures 20–22°C, macroinvertebrates density peaked at 27°C, and fish body size reduced linearly with temperature.Temperature increase in the geothermal stream resulted in a reduction of aquatic diversity and primary and secondary producers by simplifying the community structure to a few warm‐adapted taxa and reduced body size. These patterns differed from those obtained in temperate/arctic geothermal streams, but are similar to other studies at high‐elevation. In a context of increasing warming, the ecological structure of high‐elevation streams might lose cold‐adapted taxa, and change to smaller populations. Additional studies based on ecosystem functioning of geothermal streams could lead to a better understanding on how warming affects high‐elevation streams. [ABSTRACT FROM AUTHOR]

The importance of flow‐related factors to benthic organisms, as well as the role of habitat conditions in shaping aquatic communities during low‐flow periods, have been recognised. Despite this, the preferences of macroinvertebrates to the ratio of lentic to lotic habitats at the reach scale have not been accurately quantified in most instances.Aquatic invertebrates and habitat features in a range of temporary rivers in Sardinia were investigated. The investigation focused on the flow‐related characteristics that contribute to defining the lentic–lotic condition of the river reaches. The relation of habitat features to benthic taxa distributions was assessed using multidimensional scaling. The main aim of the paper was to quantify the responses of taxa to the different lentic and lotic habitat conditions by applying hierarchical logistic regressions. Finally, taxon optima were aligned along the lentic–lotic gradient and the responses of different taxonomic groups compared.Unbroken waves and imperceptible flow were correlated with benthic taxa variability, suggesting local hydraulics and turbulence have a major role in regulating community composition. The overall lentic–lotic character of the river reaches was also clearly related to the benthic taxa distribution. More than 80% of taxa were significantly related to the lentic–lotic gradient, and an asymmetrical response curve was the predominant model.Benthic groups showed taxon optima clustered in different ranges of the lentic–lotic gradient. Odonata, Coleoptera, Hemiptera, and Mollusca preferred clearly lentic conditions. Diptera mainly ranged on the lotic side of the gradient, while Trichoptera were relatively uniformly distributed across the gradient. Ephemeroptera taxa clustered in intermediate lentic–lotic conditions, with two species preferring extremely lentic habitats. In general, optima converged at intermediate and extremely lentic conditions, presumably due, respectively, to the coexistence of different lentic and lotic features and to the highly diverse environmental characteristics under extremely lentic situations.These results support the conclusion that dissimilar ecological factors act on benthic taxa along the lentic–lotic range and species favouring different lentic–lotic conditions are subjected to pressures of different nature. This should not be ignored when defining species preferences and studying community structure or relationships between species in Mediterranean rivers, which cyclically vary their habitat composition. In addition, the uneven distribution of optima of different groups along the lentic–lotic gradient might affect macroinvertebrate metrics when assessing ecological status or establishing reference conditions under variable climatic conditions. [ABSTRACT FROM AUTHOR]

Applying the environmental flows concept to human‐altered lotic ecosystems continues to face many practical challenges and barriers. Here, we modify a previously proposed framework, the Eco‐Engineering Decision Scaling, for application to part of the water supply system of Quito, Ecuador.Specifically, we used feedback from engineers and water managers to develop a common set of metrics for defining flow‐ecology relationships and assess managed‐flow impacts on stream ecology. At 12 sites over 3 years, we collected flow and benthic invertebrate data (taxonomic richness, taxa important for fish, functional feeding groups, and water quality‐sensitive taxa) during wet and dry seasons. We then used these data to identify flow thresholds (relative to unmanaged flows) where flow withdrawal caused visible ecological impacts.For this system, reduction of flow to 20% of the annual median was detrimental to benthic communities, while reductions to 40% of the annual median flow caused a variety of responses in the system. A trade‐off analysis of weighted metrics showed that a 50% benthic fauna richness could be sustained if dry season flows were maintained between 28% and 40% of the unmanaged median annual flow. This study provides a roadmap for bridging between eco‐engineering theoretical frameworks and the adoption of the environmental flows concept as actionable management thresholds. [ABSTRACT FROM AUTHOR]

Lakes play a key role in the regulation of the global carbon cycle. However, their functioning can be strongly impacted by anthropogenic pressures and climate variability. Understanding the response of the carbon cycle to environmental changes remains a crucial, elusive goal for both ecosystem managers and aquatic ecologists. In particular, the relations among lake physical and chemical properties, landscape structure and lake carbon cycling must be studied to predict future trends in lake functioning., Sediment cores were collected from the deepest part of 14 small French lakes that differed in lake properties (elevation, conductivity, area, area of the watershed) and land-use class (forest, wetland, agricultural land and urban area). The sampling strategy employed the top-bottom approach (a comparison between present-day conditions and 'reference' conditions at Medieval period, c. AD 1000). For each sample, the following variables were analysed: isotopic carbon composition of sedimentary organic carbon (δ13COM), δ13C of chironomid remains (δ13CHC), and sedimentary pigments (total carotenoids, TC)., Stepwise multiple regression analysis showed that the size of the catchment area may affect δ13COM values for the Medieval samples ( R2 = 0.36, P < 0.05), such that the flux of terrestrial organic matter increases with the size of the watershed. However, this relation is not observed in the present-day samples, and the influence apparently becomes largely anthropogenic. For these present-day samples, the proportion of agricultural land in the watershed appears to be the primary driver of lake biogeochemical cycles through a direct effect on nutrient availability ( R2 = 0.24, P < 0.05) and through an indirect effect on the benthic carbon cycle. The results also confirm the widespread existence of a pathway for methane-derived carbon contribution to chironomid biomass (up to 61% of chironomid biomass) and suggest that high-conductivity lakes are highly sensitive to the presence of this pathway (more than 75% of the lakes in our dataset have benthic food webs apparently dependent on biogenic methane; CH4)., The results may indicate that the high-conductivity lakes (from the Jura Mountains) are more vulnerable to anthropogenic activities than low-conductivity lakes because high-conductivity water provides an excellent nutritive medium for the development of photoautotrophic production. Studying within-lake CH4 dynamics and the response of the CH4 cycle in high-conductivity lakes appear to be crucial for understanding both regional carbon budgets and lake trophic functioning. [ABSTRACT FROM AUTHOR]

Land-use changes have degraded ecosystems worldwide. A particular concern for freshwater biodiversity and ecosystem function are stressors introduced by intensified agriculture. Typically several stressors affect freshwater ecosystems simultaneously. However, the combined effects of these multiple stressors on streams and rivers are still poorly understood, yet of critical importance to improve freshwater management., We investigated responses of benthic macroinvertebrates to three globally important agricultural stressors affecting streams (nutrient enrichment, fine sediment deposition and reduced current velocity), using 64 stream mesocosms (full-factorial 2 × 2 × 2 design, eight replicates of each treatment combination) established on the banks of the Breitenbach Stream (Hesse, Germany). The experiment ran for 1 month (16 days of colonisation, 14 days of manipulations), and all invertebrates in the mesocosms were collected at the end of this period., Fourteen of the 17 studied invertebrate response variables were affected by one or more stressors each. Negative effects on richness or abundance of pollution-sensitive Ephemeroptera, Plecoptera and Trichoptera ( EPT) taxa were particularly common. Overall, both sediment addition and stream flow velocity reduction had pervasive and strong effects. Responses to sediment addition were mostly negative, whereas decreased current velocity reduced several EPT metrics but increased the abundances of some of the other common taxa. Nutrient enrichment had few effects, but these were consistently negative., Combined stressor effects were mainly additive, with only two interactions found in total, both between reduced velocity and nutrients (on the crustacean Gammarus spp. and ceratopogonid midges). This finding implies that multiple-stressor responses may be predicted from knowledge of single-stressor effects in this stream community (unlike the often synergistic or antagonistic responses observed elsewhere). However, further taxon-specific responses and interactions among stressors may have been obscured by limited taxonomic resolution, especially for the numerically dominant Chironomidae. Genetic approaches are required to address this limitation in the future. [ABSTRACT FROM AUTHOR]

Principal threats to running waters are linked to human-made discharge modifications, but tools to predict the quantitative consequences of flow restoration for benthic invertebrates in large rivers remain untested., Quantitative benthos samples from two bypassed reaches (Pierre-Bénite - PBE - and Chautagne - CHAU) of the French Rhône River were collected during four years each before and after minimum flow increases (from 10 to 100 m3 s−1 at PBE and from 10 to 50 m3 s−1 at CHAU). These samples provided observed ln-density changes for the 50 and 62 ( PBE and CHAU, respectively) most abundant taxa (typically species or genera). For about half of the 'model' taxa among them, distinct preference models for bottom shear stress categories were available from four reaches of the Upper Rhône River and from various German rivers. Linking these preference models with a statistical hydraulic model predicting frequencies of shear stress categories for any given discharge, we predicted ln-density changes of the model taxa after restoration., Community structure of the abundant taxa changed clearly and rapidly after restoration at PBE but less clearly at CHAU. Our predictions explained a considerable amount of mean ln-density changes of our model taxa observed after restoration (75 and 30% at PBE and CHAU, respectively). They also explained (67 and 40% at PBE and CHAU, respectively) the model taxa scores along the principal components analysis axis that summarised the community variations of all abundant taxa before and after restoration. For taxa not identified to species (assessed as genus, tribe or family), the predicted ln-density changes were sometimes inaccurate at PBE (a Lower Rhône site), suggesting that the transferability of preference models for taxonomic levels above that of species can be problematic., If further developed, statistical habitat models focussing on ecologically relevant physical variables (in our case shear stress) should enable reliable quantitative assessments of associations between flow restoration efforts and achievable ecological improvement. [ABSTRACT FROM AUTHOR]

The response of benthic invertebrate assemblages to stream restoration is the subject of numerous recent studies, but the process of recolonisation of restored river sections is still poorly understood. Field studies are often flawed by uncertainties about whether the observed species colonised the restored sections after restoration or whether they were present before restoration., We investigated restored streams in the Boye catchment in an urbanised area in Germany. The streams were formerly open sewers and thus were not inhabitable by benthic invertebrates, except for Oligochaeta. Restoration included the construction of underground sewers for wastewater and morphological remodelling of the stream bed., In the spring of 2012, we sampled seven restored former channels connected with near-natural upstream sections, which were never used as sewage channels and are in good status morphologically, and six unconnected restored former channels. Restoration measures had been conducted between one and 19 years before sampling. Additionally, we sampled 21 near-natural sites within the catchment and eleven near-natural sites in neighbouring catchments. Near-natural sites were considered to be potential source sites from which benthic invertebrates might colonise the restored sites., We recorded 128 taxa and categorised them into five dispersal classes that reflect dispersal capabilities and degree of ecological specialisation. Assemblages at restored sites were characterised by lower numbers of taxa and/or high abundance of hololimnic taxa and poorly dispersing winged species and by higher species numbers and abundance of strongly dispersing generalists., A distinct recolonisation sequence was derived from the observed patterns, in which winged, strongly dispersing generalists colonised most rapidly and were followed by hololimnic species, weakly dispersing generalists and habitat specialists. Restored sites connected with near-natural upstream sections were colonised more rapidly than unconnected restored sites, particularly by habitat specialists. Almost 90% of the recolonisation events originated from sources within a distance of 5 km. We observed a succession from pioneer assemblages to more mature communities, which resembles that of the surrounding near-natural sites., In conclusion, assemblages in connected, restored sites needed nine to 19 years to reach maturation, while the settlement of assemblages in unconnected sites is expected to require more time. [ABSTRACT FROM AUTHOR]

As glacier shrinkage is accelerating due to climate change, it is important to understand the effect of changes in glacier runoff on downstream aquatic communities. The overall goal of this study was to test the relevance of recently developed wavelet-based metrics of flow variations caused by glacial melting cycles to deepen our knowledge about the relationship between glacial influence and aquatic biodiversity., In an equatorial glacierised catchment, we selected 15 stream sites covering a gradient of direct contribution from glacial runoff. At each site, we recorded water level time series for 10 months and sampled benthic macroinvertebrates. Wavelet analyses on the water level time series were used to calculate three indices: glacial flood intensity, frequency and temporal clustering. We then examined how these three indices were related to macroinvertebrate community composition using generalised additive models., While macroinvertebrate density decreased significantly with glacial flood intensity, we found a significant hump-shaped relationship between local taxon richness and glacial flood intensity, a pattern that was not produced simply by overlapping broad taxon distributions from either end of the environmental gradient. These results suggest that glacial meltwater contribution creates local peaks in macroinvertebrate richness and enhances regional diversity in the catchment., The significant relationships between faunal metrics and the new glacial influence indices suggest the latter are valuable for assessing the effects of altered meltwater contributions on aquatic communities of glacier-fed rivers. Relationships differed depending on the feature of the glacial disturbance considered (glacial flood intensity, frequency, temporal clustering). We anticipate that these distinctions may help disentangle the mechanisms driving aquatic biodiversity in glacierised catchments, especially in terms of identifying resistance and/or resilience as key processes in glacial macroinvertebrate communities. [ABSTRACT FROM AUTHOR]

Using the unregulated, eutrophic Someş River ( Romania/ Hungary), a tributary of the Upper Tisza River as a model system, we related phytoplankton growth to the structure of river network modified by human intervention., The Time- Averaged Phytoplankton Increase in Rivers ( TAPIR) model was developed by adding two new modules (nitrogen emission and phytoplankton growth) to the PHOSFATE model. The latter was a raster-based, long-term average GIS tool that computed the flow tree, mean hydrology and phosphorus concentration at fine spatial resolution in the entire catchment. Long-term monitoring data at the outflow and phytoplankton profiles obtained along the Someş River in 2012 were used to calibrate the models., In summer 2012, a few centric diatom species dominated the phytoplankton, with mean apparent net growth rate of 2.5 day−1 along a ˜100-km-long upstream section of the Someş River. This high growth rate was explained by enhanced benthic retention of meroplanktonic diatoms, while further downstream mean algal biomass varied between 80 and 100 mg Chl m−3., The TAPIR model realistically reproduced observed mean biomass profiles of phytoplankton in the Someş River. According to modelling results, P-determined biomass capacity prevented further growth of algae along the lower two-thirds of the river., Channel slope and form were important reach-scale determinants of phytoplankton recruitment, while the absence of large tributaries along the Someş River resulted in marginal longitudinal changes in dilution and light availability. Therefore, phytoplankton might achieve high biomass in a wide range of instantaneous net growth rates realised under strongly fluctuating environmental conditions, which combined with the abundant nutrients from urban areas underpins advanced eutrophication. Large montane reservoirs on tributaries increased mean water age at the outflow of the Someş catchment by an order of magnitude compared with pristine conditions, but had a negligible overall impact on the phytoplankton of the Someş River., Growth of river phytoplankton is intrinsically linked with network topology, including spatial distribution of nutrient inputs. Stochastic variability in discharge tends to destabilise, while specific network properties may stabilise phytoplankton growth in large rivers. Shallow rivers support meroplanktonic diatoms that, depending on discharge, may have adequate time to develop summer blooms, making shallow rivers particularly susceptible to eutrophication. [ABSTRACT FROM AUTHOR]

Flow refugia, characterised by low hydraulic stress during a flood, are key habitats that contribute to the persistence of benthic invertebrate. We investigated the use of different refugium types distributed across stream and floodplains and clarified which refugia contributed most to the persistence of assemblage and population during a seasonal snowmelt flood., We sampled invertebrates and measured physical variables from six or nine types of channel units ('riffle', 'run ', 'lateral pool', 'backwater', 'abandoned pool' and 'tributary' at base flow, plus 'fast inundated area', 'slow inundated area' and 'side channel' at high flow) at four times (before, during, immediately after and after a flood). We analysed the use of refugia by assemblages, species with different ecological 'lifestyles' (a classification into different modes of mobility: burrower, climber, sprawler, clinger and swimmer) and populations., Total density and species richness decreased significantly with flooding in riffles, runs and lateral pools. In contrast, total density and species richness did not change significantly in the other six types of channel units; therefore, these were distinguished as refugia. Among the six refugia, backwaters, tributaries and slow inundated areas had higher total densities than other refugia. The densities of the five lifestyles also decreased with flooding in riffles, runs and lateral pools. During flooding, high densities in backwaters and slow inundated areas were common for all lifestyles, whereas densities in other refugia varied with lifestyle., The results for five common species showed that refugium use is species-dependent. The mayfly Paraleptophlebia japonica (Leptophlebiidae) and the cased caddisfly Neophylax ussuriensis (Uenoidae) were more numerous in refugia during flooding and recovered rapidly after flooding. In contrast, the mayfly Epeorus latifolium ( Heptageniidae) and the net-spinning caddisfly Hydropsyche orientalis ( Hydropsychidae) were rare in all types of channel units during and immediately after flooding. The cased caddisfly Allomyia delicatula (Apataniidae) was specific to tributaries and persisted throughout the research period., Although some species did not use refugia effectively, various species with different mobility and ecological traits did persist and were found in refugia. Specifically, habitats with slowly flowing water that were spatially close to the main channel favoured the persistence of benthic invertebrates. [ABSTRACT FROM AUTHOR]

Lough Neagh is one of the most important non-estuarine sites in the British Isles for overwintering wildfowl. A change in the waterbird assemblage following the winter of 2000/2001 was driven mainly by a rapid decline in the population of overwintering diving ducks. Sudden and discrete changes in resident as well as migratory waterbirds may suggest an intrinsic cause., We compared the density and biomass of benthic macroinvertebrates, the food of overwintering diving ducks, in 2010 (following the diving duck population decline) with values from a baseline survey conducted in 1997/1998 (before the decline in diving ducks)., The mean total density of macroinvertebrates declined significantly by c. 65% from 15 300 m−2 in 1997/1998 to 5136 m−2 in 2010. There was a concomitant c. 70% decline in mean macroinvertebrate biomass from 15 667 mg m −2 to 5112 mg m−2. In terms of taxonomic composition, the relative contribution of Tanypodinae, Glyptotendipes spp. and Tanytarsini declined, while the relative contribution of Chironomus spp. increased., We describe a shift in chlorophyll- a concentration, a proxy of phytoplankton biomass, in the largest freshwater lake in the British Isles coincident with a significant reduction in macroinvertebrate density and biomass, with potential implications for ecosystem processes and ecologically and economically important consumer populations, including waterbirds and fishes. [ABSTRACT FROM AUTHOR]

Lotic ecosystems worldwide are being increasingly modified hydromorphologically, for example, by damming, fragmentation, flow regulation and channel modification. Serious threats to riverine biodiversity are suspected, yet available field data are few and rarely address the various taxonomic, functional and phylogenetic components of biodiversity., We examined benthic macroinvertebrate diversity along a gradient of hydromorphological alteration across 65 lowland river sites in the Netherlands, Germany and Poland. We calculated eight metrics describing taxonomic diversity (richness, rarefied richness, Shannon's and Simpson's diversity, Pielou's evenness), functional diversity (mean trait diversity) and phylogenetic diversity (mean taxonomic distinctness and its variance)., Threshold Indicator Taxa ANalysis ( TITAN) and Non-metric Multidimensional Scaling ( NMS) showed detailed changes in taxonomic and trait composition, respectively, with increasing hydromorphological alteration. TITAN revealed a gradual turnover under increasing impact in which taxon losses were almost balanced by gains. NMS illustrated a high degree of concordance in the traits possessed by the taxa lost and gained at the gradient's end points., Although a biologically meaningful hydromorphological gradient was evident, the biodiversity response was modest (Spearman's ρ < |0.32| for all metrics). Pielou's evenness and mean taxonomic distinctness actually increased at impaired sites., Our results suggest that taxonomic and trait replacement with hydromorphological alteration is not followed by changes in whole-community diversity. This implies some redundancy in these systems, with ecologically similar species replacing those lost through environmental change., The results highlight how whole-community-based diversity, although frequently calculated and interpreted for decades in ecology and conservation biology, is not the all-purpose concept to detect and assess the various facets of biodiversity loss. Therefore, we suggest that concerted effort is needed to develop and test novel indicators of biodiversity, capable of detecting biodiversity loss, or other changes, in response to the main environmental stressors of lotic ecosystems. [ABSTRACT FROM AUTHOR]

The impacts of climate-induced environmental changes on freshwater biodiversity are not well understood in Arctic regions., We quantified water source contributions (meltwater, ground water), environmental habitat conditions and benthic macroinvertebrate community dynamics in north-west Svalbard. The aim was to use contemporary findings to infer how future environmental change may affect these Arctic river ecosystems., Water source dynamics played an important role in influencing environmental habitat conditions; meltwater contributions to flow were related significantly to discharge, channel stability, electrical conductivity and p H., Low regional benthic macroinvertebrate diversity relative to other Arctic regions was attributed to harsh winter conditions and biogeographical dispersal constraints associated with the Svalbard archipelago., Generalised estimating equations and multivariate ordination models showed benthic macroinvertebrate diversity and abundance were influenced significantly by several environmental habitat variables. Rivers in non-glacierised basins typically supported more diverse and abundant communities than those in glacierised basins, most likely as a consequence of the warmer water temperature and less-disturbed habitat conditions associated with these systems., Consequently, shifts in water source contributions driven by changes in climate may alter environmental habitat conditions in Svalbard rivers and could lead to an increase in abundance and diversity among some freshwater macroinvertebrate communities. [ABSTRACT FROM AUTHOR]

Benthic animals readily consume benthic algae, phytoplankton and terrestrial organic matter and are themselves a major component of fish diets. However, the effect of variation in resource availability on resource use by littoral macroinvertebrates remains poorly resolved., Using stable isotopes of carbon, we quantified depth-specific resource use by zoobenthic functional feeding groups in five lakes in northern Wisconsin. The littoral zoobenthos was collected from soft sediments at several depths in conjunction with samples of bulk periphyton (top 5 mm of sediment and biofilm) and measurements of benthic algal primary productivity., Periphyton δ13 C was positively correlated with depth-specific benthic algal primary productivity, but grazer δ13 C was consistently higher than that of the periphyton., The δ13 C of infaunal collectors and predators was tightly correlated with, and nearly identical to, bulk periphyton δ13 C (collectors: R2, 0.88; slope, 0.97; P < 0.0001; predators: R2, 0.78; slope, 0.88; P < 0.0001). Reliance of collectors and predators on benthic algal carbon varied between 43 and 100%, depending on whether grazers or bulk periphyton was used as the benthic algal end-member., Despite the apparent homogeneity of the sediments, benthic grazers and collectors partitioned resources in a consistent way in our study lakes, indicating either selective ingestion or assimilation of different components of the biofilm. [ABSTRACT FROM AUTHOR]

We studied amino acid ( AA) composition of epilithic biofilms and zoobenthos near the shore at a middle section of the Yenisei River ( Siberia, Russia). We hypothesised that there was an imbalance between the composition and content of amino acids in the biofilm and its consumers, the zoobenthos, as well as between those in the zoobenthos and fish., Based on monthly sampling from 2007 to 2010, there was seasonal variation in AA profiles in the epilithic biofilms, probably caused by the succession of microalgal and cyanobacterial species., Overall, there was an imbalance in the percentage of the essential amino acids (lysine and histidine) between benthic animals and their food (the epilithic biofilm), which suggests that benthic animals may be limited by food quality. Moreover, the zoobenthos had a significantly higher content of AA, relative to carbon, than the biofilm., Based on sampling in 2012, there was an imbalance between the AA profiles of zoobenthos and that of their main consumer, the Siberian grayling ( Thymallus arcticus), particularly in the percentages of two essential amino acids, lysine and leucine., In terms of overall content of essential amino acids, the nutritional value to fish of gammarids, which have recently invaded the river, was significantly lower than that of indigenous taxa, trichopteran and chironomid larvae. [ABSTRACT FROM AUTHOR]

1. Empirical and theoretical research over the past decade has demonstrated the widespread importance of aquatic subsidies to terrestrial food webs. In particular, adult aquatic insects that emerge from streams and lakes are prey for terrestrial predators. While variation in the magnitude of this subsidy is clearly important, the potential top-down effects of the predatory adults of some aquatic insects in terrestrial food webs are largely unknown. 2. I used published data on benthic insect density (as a proxy for emergence) in North and South America to explore how the proportion of benthic insects that are predatory as adults varies across a gradient of mean annual stream temperature. 3. The proportion of benthic insects that are predatory as adults varied widely across sites (0-12% by abundance; 0-86% by biomass). There was a positive relationship between mean annual stream temperature and the proportion of predatory adults across all sites, driven largely by the greater abundance/biomass of predatory taxa (e.g. odonates), relative to non-predators (e.g. midges, mayflies, caddisflies), in tropical than in temperate streams. 4. The 'trophic structure' (i.e. the proportion of predators) of emerging adult aquatic insects is an understudied source of variation in aquatic-terrestrial interactions. Incorporation of trophic structure in future studies is needed to understand how future modification of fresh waters may affect adjacent terrestrial food webs through both bottom-up and top-down effects. [ABSTRACT FROM AUTHOR]

Summary 1. The effects of eutrophication on phytoplankton, zooplankton and fish in lakes are well known. By contrast, little is known about the response of the zoobenthos to nutrient enrichment, while smaller organisms, such as the meiofauna, have for the most part been neglected. 2. In a long-term (16 months) microcosm experiment, we assessed the effects of five levels of nutrients [total phosphorus (TP), 7-250 μg L−1; nitrate, 2-8 mg L−1] on a freshwater meiofaunal assemblage and on nematode diversity in particular. 3. Within the first 8 months, meiofaunal succession was only weakly affected, whereas, during the last 4 months, nutrient addition influenced most of the main taxa, with a concomitant change in the assemblage structure. 4. The density of the numerically dominant nematodes decreased upon nutrient enrichment, whereas ostracods became more numerous. Other taxa, including copepods, reached a maximum at intermediate nutrient levels or, in case of oligochaetes, were almost unaffected by nutrient enrichment. However, the changes in the density of the main taxa were usually insufficient to alter their biomass. Consequently, meiofaunal biomass was remarkably unresponsive to nutrient addition, while meiofaunal density displayed a unimodal relationship, with a peak at a TP concentration of 30 μg L−1. In addition, nematode species richness decreased significantly with increasing nutrient concentrations. 5. We hypothesise that the response of meiofaunal taxa to nutrients is attributable to the development of primary producers, which shifted with enrichment from low densities of edible diatoms and unicellular green algae to large standing stocks of inedible forms, such as Lemna minor and Cladophora spp. [ABSTRACT FROM AUTHOR]

Summary 1. Benthic macroinvertebrates (MI) are commonly used to assess freshwater ecosystems with the reference condition approach. Such assessments necessitate control for natural community variation, either by categorical typologies or by predictive models that have been widely and successfully developed for running water biota but not previously for lake profundal invertebrates. 2. We evaluated four modelling techniques [multivariate regression tree (MRT), limiting environmental differences, nonparametric multiplicative regression (NPMR) and River Invertebrate Prediction And Classification System (RIVPACS) and the operative Finnish lake typology for assessing taxonomic completeness (observed-to-expected number of taxa, O/ E) of profundal MI assemblages. We used data from 74 and 33 minimally disturbed reference lake basins for calibration and validation of the approaches, respectively, and 72 test basins subject to various anthropogenic pressures to evaluate sensitivity to detect impact. Either all predicted taxa (threshold probability of capture Pt = 0+) or only those predicted to be captured with ≥0.25 probability were used to calculate O/ E. 3. With Pt = 0.25, all four modelling approaches were accurate (mean O/ E = 0.966-1.053) but imprecise (SD of O/ E = 0.279-0.304) in predicting the fauna actually observed in validation sites. All models were subtly more precise than a null model (mean 1.038, SD 0.343) or the typology (1.046, 0.327). The taxon-specific NPMR model was slightly more precise than the other three models based on site groupings. 4. The O/ E values correlated relatively weakly ( r = 0.55-0.86) among the approaches, which thus produced contrasting lake-specific assessments, despite their seemingly comparable performances. Indeed, typology, suggesting that MI assemblages were impaired in 56% of test sites, was more sensitive than the other approaches (26-46%) as an indicator of human-induced deterioration. However, this greater ostensible sensitivity seemed to be biased, as lake morphometry, a main driver of natural community variation, remained uncontrolled by the typology. 5. Generally, our exercise illustrates the inconclusiveness of the common validation criteria for the assessment methods. The apparent poor predictability of the profundal fauna, irrespective of the method, may partly stem from large observation error, which could be alleviated by more intensive sampling. However, instead of an O/ E-taxa index, some other metric encompassing quantitative aspects might be preferable for assessing these species-poor communities. [ABSTRACT FROM AUTHOR]

Summary 1. Stream managers need to understand relationships between multiple stressors and ecological responses. We examined responses of benthic invertebrates and algae along two land-use-related stressor gradients of concern in running waters. Our correlative study of the consequences of augmented deposited fine sediment and nutrient concentrations was conducted in a regional set of streams and rivers monitored by a water management authority in New Zealand and incorporated a wide range of catchment geologies and stream orders. 2. We used multiple linear regression analysis and an information-theoretic approach to select the best predictive models for our biological response variables by testing multiple competing hypotheses that include nonlinear subsidy-stress relationships and interactive effects between the two stressors. 3. Patterns consistent with a subsidy-stress response to increasing dissolved inorganic nitrogen concentration were found for the relative abundances of the common invertebrate genera Pycnocentrodes and Deleatidium and for the relative abundance of total individuals in the EPT orders (Ephemeroptera, Plecoptera, Trichoptera). 4. Fine sediment seemed the more pervasive stressor, apparently counteracting and overwhelming any initial subsidy effect of increased nutrients, and accounting for more of the variance in biological response variables. Relationships with high nutrient concentrations were weaker and modelled with less certainty, probably reflecting the indirect modes of action of nutrients compared to those underlying sediment effects. Nevertheless, in several cases, the models indicated that nutrients interacted synergistically with fine sediment, lending further weight to the conclusion that managers need to address both stressors to achieve the best outcomes. [ABSTRACT FROM AUTHOR]

Summary [ABSTRACT FROM AUTHOR]

1. Benthic chironomid larvae and the amphipod Gammarus lacustris have been observed in the pelagic habitats of many mountain lakes. The main goal of this study was to determine if chironomid larvae and gammarids potentially affect predator-prey and nutrient dynamics in pelagic food webs of mountain lakes. 2. Eighty-six mountain lakes were surveyed in Alberta and eastern British Columbia during the years 1965-1984, 1991-2004 and 2005-2007. Pelagic chironomid larvae were found in 86% of these lakes, and pelagic gammarids were found in 29% of lakes. Densities of pelagic chironomid larvae were 92% lower in lakes with pelagic gammarids and 76% lower in lakes with trout ( P < 0.05). Intraguild predation of trout on gammarids appeared to reduce predation pressure on chironomid larvae. Gammarids consumed in vitro about 1 chironomid per gammarid per day or about 20% of their body mass in chironomid biomass per day. 3. Concentrations of total dissolved P and N, particulate C, and chlorophyll-a increased with increasing densities of pelagic gammarids and chironomid larvae in situ ( R = 0.14 ± 0.19 SD, P < 0.1) and in vitro ( P < 0.001). 4. Our findings suggest that gammarids and chironomid larvae are linked as predators and prey in pelagic food webs, possibly stimulating phytoplankton abundance via nutrient release. [ABSTRACT FROM AUTHOR]

1. Pacific salmon ( Oncorhynchus spp.) returning to streams deliver substantial quantities of nutrients (nitrogen and phosphorus) that may stimulate primary production. Salmon can also affect the phytobenthos negatively via physical disturbance during nest excavation, a process that may counteract the positive effects of salmon-derived nutrients on benthic algae. The ability of salmon to disturb benthic habitats may be a function of substratum particle size, and therefore, the geomorphology of streams could determine the net effect of salmon on benthic communities. 2. Based on surveys of 17 streams in southwest Alaska before the salmon run and during peak salmon density, we identified size thresholds for the disturbance of substratum particles by salmon and classified particles as vulnerable (<60 mm B-axis), invulnerable (>110 mm) or transitional (61-110 mm). At the scale of individual rocks, algal biomass on vulnerable substrata decreased at peak spawning (relative to values before the run) as a power function of salmon density; transitional and invulnerable substrata showed no quantifiable pattern. However, invulnerable substrata in streams with more than 0.11 salmon m showed net algal accrual, or relatively smaller declines in algal biomass, than vulnerable substrata, indicating that large rocks provide refuge for benthic algae from salmon disturbance. 3. We expected that streams with proportionally larger rocks would respond positively to salmon at the whole-stream scale, after accounting for the relative abundance of rocks of different sizes within streams. Invulnerable rocks made up only 0-12% of the total substratum particle size distribution in salmon-bearing streams, however, and algal accrual on invulnerable substrata did not outweigh the strong disturbance effects on the more spatially extensive vulnerable substrata. The change in whole-stream benthic algal biomass among streams was negatively related to salmon density. 4. Stable isotopes of nitrogen (δN) were used to track nutrients from salmon into benthic biota. Periphyton δN on rocks of all size classes was higher at peak salmon spawning than before the salmon run, indicating the uptake of salmon-derived nitrogen. Peak δN values were positively related to salmon abundance and followed a two-isotope mixing relationship. The per cent of N from salmon in periphyton was also related to salmon density and was best explained by a saturating relationship. Spring δN was unrelated to salmon returns in the previous year, suggesting little annual carryover of salmon nutrients. [ABSTRACT FROM AUTHOR]

1. Despite the recognition of its importance, benthic primary production is seldom reported, especially for large lakes. We measured in situ benthic net primary production by monitoring flux in dissolved inorganic carbon (DIC) concentration in benthic incubation chambers, based on continuous measurements of CO flux, alkalinity, and the temperature-dependent dissociation constants of carbonic acid ( K and K). This methodology has the advantages of monitoring net primary production directly as change in carbon, maintaining continuous water recirculation, and having sufficient precision to detect change in DIC over short (i.e. 15 min) incubations, even in alkaline waters. 2. Benthic primary production on Cladophora-dominated rocky substrata in western Lake Ontario was measured biweekly. Maximum biomass-specific net photosynthetic rates were highest in the spring (2.39 mgC g Dry Mass h), decreased to negative rates by early summer (−0.76 mgC g DM h), and exhibited a regrowth in late summer (1.98 mgC g DM h). 3. A Cladophora growth model (CGM), previously validated to predict Cladophora biomass accrual in Lake Ontario, successfully simulated the seasonality and magnitude of biomass-specific primary production during the first cohort of Cladophora growth. Averaged over this growing season (May-Aug), mean areal net benthic production at the estimated depth of peak biomass (2 m) was 405 mg C m d. 4. We measured planktonic primary production in proximity to the benthic study and constructed a depth-resolved model of planktonic production. Using the CGM, benthic primary production was compared with planktonic primary production for the period May-Aug. Net benthic production from the shoreline to the 12 m contour (1-2 km offshore) equalled planktonic production. Closer to shore, benthic primary production exceeded planktonic primary production. Failure to account for benthic primary production, at least during abundant Cladophora growth, will lead to large underestimates in carbon and nutrient flows in the nearshore zone of this Great Lake. [ABSTRACT FROM AUTHOR]

1. Non-indigenous ecosystem engineers can substantially affect native biodiversity by transforming the physical structure of habitats. In the Great Lakes–St. Lawrence River system, introduced dreissenid mussels ( Dreissena polymorpha and D. bugensis) and the native benthic macroalga Cladophora act as ecosystem engineers by increasing substratum complexity and providing interstitial habitat for benthic macroinvertebrates. 2. We manipulated the topography and perimeter-to-area ratio of patches of dreissenid mussels in a series of colonisation experiments conducted at two sites in the St. Lawrence River. Experimental substrata were variably colonised by Cladophora, prompting us to examine (i) how the topography of Dreissena patches affects benthic macroinvertebrate diversity and (ii) the extent to which the effects of Dreissena are altered by the presence of another habitat-modifying organism ( Cladophora). 3. The results of our first experiment suggested that a patchy distribution of dreissenid mussels is an important driver of benthic diversity at small spatial scales. The results of our second and third experiments suggested that a native habitat engineer, Cladophora, modifies the impact of Dreissena on benthic macroinvertebrate communities. 4. While macroalgal blooms have been linked to the large-scale impacts of Dreissena on light and nutrient availability, Dreissena shells inhibited Cladophora growth at our experimental scale. These findings demonstrate that the interactions between habitat-modifying species can complicate efforts to predict the community-level effects of an invasion. [ABSTRACT FROM AUTHOR]

1. Compared to lakes and streams, we know relatively little about the factors that regulate algae in freshwater wetlands. This discrepancy is particularly acute in boreal regions, where wetlands are abundant and processes related to climate change (i.e. increased permafrost collapse and soil weathering) are expected to increase nutrient inputs into aquatic systems. To investigate how accelerated nutrient inputs might affect algal structure and function in northern boreal wetlands, we added nitrogen, phosphorus and silica to mesocosms in an oligotrophic marsh in interior Alaska. 2. We conducted two in situ mesocosm enrichment experiments during consecutive summer growing seasons, each lasting 24 days. In 2007, we investigated the effects of +N, +P, +Si and +N+P+Si enrichment on benthic algal biomass (chlorophyll- a, ash-free dry mass, biovolume), chemistry (N : P ratio) and community composition. In 2008, we expanded our first experiment to investigate the effects +N+P, +N+Si, +P+Si and +N+P+Si on the same algal parameters as well as productivity (mg C m−2 h−1). 3. In both experiments, we measured water-column dissolved organic carbon (DOC) inside treatment enclosures and related changes in DOC to standing algal biomass. 4. Benthic algal accrual did not increase following 24 days of enrichment with any nutrient alone or with P and Si together (+P+Si), but increased significantly with the addition of N in any combination with P and Si (+N+P, +N+Si, +N+P+Si). 5. Algal productivity (20 mg C m−2 h−1) increased between three- and seven-fold (57–127 mg C m−2 h−1) with the addition of N in combination with any other nutrient (+N+P, +N+Si, +N+P+Si). Water-column DOC concentration was significantly higher inside N-combination treatments compared to the control during each season, and DOC increased linearly with benthic algal biomass in 2007 ( r 2 = 0.89, P < 0.0001) and 2008 ( r 2 = 0.74, P < 0.0001). 6. Taxonomic composition of the wetland algal community responded most strongly to N-combination treatments in both seasons. In 2007, there was a significant shift from Euglena and Mougeotia in the control treatment to Chroococcus and Gloeocystis with +N+P+Si enrichment, and in 2008, a Mougeotia-dominated community was replaced by Gloeocystis in the +N+P treatment and by Nitzschia in +N+Si and +N+P+Si treatments. 7. Together, these data provide several lines of evidence for co-limitation, and the central importance of N as a co-limiting nutrient for the wetland algal community. Changes in algal dynamics with increased nutrient concentrations could have important implications for wetland food webs and suggest that algae may provide a functional link between increasing nutrient inputs and altered wetland carbon cycling in this region. [ABSTRACT FROM AUTHOR]

1. Top-down control of prey assemblages by fish predators has been clearly demonstrated in lakes (for zooplankton prey) and rivers (for macroinvertebrate prey). Fish predation can have a significant impact on the body size of prey assemblages; often large-bodied prey are reduced in abundance, and indirect facilitation of small-bodied prey occurs potentially initiating a trophic cascade. 2. Benthic communities in aquatic ecosystems also include a numerous and functionally important meiofaunal-sized component, but in freshwaters the impact of fish predation on meiofaunal assemblages is unknown. We used a laboratory microcosm study to explore the impact of juvenile fish predation on the abundance and size structure of a riverine meiofaunal assemblage. 3. The presence of fish in our microcosms had no significant effect on overall meiofaunal (temporary and permanent) abundance. However, for the Copepoda, we found the first evidence of top-down control of freshwater meiofaunal assemblages; in microcosms with juvenile fish, the abundance of large-bodied Copepoda was significantly reduced, whereas small-bodied Copepoda were significantly more abundant suggesting indirect facilitation. 4. We conclude that predation by juvenile fish can alter the structure of freshwater meiofaunal assemblages, although we do not yet know whether these relatively subtle changes are overwhelmed by large-scale events such as flow disturbances. [ABSTRACT FROM AUTHOR]

1. Abundance and composition of periphyton and benthic macroinvertebrates were treated as potential nutrient response variables for 74 streams in montane Colorado. The streams ranged from unenriched to mildly enriched with nutrients (N, P). 2. The study showed no meaningful relationship between periphyton biomass accumulation and concentrations of total or dissolved forms of nitrogen or phosphorus. Nutrient concentrations were also unrelated to periphyton and macroinvertebrate richness, diversity and community composition. Macroinvertebrate communities did, however, show a strong positive relationship to periphyton abundance. 3. A positive response of periphyton biomass to increasing nutrient concentrations has been well documented over large ranges of nutrient concentrations. Our study suggests that the nutrient response is suppressed by other controlling factors on the lower limb of the nutrient response curve (i.e. at low nutrient concentrations); a quantitatively significant response occurs only in excess of a threshold beyond which nutrients become dominant over other controlling factors. This interpretation of the results is consistent with published meta-analyses showing lack of nutrient response for a high proportion of experimentally enriched periphyton communities, and division of responses between N and P for communities that do show growth in response to enrichment. 4. Grazing probably is not the key controlling variable for periphyton in Colorado mountain streams, given that the highest chlorophyll concentrations are associated with the highest abundances of macroinvertebrates. Modelling indicates that the initial amount of periphyton biomass at the start of the growing season, in conjunction with elevation-related length of the growing season and water temperature, explains most of the variation in periphyton accumulation among these streams, but there is a yet unexplained suppression of periphyton growth rates across all elevations. [ABSTRACT FROM AUTHOR]

1. Reservoir creation and management can enhance many ecological services provided by freshwater ecosystems, but may alter the natural conditions to which aquatic biota have adapted. Benthic macroinvertebrates often reflect environmental conditions, and this community may be particularly susceptible to water-level changes that alter sediment exposure, temperature regime, wave-induced sediment redistribution and basal productivity. 2. Using a before–after control–impact experimental design, we assessed changes in macroinvertebrate community structure corresponding with changes in water-level management in two lentic systems in the Voyageurs National Park, Minnesota, U.S.A. Littoral zone (depths 1–5 m) benthic macroinvertebrate assemblages were sampled in Rainy Lake (control system) and Namakan Reservoir (impact system) in 1984–85, and again in 2004–05 following a change in water-level management that began in January 2000. The new regime reduced the magnitude of winter drawdown in Namakan Reservoir from 2.5 to 1.5 m, and allowed the reservoir to fill to capacity in late May, a month earlier than under the prior regime. Rainy Lake water levels were not altered substantially. 3. We found changes in macroinvertebrate community structure in Namakan Reservoir relative to Rainy Lake at 1–2 m depths but not at 3–5 m depths. These shallower depths would have been most directly affected by changes in sediment exposure and ice formation. 4. In 2004–05, Namakan Reservoir benthos showed lower overall abundance, more large-bodied taxa and an increase in non-insect invertebrates relative to 1984–85, without corresponding changes in Rainy Lake. 5. Changes in the benthic community in Namakan may reflect cooler water in spring and early summer as well as lower resource availability (both autochthonous production and allochthonous inputs) under the new regime. [ABSTRACT FROM AUTHOR]

1. The delivery, entrainment and deposition of inert fine sediments are among the most significant contributors to stream and river impairment worldwide. Associated ecological effects have been observed frequently, but specific experiments to identify sensitivity and avoidance behaviour in stream organisms are few, particularly in headwaters. 2. In a field-experiment, we added fine sand at low levels ( c. 4–5 kg m−2) to 10 m reaches of two replicate headwater streams in the Usk catchment (Wales, U.K.) over two periods (autumn and summer). Upstream reaches were used as control in a classic before-after-control-impact design. Invertebrate drift and benthic composition were measured for 2 days before and 1 day after sediment impact. 3. Sediment addition significantly increased overall drift density (by 45%) and propensity (by 200%), with effects largest on the night following addition rather than immediately (i.e. within 9 h). The mayflies Baetis rhodani, B. muticus and Ecdyonurus spp., simuliid and chironomid dipterans, and helodid beetles were the strongest contributors. 4. There were no marked effects on benthic composition, but density declined in treated reaches by 30–60%, particularly in B. rhodani, Ecdyonurus spp. and Leuctra hippopus + L. moselyi. 5. All effects were consistent between both seasons and streams. 6. These data show how even low-level, short-term, increases in fine sediment loading to upland, stony streams can reduce overall benthic density through increased drift. We suggest that the likely cause of the delayed drift response was a change in habitat quality which prompted avoidance behaviour. Longer-term experiments are required to assess whether these effects reduce fitness or explain the losses of some types of organisms observed recently in sediment-impaired reaches of this and other catchments. [ABSTRACT FROM AUTHOR]

1. Landscape management practices that alter energetic linkages between aquatic and terrestrial habitats can affect associated ecosystem processes, and ultimately the provision of ecosystem services of importance to humanity. Such effects cannot always be inferred from current biomonitoring schemes, which are typically based on assessment of community structural parameters rather than functional attributes related to important ecosystem-level processes. 2. We investigated effects of forest clearcutting, a major landscape-level disturbance known to alter the energetic basis of aquatic food webs, on headwater streams in northern Sweden. The key ecosystem process of leaf decomposition was measured as an index of ecosystem functioning. The biomass of detritivorous shredders was also quantified, along with various community structural parameters associated with the diversity, composition and functional guild organisation of benthic macroinvertebrate assemblages. 3. No differences in macroinvertebrate abundance, diversity or assemblage composition were detected between forested and clearcut streams, and most functional guilds were similarly unaffected, though species density of scrapers was higher in forested than clearcut channels. 4. In contrast, mass loss of two leaf species was elevated in all clearcut streams, with evidence for increases in the efficiency per degree-day of both the microbial and detritivore mediated fractions of decomposition. 5. Increased rates of leaf mass loss in the clearcut streams were associated with greater phosphate concentrations and shredder biomass, and with an increased relative abundance of broadleaves in standing stocks of benthic litter. Together, these findings indicate a more rapid transfer of energy and nutrients through the detrital pathways of our clearcut streams. 6. These results demonstrate the utility of litter decomposition assays for monitoring effects of forest management on stream ecosystem functioning, and have implications for nutrient cycles in landscapes extensively influenced by forest management. The markedly different responses of our functional and structural measures to clearcutting highlight the value of incorporating methods for the functional assessment of ecosystems into biomonitoring schemes. [ABSTRACT FROM AUTHOR]

1. Pacific salmon ( Oncorhynchus spp.) deliver marine-derived nutrients to the streams in which they spawn and die, and these resource subsidies can increase the abundance of stream biota. In strong contrast, physical disturbance from salmon spawning activity can reduce the abundance of benthic organisms. Previous experimental designs have not established the relative effects of these two contrasting processes on stream organisms during a salmon run. 2. We combined manipulative and observational field studies to assess the degree of nutrient enrichment, physical disturbance, and the net effect of salmon on the abundance of benthic periphyton. Related salmon-mediated processes were also evaluated for benthic macroinvertebrates. Mesh exclosures (2 × 2 m plots) prevented salmon from disturbing areas of the stream channel, which were compared with areas to which salmon had access. Sampling was conducted both before and during the late-summer spawning run of pink ( O. gorbushca) and chum ( O. keta) salmon. 3. Streamwater nitrogen and phosphorus concentrations increased sharply with the onset of the salmon run, and highly significant positive relationships were observed between the numbers of salmon present in the stream and these dissolved nutrients. Before the salmon run, periphyton biomass (as chlorophyll a) and total macroinvertebrate abundance were very similar between control and exclosure plots. During the salmon run, exclosures departed substantially from controls, suggesting significant disturbance imparted on benthic biota. 4. Comparing exclosures before and during the salmon run enabled us to estimate the effects of salmon in the absence of direct salmon disturbance. This ‘nutrient enrichment potential’ was significant for periphyton biomass, as was a related index for macroinvertebrate abundance (although enhanced invertebrate drift into exclosures during the salmon run could also have been important). Interestingly, however, the net effect of salmon, evaluated by comparing control plots before and during the salmon run, was relatively modest for both periphyton and macroinvertebrates, suggesting that nutrient enrichment effects were largely offset by disturbance. 5. Our results illustrate the importance of isolating the specific mechanisms via which organisms affect ecosystems, and indicate that the relative magnitude of salmon nutrient enrichment and benthic disturbance determines the net effect that these ecologically important fish have on stream ecosystems. [ABSTRACT FROM AUTHOR]

1. Blooms of the benthic, stalked diatom Didymosphenia geminata were first observed in New Zealand in 2004. Since then, D. geminata has spread to numerous catchments in the South Island and is also spreading in its native range. The species is a rare example of an invasive alga in lotic systems. 2. Ecosystem effects may be expected as D. geminata attains unusually high biomass in rivers. We examined data from three independent studies in three South Island, New Zealand, rivers for evidence of effects on periphyton biomass and benthic invertebrate communities. 3. The combined results confirmed that the presence of D. geminata was associated with greatly increased periphyton biomass and, in most cases, increased invertebrate densities. We also recorded shifts in community composition, dominated by increased densities of Oligochaeta. Chironomidae, Cladocera and Nematoda also generally increased in density with D. geminata. Significant increases or declines in other invertebrate taxa were inconsistent among rivers. 4. In all three studies, increased spatial invertebrate community homogeneity was associated with high D. geminata biomass at the within-river scale. However, no declines in taxon richness or diversity were detected. 5. Although ecosystem effects of D. geminata on existing periphyton biomass and invertebrate communities are measurable, no inferences can be made from the present data about effects on higher trophic levels (fish). [ABSTRACT FROM AUTHOR]

1. The zebra mussel ( Dreissena polymorpha) is one of the most successful invasive species; it has colonised many aquatic systems in Europe and North America with strong impacts on various ecosystem processes. The effect of D. polymorpha filtration on pelagic seston concentrations has been quantified in several studies, but the magnitude and stoichiometry of the transfer of sestonic biomass into benthic detritus by D. polymorpha and the accompanying enrichment of the benthic habitat is still under-investigated. 2. We studied biodeposition by zebra mussels in two series of laboratory experiments with the food algae Cryptomonas erosa and Scenedesmus obliquus. We also measured the year-round biodeposition rate under natural conditions in the oligotrophic Lake Constance. 3. In all experiments, zebra mussel biodeposition was linearly related to seston concentration. In the field, the relationship changed with a seasonal shift in algal composition and lower biodeposition rates during the spring algal bloom. 4. For both algal species in laboratory experiments, biodeposited material was depleted in phosphorous at an algal concentration ≤0.6 mg ash-free dry mass L−1, but not at higher concentrations. This effect was not observed in the field, probably because of high variation in C : N : P stoichiometry. 5. By mediating the transfer of pelagic resources into the benthos zebra mussels provide a sufficient amount of detritus for benthic invertebrates, especially during summer. Thus, material biodeposited by the mussels might increase benthic secondary production from pelagic resources, and zebra mussels are important mediators of this flux of organic matter from the pelagic zone into the benthos. [ABSTRACT FROM AUTHOR]

1. We set out to evaluate the reliability of bacterial communities as an indicator of freshwater ecological health. 2. Samples of epilithic biofilm were taken over a 1-year period from four streams, each impacted by varying degrees of human modification. The bacteria within each sample were characterised using a whole community DNA fingerprinting technique (automated ribosomal intergenic spacer analysis). Spatial and temporal differences in community structure between samples were visualised using multi-dimensional scaling and quantified using permutational multivariateanova. Macrobenthic invertebrates, which are commonly used as indicators of stream ecological health, were also sampled for comparison. 3. Multivariate analysis revealed a clear gradient in macroinvertebrate community structure between sites exposed to increased human impact. Bacterial communities, however, could only distinguish the most impacted site from the remainder. 4. Additional research is required to increase the sensitivity of bacterial community analyses before endorsing their use as an indicator of freshwater ecological health. [ABSTRACT FROM AUTHOR]

1. Alpine river basins are dynamic and heterogeneous environments both hydrologically and biologically. However, classification approaches that identify structure and patterns in alpine river ecosystems are not well developed or evaluated compared with methods for streams at lower altitude. 2. We undertook field validation of the novel Alpine RIver and Stream Ecosystem classification (ARISE) approach, using data collected from three streams in the French Pyrénées. Specifically, we evaluated the potential of ARISE to differentiate physicochemical habitat and benthic macroinvertebrate communities between sites in space and time. 3. Using quantitative water source contributions to classify samples, ARISE differentiated streams with contrasting electrical conductivity, water temperature and channel stability. Significant differences were identified between ARISE classifications for selected benthic macroinvertebrate community level descriptors (taxonomic richness, beta diversity, total abundance) and for some individual species. 4. Although ARISE needs to be validated further for other alpine river systems, our results indicate its potential in providing a more objective, quantitative basis to underpin management of alpine stream ecosystems. [ABSTRACT FROM AUTHOR]

1. Australian dryland rivers have among the most variable discharge of any rivers worldwide and are characterized by extended periods of no flow during which aquatic habitat contracts into isolated waterholes. Despite naturally high turbidity, benthic primary production is known to be the main source of carbon to waterhole food webs. The objective of this study was to quantify rates of benthic metabolism and identify factors influencing these rates in two Australian dryland rivers, the Cooper Creek and the Warrego River. 2. Both rivers have similar variable hydrology and high levels of turbidity (photic depths < 0.4 m), but fish abundance in Cooper Creek is 10 times than that of the Warrego River. Therefore, an additional aim of the study was to determine if fish abundances reflected underlying differences in benthic primary production. 3. Benthic gross primary production (GPP), benthic respiration, nutrient concentrations and light penetration were measured immediately after flow had ceased (‘post-flow’) and after at least 2 months of zero flow (‘no-flow’) in 15 waterholes from each river. A subset of four waterholes from each river was sampled on two additional occasions to determine if patterns were consistent over time. 4. Cooper Creek generally had higher rates of GPP and a more autotrophic benthic zone than the Warrego River. As a result, the expected positive relationship between fish abundance and GPP was generally observed at a broad catchment scale. 4. Light was the major control in benthic GPP in both rivers, as nutrient concentrations were high on all sampling occasions. However, for similar values of photic depth, GPP was greater in Cooper Creek than in the Warrego River. This suggests that more frequent disturbance of the littoral zone may inhibit biofilm development in waterholes of the Warrego River. 5. Although flow variability in dryland rivers is extreme compared with other rivers worldwide, cycles of expansion and contraction of aquatic habitat in these two rivers were associated with a shift in the dominance of regional scale (subcatchments contributing to river flow) versus local scale (waterhole morphology) influences on ecosystem functioning, similar to floodplain rivers in tropical and temperate regions. [ABSTRACT FROM AUTHOR]

1. Unionid mussels often account for a large portion of benthic biomass and contribute to nutrient cycling and sediment processes, but are thought to be limited to shallow areas (<2–3 m). 2. The depth distribution and body size of Elliptio complanata were compared in seven Canadian Shield lake basins of different sizes to test what factors determine the upper and lower limit of their depth range. Specifically, I tested whether (i) the upper range of their distribution is limited by exposure to winds and wave action and (ii) the lower range of their distribution is limited by the depth of the thermocline or by the boundary of mud deposition. 3. The average depth distribution of E. complanata shifted to greater depths in larger lake basins. When comparing individual transects, maximum mussel density was found deeper at more exposed sites. Mussel size decreased with increasing depth and was larger, on average, in larger lake basins. These results suggest that physical forces limit the upper range of mussel distribution in lakes. 4. The maximum depth at which mussels were found in different lakes was closely related to thermocline depth. However, mussels were commonly observed below the predicted depth of the mud deposition boundary. The thermocline limits the lower range of mussel distribution in lakes, probably by limiting food availability and by determining water temperature. Substratum type does not limit the lower distribution of mussels. 5. These results suggest that unionid mussels are present in the deeper parts of the littoral zone, especially in large lakes. Therefore, comparisons of mussel populations between sites and between lakes would be biased unless the full depth distribution of these mussels is considered. These results also suggest that long-term changes in the thermal structure of lakes could affect the range of unionid mussel populations and their functional role in littoral ecosystems. [ABSTRACT FROM AUTHOR]

1. Human use of land and water resources modifies many streamflow characteristics, which can have significant ecological consequences. Streamflow and invertebrate data collected at 111 sites in the western U.S.A. were analysed to identify streamflow characteristics (magnitude, frequency, duration, timing and variation) that are probably to limit characteristics of benthic invertebrate assemblages (abundance, richness, diversity and evenness, functional feeding groups and individual taxa) and, thus, would be important for freshwater conservation and restoration. Our analysis investigated multiple metrics for each biological and hydrological characteristic, but focuses on 14 invertebrate metrics and 13 streamflow metrics representing the key associations between streamflow and invertebrates. 2. Streamflow is only one of many environmental and biotic factors that influence the characteristics of invertebrate assemblages. Although the central tendency of invertebrate assemblage characteristics may not respond to any one factor across a large region like the western U.S.A., we postulate that streamflow may limit some invertebrates. To assess streamflow characteristics as limiting factors on invertebrate assemblages, we developed a nonparametric screening procedure to identify upper (ceilings) or lower (floors) limits on invertebrate metrics associated with streamflow metrics. Ceilings and floors for selected metrics were then quantified using quantile regression. 3. Invertebrate assemblages had limits associated with all streamflow characteristics that we analysed. Metrics of streamflow variation at daily to inter-annual scales were among the most common characteristics associated with limits on invertebrate assemblages. Baseflow recession, daily variation and monthly variation, in streamflow were associated with the largest number of invertebrate metrics. Since changes in streamflow variation are often a consequence of hydrologic alteration, they may serve as useful indicators of ecologically significant changes in streamflow and as benchmarks for managing streamflow for ecological objectives. 4. Relative abundance of Plecoptera, richness of non-insect taxa and relative abundance of intolerant taxa were associated with multiple streamflow metrics. Metrics of sensitive taxa (Ephemeroptera, Plecoptera and Trichoptera), and intolerant taxa generally had ceilings associated with flow metrics while metrics of tolerant taxa, non-insects, dominance and chironomids generally had floors. Broader characteristics of invertebrate assemblages such as abundance and richness had fewer limits, but these limits were nonetheless associated with a broad range of streamflow characteristics. [ABSTRACT FROM AUTHOR]

1. Large amounts of terrestrial detritus enter many low-order forested streams, and this organic material is often the major basal resource in the metazoan food webs of such systems. However, despite their apparently low biomass, algae are the dominant food of organisms in a number of aquatic communities which conventionally would have been presumed to be dependent on allochthonous detritus, particularly those in the tropics and also in lowland intermittent streams in arid Australia. 2. The dual stable isotope signatures (δ13C and δ15N) of potential primary food sources were compared with the isotopic signatures of common aquatic animals in lowland intermittent streams in south-eastern Australia, in both spring and summer, to determine whether allochthonous detritus was an important nutritional resource in these systems. The isotopic signatures of the major potential allochthonous plant food sources ( Eucalyptus, Phalaris and Juncus) overlapped, but were distinct from algae and the dominant macrophytes growing in the study reaches. The isotopic signatures of biofilm were more spatially and temporally variable than those of the other basal resources. 3. Despite allochthonous detritus having relatively high C : N ratios compared to other potential basal resources, results fromisosource mixing model calculations demonstrated that this detritus, and the associated biofilm, were the major energy sources assimilated by macroinvertebrate primary consumers in both spring and summer. The importance of these energy sources was also reflected in animals higher in the food web, including predatory macroinvertebrates and fish. These resources were supplemented by autochthonous sources of higher nutritional value (i.e. filamentous algae and macrophytes, which had relatively low C : N ratios) when they became more prolific as the streams dried to disconnected pools in summer. 4. The results highlight the importance of allochthonous detritus (particularly from Eucalyptus) as a dependable energy source for benthic macroinvertebrates and fish in lowland intermittent streams of south-eastern Australia. This contrasts with previous stable isotope studies conducted in lowland intermittent streams in arid Australia, which have reported that the fauna are primarily dependent on autochthonous algae. [ABSTRACT FROM AUTHOR]

1. Gut content analyses (GCA) of benthic macroinvertebrates, supplemented by carbon and nitrogen stable isotope analyses (SIA), were used to determine the relative contribution of leaf litter and autochthonous food sources to consumer biomass in five shaded and five unshaded streams in tropical Hong Kong. 2. Only four obligate shredders and two facultative shredders were identified out of 58 morphospecies dissected. Non-shredder taxa consumed little (<23% food eaten) coarse particulate organic matter (CPOM) in spite of its abundance in streams, and GCA revealed that fine particulate organic matter was the major food (25–99%) of most primary consumers. 3. Stable isotope analysis results were in general agreement with the findings of GCA, and confirmed that three of the four obligate shredders had a high dependence (55–78% of assimilated carbon) on CPOM. 4. Autochthonous energy sources were important in all streams: non-shredding primary consumers examined, which accounted for 72% of total macroinvertebrate abundance in shaded streams, derived (on average) 61% of their biomass from autochthonous foods; the equivalent values for unshaded streams were 72% (abundance) and 71% (biomass). [ABSTRACT FROM AUTHOR]

1. Aquatic herbivores typically have much higher concentrations of nutrients (e.g. N and P) in their tissues than there is in the food they eat. These stoichiometric differences can cause herbivores to be limited by the elemental quality of their food, which could affect, in turn, the structure of consumer communities and even alter key ecosystem processes. 2. In streams and in the littoral zone of shallow lakes, periphyton is an important food resource for benthic animals. Studying the elemental composition of periphyton may help us to understand food-web structure, and any reciprocal effect of this structure on periphyton stoichiometry. 3. To understand how alterations in the food-web structure affect the elemental composition of periphyton in a eutrophic lake, we carried out a long-term experiment (14 months) in large-scale mesocosms (40 m3), in which we manipulated food-web structure, and which were dominated either by planktivorous fish ( Rutilus rutilus) or herbivorous invertebrates (without fish). Periphyton was sampled monthly at three depths (0.5, 1.5 and 2.5 m) to determine its biomass and elemental composition (C/N/P ratio). Food-web structure, physical and chemical parameters were monitored throughout the experiment. 4. Fish had indirect positive effect on periphyton biomass, leading to twofold higher levels than in herbivore-dominated mesocosms. This result was probably due to control of benthic consumers by fish, suggesting a strong top–down control on periphyton by their consumers in fishless enclosures. 5. The elemental ratios C/P and C/N were lower in deep water in both treatments, mainly mediated by light availability, in accordance with the light/nutrient ratio hypothesis. These ratios were also lower in fishless treatments, probably due to increases in inorganic nutrient availability and grazing pressure in herbivore-dominated systems. During winter, periphyton elemental composition was similar in both treatments, and was unrelated to inorganic nutrient availability. 6. These results indicate that any alteration of food-web structure in lakes, such as in biomanipulation experiments, is likely to modify both the biomass and elemental quality of periphyton. Resultant effects on the consumers of periphyton and macrophytes could play a key role in the success of biomanipulations and should be taken into account in further studies. [ABSTRACT FROM AUTHOR]

1. Ecosystems can enhance the biodiversity of adjacent ecosystems through subsidies of prey, nutrients and also habitat. For example, trees can fall into aquatic ecosystems and act as a subsidy that increases aquatic habitat heterogeneity. This habitat subsidy is vulnerable in lakes where anthropogenic development of shorelines coincides with a thinning of riparian forests and the removal of these dead trees (termed coarse woody debris: CWD). How the disruption of this subsidy affects lake ecosystems is not well understood. 2. We performed a whole ecosystem experiment on Little Rock Lake, a small (18 ha), undeveloped, and unfished lake in Vilas County, WI, U.S.A., that is divided into two similar-sized basins by a double poly-vinyl chloride curtain that prevents both fish and water exchange between basins. In 2002, we removed about 70% of the littoral CWD in the treatment basin, while the reference basin was left unaltered. We tested for changes in both fish and benthic macroinvertebrate community composition in the two years following the CWD reduction. 3. Yellow perch ( Perca flavescens) was the most abundant fish species in the lake prior to our experiment, but declined to very low densities in the treatment basin after manipulation. We found no evidence of an effect on macroinvertebrates – the treatment basin’s macroinvertebrate community composition, diversity and density did not change relative to the reference basin. 4. Our results indicate that different trophic groups may have differential responses to the loss of a habitat subsidy, even if anthropogenic effects on that subsidy are severe. In the case of Little Rock Lake, fish community responses were evident on a short-time scale, whereas the macroinvertebrate community did not rapidly change following CWD reduction. [ABSTRACT FROM AUTHOR]

1. In sub-Saharan Africa, tropical forests are increasingly threatened by accelerating rates of forest conversion and degradation. In East Africa, the larger tracts of intact rainforest lie largely in protected areas surrounded by converted landscape. Thus, there is critical need to understand the functional links between large-scale land use and changes in river conditions, and the implications of park boundaries on catchment integrity. 2. The objective of this study was to use the mosaic of heavily converted land and pristine forest created by the protection of the high-altitude rainforest in Bwindi Impenetrable National Park, Uganda to explore effects of deforestation on aquatic systems and the value of forest in buffering effects of adjacent land conversion. A set of 16 sites was selected over four drainages to include four categories of deforestation: agricultural land, deforested upstream (of the park boundary), forest edge (park boundary) and forest. We predicted that forest buffer (downstream or on the edge) would moderate effects of deforestation. To address this prediction, we quantified relationships between disturbance level and both physicochemical characters and traits of the macroinvertebrate assemblages during six sampling periods (February 2003 and June 2004). 3. Results of both principal components analysis and cluster analyses indicated differences in limnological variables among deforestation categories. PC1 described a gradient from deforested sites with poor water quality to pristine forested sites with relatively good water quality. Agricultural sites and deforested upstream sites generally had the highest turbidity, total dissolved solids (TDS), and conductivity values and low transparency values. Forest sites and boundary site groups generally exhibited low turbidity, TDS, and conductivity values and high water transparency values. Sites also clustered according to deforestation categories; forest and forested edge sites formed a cluster independent of both agricultural land and deforested-upstream. 4. Water transparency, water temperature, and pH were the most important factors predicting benthic macroinvertebrate assemblages. Sensitive invertebrate families of Trichoptera, Ephemeroptera, Plecoptera, and Odonata dominated forested sites with high water transparency, low water temperature, and low pH while the tolerant families of Ephemeroptera, Diptera, Hemiptera, and Coleoptera were abundant in agriculturally impacted sites with low water transparency, high water temperature, and high pH. 5. This study provides support for the importance of riparian buffers in moderating effects of deforestation. Forest and forested edge sites were more similar in both limnological and macroinvertebrate assemblage structure than sites within or downstream from agricultural lands. If the protected area cannot encompass the catchment, the use of rivers as park boundaries may help to maintain the biological integrity of the rivers by buffering one side of the watercourse. [ABSTRACT FROM AUTHOR]

1. There is a paucity of information on ontogenetic changes in the dispersal of benthic invertebrates, which is an important aspect of their ecology. This study quantifies ontogenetic changes in diel periodicity in drift, and in upstream–downstream dispersal on the substratum for Elmis aenea, Oulimnius tuberculatus, Esolus parallelepipedus and Limnius volkmari (Coleoptera: Elmidae). Three drift nets were emptied every 3 h over 24 h in each month (October 1965–December 1968) at two contrasting sites: one in a deep section with abundant macrophytes, the other in a shallow stony riffle. Comparisons of periodicity between life-stages of the same species were limited to months when numbers in the drift were highest. Dispersal was evaluated in six experimental stream channels, placed above the stream, with initial numbers of each life-stage varying from 20 to 80. 2. Drift numbers were always highest at night with few or no animals in the day samples. Ontogenetic shifts in diel periodicity were similar for all four species. Drift catches were similar throughout the night for the early and intermediate larval instars and for mature adults, but were highest in the early hours of the night with a gradual decline thereafter for later larval instars and immature adults. These patterns were unaffected by a severe spate, even though drift numbers increased considerably. 3. Dispersal was density-independent; the number of dispersing animals was a constant proportion of the initial number for each life-stage. The relationship between dispersal distance and the number of animals travelling that distance was well described by an inverse power function. Median and maximum distances (m day−1) were estimated for each life-stage. 4. Ontogenetic shifts in dispersal in the stream channels matched those shown in diel drift periodicity. For all four species, the later larval instars and immature adults showed little movement in either direction, whereas early and intermediate larval instars and mature adults dispersed predominantly upstream, adults travelling further than any other life-stage. 5. Ontogenetic shifts in diel drift periodicity and dispersal were related to seasonal changes in drift density and critical periods in the life cycle. Such shifts have not been quantified in other stream invertebrates, but should be considered when evaluating the role of dispersal in their population dynamics and their colonization ability. [ABSTRACT FROM AUTHOR]

1. Few studies have directly addressed the role played by parasites in the structure and function of ecosystems. Parasites influence the behaviour, reproduction and overall fitness of their hosts, but have been usually overlooked in community and ecosystem-level studies. We investigated the effects of trematode parasites on snail–periphyton interactions. 2. Physa  acuta (Gastropoda: Pulmonata) snails infected with the trematode Posthodiplostomum minimum (often >30% of within-shell biomass) grazed more rapidly than uninfected snails. Trematode effects on snail grazing indirectly affected the standing stock and community structure of periphyton. Populations of snails with 50% infected individuals reduced algal biomass by 20% more than populations with lesser (10% or 0%) infection rates. 3. The alga Cladophora glomerata dominated periphyton communities grazed by snail populations with 50% infection rates, whereas diatoms and blue–green algal taxa dominated when grazed by snail populations with lower infection rates. 4. Thus, trematodes indirectly affected periphyton communities by altering host snail behaviour, a trait-mediated indirect effect. These results indicate that trematodes can indirectly influence benthic community structure beyond simple population fitness, with possible related effects on ecosystem function. [ABSTRACT FROM AUTHOR]

1. This study aimed to quantify ontogenetic changes in the drifting of Elmis aenea, Oulimnius tuberculatus, Esolus parallelepipedus and Limnius volkmari (Coleoptera: Elmidae), and to relate their drift to benthic density. Monthly samples were taken over 39 months, using three surface nets at each of two contrasting sites in a small stream: one in a deep section with abundant macrophytes, and the other in a shallow stony section. 2. Most larvae and adults were taken in the drift at night with little variation between catches in the three nets at each site. Day catches were very low, often zero. No significant relationships could be established between mean numbers in the drift catches and benthic densities. 3. When night catches were converted to drift densities (number caught per 100 m3 of water sampled), the latter were positively related to monthly losses in the benthos, but not to benthic densities. A linear regression described the relationship, and equations for the different life-stages within each species were not significantly different from the equation for all life-stages combined. However, drift losses were only about 0.07% of total losses in the benthos. A severe spate in October 1967 increased the number of larvae and adults in the drift, but not drift densities, except for immature adults of E. aenea, O. tuberculatus and E. parallelepipedus. 4. Key life-stages with the highest drift density were the earliest life-stage soon after egg hatching for E. aenea, the start of the larval overwintering period for O. tuberculatus and L. volkmari, and mature adults during the mating season for all three species. Drift density for E. parallelepipedus was too low to identify a key life-stage. These key life-stages corresponded with critical periods for survival in the life cycle, as identified in an earlier study in the same stream. Mortality was high during these critical periods, hence the strong relationship between drift density and benthic losses. The latter relationship was very consistent for different life-stages within each species, and partially supported the rarely-tested hypothesis that drift represents surplus production in the benthos. [ABSTRACT FROM AUTHOR]

1. The replicability of mesocosms is assessed in a case study of artificial streams (4 m2) flanking a lowland chalk river in southern U.K. Among-mesocosm comparisons of physicochemistry and macroinvertebrate assemblage composition (in drift and benthos) were made during a 2-year survey of 12 outdoor once-through linear channels. 2. Mesocosm physicochemistry was highly replicable, with statistically significant congruence in temporal variation across the mesocosm series, low spatial variation and no significant blocking or positional effects arising from mesocosm layout. Parallel physicochemistry was attributed to the outdoor stream-side location and short water residence times. 3. Mesocosms were colonized by 127 macroinvertebrate taxa from 15 taxonomic orders. Both benthic and drifting assemblages were comparable among mesocosms, with no significant effect of mesocosm layout. Small differences in taxonomic composition were, however, evident among particular mesocosms, with higher (e.g. Tinodes, Limnius and Elmis) or lower (e.g. Pisidium and Valvata) abundances observed for a minority (5%) of taxa. We conclude that large (4 m2) outdoor flow – through mesocosms can be replicable when located near to the source system and allowed to establish naturally. [ABSTRACT FROM AUTHOR]

1. According to the guidelines of the European Water Framework Directive, assessment of the ecological quality of streams and rivers should be based on ecotype-specific reference conditions. Here, we assess two approaches for establishing a typology for Mediterranean streams: a top-down approach using environmental variables and bottom-up approach using macroinvertebrate assemblages. 2. Classification of 162 sites using environmental variables resulted in five ecotypes: (i) temporary streams; (ii) evaporite calcareous streams at medium altitude; (iii) siliceous headwater streams at high altitude; (iv) calcareous headwater streams at medium to high altitude and (v) large watercourses. 3. Macroinvertebrate communities of minimally disturbed sites ( n = 105), grouped using UPGMA (unweighted pair-group method using arithmetic averages) on Bray–Curtis similarities, were used to validate four of the five ecotypes obtained using environmental variables; ecotype 5, large watercourses, was not included as this group had no reference sites. 4. Analysis of similarities (anosim) showed that macroinvertebrate assemblage composition differed among three of the four ecotypes, resulting in differences between the bottom-up and top-down classification approaches. Siliceous streams were clearly different from the other three ecotypes, evaporite and calcareous ecotypes did not show large differences in macroinvertebrate assemblages and temporary streams formed a very heterogeneous group because of large variability in salinity and hydrology. 5. This study showed that stream classification schemes based on environmental variables need to be validated using biological variables. Furthermore, our findings indicate that special attention should be given to the classification of temporary streams. [ABSTRACT FROM AUTHOR]