Benthic Macroinvertebrate Density Research Articles

Effects of low-head dam removal on benthic macroinvertebrate communities in a Korean stream

This study was conducted to examine how a low-head dam removal (partial removal) could affect benthic macroinvertebrate communities in a stream. Benthic macroinvertebrates and substrates were seasonally sampled before and after dam removal (March 2006–April 2007). Benthic macroinvertebrates and substrates were quantitatively sampled from immediately upstream (upper: pool) and downstream (lower: riffle) sites, the location of the dam itself (middle), and immediately above the impoundment (control: riffle). After the removal, species richness and density of benthic macroinvertebrates as well as the EPT group (Ephemeroptera, Plecoptera and Trichoptera) increased to higher levels than those before the removal, while functional feeding groups and habitat orientation groups changed more heterogeneously at the upper site. At the lower site, species richness and density decreased somewhat immediately after dam removal, which was associated with an increase of silt and sand, but recovered after monsoon floods which helped to enhance substrate diversity at the upper site. Decreased dominance index and increased diversity index in both the upper and lower sites are evidence of positive effects from the dam removal. In conclusion, we suggest that even a partial removal of a dam, resulting in increased substrate diversity in the upper site, could sufficiently help rehabilitate lost ecological integrity of streams without major habitat changes.

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.

Hyporheic and benthic macroinvertebrate communities in glacial, clearwater, and brownwater streams in Alaska

The macroinvertebrate communities of hyporheic and benthic habitats were investigated in relation to stream physicochemistry in glacial, clearwater, and brownwater stream types (n = 1) during the summer (June–August) of 2004 near Juneau, Alaska. Hyporheic macroinvertebrates were sampled using a series of PVC wells driven into parafluvial bars in the three stream types. Benthic invertebrates were collected using Hess samples from the stream channel adjacent to parafluvial well locations to compare surface macroinvertebrate communities to that of the hyporheic communities. Temperature, total phosphorus, dissolved organic carbon, and total nitrogen concentrations were significantly higher in the brownwater stream compared to the other stream types. Hyporheic macroinvertebrate density was 88% higher in the brownwater stream, despite significantly lower dissolved oxygen concentrations. Benthic macroinvertebrate density was 95% greater in the brownwater stream type than the benthos of the two other stream types. Benthic and hyporheic samples were collector-gatherer driven and the hyporheic zone was functionally more diverse than the benthic habitat with a similar taxa composition across all habitats and stream types. The study of aquatic ecosystems is especially important in Southeast Alaska, where the temperate rainforests are still relatively un-disturbed, and most watersheds still have healthy salmon runs. Our study provides useful data for future management and research in this unique ecoregion, which is predicted to experience substantial climatic changes in temperature and precipitation patterns in the future.

Restoration of an incised mountain stream using artificial step-pool system

A field experiment using an artificial step-pool system was conducted to restore the Diaoga River, a seriously incised mountain stream in Yunnan-Guizhou Plateau, southwest China. Twenty-four artificial steps, designed to mimic natural step forms, were constructed on three stretches of about 260 m length in the middle reach of the river. Channel topography, hydraulic features, aquatic habitats and stream ecology were monitored for 20 months. Following the construction of the artificial step-pool system, the stream bed development coefficient increased significantly. This indicates that actions helped to dissipate flow energy more effectively, enhancing the stability of the stream bed. The step-pools have effectively controlled the incision and stabilized the river morphology. In addition, they have created multiple habitats for different species and increased the habitat diversity. Improvement of the aquatic ecosystem is confirmed by increased density and taxa richness of benthic macro-invertebrates, which are used as an indicator species to evaluate stream ecology.

Littoral benthic macroinvertebrates of alpine lakes (Tatra Mts) along an altitudinal gradient: a basis for climate change assessment

Littoral benthic macroinvertebrates were studied in three alpine lakes in the High Tatra Mountains (Slovakia) located at different elevations: 2157, 1940 (alpine zone) and 1725 m (sub-alpine zone). The study sites were selected in order to obtain a gradient in thermal regimes and particular organic matter (POM). Differences in the faunal composition of lakes were tested for the ability of these differences to indicate climatic changes, and species/taxa were identified that could be used for the purposes of monitoring and climate change assessment. Macroinvertebrates were sampled quantitatively during the ice-free seasons of 2000 and 2001, and lake surface water temperature (LSWT) and POM were measured. LSWT and POM were negatively correlated with elevation, whereas ice cover was positively correlated with elevation. A total of 60 oligostenothermic macroinvertebrate species/taxa were collected belonging to ten higher taxonomic groups. Statistical analysis showed trends in several biotic metrics with altitude. More specifically, there was a clear increase in the number of species/taxa, genera, and higher taxonomic groups, as well as an increase in the Shannon–Wiener diversity with decreasing altitude. On the contrary, evenness and density of benthic macroinvertebrates did not show any clear relationship with altitude. Gatherers of detrital particles dominated the assemblages’ trophic structures, but no distinct changes in the proportion of functional feeding groups along the altitudinal gradient were found. While the non-insect fauna of the lakes was rather uniform across the elevational gradient, the insect fauna composition was highly correlated with altitude, as confirmed by Detrended Correspondence Analysis. Aquatic insects, in particular chironomids and caddisflies, can therefore be used as good indicators of temperature changes. Our results suggest that under warmer conditions, non-insect benthic macroinvertebrates will remain more or less stable, while aquatic insects will undergo an increase in the number of thermophilic species typical for lower altitudes. These colonizers will increase the diversity of alpine lakes, while the extinction of cold stenothermal species will lead to impoverishment of the native fauna. An indirect impact on benthic macroinvertebrates through changes in food sources is likely, and changes in trophic structure of the littoral assemblages can be expected.

Spatial variation in the invertebrate macrobenthos of three large Missouri River reservoirs

Although benthic macroinvertebrates have been used as indicators of ecological condition for a variety of aquatic ecosystems, large reservoirs present challenges for assessment design. Reservoir embayments may have unique characteristics relevant for assessment, and the reservoirs may include zones that combine the characteristics of lotic and lentic systems. The purpose of this study was to characterize spatial variation in benthic macroinvertebrate assemblages of three large upper Missouri River reservoirs in the USA. A probability design was used to select sample sites from Lake Oahe (North and South Dakota), Lake Sakakawea (North Dakota), and Fort Peck Lake (Montana). Sites were chosen to represent the main stem of each reservoir, as well as small, medium, and large bays. The assemblages in all lakes were dominated by oligochaetes (46―60 % of total organisms) and chironomids (29―49 %). Small and medium bays generally had greater total densities, particularly of chironomids and the burrowing mayfly Hexagenia. Composition and density of the benthos were strongly influenced by depth. Information on the density, distribution, and variability of benthic macroinvertebrates will be used to further refine assessment strategies for large reservoirs.

Biodiversity loss in benthic macroinfaunal communities and its consequence for organic mercury trophic availability to benthivorous predators in the lower Hudson River estuary, USA

Organic mercury such as methylmercury is not only one of the most toxic substances found in coastal ecosystems but also has high trophic transfer efficiency. In this study, we examined implications of chronically altered benthic macroinfaunal assemblages for organic mercury trophic availability (based on organic mercury intracellular partitioning) to their predators in the Arthur Kill-AK (New York, USA). Despite low species diversity, both density and biomass of benthic macroinvertebrates in AK were significantly higher than those at the reference site. Disproportionately high biomass of benthic macroinvertebrates (mostly polychaetes) in the northern AK resulted in a more than twofold increase (‘ecological enrichment’) in the trophically available organic mercury pool. These results suggest that altered benthic macroinfaunal community structure in AK may play an important role in organic mercury trophic availability at the base of benthic food webs and potentially in mercury biogeochemical cycling in this severely urbanized coastal ecosystem.

Invasive reed effects on benthic community structure in Lake Erie coastal marshes

We examined how dominance (% canopy cover) and invasion history of common reed, Phragmites australis, affected benthic macroinvertebrate diversity and density in 8 marshes along Lake Erie’s southern shoreline. We also compared macroinvertebrate densities among patches (0.25 m2) of reed, cattail (Typha spp.), and native flora (e.g., Sagittaria, Sparganium) and epiphytic algal communities on submerged stems of reed and cattail. Narrow-leaf cattail (T. angustifolia) is also a common invasive plant to these wetlands, but does not greatly change plant community composition or ecosystem conditions like reed. Macroinvertebrate diversity (Shannon–Weaver H′) was positively related to reed cover and was highest (4.6) in two marshes with ~35- and 5-year invasion histories. Shading from high reed cover increased H′-diversity, in part, by reducing the abundance of floating duckweed, which harbored many Hyalella azteca amphipods. Percent Ephemeroptera, Odonata, and Trichoptera was low to moderate across marshes, regardless of reed cover and invasion history. Macroinvertebrate density was not affected by reed cover or average plant stem density, and did not differ among plant types. However, epiphyton densities and % diatoms were greater on reed than on cattail, suggesting reed provides a better feeding habitat for microalgal grazers than Typha. Abundance rankings of common species in these diatom-dominated communities were also typically dissimilar between these plant types. Although % grazers was unrelated to epiphyton densities and % diatoms, grazer identity (snails) differed between natural and diked marshes, which had different microalgal food supplies. Our findings suggest that Phragmites does not necessarily adversely affect macroinvertebrate community structure and diversity and that invasion history alone has little effect on the H′-diversity–reed dominance relationship.

Ecological and Hydraulic Studies of Step-Pool Systems

The ecological and hydraulic features of step-pool systems are studied by field investigation, measurement, sampling, and analysis. The study is done on Shengou and Jiuzhai Creeks, where step-pool systems have developed, Fork Gully, where a step-pool system is developing, and the Jinsha River and Jiangjia and Xiaobaini Ravines, where there is no step-pool system. Boulders, cobbles, and gravel tightly interlock and form the steps having an inherent stability that only extreme floods are likely to disturb. Gravel and sand deposit in the pools behind the steps. These steps and pools provide high diversity of habitat for the stream biocommunity. The density of benthic macroinvertebrates in streams with step-pool systems is several 100 times higher than neighboring streams without step-pool systems. A new habitat diversity index is proposed considering the spatial distribution of various substrates, velocity, and water depth. The study reveals that the biodiversity of benthic macroinvertebrates increases with habitat diversity. Measurements with a specially designed instrument were done to study the development of step-pool systems and its effects on resistance to the flow and stream bed stability. A step-pool system maximizes the flow resistance and protects the bed sediment from erosion. Thus, the riverbed and bank slope are stabilized. The development degree of step pools is proportional to the streambed slope. The bed resistance increases with the development degree of step pools. Riverbed inertia represents the stability of the streambed. The development of step-pool systems greatly increases the riverbed inertia, and, therefore, maximizes streambed stability.

Changes in the macrobenthic community structure following the introduction of the invasive algae Didymosphenia geminata in the Matapedia River (Québec, Canada)

In July 2006, blooms of Didymosphenia geminata (didymo) were, for the first time, officially observed and identified in the Matapedia River, an Atlantic salmon river of the Gaspesie peninsula (Quebec, Canada). This invasive diatom can form thick and extensive benthic layers in stable flow and oligotrophic rivers. This study aimed to evaluate the potential effect of didymo on the macrobenthic community structure of the Matapedia River. Macrobenthic samples were obtained in 2006, upstream of the blooms and, at the same sampling sites a year later, when they were affected by didymo. The Causapscal River remained free of didymo blooms for both years; therefore, this tributary is considered as a control site. Results show a significant difference (P < 0.001) in the community distribution before and after didymo presence in two of the three sites. Significant data show an increase Chironomidae proportions in all the sites (P = 0.011). Significantly higher benthic macroinvertebrate (BMI) densities were also observed in 2007 (P < 0.001). Simpson’s Evenness Index and total family richness was not significantly different when comparing pre- and post-incursion data (P = 0.90 and P = 0.83, respectively). Nevertheless, it is concluded that the presence of didymo has an effect on the base of the aquatic food web of the Matapedia River. This study is the first to assess the effect of this invasive alga on BMIs in Eastern Canada.

Effects of land use on fish assemblages in Patagonian low order streams

We assessed the effects of land use on the structure of stream fish assemblages in Northwest Patagonia, Argentina. To this end, a total of 18 sites distributed in 15 streams were sampled during the low water period. At each site, 26 regional and local scale variables were used to describe the environmental conditions. The macroinvertebrate density, and the composition and abundance of fish were then recorded. Statistical associations between local assemblage structures and environmental variables were quantified by canonical correspondence analyses. The results revealed that, at a regional scale, the fish assemblages were primarily determined by watershed features like altitude and catchment area, and by land use effects (exotic forest and pasture). Assemblage compositions were also related to some local-scale features such as water velocity, food availability (density of benthic macroinvertebrates), instream characteristic and riparian features. Also, the observed fish species richness was low. Overall, exotic salmonids largely dominated in the samples both in numbers of individuals (98.9%) and in biomass (99.9%), whereas native fish (Hatcheria macraei and Odontesthes hatcheri ) were scarcely represented. Rainbow trout (Oncorhynchus mykiss ) was the most abundant fish, and was present in all streams. Native species were restricted to five streams located in the ecotone between the Andes and the steppe, where salmonids were also present. Salmonids were the only fish at Andean streams which suggest the existence of a strong geographic segregation between native and exotic species. Some aspects related to the incidence of the introduced species in the structure of fish assemblages are discussed.

Effects of forest fire on headwater stream macroinvertebrate communities in eastern Washington, U.S.A.

Summary1. Recent increases in fire frequency in North America have focused interest on potential effects on adjacent ecosystems, including streams. Headwaters could be particularly affected because of their high connectivity to riparian and downstream aquatic ecosystems through aquatic invertebrate drift and emergence.2. Headwater streams from replicated burned and control catchments were sampled in 2 years following an intense forest fire in northeastern Washington (U.S.A.). We compared differences in benthic, drift and emergent macroinvertebrate density, biomass and community composition between five burned and five unburned catchments (14–135 ha).3. There were significantly higher macroinvertebrate densities in burned than control sites for all sample types. Macroinvertebrate biomass was greater at burned sites only from emergence samples; in benthic and drift samples there was no significant difference between burn and control sites.4. For all sample types, diversity was lower in the burned catchments, and the macroinvertebrate community was dominated by chironomid midges.5. Compared to the effects of fire in less disturbed ecosystems, this study illustrated that forest fire in a managed forest may have greater effects on headwater macroinvertebrate communities, influencing prey flow to adjacent terrestrial and downstream aquatic habitats for at least the first 2 years post‐fire.

Spatial and temporal variation in prey selection of brown trout in a cold Arkansas tailwater

Abstract – We examined prey utilisation patterns of brown trout (Salmo trutta Linnaeus) as related to available benthos in a cold tailwater (Little Red River, Arkansas) having low biodiversity of benthic macroinvertebrates and low availability of fish as prey. Benthic macroinvertebrates were sampled monthly in upstream and downstream sites over a 1‐year period. Stomach content analysis was also performed on 30 brown trout (10 each of three size classes) collected monthly from each site. Benthic and diet diversities were low at both sites, as isopods (Lirceus) accounted for 67% and 51% of the numerical abundance upstream and downstream, respectively, and 80% and 70% of all prey consumed by upstream and downstream brown trout. Physid snails (upstream) and chironomid larvae (downstream) accounted for most of the remaining prey taxa consumed. Piscivory and consumption of terrestrial invertebrates were rare. There was no clear relation between diet diversity and trout size. Densities of benthic macroinvertebrates and prey consumption were significantly greater upstream than downstream. Benthic macroinvertebrate assemblages and prey consumption were seasonally constant at both sites. Generally, prey consumption was consistent with availability of each prey in the benthos; the lack of benthic diversity and overwhelming abundance of one taxon (Lirceus) most likely contributed to food selection patterns. Although isopods are abundant within this tailwater to serve as a forage base, the displacement of native fish fauna because of the thermal regime of hypolimnetic release from Greers Ferry Reservoir probably serves as a major limitation to brown trout growth.

Impact of commercial salt production on wetland quality and waterbirds on coastal lagoons in Ghana

A comparative study conducted on two saline coastal wetlands that have been developed into saltpans and two others (referred to as 'non-saltpans'), that are also saline but have no saltpans, describes the quality of lagoon water, benthic macroinvertebrates and waterbird communities characterising these wetlands. The wetlands were sampled monthly from September 2005–April 2006. Except for turbidity, which was significantly higher in the non-saltpans, (p < 0.05), all other physico-chemical parameters studied were not significantly different between the two wetland types (p > 0.05). The waterbird communities of the saltpans and non-saltpans, characterised by 48 and 50 species respectively, scored a Sorenson Index value of 0.88, indicating a high similarity. The population density of benthic macroinvertebrates in the saltpans and the non-saltpans was statistically similar (p > 0.05) but the population densities of waterbirds feeding exclusively on benthic macroinvertebrates were significantly higher in the non-saltpans (p < 0.05). Although the shallow ponds created for salt production might be providing more suitable feeding habitats for fish-eating birds, the development of these ponds has also reduced the exploitable area available to the birds feeding exclusively on invertebrates, requiring them to depend largely on the non-saltpans. Birds feeding exclusively on fish had significantly higher population densities in the saltpans (p < 0.05) than in non-saltpans. This was attributed to reduced efficiency of piscivory, due to the high turbidity associated with the non-saltpans. Waterbirds feeding on a wide range of food types showed no significant differences in their population densities (p > 0.05) in the two wetland types.

Impacts of Dreissena invasions on benthic macroinvertebrate communities: a meta‐analysis

ABSTRACTDreissenid mussels (the zebra mussel Dreissena polymorpha and the quagga mussel Dreissena bugensis) have invaded lakes and rivers throughout North America and Europe, where they have been linked to dramatic changes in benthic invertebrate community diversity and abundance. Through a meta‐analysis of published data from 47 sites, we developed statistical models of Dreissena impact on benthic macroinvertebrates across a broad range of habitats and environmental conditions. The introduction of Dreissena was generally associated with increased benthic macroinvertebrate density and taxonomic richness, and with decreased community evenness (of taxa excluding Dreissena). However, the strength of these effects varied with sediment particle size across sites. The effects of Dreissena differed among taxonomic and functional groups of macroinvertebrates, with positive effects on the densities of scrapers and predators, particularly leeches (Hirudinea), flatworms (Turbellaria), and mayflies (Ephemeroptera). Gastropod densities increased in the presence of Dreissena, but large‐bodied snail taxa tended to decline. Dreissena was associated with declines in the densities sphaeriid clams and other large filter‐feeding taxa, as well as burrowing amphipods (Diporeia spp.), but had strong positive effects on gammarid amphipods. These patterns are robust to variation in the methodology of primary studies. The effects of Dreissena are remarkably concordant with those of ecologically similar species, suggesting universality in the interactions between introduced byssally attached mussels and other macroinvertebrates.

Point source effects on density, biomass and diversity of benthic macroinvertebrates in a Mediterranean stream

AbstractWe sampled benthic macroinvertebrates above and below a point source effluent in La Tordera stream (NE, Spain) over 2001–2002 to assess the effects of nutrient enrichment on the structure, and taxonomic composition of the benthic macroinvertebrate community. Below the point source, discharge, specific conductance and nutrient concentrations were higher than at the upstream reach, while dissolved oxygen (DO) decreased. Macroinvertebrate density was higher at the downstream reach than at the upstream reach on most dates but the two reaches did not differ in macroinvertebrate biomass.On average, taxa richness at the upstream reach was 20% higher than at the downstream reach. Several taxa, especially mayflies, stoneflies and caddisflies, were present only at the upstream reach. Shannon diversity was similar between the two reaches on 50% of the dates. Ordination analysis clearly separated the samples of the upstream reach from the samples of the downstream reach in the first axis and corroborated the effect of the point source on the benthic community. The two reaches followed a similar temporal pattern with respect to the distribution of taxa along the second axis of the ordination analysis. Higher similarities between the two reaches in taxa composition, densities and biomass after the spates of April and May 2002, suggest that flooding events may act as a reset mechanism for benthic communities and play an important role in stream restoration. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Benthic Macroinvertebrates in the Watershed of an Urban Reservoir in Southeastern Brazil

The Ibirite watershed is subject to several forms of environmental degradation such as the presence of a petroleum refinery industry, urbanization of its surrounding landscape, and non treated domestic sewage from over 135,000 inhabitants. Benthic macroinvertebrates represent a useful tool in the evaluation of environmental quality through studies of the structure of communities and their relationship to anthropic activities within the watersheds. The objective of this study was to evaluate the environmental impact to the Ibirite reservoir caused by the petroleum refinery industry, urbanization, and sulphatation. Degradation of the watershed was measured by using the richness, diversity, evenness, and density of benthic macroinvertebrates. Twelve sampling stations were established as follows: five stations on Pintados and Ibirite streams (upstream from the reservoir), six in the reservoir and one station downstream from the reservoir. From 2002 to 2003, during both the dry and rainy seasons (in the tributaries) and the stratified and non-stratified periods (in the reservoir) were evaluated. A total of 289,777 organisms were collected and the most abundant organisms found in the streams were Oligochaeta (60%), Chironomidae (Chironomus, Goeldichironomus, Dicrotendipes, Cryptochironomus, Polypedilum, Parachironomus, Tanytarsus, Tribelos, Tanypus, Ablabesmyia, Cricotopus, Oliveriella) (38%) and Gastropoda (Biomphalaria straminea, Physa sp., Melanoides tuberculatus, Pomacea haustrum) (2%). In the reservoir, the most abundant specimens were Chaoboridae (46%) and Chironomidae larvae (Chironomus, Goeldichironomus, Tanypus, Coleotanypus, Labrundinia) (17%), in addition to Oligochaeta (24%) and Gastropoda (Melanoides tuberculatus) (13%). Evaluation of the structure and distribution of benthic communities showed a rapid environmental degradation process within the studied aquatic systems, in which low values of richness and diversity and high densities of tolerant organisms were observed. This environmental degradation is a result of the intense discharge of domestic sewage into the streams, reducing water quality and contributing to rapid artificial eutrophication.

An individual-based simulation model for mottled sculpin ( Cottus bairdi) in a southern Appalachian stream

We describe and analyze a spatially explicit, individual-based model for the local population dynamics of mottled sculpin ( Cottus bairdi). The model simulated daily growth, mortality, movement and spawning of individuals within a reach of stream. Juvenile and adult growth was based on consumption bioenergetics of benthic macroinvertebrate prey; benthic macroinvertebrate densities were a function of flow, season, and habitat quality. We based mortality rates of individual sculpin on their condition. Fish movement was determined by a growth maximization rule. We adjusted selected parameters to calibrate the model for a sculpin population in a southern Appalachian stream, in terms of adult and juvenile abundance and mean adult weight and length. Sensitivity and correlation analysis of the calibrated model suggested that this population was regulated by overwinter density-dependence among juveniles and adults.

Nearshore Community Characteristics Related to Shoreline Properties in the Great Lakes

Successful protection and restoration of Great Lakes nearshore ecosystems will likely rely on management of terrestrial resources along Great Lakes shorelines. However, relationships between biological communities and changing shoreline environmental properties are poorly understood. We sought to begin understanding the potential roles of shoreline geomorphological and land cover properties in structuring nearshore biological communities in the Laurentian Great Lakes. Despite high variability in densities (benthic macroinvertebrates and zooplankton) and catch per unit effort (CPUE, shallow water and nearshore fish) within and among lake areas, several biological community patterns emerged to suggest that nearshore aquatic communities respond to shoreline features via the influences of these features on nearshore substrate composition and stability. Benthic macroinvertebrate densities were not different between shoreline types, although they were generally lower at nearshore sites with less stable substrates. Shallow water fish CPUE and zooplankton densities were generally lower for nearshore areas adjacent to developed mid-bluff shorelines and sites characterized by less stable substrates. Larger fish CPUE appeared to be unresponsive to local shoreline and substrate properties of nearshore zones. The emergence of these patterns despite significant ecological differences among lake areas (e.g., productivity, community composition, etc.) suggests that shoreline development may have comparable influences on nearshore ecosystems throughout the Great Lakes, providing a terrestrialbased indicator of relative nearshore biological and ecological integrity.

Effects of gravel augmentation on macroinvertebrate assemblages in a regulated California River

Enhancement projects within anadromous salmonid rivers of California have increased in recent years. Much of this work is intended as mitigation in regulated streams where salmon and steelhead spawning habitat is inaccessible or degraded due to dams, water diversions and channelization. Little research has been done to assess the benefits of spawning habitat enhancement to stream organisms other than salmon. We monitored benthic macroinvertebrates at seven spawning gravel augmentation sites in the lower Mokelumne River, a regulated stream in the Central Valley of California. Placement of cleaned floodplain gravel decreased depths and increased stream velocities. Benthic organisms colonized new gravels quickly, equalling densities and biomass of unenhanced spawning sites within 4 weeks. Macroinvertebrate species richness equalled that of unenhanced sites within 4 weeks and diversity within 2 weeks. Standing crop, as indicated by densities and dry biomass, was significantly higher in enhancement sites after 12 weeks than in unenhanced sites and remained so over the following 10 weeks. Although mobile collector/browsers initially dominated new gravels, sedentary collectors were the most common feeding category after 4 weeks, similar to unenhanced sites. These data suggest that cleaned gravels from adjacent floodplain materials, used to enhance salmonid spawning sites, are quickly incorporated into the stream ecosystem, benefiting benthic macroinvertebrate densities and dry biomass. Copyright © 2005 John Wiley & Sons, Ltd.