Are native cyprinids or introduced salmonids stronger regulators of benthic invertebrates in South African headwater streams?

The introduction of nonnative salmonids in the Southern Hemisphere generally leads to a reduction in invertebrate abundance and changes in assemblage composition. In the Cape Floristic Region of South Africa, introduced rainbow trout Oncorhynchus mykiss is the dominant predator in many headwater streams, where they have replaced small‐bodied native fishes such as Breede River redfin Pseudobarbus burchelli. To examine the consequences of this species replacement on food web structure, we used a month‐long field experiment to compare the top‐down effects of Breede River redfin and rainbow trout on benthic invertebrate assemblages (abundance and composition) and basal resources (periphyton and particulate organic matter) in 1 × 1.5 m of plastic cages. Benthic invertebrate abundance was more strongly depleted in the cages with redfin than in the cages with trout, and redfin and trout had distinct effects on invertebrate assemblage composition. On the other hand, neither redfin nor trout had a significant influence over standing stocks of periphyton or organic matter, implying that their differential effects on benthic invertebrates did not cascade down to the base of the stream food web in our experiment. Gut content analysis showed that aquatic invertebrates contributed more to the diet of redfin, while terrestrial invertebrates contributed more to the diet of trout, which may be responsible for the relatively weak effect of trout on aquatic invertebrates. This pattern contrasts with nonnative salmonid impacts elsewhere in the Southern Hemisphere. That trout can strongly alter the structure of benthic invertebrate assemblages, in addition to severely depleting native fish abundance, in Cape Floristic Region headwater streams should be weighed into management decisions, and our findings highlight the need for a detailed understanding of species‐specific top‐down effects where native predators are replaced by invasive predators.     

Fouling mussels (Dreissena spp.) colonize soft sediments in Lake Erie and facilitate benthic invertebrates

• 1 We conducted survey and transplant studies to determine whether colonization and residency on soft sediments by introduced, fouling mussels (Dreissena polymorpha and D. bugensis) were affected by physical disturbance, and whether Dreissena presence in turn influenced the diversity and population densities of other benthic invertebrates. Surveys revealed that colony density was typically higher at moderate depths than at shallower and greater ones. However, the largest, midsummer colonies and greatest coverage of sediments by mussels occurred at deeper sites.
• 2 Disturbance of transplanted colonies varied by depth and colony size, with deeper and larger colonies experiencing the lowest destruction rates. Colony destruction rate was positively correlated with current velocity adjacent to the lakebed.
• 3 Absence of mussel colonies at shallow sites was not determined by recruitment or substrate limitation, as recruit density was higher and sediment characteristics more suitable for postveliger settlement at shallow than at deeper sites. Rather, seasonal storms have much stronger effects in shallow than in deep water.
• 4 Mussel residency on soft sediment has profound effects on invertebrate biodiversity. Invertebrate species (taxon) richness and total abundance were positively correlated with mussel colony area. Mussel‐sediment habitat supported between 462 and 703% more taxa, and between 202 and 335% more individuals (exclusive of Dreissena) than adjacent soft‐sediment lacking mussels.
• 5 Results from this study illustrate that physical disturbance directly limits the distribution of mussels on soft sediments, and the diversity and abundance of other benthic invertebrates in consequence.

     

Effects of Adult Dreissena polymorpha on Settling Juveniles and Associated Macroinvertebrates

The impact of Dreissena polymorpha settlement on recruitment of juvenile mussels and density of other macroinvertebrates was studied in field experiments using blank concrete blocks and tiles (control), blocks and tiles with attached empty zebra mussel shells, and blocks and tiles with attached living mussels. On blocks, dominant invertebrate taxa showed colonization patterns coinciding with increased habitat complexity owing to zebra mussel settlement or the biodeposition of faeces and pseudofaeces. Adult and especially juvenile zebra mussels preferred blocks with empty shells to blank blocks and blocks with living mussels; this might possibly be caused by a chemical cue that induces gregarious settlement. Lower recruitment on blocks with attached living mussels compared to blocks with only shells could be the consequence of ingestion of larvae by adult mussels and of competition for food. On tiles, the sediments deposited and the organic content of the sediment were investigated. Sedimentation was significantly higher on shell‐only and live‐mussel tiles compared to blank tiles. Organic matter differed significantly between blank and live‐mussel tiles.     

Spatial variation in density of stream benthic fishes in northern Hokkaido, Japan: does riparian vegetation affect fish density via food availability?

The densities of two benthic fishes, the Siberian stone loach (Noemacheilus barbatulus) and the wrinklehead sculpin (Cottus nozawae), and the biomass of their food resources (i.e., periphyton and benthic invertebrates) were compared between forest and grassland streams in northern Hokkaido, Japan, to examine whether riparian deforestation had positive effects on the benthic fishes via enhancement of food availability. The comparisons indicated that riparian vegetation had little influence on periphyton, invertebrates, or fishes. Regression analysis indicated that spatial variations in loach and sculpin densities were explained more by substrate heterogeneity, competitor abundance, or both, rather than by food abundance. However, when the two species were combined as benthic insectivores, a strong correlation was found between total benthic fish density and invertebrate biomass. Our results suggest that, although total benthic fish abundance was food limited, riparian vegetation had no positive effects via food availability on the benthic fishes in our streams.     

An indirect effect of biological invasions: the effect of zebra mussel fouling on parasitisation of unionid mussels by bitterling fish

Invasive species represent a major threat with both direct and indirect effects on natural ecosystems, including effects on established and coevolved relationships. In a series of experiments, we examined how the interaction between two native species, a unionid mussel (Unio pictorum) and the European bitterling (Rhodeus amarus), a fish that parasitises unionids, was affected by the non-native zebra mussel (Dreissena polymorpha). The zebra mussel fouls hard substrates, including shells of living unionids, and its presence is often associated with a decrease in population density of native unionid mussels. Bitterling lay their eggs into live unionids and the embryos develop inside their gills. Using a range of zebra mussel densities, we demonstrated that zebra mussel fouling had a negative effect on the number of bitterling eggs inside the mussel host, with abundances of 5–10 zebra mussels (shell size 15–25 mm) per unionid critical for bitterling ability to utilise the host. In a further experiment, we found that bitterling did not discriminate between unfouled unionids and those fouled with five zebra mussels. Most ovipositions into fouled hosts, however, were unsuccessful as eggs failed to reach the unionid gills. We discuss implications of such unsuccessful ovipositions for bitterling recruitment and population dynamics.     

Habitat engineering by the invasive zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> (Pallas) in a boreal coastal lagoon: impact on biodiversity

Habitat engineering role of the invasive zebra mussel Dreissena polymorpha (Pallas) was studied in the Curonian lagoon, a shallow water body in the SE Baltic. Impacts of live zebra mussel clumps and its shell deposits on benthic biodiversity were differentiated and referred to unmodified (bare) sediments. Zebra mussel bed was distinguished from other habitat types by higher benthic invertebrate biomass, abundance, and species richness. The impact of live mussels on biodiversity was more pronounced than the effect of shell deposits. The structure of macrofaunal community in the habitats with >10³ g/m² of shell deposits devoid of live mussels was similar to that found within the zebra mussel bed. There was a continuous shift in species composition and abundance along the gradient ‘bare sediments—shell deposits—zebra mussel bed’. The engineering impact of zebra mussel on the benthic community became apparent both in individual patches and landscape-level analyses.     

Spatially Extended Habitat Modification by Intertidal Reef-Building Bivalves has Implications for Consumer-Resource Interactions

Ecosystem engineers can strongly modify habitat structure and resource availability across space. In theory, this should alter the spatial distributions of trophically interacting species. In this article, we empirically investigated the importance of spatially extended habitat modification by reef-building bivalves in explaining the distribution of four avian predators and their benthic prey in the Wadden Sea—one of the world’s largest intertidal soft-sediment ecosystems. We applied Structural Equation Modeling to identify important direct and indirect interactions between the different components of the system. We found strong spatial gradients in sediment properties into the surrounding area of mixed blue mussel (Mytilus edulis) and Pacific oyster (Crassostrea gigas) reefs, indicating large-scale (100s of m) engineering effects. The benthic community was significantly affected by these gradients, with the abundance of several important invertebrate prey species increasing with sediment organic matter and decreasing with distance to the reefs. Distance from the reef, sediment properties, and benthic food abundance simultaneously explained significant parts of the distribution of oystercatchers (Haematopus ostralegus), Eurasian curlews (Numenius arquata), and bar-tailed godwits (Limosa lapponica). The distribution of black-headed gulls (Chroicocephalus ridibundus)—a versatile species with many diet options—appeared unaffected by the reefs. These results suggest that intertidal reef builders can affect consumer-resource dynamics far beyond their own boundaries, emphasizing their importance in intertidal soft-bottom ecosystems like the Wadden Sea.     

Effect of the western pearlshell mussel Margaritifera falcata on Pacific lamprey Lampetra tridentata and ecosystem processes

Suspension feeders concentrate organic material from the water column and enhance deposition to the surrounding benthos. On the South Fork of the Eel River (Mendocino, California) two suspension feeders, the freshwater mussel Margaritifera falcata and Pacific lamprey larvae Lampetra tridentata, co‐occur in areas with low flow velocities and boundary sheer stresses. We investigated mussel/lamprey larvae interactions, and their impacts on nutrient and organic matter cycling, in flow‐through enclosures placed where lamprey larvae and mussels naturally occurred. Over the 80‐day study, lamprey larvae grew faster in the presence of mussels and in food addition treatments. Our results suggest that lamprey larvae benefit from native mussels, and that lamprey populations and organic matter retention in rivers may decrease with the rapid decline of native freshwater mussels.     

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.     

Space as a limiting resource in freshwater systems: competition between zebra mussels (Dreissena polymorpha) and freshwater sponges (Porifera)

Species interactions between two types of sessile benthic invertebrates, the zebra mussel (Dreissena polymorpha) and freshwater sponges (Porifera), were evaluated in Michigan City IN Harbor in southern Lake Michigan during 1996. The study objective was to define whether competition plays a role in structuring benthic communities using experimental techniques commonly employed in marine systems. Sponges were uninhibited by zebra mussel presence and overgrew zebra mussel shells on hard vertical substrata. In contrast, zebra mussels did not overgrow sponge colonies, but did show an ability to re-capture hard substrata if relinquished by the sponge. The negative affect of sponges on zebra mussels through overgrowth and recruitment suggests interactions that could eventually displace zebra mussels from these benthic communities. However, seasonal reduction of sponge biomass from autumn through winter appears to allow the zebra mussel a periodic respite from overgrowth, preventing exclusion of zebra mussels from the community and allowing these two taxa to co-exist.     

Muskrat predation on a diverse unionid mussel community: impacts of prey species composition,size and shape

1. The muskrat, Ondatra zibethicus, is a predator known to affect species composition, population size and age structure of freshwater unionid mussel communities. Muskrats leave large piles of dead shells (middens) on the edges of rivers, lakes and streams. We compared the species composition and size structure of shells collected from muskrat middens to the nearby live unionid community in the lower Licking River (Kentucky, USA). 2. Like previous studies, our results suggest that muskrats are both size‐selective and species‐specific predators; however, our results indicate that mussel shape is also an important factor. 3. We generated a shape metric (‘cubocity’) sensitive to the overall shape of the mussel. Species with relatively lower cubocity values (around 0.85) are plate‐like or spike‐like, while mussels with more cuboidal shells have higher cubocity values (near 1.0). 4. Our results suggest muskrats prefer cuboidal mussels and generally avoid spike‐shaped mussels. The endangered fanshell, Cyprogenia stegaria, was the most favoured prey; the fanshell’s relative size and shape appear to make it particularly vulnerable to muskrats. 5. We believe the predictive capabilities of this shape metric will be of benefit to those who monitor and manage threatened mussel populations.     

Patterns in benthic food webs: a role for omnivorous crayfish?

1. The biomass and species richness of macrophytes and invertebrates in artificial ponds at two sites in southern Sweden (twenty-one ponds at each site) were investigated. Alkalinity was high at one site (H ponds) and low at the other site (L ponds). The ponds chosen had different densities of signal crayfish (Pacifastacus leniusculus), with mean crayfish abundance (estimated by trapping and expressed as catch per unit effort) significantly higher in the L ponds (10.7) than in the H ponds (4.9). Macrophytes, invertebrates, the amount of periphyton on stones and the organic content of the sediment were determined in each pond. 2. Macrophyte biomass, cover and species richness declined with increasing crayfish density. Macrophyte species composition differed between ponds and was related to crayfish abundance. 3. The total biomass of invertebrates and the biomass of herbivorous/detritivorous invertebrates declined with increasing crayfish abundance, but the biomass of predatory invertebrates declined only in the L ponds. The relative biomass of Gastropoda and Odonata declined in ponds where crayfish were abundant. In ponds where crayfish were abundant the invertebrate fauna was dominated by sediment-dwelling taxa (Sialis (H and L ponds) and Chironomidae (H ponds)). 4. The number of invertebrate taxa in macrophytes declined with increasing crayfish abundance. The percentage of macrophyte-associated invertebrate taxa differed between ponds, but also between sites. The relative biomass of Gastropoda declined in H ponds where crayfish were abundant. In H ponds Trichoptera or Gammarus sp. and Heteroptera dominated where crayfish were abundant, whereas Odonata dominated in L ponds with abundant crayfish. 5. The organic content of the sediment decreased in ponds with high crayfish densities, while the amount of periphyton on stones was not related to crayfish density. 6. We conclude that the signal crayfish may play an important role as a keystone consumer in pond ecosystems, but lower trophic levels did not respond to changes in the abundance of the crayfish according to the trophic cascade model. Omnivorous crayfish may decouple the cascading effect.     

Habitat modification by the stream macrophyte Justicia americana and its effects on biota

We conducted an in-stream experiment to determine if and by what mechanisms the emergent macrophyte, Justicia americiana, enhances streambed stability and influences associated benthic organisms. Treatments included removal of aboveground stems, removal of stems and rhizomes, and a control. Stone stability and embeddedness were higher within intact patches of Justicia compared with areas where stems and rhizomes were removed. Presence of belowground structures binding stones and higher embeddedness were responsible for differences in stone stability among treatments. Sediment deposition was highly variable among treatments; however, silt and clay deposition was highest in the control when Justicia stems reached maximum biomass. Response of neighboring benthic organisms to Justicia treatments varied with organism mobility and trophic level. Sedentary unionid mussels were more abundant in the control than in the stem and rhizome-removal treatment, whereas abundance of mobile snails (Elimia ucheensis) and sessile plants (Podostemon ceratophyllum and mosses) did not differ among treatments. Justicia appears to modify the stream environment by: (1) increasing stability of streambed sediments, and (2) reducing current velocity, thereby enhancing deposition of fine sediments and organic matter.     

Does the morphology of beaver ponds alter downstream ecosystems?

Differences among lake morphologies often explain variation in characteristics of lentic ecosystems. Although beaver ponds also vary in morphology, previous studies have not examined the effects of such variation on downstream ecosystems. This study evaluated downstream effects of multiple beaver ponds in the Colorado Rocky Mountains during one low and one high-flow year. Beaver pond morphology was described as the natural log transformed ratio of beaver dam height (which determines hydraulic head) to pond surface area and related to pond spillover phytoplankton and characteristics of the ecosystem downstream (nutrient concentrations, limiting nutrients, periphyton, benthic organic matter (BOM), and benthic invertebrate consumers). Nitrate concentration increased systematically downstream of beaver ponds, but only in the low flow year when groundwater influences predominated. Effects of beaver ponds on soluble reactive phosphorus concentration depended on pond morphology, increasing downstream of small ponds with high dams, but only during the low-flow year. In situ experiments showed that neither beaver activity nor pond morphology predicted periphyton-limiting nutrients downstream. Both periphyton biomass and BOM decreased downstream of small ponds with high dams but pond morphology did not predict abundance of invertebrate grazers or detritus-feeding consumers. While suspension feeding invertebrates increased downstream from small ponds with high dams, variation in chlorophyll a from water spilling over beaver dams did not follow a similar pattern. We conclude that the effects of beaver ponds on downstream nutrients, resources and consumers are rarely systematic, but instead depend on variation in pond morphology and on annual hydrologic variation.     

Potential effects on zooplankton from species shifts in planktivorous mussels: a field experiment in the St Lawrence River

1. Suspension feeding by bivalves exceeds that by other planktivores in many North American rivers, and food webs may be altered substantially by differences in feeding patterns between native unionid mussels and invading dreissenid mussels. 2. We conducted an experiment comparing zooplanktivory by one unionid and two dreissenid species that addressed several primary questions. Is benthic planktivory important in this river? Has this linkage been altered substantially by dreissenids? Do the two dreissenid species differ in planktivory, and is this ecologically important if quagga mussels extend their geographical range? 3. Our 12‐day experiment consisted of controls (no mussels) and treatments with unionid (Elliptio complanata), quagga (Dreissena bugensis) or zebra (D. polymorpha) mussels in 3500‐L, 80‐μm mesh enclosures placed in a slackwater area of the St Lawrence River. 4. The density of the most abundant calanoid copepod Eurytemora affinis increased in the presence of dreissenids, probably as an indirect food web response. By day 12, a cumulative effect was shown by the most overwhelmingly abundant rotifer, Polyarthra, whose density declined dramatically in dreissenid enclosures compared with control and unionid enclosures. Rotifer densities in unionid enclosures were not different from controls, nor were dreissenid treatments different from each other. The effects on rotifers were probably from predation, as Chl‐a did not vary among treatments. 5. We conclude that benthic‐pelagic coupling via planktivory is important in slackwater areas. Dreissenids have strengthened this linkage, but range extension of quaggas should not appreciably alter effects produced by a similar biomass of zebra mussels.     

Zebra mussels affect benthic predator foraging success and habitat choice on soft sediments

The introduction of zebra mussels (Dreissena spp.) to North America has resulted in dramatic changes to the complexity of benthic habitats. Changes in habitat complexity may have profound effects on predator-prey interactions in aquatic communities. Increased habitat complexity may affect prey and predator dynamics by reducing encounter rates and foraging success. Zebra mussels form thick contiguous colonies on both hard and soft substrates. While the colonization of substrata by zebra mussels has generally resulted in an increase in both the abundance and diversity of benthic invertebrate communities, it is not well known how these changes affect the foraging efficiencies of predators that prey on benthic invertebrates. We examined the effect of zebra mussels on the foraging success of four benthic predators with diverse prey-detection modalities that commonly forage in soft substrates: slimy sculpin (Cottus cognatus), brown bullhead (Ameirus nebulosus), log perch (Percina caprodes), and crayfish (Orconectes propinquus). We conducted laboratory experiments to assess the impact of zebra mussels on the foraging success of predators using a variety of prey species. We also examined habitat use by each predator over different time periods. Zebra mussel colonization of soft sediments significantly reduced the foraging efficiencies of all predators. However, the effect was dependent upon prey type. All four predators spent more time in zebra mussel habitat than in either gravel or bare sand. The overall effect of zebra mussels on benthic-feeding fishes is likely to involve a trade-off between the advantages of increased density of some prey types balanced against the reduction in foraging success resulting from potential refugia offered in the complex habitat created by zebra mussels.     

Contrasting effects of an invasive crayfish (Procambarus clarkii) on two temperate stream communities

1. The effects of omnivorous exotic species on native communities are often difficult to predict because of the broad diets and behavioural flexibility of the omnivore, and the diverse abiotic and biotic characteristics of invaded systems. We investigated experimentally the effects of a gradient of density of the introduced, omnivorous red swamp crayfish Procambarus clarkii (Decapoda: Cambaridae) on two stream communities in southern California, U.S.A. 2. The Ventura River is a clear, flowing stream with a cobble substratum, with abundant algae but low densities of large invertebrates, small herbivores and snails. The Santa Ynez River at the time of the study consisted of a series of drying pools underlain by sand, with abundant charophytes, large predatory invertebrates and herbivores, including snails. 3. In the Ventura River, periphyton biomass and inorganic sediment decreased with increasing crayfish abundance, but in the Santa Ynez River, periphyton and sediment were unrelated to crayfish densities. 4. In the Ventura River, the biomass and density of all benthic invertebrates combined, chironomids, micropredators, the meiofauna (chydorid cladocerans, copepods and ostracods), and specific predatory and herbivorous taxa, as well as taxon richness, were negatively related to crayfish density. In the Santa Ynez River, the biomass and average body size of benthic invertebrates, predatory invertebrates, herbivores and chironomids, but not total invertebrate density or taxon richness, were negatively related to crayfish density. 5. Fewer large predatory invertebrates and snails (Physella gyrina) in both streams, and baetid mayflies in the Ventura River, were visible at night in channels where crayfish were abundant. Snails responded to crayfish by moving above the water line in the Santa Ynez River, but not in the Ventura River. 6. We suggest that the same omnivore had different effects on these neighbouring streams because of crayfish predation on large invertebrates in the Santa Ynez River and the scarcity of such prey in the Ventura River, leading to increased crayfish grazing on periphyton, and reductions in periphyton‐associated invertebrates, in the Ventura River.     

Nutrient loading associated with agriculture land use dampens the importance of consumer‐mediated niche construction

The linkages between biological communities and ecosystem function remain poorly understood along gradients of human‐induced stressors. We examined how resource provisioning (nutrient recycling), mediated by native freshwater mussels, influences the structure and function of benthic communities by combining observational data and a field experiment. We compared the following: (1) elemental and community composition (algal pigments and macroinvertebates) on live mussel shells and on nearby rocks across a gradient of catchment agriculture and (2) experimental colonisation of benthic communities on live vs. sham shells controlling for initial community composition and colonisation duration. We show that in near pristine systems, nutrient heterogeneity mediated by mussels relates to greater biodiversity of communities, which supports the notion that resource heterogeneity can foster biological diversity. However, with increased nutrients from the catchment, the relevance of mussel‐provisioned nutrients was nearly eliminated. While species can persist in disturbed systems, their functional relevance may be diminished or lost.     

Physical forces constrain the depth distribution of the abundant native mussel Elliptio complanata in lakes

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.     

Assessment of Littoral Benthic Invertebrate Communities at the Land–Water Interface in Lakes Recovering from Severe Acid- and Metal-Damage

Benthic invertebrate communities within confluence sites, or areas of sediment deposition, are shaped by the input of catchment products including coarse woody debris, organic and inorganic particulates, and contaminants, but these sites also appear to be potential “hotspots” where recolonization of severely damaged ecosystems begins. Two species of leaf packs and a sweep netting technique were used to assess benthic invertebrate communities across a gradient of 14 confluence sites in 3 recovering lakes near the copper and nickel smelters in Sudbury, Canada. Environmental variables including delta habitat composition, delta area and length, and composition of deposited materials were used to detect spatial patterns in littoral benthic invertebrate communities. Benthic invertebrate community relationships with water chemistry were also assessed. Partial redundancy analysis (pRDA) showed that all sampling methods detected similar gradients of increasing invertebrate community richness and diversity as area and length of the sediment delta and the surface organic matter abundance increased. Two-way nested ANOVAs showed significant differences (p < .05) in taxa richness and diversity metrics among sites. Of the three methods, the benthic invertebrate community measurements from the birch leaf packs provided the strongest correlations with measures of organic matter inputs or habitat characteristics of the confluence zones. These correlations suggest that tree planting in riparian areas, or organic matter or macrophyte additions to littoral zones, may enhance littoral benthic invertebrate richness and diversity in acid and metal damaged lakes.