Grazing management influences the subsidy of terrestrial prey to trout in central Rocky Mountain streams (USA)

1. Research in forest and grassland ecosystems indicates that terrestrial invertebrates that fall into streams can be an important prey resource for fish, providing about 50% of their annual energy and having strong effects on growth and abundance. However, the indirect effects of land uses like cattle grazing on this important prey subsidy for stream salmonids are unclear. 2. During summer 2007, we compared the effects of three commonly used grazing systems on terrestrial invertebrate inputs to streams in northern Colorado and their use by trout. Cattle graze individual pastures for about 120 days under traditional season‐long grazing (SLG), about 35–45 days under simple rotational grazing and 10–20 days under intensive rotational grazing in this region. We also compared these effects to a fourth group of sites grazed only by wildlife (i.e. no livestock use). 3. Overall, rotational grazing management (either simple or intensive), resulted in more riparian vegetation, greater inputs of terrestrial invertebrates, greater biomass of terrestrial invertebrate prey in trout diets, a higher input compared to trout metabolic demand and more trout biomass than SLG. However, these differences were frequently not statistically significant owing to high variability, especially for trout diets and biomass. 4. Despite the inherent variability, riparian vegetation and terrestrial invertebrates entering streams and in trout diets at sites managed for rotational grazing were similar to sites managed for wildlife grazing only. 5. These results indicate that rotational grazing systems can be effective for maintaining levels of terrestrial invertebrate subsidies to streams necessary to support robust trout populations. However, factors influencing the effect of riparian grazing on stream subsidies are both spatially variable and complex, owing to differences in microclimate, invertebrate and plant populations and the efforts of ranchers to tailor grazing systems to specific riparian pastures.     

Response of grazing impacts of an algivorous fish (Pseudogastromyzon myersi: Balitoridae) to seasonal disturbance in Hong Kong streams

1. Manipulative experiments were carried out in four Hong Kong streams (two shaded, two unshaded) to investigate the impact of grazing by an algivorous fish, Pseudogastromyzon myersi, on benthic algal biomass and assemblage composition. Experiments were conducted and repeated during both the dry and wet seasons to determine whether spate‐induced disturbance modified any grazing effect. Treatments comprised fish exclusion and inclusion via closed and open cages, with a no‐cage treatment used as a control for the cage effect. Treatments were maintained for 4 weeks in each experimental run. 2. Grazing by P. myersi reduced benthic algal biomass and the organic matter content of periphyton in open cages and the no‐cage treatment relative to closed cages. The similarity between open‐cage and no‐cage treatments was evidence that the overall difference among treatments was caused by limiting fish access to closed cages and not merely an artifact of caging. Grazing effects were broadly similar in all streams, but there was a significant statistical interaction between treatments and seasons. 3. Analysis of dry‐season data matched the overall trend in inter‐treatment differences, confirming the effects of grazing by P. myersi on algal biomass and periphyton organic matter. Significant differences in algal assemblage composition between closed‐cage and no‐cage treatments during the dry season reflected reductions in the abundance of erect, stalked diatoms (Gomphonema) and filamentous cyanobacteria (Homeothrix). Removal of these vulnerable overstorey algae by P. myersi resulted in greater abundance of understorey diatoms (Achnanthes and Cocconeis) in the no‐cage treatment in all streams during the dry season. The composition of algal assemblages in open cages was intermediate between the other two treatments. 4. Although fish densities were greater in all streams during the wet season, spate‐induced disturbance obscured grazing effects and there were no significant differences among treatments attributable to fish grazing. Seasonal variation in impacts of P. myersi grazing provides support for the harsh‐benign hypothesis, and confirms that biotic factors are less important controls of stream algal biomass and assemblage structure during periods (i.e. the wet season in Hong Kong) when abiotic disturbances are frequent or intense.     

Brown trout and food web interactions in a Minnesota stream

1. We examined indirect, community‐level interactions in a stream that contained non‐native brown trout (Salmo trutta Linnaeus), native brook trout (Salvelinus fontinalis Mitchill) and native slimy sculpin (Cottus cognatus Richardson). Our objectives were to examine benthic invertebrate composition and prey selection of fishes (measured by total invertebrate dry mass, dry mass of individual invertebrate taxa and relative proportion of invertebrate taxa in the benthos and diet) among treatments (no fish, juvenile brook trout alone, juvenile brown trout alone, sculpin with brook trout and sculpin with brown trout). 2. We assigned treatments to 1 m² enclosures/exclosures placed in riffles in Valley Creek, Minnesota, and conducted six experimental trials. We used three designs of fish densities (addition of trout to a constant number of sculpin with unequal numbers of trout and sculpin; addition of trout to a constant number of sculpin with equal numbers of trout and sculpin; and replacement of half the sculpin with an equal number of trout) to investigate the relative strength of interspecific versus intraspecific interactions. 3. Presence of fish (all three species, alone or in combined‐species treatments) was not associated with changes in total dry mass of benthic invertebrates or shifts in relative abundance of benthic invertebrate taxa, regardless of fish density design. 4. Brook trout and sculpin diets did not change when each species was alone compared with treatments of both species together. Likewise, we did not find evidence for shifts in brown trout or sculpin diets when each species was alone or together. 5. We suggest that native brook trout and non‐native brown trout fill similar niches in Valley Creek. We did not find evidence that either species had an effect on stream communities, potentially due to high invertebrate productivity in Valley Creek.     

Spatial and seasonal associations of benthic macroinvertebrates and detritus in an Alaskan subarctic stream

Summary Seasonal and spatial patterns of benthic invertebrate abundance were examined in relation to benthic detritus in Monument Creek, an Alaskan subarctic stream. The total macroinvertebrate fauna showed a mid-summer low in abundance, increasing to seasonal highs in winter/early spring (November/May). Shredders were a small portion of the benthic fauna or leaf pack fauna in summer but increased rapidly (in biovolume) following autumnal leaf fall to dominate the fauna by early winter (October/November). Abundance was strongly correlated with quantity of detritus in the sample. Comparison of benthic macroinvertebrate densities from Alaskan streams with comparable data from temperate zone streams shows that Alaskan streams are similar to temperate zone streams in range of abundance. Each unit of benthic detritus in Monument Creek is associated with a relatively large number of small (low individual biomass) shredders compared to streams in temperate regions. Detrital resources in this subarctic stream were meager, compared to temperate streams, and appeared to strongly influence the spatial and temporal patterns of detritivores.     

Temporal and Spatial Patterns in Inputs and Stock of Organic Matter in Savannah Streams of Central Brazil

Coarse particulate organic matter (CPOM) inputs from riparian vegetation into streams and CPOM benthic stock vary naturally in space and time, but most studies in the tropical savannah (Cerrado) have been done over a small temporal scale (<1 year), which does not allow for the determination of inter-annual patterns. We found that CPOM collected over two years differed temporally and spatially, whereas there was no significant variation between years for the benthic stock, which indicates high stability in the energy balance of streams. The largest monthly inputs occurred between August and October, at the end of the dry season and the onset of the rainy season, which was partially explained by precipitation. Other factors such as photoperiod, which was not studied, could also have important roles in this pattern. Spatial differences in CPOM between streams were attributed to topography and channel morphology. The plant density was lowest in the stream with a more irregular topography and a deeper channel, which results in drier riparian soil. The benthic stock was highest in the stream with a flat channel, where the lower water speed facilitates the accumulation of CPOM in the stream bed. Inter-annual differences in CPOM were attributed more to the differences in the beginning of the dry and wet periods between years than to the average values of precipitation. Longer-term studies are needed to clarify this temporal pattern.     

Exotic crayfish in a brown water stream: effects on juvenile trout, invertebrates and algae

SUMMARY 1. The impact of the introduced omnivorous signal crayfish (Pacifastacus leniusculus) on trout fry, macroinvertebrates and algae was evaluated in a brown water stream in southern Sweden using in situ enclosures. We also examined the gut content of all surviving crayfish in the enclosures. Two crayfish densities in addition to a control without crayfish were used in replicate enclosures (1.26 m²) in a 1‐month experiment. Additionally, 20 trout fry (Salmo trutta) were stocked in each enclosure to assess the effects of crayfish on trout survival and growth. 2. Detritus was the most common food item in crayfish guts. Animal fragments were also frequent while algae and macrophytes were scarcer. Crayfish exuviae were found in crayfish guts, but the frequency of cannibalism was low. 3. Trout survival in enclosures was positively related to water velocity but was unaffected by crayfish. 4. Total invertebrate biomass and taxon richness were lower in crayfish treatments. The biomass of all predatory invertebrate taxa was reduced but only three of six non‐predatory taxa were reduced in the crayfish treatments. 5. Epiphytic algal biomass (measured as chlorophyll a, on plastic strips) was not related to crayfish density, whereas the biomass of epilithic algae (measured as chlorophyll a) was enhanced by high water velocity and high crayfish density. The latter was possibly mediated via improved light and nutrient conditions, as active crayfish re‐suspend and/or remove detritus and senescent algal cells during periods of low water velocity. 6. We conclude that the introduced signal crayfish may affect stream communities directly and indirectly. Invaded communities will have reduced macroinvertebrate taxon richness and the signal crayfish will replace vulnerable invertebrate predators such as leeches. In streams that transport large amounts of sediment or organic matter, a high density of crayfish is likely to enhance benthic algal production through physical activity rather than via trophic effects.     

Effects of woody debris and the supply of terrestrial invertebrates on the diet and growth of brown trout (Salmo trutta) in a boreal stream

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Periphyton responses to invertebrate grazing and riparian canopy in three northern California coastal streams

SUMMARY. 1. Field experiments were conducted to examine the impact of grazing invertebrates on periphyton biomass in twenty-one pools across three northern California coastal streams (U.S.A.): Big Sulphur Creek, the Rice Fork of the Eel River, and Big Canyon Creek. Periphyton accrual on artificial substrate tiles was compared in each stream between two treatments: those elevated slightly above the stream bottom to reduce access by grazers (= platforms) and those placed directly on the stream bottom to allow access by grazers (=controls).
2. Crawling invertebrate grazers (cased caddisflies and snails) were numerically dominant in each stream (86% of all grazers in Big Sulphur Creek, 61% in the Rice Fork, 84% in Big Canyon Creek). Platforms effectively excluded crawling grazers, but were less effective in excluding swimming mayfly grazers (Baetidae).
3. Periphyton biomass (as AFDM) on tiles was significantly lower on controls compared to platforms for the Rice Fork, an open-canopy stream, and Big Sulphur Creek, a stream with a heterogeneous canopy. In contrast, no grazer impact was found for Big Canyon Creek, a densely shaded stream. Here, extremely low periphyton biomass occurred for both treatments throughout the 60 day study.
4. The influence of riparian canopy on periphyton growth (i.e. accrual on platforms), grazer impact on periphyton, and grazer abundance was examined for Big Sulphur Creek. As canopy increased (15–98% cover), periphyton biomass on platforms decreased. In contrast, canopy had little influence on periphyton accrual on controls; apparently, grazers could maintain low periphyton standing crops across the full range of canopy levels. The abundance of one grazer species, the caddisfly Gumaga nigricula , was highest in open, sunlit stream pools; abundance of two other prominent grazers, Helicopsyche borealis (Trichoptera) and Centroptilum convexum (Ephemeroptera), however, was unrelated to canopy.     

Plant—herbivore interactions in streams near Mount St Helens

1. In four separate field experiments near Mount St Helens (Washington, U.S.A.) during 1986, the grazing effects of two large benthic herbivores, tadpoles of the tailed frog Ascaphus truei and larvae of the caddisfly Dicosmoecus gilvipes, were investigated using streamside channels and in-stream manipulations. In the experimental channels, abundances of periphyton and small benthic invertebrates declined significantly with increasing density of these larger herbivores. 2. In eleven small, high-gradient streams affected to varying degrees by the May 1980 eruption, in-stream platforms were used to reduce grazing by A, truei tadpoles on tile substrates. Single platforms erected in each tributary and compared to grazed controls revealed only minor grazing effects, and no significant differences among streams varying in disturbance intensity (and, consequently, tadpole density). However, results probably were confounded by high variability among streams in factors other than tadpole abundance. 3. Grazing effects were further examined in two unshaded streams with different tadpole densities, using five platforms per stream. In the stream with five tadpoles m^?2, grazing reduced periphyton biomass by 98% and chlorophyll a by 82%. In the stream lacking tadpoles, no significant grazing effects were revealed. Low algal abundance on both platforms and controls, and high invertebrate density in that stream (c. 30000m^?2) suggests that grazing by small, vagile invertebrates was approximately equivalent to that of tadpoles. 4. The influence of large benthic herbivores on algal and invertebrate communities in streams of Mount St Helens can be important, but reponses vary spatially in relation to stream disturbance history, local environmental factors, and herbivore distributional patterns and abundance.     

Benthic invertebrate communities in six Danish forest streams: Impact of forest type on structure and function

I investigated the impact of riparian vegetation type on stream invertebrate communities in SIX Danish forest streams during the period 1992–1993 Two of the streams ran through beech forest Fagus sylvatica , two through mixed, mainly deciduous forest, and two through conifer plantations Algal biomass and detritus standing stock differed significantly depending on forest type In mixed deciduous forest streams algal biomass was higher and detritus standing stock lower than in beech and conifer forest streams Benthic invertebrate community composition was functionally similar in all streams, with detritivores comprising >80% by numbers of the community Grazer abundance was low in all streams Shredder abundance in the four deciduous streams was significantly correlated to coarse detritus standing stock When taking into account both quantitative and qualitative POM parameters for all six streams combined, shredder abundance correlated significantly to the amount of CPOM There were significantly more invertebrates with a ≥ 2 yr life cycle in the conifer and beech forest streams than m the mixed forest streams, probably reflecting the larger and more stable food resource For all streams combined there was a significant correlation between predator abundance and the abundance of potential prey My findings suggest that Danish forest streams are regulated by "bottom-up control" at all trophic levels within the invertebrate community, and hence that forest type can structure benthic communities in forest streams     

The effects of predation and detritus on the structure of a stream insect community: a field test

Summary The role of predator density and plant detritus in determining patterns of insect abundance was tested in an Appalachian stream community (Reeds Creek, Pendleton Co, West Virginia). Insect colonization was followed over a 21-day period in field enclosures containing different densities of sculpins (Cottus bairdi and Cottus girardi). Sculpins caused no significant reductions in prey abundance; however, the combined effect of a guild of vertebrate predators caused a significant depression in the abundance of Chironomidae and the stonefly Leuctra. Since Chironomidae comprised approximately 85% of the total benthic fauna, vertebrate predation had an important role in the overall structure of the invertebrate community.Total insect abundance and diversity were correlated to the presence of plant detritus. However, this relationship was taxon specific, as abundance was highly correlated to detritus for only selected insect taxa. In general, abundance was best correlated with coarse particulate organic matter (CPOM), compared to fine particulate organic matter (FPOM) or total detritus (FPOM+CPOM+Whole leaf organic matter (LVOM)).This experiment illustrates that the influence of various potential structuring mechanisms is highly taxon dependent.     

Seasonality and composition of benthic coarse particulate organic matter in two coastal tropical streams with different land uses

This work studies benthic CPOM in two streams of Ecuador: the Atacames stream, located in a developed watershed, and the Súa stream, located in a rural watershed and used as a reference. It is tested whether the amount, composition and timing of benthic CPOM will differ between them as a function of watershed and riparian land uses. Benthic CPOM was collected at five study sites on each stream with a Surber net and classified into four categories: leaves, twigs and bark, flowers and fruits and debris. Leaves were further identified to genus or species. There were no significant differences in the amount, composition and timing of benthic CPOM between the streams. CPOM storage showed strong seasonality linked to seasonal rainfall and a weak relation with land uses, channel width and stream order. Diversity of the benthic CPOM was high and 30 species contributed to the benthic leaf pool. Presence or absence of Ficus species with heavy leaves that are easily retained in the streambed explained the spatial distribution of benthic CPOM, so spatial differences in the composition of the riparian vegetation in these tropical streams seem to be more important to explain CPOM distribution than in their temperate counterparts.

     

Impact of a eucalyptus (Eucalyptus globulus Labill.) plantation on the nutrient content and dynamics of coarse particulate organic matter (CPOM) in a small stream

Litterfall inputs, benthic storage and the transport of coarse particulate organic matter (CPOM) were studied in two headwater streams, one flowing through a mixed deciduous forest and one through a plantation of Eucalyptus globulus. Vertical and lateral traps, transported CPOM and benthic CPOM were sampled monthly to biweekly and sorted into four categories: leaves, twigs and bark, fruits and flowers and debris. The litterfall inputs were about 20% lower at the eucalyptus site but this reduction was unevenly distributed among the litter categories. The reduction of the nitrogen and phosphorus inputs was larger (50%) than that of CPOM because of the low nutrient concentration of the CPOM at the eucalyptus site. Transported CPOM was also lower at the eucalyptus site. Although total CPOM inputs to the stream were reduced in the eucalyptus plantation, benthic storage of CPOM was 50% higher due to (1) high inputs of CPOM and low discharge during summer, (2) more twig and bark inputs, (3) eucalyptus leaves being retained more efficiently in the stream than deciduous leaves (4) a lower discharge, which may in part be attributable to eucalyptus-induced changes in the hydrological cycle. Increased retention balanced lower nitrogen and phosphorus content of CPOM, so benthic storage of nitrogen and phosphorus was similar at both sites. This work demonstrates that the timing, quality and quantity of inputs and benthic storage of CPOM in streams changes substantially because of the substitution of natural deciduous forest with eucalyptus plantation. Maintenance of buffer strips of natural vegetation may be the best way to protect ecological functioning of small, forested streams.     

Responses to Riparian Restoration in the Spring Creek Watershed, Central Pennsylvania

Riparian treatments, consisting of 3‐ to 4‐m buffer strips, stream bank stabilization, and rock‐lined stream crossings, were installed in two streams with livestock grazing to reduce sediment loading and stream bank erosion. Cedar Run and Slab Cabin Run, the treatment streams, and Spring Creek, an adjacent reference stream without riparian grazing, were monitored prior to (1991–1992) and 3–5 years after (2001–2003) riparian buffer installation to assess channel morphology, stream substrate composition, suspended sediments, and macroinvertebrate communities. Few changes were found in channel widths and depths, but channel‐structuring flow events were rare in the drought period after restoration. Stream bank vegetation increased from 50% or less to 100% in nearly all formerly grazed riparian buffers. The proportion of fine sediments in stream substrates decreased in Cedar Run but not in Slab Cabin Run. After riparian treatments, suspended sediments during base flow and storm flow decreased 47–87% in both streams. Macroinvertebrate diversity did not improve after restoration in either treated stream. Relative to Spring Creek, macroinvertebrate densities increased in both treated streams by the end of the posttreatment sampling period. Despite drought conditions that may have altered physical and biological effects of riparian treatments, goals of the riparian restoration to minimize erosion and sedimentation were met. A relatively narrow grass buffer along 2.4 km of each stream was effective in improving water quality, stream substrates, and some biological metrics.     

Disturbance frequency and functional identity mediate ecosystem processes in prairie streams

A major consequence of climate change will be the alteration of precipitation patterns and concomitant changes in the flood frequencies in streams. Species losses or introductions will accompany these changes, which necessitates understanding the interactions between altered disturbance regimes and consumer functional identity to predict dynamics of streams. We used experimental mesocosms and field enclosures to test the interactive effects of flood frequency and two fishes from distinct consumer groups (benthic grazers and water-column minnows) on recovery of stream ecosystem properties (algal form and biomass, invertebrate densities, metabolism and nutrient uptake rates). Our results generally suggest that periphyton communities under nutrient limitation are likely to recover more quickly when grazing and water-column minnows are present and these effects can diminish or reverse with time since the disturbance. We hypothesized that increased periphyton production and biomass was the result of increased nutrient turnover, but decreased light limitation and indirect effects on other trophic levels are alternative explanations. Recovery of stream ecosystem properties after a natural flood differed from mesocosms (e.g. lower algal biomass and no long algal filaments present) and species manipulations did not explain recovery of ecosystem properties; rather, ecosystem processes varied along a downstream gradient of increasing temperature and nutrient concentrations. Different results between field enclosures and experimental mesocosms are attributable to a number of factors including differences in algal and invertebrate communities in the natural stream and relatively short enclosure lengths (mean area=35.8 m²) compared with recirculating water in the experimental mesocosms. These differences may provide insight into conditions necessary to elicit a strong interaction between consumers and ecosystem properties.     

The ecological effect of acid conditions and precipitation of hydrous metal oxides in a Rocky Mountain stream

Periphyton and benthic invertebrates assemblages were studied at the confluence of two Rocky Mountain streams, Deer Creek and the Snake River near Montezuma, Colorado. Upstream from the confluence the Snake River is acidic and enriched in dissolved trace metals, while Deer Creek is a typical Rocky Mountain stream. In the Snake River, downstream from the confluence, the pH increases and hydrous metal oxides precipitate and cover the streambed. The algal and benthic invertebrate communities in the upstream reaches of the Snake River and in Deer Creek were very different. A liverwort, Scapania undulata var. undulata, was abundant in the Snake River, and although periphyton were very sparse, there were as many benthic invertebrates as in Deer Creek. Downstream from the confleunce, the precipitation of hydrous metal oxides greatly decreased the abundance of periphyton and benthic invertebrates. This study shows that in streams metal precipitates covering the streambed may have a more deleterious effect on stream communities than high metal-ion activities.     

Long-term recovery of a mountain stream from clear-cut logging: the effects of forest succession on benthic invertebrate community structure

1. Changes in benthic invertebrate community structure following 16 years of forest succession after logging were examined by estimating benthic invertebrate abundance, biomass and secondary production in streams draining a forested reference and a recovering clear-cut catchment. Benthic invertebrate abundance was three times higher, and invertebrate biomass and production were two times higher in the disturbed stream.
2. Comparison of invertebrate community abundance 1, 5 and 16 years after clear-cutting indicated that the proportion of scrapers had decreased, whereas shredders had increased. Functional group percentage similarity indicated that the invertebrate community in the disturbed stream 16 years after clear-cutting was more similar to the reference than to that found earlier in the disturbed stream.
3. The five indices calculated from data collected over the past 16 years, as well as the abundance, biomass and production data collected during this study, proved to be of differing value in assessing recovery of the disturbed stream from logging. Percent dominant taxon and EPT (Ephemeroptera, Plecoptera and Trichoptera) taxon richness failed to show any initial differences between reference and disturbed streams, indicating that these indices may not be useful for measuring recovery from logging. The percentage Baetis and shredder–scraper indices showed significant differences only during the 1977 study and suggest recovery (no difference between reference and disturbed) by 1982. The North Carolina Biotic Index showed continued differences during 1982 in the riffle and depositional habitats and recovery by 1993. Total macroinvertebrate abundance, biomass and production, as well as EPT abundance, indicated continued differences between the reference and disturbed streams in the 1993 study.     

Invertebrate responses to short-term water abstraction in small New Zealand streams

1. Small permanent streams are coming under increasing pressure for water abstraction. Although these abstractions might only be required on a short‐term basis (e.g. summer time irrigation), the highest demand for water often coincides with seasonal low flows. 2. We constructed weirs and diversions that reduced discharge in three small streams (<4 m width) to test the hypotheses that short‐term water abstractions would decrease habitat availability and suitability for invertebrates, resulting in increased invertebrate drift, reduced taxonomic richness and decreased benthic invertebrate densities. 3. We sampled benthic invertebrates, invertebrate drift and periphyton at control (upstream) and impact (downstream) sites on each stream before and during 1 month of discharge reduction. 4. Discharge decreased by an average of 89–98% at impact sites and wetted width decreased by 24–30%. Water depth decreased by 28–64% while velocity decreased by 50–62%. Water conductivity, temperature and dissolved oxygen showed varying responses to flow reduction among the three streams, whereas algal biomass and pH were unaffected in all streams. 5. The densities of invertebrate taxa tended to increase in the impact reaches of these streams, even though invertebrate drift increased at impact sites in the first few days following discharge reduction. There were a higher proportion of mayflies, stoneflies and caddisflies at the impact site on one stream after flow reduction. There were no changes to the number of taxa or species evenness at impact sites. 6. Our results suggest that for these small streams, the response of invertebrates to short‐term discharge reduction was to accumulate in the decreased available area, increasing local invertebrate density.     

Invertebrate grazing and riparian shade as controllers of nuisance algae in a eutrophic river

1. Algal growth in lotic systems is controlled either from the bottom‐up (e.g. nutrients and light, which determine growth rates) or from the top‐down (e.g. grazing pressure, which reduces accumulated biomass). Nutrient‐enriched streams that support large and diverse grazing macroinvertebrate populations and those with shaded riparian corridors rarely suffer from excessive algal growth. 2. In this study, the density of benthic algivorous macroinvertebrates was experimentally manipulated in shaded and open nutrient‐enriched stream habitats of the Owennagearagh River, south‐west Ireland. The ability of macroinvertebrate grazers and riparian shade to control benthic algal growth [particularly the nuisance alga, Cladophora glomerata (L. Kütz)] was investigated. Three sites with markedly different concentrations of plant nutrients (one site upstream and two sites downstream of the sewage outfall) were selected. The density of grazing invertebrates colonising ceramic tiles was reduced using high‐voltage localised electric pulses. Replicates of treatment (grazer‐excluded) and control (grazed) tiles were deployed in open and shaded (<25 and >80% canopy cover, respectively) patches of stream bed, in each site. 3. After 2‐week Cladophora cover, periphytic chlorophyll a and biofilm ash‐free dry mass (AFDM) were quantified for all experimental tiles. Values for all three parameters were highest on grazer‐excluded tiles from open patches. Grazed tiles from open patches accrued little Cladophora and had significantly lower levels of chlorophyll a and AFDM. Nutrient inputs were found to have an impact on the density of grazing invertebrates, with higher densities of Baetis nymphs at the most nutrient‐enriched site. 4. Our results demonstrate that in eutrophic, high‐light streams, filamentous algae can quickly accumulate to nuisance levels in the absence of invertebrate grazers. In future, greater attention should be paid to the role of grazing invertebrates in controlling nuisance algae in streams, in addition to algal–nutrient relationships.