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The Topeka shiner (Notropis topeka), a federally endangered species of minnow endemic to the Great Plains region of the central United States, has experienced widespread population declines resulting from loss of habitat. N. topeka habitat in Iowa, most notably oxbow wetlands, was mostly eliminated from the landscape during European settlement and agriculturalization of the region. Over the last two decades, restoration of oxbow habitats in Iowa has been increasing. Restorations provide critical habitat for N. topeka and regenerate a variety of ecosystem services that benefit many species of flora and fauna. There are signs that restoration of oxbow ecosystems is generating positive impacts on N. topeka recovery. Recent studies revealed that N. topeka populations are recovering within a few Iowa watersheds. In the investigation described here, we report the 2020 discovery of two N. topeka specimens in different restored oxbows within the White Fox Creek HUC10 of north central Iowa. Prior to these collections, the species had been undetected within this basin for 36 years. (It is possible that N. topeka persisted within the basin but remained undetected during sampling efforts.) Multiple oxbows have been restored within the White Fox Creek basin in recent years, and significant source populations of N. topeka can be found in nearby watersheds. These collections suggest that as oxbow restorations continue and land stewardship practices improve, N. topeka populations might recover and become reestablished within the historical range.

Landscape alterations can alter fish occurrence and abundance in wetlands. By increasing turbidity in wetland ponds, fishes can induce a shift from a clear- to a turbid-water state, resulting in reduced plant and amphibian abundance. In 2012, a drought reduced water levels and eliminated fishes from many wetlands of the prairie-pothole region (PPR) in the Midwestern United States. Our study objective was to evaluate if fish eliminations were associated with changes in wetland condition. A one-way ANOVA was used to compare the magnitude of change in parameters indicative of wetland condition (turbidity, plant cover and taxon richness, and tiger-salamander (Ambystoma tigrinum) biomass and numerical abundance) from 29 Iowa PPR wetlands between 2010 and 2011 (pre-drought) and 2014–2015 (post-drought) among wetlands where 1) all fishes were eliminated 2) large-bodied fishes were eliminated, 3) small-bodied fishes were eliminated, 4) fishes were retained, and 5) fishes were never detected. Turbidity decreased and plant cover increased more where large-bodied fishes were eliminated compared to the other groups. Changes in tiger-salamander biomass and abundance and plant-taxon richness were not different among groups. Results indicate that wetlands can shift from a turbid- to a clear-water state following drought and elimination of large-bodied fishes.

Macroinvertebrates are often excluded from wetland monitoring because samples collected using a conventional 500-μm mesh sieve are time consuming to process. To facilitate increased cost-effectiveness of obtaining macroinvertebrate data, influence of sieve mesh size on relationships between macroinvertebrate and environmental variables was evaluated in 27 prairie pothole wetlands. Benthic and water-column samples were washed through sieves with mesh sizes of 6 mm, 4 mm, 2 mm, and 500 μm, and macroinvertebrate numerical densities and taxon richness were quantified. Influence of particulate matter was evaluated by washing invertebrates through sieves before and after removal of this material from samples, and calculating differences in density and taxon richness. Regardless of sieve mesh size and particulate matter abundance, macroinvertebrate taxon richness exclusive of taxa occurring in all wetlands (planorbid snails, oligochaetes, leeches, chironomids) was positively correlated with plant cover, and negatively correlated with turbidity and fish biomass (p ≤ 0.05).Use of a 6-mm mesh sieve reduced sample volume by 35% and processing time by 54% relative to the 500-μm mesh sieve. Results suggest that reliance on taxon richness metrics and a sieve with 6-mm mesh will reduce macroinvertebrate sampling costs while still generating data that reflect wetland condition.

In the North American Prairie Pothole Region (PPR), agricultural and developed land uses may affect wetland condition by influencing contaminant inputs and invasions by fishes. To improve understanding of human impacts on wetlands, we quantified relationships between land use, physical attributes (herbicides, chloride, turbidity, wetland size), and biological attributes (tiger salamander [Ambystoma tigrinum] abundance; fish, plant, and invertebrate assemblages) of 45 permanently-ponded Iowa wetlands. Wetland area and water-column chloride concentration increased as cropped and developed land-covers increased in the watershed. However, we did not find strong relationships between land-cover type and biological attributes, with the exception of plant cover, which declined as water-column herbicide concentration increased. Fish abundance was an especially important determinant of wetland condition. As fish abundance increased, turbidity increased, and plant cover declined. Tiger salamander abundance and macroinvertebrate taxon richness also declined as fish abundance increased. Our findings suggest that in Iowa PPR wetlands, chloride concentration is an indicator of land-use intensity, and plant abundance can be predicted to some extent by herbicide concentrations. However, wetlands with low macroinvertebrate diversity, plant abundance, and salamander abundance tend to be those with high fish abundance.

Swanson, Jennifer E., Pierce, Clay L., Dinsmore, Stephen J., Smalling, Kelly L., Vandever, Mark W., Stewart, Timothy W., Muths, Erin (2019): Factors Influencing Anuran Wetland Occupancy in an Agricultural Landscape. Herpetologica 75 (1): 47-56, DOI: 10.1655/D-18-00013, URL: https://bioone.org/journals/herpetologica/volume-75/issue-1/D-18-00013/Factors-Influencing-Anuran-Wetland-Occupancy-in-an-Agricultural-Landscape/10.1655/D-18-00013.full

Urban stream condition is often degraded by human activities in the surrounding watershed. Given the complexity of urban areas, relationships among variables that cause stream degradation can be difficult to isolate. We examined factors affecting stream condition by evaluating social, terrestrial, stream hydrology and water quality variables from 20 urban stream watersheds in central Iowa, U.S.A. We used path analysis to examine and quantify social and ecological factors related to variation in stream conditions. Path models supported hypotheses that stream water quality was influenced by variables in each category. Specifically, one path model indicated that increased stream water conductivity was linked to high road density, which itself was associated with high human population density. A second path model revealed nitrogen concentration in stream water was positively related to watershed area covered by cropland, and that cropland increased as human population density declined. A third path model indicated phosphorus concentration in stream water declined as percent of watershed residents with college education increased, although the mechanism underlying this relationship was unclear and could have been an artifact of lower soil-derived nutrient input from watersheds dominated by paved surfaces. To improve environmental conditions in urban streams, land use planning strategies should include limiting or reducing road density near streams, installing treatment trains for surface water runoff associated with roads, and establishing vegetated buffer zones to reduce inputs of road salt and other pollutants. Additionally, education/outreach should be conducted with residents to increase understanding of how their own behaviors influence stream water quality.

a b s t r a c t Food web modeling is recognized as fundamental to understanding the complexities of aquatic systems. Ecopath is the most common mass-balance model used to represent food webs and quantify trophic inter- actions among groups. We constructed annual Ecopath models for four consecutive years during the first half-decade of a zebra mussel invasion in shallow, eutrophic Clear Lake, Iowa, USA, to evaluate changes in relative biomass and total system consumption among food web groups, evaluate food web impacts of non-native common carp and zebra mussels on food web groups, and to interpret food web impacts in light of on-going lake restoration. Total living biomass increased each year of the study; the majority of the increase due to a doubling in planktonic blue green algae, but several other taxa also increased including a more than two-order of magnitude increase in zebra mussels. Common carp accounted for the largest percentage of total fish biomass throughout the study even with on-going harvest. Chironomids, common carp, and zebra mussels were the top-three ranking consumer groups. Non-native common carp and zebra mussels accounted for an average of 42% of the total system consumption. Despite the rel- atively high biomass densities of common carp and zebra mussel, food web impacts was minimal due to excessive benthic and primary production in this eutrophic system. Consumption occurring via benthic pathways dominated system consumption in Clear Lake throughout our study, supporting the argument that benthic food webs are significant in shallow, eutrophic lake ecosystems and must be considered if ecosystem-level understanding is to be obtained. © 2015 Published by Elsevier B.V.

To improve understanding of human impacts on headwater stream condition, we quantified relationships between human, terrestrial landscape, and stream system variables in 29 central Iowa watersheds. Across study watersheds, between 0 and 100 % of total land area was characterized as “urban” (developed and barren land), whereas cultivated land constituted between 0 and 71 % of watershed area. Several variables were measured for each stream and associated watershed. Strengths of correlative relationships were used to select variables for path analysis, which we used to gain insight into factors affecting stream condition by evaluating direct and indirect effects of human system variables, terrestrial landscape variables, and physical stream variables on stream invertebrates. Results indicated that in predominantly urban watersheds, contaminant inputs to streams (measured by streamwater conductivity) negatively affected invertebrates, including EPT taxa (Ephemeroptera, Plecoptera, Trichoptera), and streamwater contaminant concentrations increased with impervious surface and human population density in the watershed. In rural watersheds, high streamwater nitrogen concentrations associated with cultivated land were related to declines in invertebrate taxon richness. Independent of land use, invertebrate abundance and taxonomic diversity were positively related to coarse substrate abundance on the streambed. Additionally, stream flow (discharge) increased with watershed area, which in turn increased invertebrate taxonomic diversity. Apparently, mechanisms responsible for human impacts on stream condition in central Iowa depend on dominant land use in the watershed. Additionally, stream ecosystems with high quality benthic habitat, and those located in large watersheds with greater flow, appear to be more resilient to land use effects.

Streams are natural features in urban landscapes that can provide ecosystem services for urban residents. However, urban streams are under increasing pressure caused by multiple anthropogenic impacts, including increases in human population and associated impervious surface area, and accelerated climate change. The ability to anticipate these changes and better understand their effects on streams is important for developing and implementing strategies to mitigate potentially negative effects. In this study, stream flow was monitored during April–November (2011 and 2012), and the data were used to apply the Storm Water Management Model (SWMM) for five urban watersheds in central Iowa, USA, representing a gradient of percent impervious surface (IS, ranging from 5.3 to 37.1%). A set of three scenarios was designed to quantify hydrological responses to independent and combined effects of climate change (18% increase in precipitation), and land cover change (absolute increases between 5.2 and 17.1%, based on separate projections of impervious surfaces for the five watersheds) for the year 2040 compared to a current condition simulation. An additional set of three scenarios examined stream response to different distributions of land cover change within a single watershed. Hydrological responses were quantified using three indices: unit-area peak discharge, flashiness (R-B Index; Richards–Baker Index), and runoff ratio. Stream hydrology was strongly affected by watershed percent IS. For the current condition simulation, values for all three indices were five to seven times greater in the most developed watershed compared to the least developed watershed. The climate change scenario caused a 20.8% increase in unit-area peak discharge on average across the five watersheds compared to the current condition simulation. The land cover change scenario resulted in large increases for all three indices: 49.5% for unit-area peak discharge, 39.3% for R-B Index, and 73.9% for runoff ratio, on average, for the five watersheds. The combined climate and land cover change scenario resulted in slight increases on average for R-B Index (43.7%) and runoff ratio (74.5%) compared to the land cover change scenario, and a substantial increase, on average, in unit area peak discharge (80.1%). The scenarios for different distributions of land cover change within one watershed resulted in changes for all three indices, with an 18.4% increase in unit-area peak discharge for the midstream scenario, and 17.5% (downstream) and 18.1% (midstream) increases in R-B Index, indicating sensitivity to the location of potential additions of IS within a watershed. Given the likelihood of increased precipitation in the future, land use planning and policy tools that limit expansion of impervious surfaces (e.g. by substituting pervious surfaces) or mitigate against their impacts (e.g. by installing bioswales) could be used to minimize negative effects on streams.

Commercial fisheries are commonly used to manage nuisance fishes in freshwater systems, but such efforts are often unsuccessful. Strategies for successfully controlling a nuisance population of common carp Cyprinus carpio by pulsed commercial harvest were evaluated with a combination of (1) field sampling, (2) population estimation and CPUE indexing, and (3) simulation using an exponential semidiscrete biomass dynamics model (SDBDM). The range of annual fishing mortalities (F) that resulted in successful control (F = 0.244–0.265) was narrow. Common carp biomass dynamics were sensitive to unintentional underharvest due to high rates of surplus production and a biomass doubling time of 2.7 years. Simulations indicated that biomanipulation never achieved successful control unless supplemental fishing mortality was imposed. Harvest of a majority of annual production was required to achieve successful control, as indicated by the ecotrophic coefficient (EC). Readily available biomass data and tools su...

Continuous harvest over an annual period is a common assumption of continuous biomass dynamics models (CBDMs); however, fish are frequently harvested in a discrete manner. We developed semidiscrete biomass dynamics models (SDBDMs) that allow discrete harvest events and evaluated differences between CBDMs and SDBDMs using an equilibrium yield analysis with varying levels of fishing mortality (F). Equilibrium fishery yields for CBDMs and SDBDMS were similar at low fishing mortalities and diverged as F approached and exceeded maximum sustained yield (FMSY). Discrete harvest resulted in lower equilibrium yields at high levels of F relative to continuous harvest. The effect of applying harvest continuously when it was in fact discrete was evaluated by fitting CBDMs and SDBDMs to time series data generated from a hypothetical fish stock undergoing discrete harvest and evaluating parameter estimates bias. Violating the assumption of continuous harvest resulted in biased parameter estimates for CBDM while SDBDM parameter estimates were unbiased. Biased parameter estimates resulted in biased biological reference points derived from CBDMs. Semidiscrete BDMs outperformed continuous BDMs and should be used when harvest is discrete, when the time and magnitude of harvest are known, and when F is greater than FMSY.

Land use changes and channelization of streams in the deep loess region of western Iowa have led to stream channel incision, altered flow regimes, increased sediment inputs, decreased habitat diversity and reduced lateral connectivity of streams and floodplains. Grade control structures (GCSs) are built in streams to prevent further erosion, protect infrastructure and reduce sediment loads. However, GCS can have a detrimental impact on fisheries and biological communities. We review three complementary biological and hydraulic studies on the effects of GCS in these streams. GCS with steep (≥1:4 rise:run) downstream slopes severely limited fish passage, but GCS with gentle slopes (≤1:15) allowed greater passage. Fish assemblages were dominated by species tolerant of degradation, and Index of Biotic Integrity (IBI) scores were indicative of fair or poor biotic integrity. More than 50% of fish species had truncated distributions. After modification of GCS to reduce slopes and permit increased passage, IBI scores increased and several species were detected further upstream than before modification. Total macroinvertebrate density, biomass and taxonomic diversity and abundance of ecologically sensitive taxa were greater at GCS than in reaches immediately upstream, downstream or ≥1km from GCS. A hydraulic study confirmed results from fish passage studies; minimum depths and maximum current velocities at GCS with gentle slopes (≤1:15) were more likely to meet minimum criteria for catfish passage than GCS with steeper slopes. Multidisciplinary approaches such as ours will increase understanding of GCS-associated factors influencing fish passage, biological assemblage structure and other ecological relationships in streams. Copyright © 2011 John Wiley & Sons, Ltd.

Knowledge of relationships between land cover (i.e., land use) and abiotic and biotic features of headwater streams enhances our ability to predict and effectively assess conditions in a variety of aquatic ecosystems. We evaluated land use effects on stream condition in an Iowa watershed dominated by intensive row crop agriculture and low- intensity urban development by quantifying relationships among land cover, stream invertebrate assemblages and other stream biophysical characteristics (i.e., invertebrate habitat) at 29 sites. On average, 81% of subbasin land cover was agricultural and 6% of land cover was urban across study sites. High nitrate concentrations (range = 5.6–29.0 mg/L) and high relative abundance of oligochaetes and chironomid midges reflected degraded conditions at all sites. However, agriculture and urban land use appeared to have different effects on stream features. Nitrate concentrations were positively related to agricultural land cover, and turbidity and nitrate concentr...

Restoration of ecosystem functions in urban environments is made challenging by 1) a public that often lacks understanding of ecological principles, 2) inadequate evidence of the effectiveness of restoration practices, and 3) difficulty integrating social and biophysical factors in studies of urban ecosystems. This paper describes a case study in which potential solutions to these challenges were explored. We facilitated collaborative learning through public participation in the design and implementation of an urban riparian buffer along a headwater stream in a neighborhood park, a process that was informed by ecological research. Learning outcomes were evaluated using surveys and qualitative assessment of discussion. Results indicated that participants’ knowledge about water quality problems associated with urbanization, stormwater, and nonpoint-source pollution increased, familiarity with stormwater management practices increased, and perceptions about the importance of stream ecosystem functions changed. In-stream monitoring of sediment delivery, as well as direct measurements of buffer infiltration capacity, provided early evidence of buffer effectiveness in prevention of sediment inputs to the stream and absorption of runoff from surrounding surfaces. This study provides a useful model for integration of collaborative learning through participation, ecological restoration, and ecological research in an urban setting. Elements deemed essential to success of this model included an opportunity for dialog focused on a specific natural feature, sustained interaction between participants and researchers, opportunities for hands-on participation by urban residents, and flexibility in restoration practice installation.

Macroinvertebrate assemblage characteristics and other biophysical features were measured in the open-water zone of 17 semipermanent/permanent prairie pothole wetlands in Iowa. Relations among variables were used to identify likely determinants of invertebrate abundance and diversity, and useful indicators of wetland condition (i.e., health). Abundant invertebrates included physid and planorbid snails, oligochaetes, leeches, caenid mayflies, corixid bugs, chironomid midges, and amphipods. Abundant taxa were distributed across multiple functional feeding and habit groups. Invertebrate densities and taxonomic diversity were positively associated with plant/coarse particulate organic matter (plant/CPOM) abundance, and negatively related to turbidity, water-column concentrations of nitrogen and phosphorus, and presence of large-bodied fishes. Results supported hypotheses that plant/CPOM was an important invertebrate resource, and that plant/CPOM abundance was reduced in turbid, hypereutrophic wetlands. Fish likely reduced invertebrate abundance and diversity through predation and/or cascading effects on plants, turbidity, and nutrients. Wetlands with high invertebrate abundance and diversity, abundant plant/CPOM, low turbidity and nutrient concentrations, presence of tiger salamanders (Ambystoma tigrinum), and absence of large-bodied fishes appeared to be in the best condition. These features should be routinely measured to effectively assess condition of Iowa prairie pothole wetlands. Additionally, eliminating non-native fish populations may be critical to improving condition of these wetlands.

Riparian buffers can improve stream water and habitat quality by reducing non-point-source pollution (e.g., nutrients and sediment), increasing canopy cover and thereby reducing water temperature, and contributing allochthonous organic matter (e.g., leaf litter and woody debris). However, the influence of riparian buffers on biotic assemblages in streams is poorly understood, particularly in the Midwestern United States. In this study, we evaluated the effects of riparian buffers on instream habitat, fish assemblage structure, and population characteristics (i.e., the growth of two small-bodied species) in three streams in central Iowa. The streams were surveyed at two spatial scales; specifically, 41 reaches were sampled and 247 macrohabitat types (i.e., pool, riffle, and run) were subsampled in the summer of 2007. Fish assemblage structure data were summarized into separate data sets by the relative abundance of individual species (i.e., fish per minute of electrofishing) and guilds (e.g., trop...

Grade control structures (GCSs) are commonly used in streams of western Iowa to control bank erosion and channel headcutting but may be barriers to fish passage. From May 2002 to May 2006, we used mark–recapture methods to evaluate fish passage over a total of five GCSs, ranging in slope (run : rise) from 13:1 to 18:1 in Turkey Creek, Cass County, Iowa. Three structures, over which limited fish movement was documented from 2002 to 2004, were modified in the winter of 2004–2005 to facilitate fish passage. Before modification, the majority of recaptured fish were recaptured at the station where they were originally marked; only 1% displayed movement between sites and either upstream or downstream over a GCS. After modification fish passage improved, 14% of recaptured fish displayed movement either upstream or downstream over a GCS. Individuals of four target species—channel catfish Ictalurus punctatus, yellow bullhead Ameiurus natalis, black bullhead A. melas, and creek chub Semotilus atromaculatus...

We quantified macroinvertebrate community characteristics in nine temporary or permanent wetlands, and related these to environmental conditions. Macroinvertebrates inhabiting the water column and shallow sediment (42-cm depth) were sampled 20 months after wetland construction in June 2005. A total of 29 taxa were collected, and macroinvertebrate communities varied among wetlands. Total macroinvertebrate biomass (mean ± SE = 16.44 ± 4.72 g AFDW/m3) and densities (mean ± SE = 372,096 ± 124,972 individuals/m3) were positively related to coarse particulate organic matter abundance (living and nonliving plant matter; CPOM) and negatively related to turbidity. Density of ecologically sensitive EOT (Ephemeroptera, Odonata, Trichoptera) taxa was also positively related to CPOM and negatively related to turbidity. Total taxa richness was negatively related to turbidity, and percent of total macroinvertebrate density consisting of EOT (% EOT) was positively related to CPOM. These relationships were gr...

Nearly 400 rock rip-rap grade control structures (hereafter GCS) were recently placed in streams of western Iowa, USA to reduce streambank erosion and protect bridge infrastructure and farmland. In this region, streams are characterized by channelized reaches, highly incised banks and silt and sand substrates that normally support low macroinvertebrate abundance and diversity. Therefore, GCS composed of rip-rap provide the majority of coarse substrate habitat for benthic macroinvertebrates in these streams. We sampled 20 sites on Walnut Creek, Montgomery County, Iowa to quantify macroinvertebrate assemblage characteristics (1) on GCS rip-rap and at sites located (2) 5–50 m upstream of GCS, (3) 5–50 m downstream of GCS and (4) at least 1 km from any GCS (five sites each). Macroinvertebrate biomass, numerical densities and diversity were greatest at sites with coarse substrates, including GCS sites and one natural riffle site and relatively low at remaining sites with soft substrates. Densities of macroinvertebrates in the orders Ephemeroptera, Trichoptera, Diptera, Coleoptera and Acariformes were abundant on GCS rip-rap. Increases in macroinvertebrate biomass, density and diversity at GCS may improve local efficiency of breakdown of organic matter and nutrient and energy flow, and provide enhanced food resources for aquatic vertebrates. However, lack of positive macroinvertebrate responses immediately upstream and downstream of GCS suggest that positive effects might be restricted to the small areas of streambed covered by GCS. Improved understanding of GCS effects at both local and ecosystem scales is essential for stream management when these structures are present. Copyright © 2007 John Wiley & Sons, Ltd.

I I uman activities have caused thousands of species to suffer severe population declines or become extinct during the past few centuries (Chapin et al., 2000). Unfortunately, the rate of decline in species diversity is expected to remain high or even increase in the future as human populations continue to grow, consume resources, and pollute the environment with their wastes (Chapin et al., 2000). Although many factors contribute to declining species diversity, loss of habitat structure through human-generated alteration of landscapes is perhaps the most important cause (Chapin et al., 2000; Keymer et al., 2000).

We used an experiment and regression analyses to quantify effects of spatial variation in habitat structure abundance on a riverine macroinvertebrate community under winter conditions. Concrete slabs (0.21 m2; n = 24) with different numbers of stones (mean individual stone surface area = 6.44 cm2) attached to upper faces were placed in the James River and retrieved after 28 d. Macroinvertebrate abundance and taxonomic richness on slabs were significantly positively related to stone abundance. Total macroinvertebrate abundance and abundance of oligochaetes (Nais spp.), Asiatic clams (Corbicula fluminea), caddisflies (Leptoceridae), riffle beetles (Elmidae) and stoneflies (Strophopteryx sp.) were linearly related to stone abundance. However, nonlinear relationships occurred between stone abundance and macroinvertebrate taxonomic richness and between stone abundance and abundance of dragonflies (Erpetogomphus sp.), caddisflies (Hydropsychidae), chironomids (Eukiefferiella spp.), mayflies (Ephemerell...

Snails in the family Pleuroceridae have strong effects on community structure and energy and nutrient pathways in many North American rivers and streams. Identifying factors determining densities and biomass of pleurocerids is, therefore, an important step toward predicting the relative importance of these snails in an ecosystem. We used plot sampling to identify environmental factors causing variation in demographic features of the pleurocerid snail Leptoxis carinata in a 3rd order stream in south central Virginia. Snails were collected from forty 0.22 m2 plots located within a 165 m segment of Fishpond Creek and L. carinata density, mean shell width, mean body mass and total biomass in each plot were measured. Measurements were also taken for several environmental variables. Multiple regression indicated that topographic complexity of substratum was the primary cause of variation in L. carinata density and total biomass among plots. Snail density and total biomass were both greater in topograph...

Results from several previous studies showed that zebra and quagga mussels (Dreissena polymorpha and D. bugensis, respectively) are key structuring agents of benthic invertebrate communities. However, the relative effects of Dreissena and other potentially important biotic factors on these communities remain poorly understood. The goal of this study was to improve our understanding of community-structuring mechanisms in habitats with Dreissena by quantifying simultaneous effects of Dreissena and large benthic predators (primarily fish) on invertebrates inhabiting hard substrates in western Lake Erie. Biomass, densities, and diversity of invertebrates were compared on bricks with low and high (=ambient) Dreissena biomass that were held in western Lake Erie for 49 d within cages that excluded large predators, partial cages where predators had access to invertebrates, and cageless-reference plots. Dreissena had positive effects on total invertebrate biomass, and biomass of gastropods, chironomid larvae, and ...

Prey employ various strategies to avoid predators, including use of structurally complex habitat where predator foraging efficiency can be reduced. We used laboratory experiments to quantify combined effects of antipredator behavior and habitat provided by zebra mussel (Dreissena polymorpha) shells on survivorship of snails (Physella heterostropha) co-occurring with molluscivorous fish. First we determined predator effects on prey habitat use in aquaria with and without Dreissena-shell beds (i.e., ceramic tiles with and without shells attached to them, respectively) by comparing snail distribution in the absence of fish and in the presence of chemical cues produced from redear sunfish (Lepomis microlophus) preying on snails. Effectiveness of shell beds and other habitats as refuges from actual predation were then evaluated by introducing fish to aquaria that previously received chemical cues, and recording numbers of snails remaining in various habitats 24 h later. Shells and fish had strong independent a...

Benthic macroinvertebrate communities were compared and quantified at natural cobble and artificial reef sites in Lake Ontario in 1983 (pre-Dreissena invasion), and in both 1991–1992 and 1995 (1 to 2 and 5 years post-Dreissena invasion, respectively). Diversity and abundance of non-dreissenid macroinvertebrates generally rose from 1983 to 1991–1992, but returned to 1983 levels or lower by 1995. Although community similarity (excluding Dreissena from analysis) remained high across study years, the 1995 invertebrate community more closely resembled the pre-Dreissena community of 1983 than the initial post-Dreissena community of 1991–1992 because of recent declines in the absolute abundance and diversity of macroinvertebrates. In particular, gastropods responded negatively to Dreissena or to associated benthic habitat or community changes that occurred from 1991–1992 to 1995. These results suggest that short- and long-term effects of Dreissena on other organisms may be quite different, and illustrate the need for long-term monitoring of biological communities in order to more fully determine effects of invasive species or other environmental perturbations on ecosystems.

Quantitative descriptions of trophic interactions between Dreissena (zebra and quagga mussels) and other organisms are needed for an understanding of Dreissena's effects on energy flow and community dynamics in the Great Lakes. We used a field experiment to quantify effects of crayfish (Orconectes rusticus) predation on a Dreissena-dominated benthic macroinvertebrate community in western Lake Erie. Rocks colonized by Dreissena and associated macroinvertebrates were placed in cages and cageless reference plots located at a depth of 4 m. Crayfish (0, 8.3, and 20.8 individuals ·m-2) placed in cages were allowed to graze for 28 days. Dreissena had a greater effect than crayfish on the macroinvertebrate community, with positive relationships observed between Dreissena densities and both total macroinvertebrate biomass and densities of the amphipod Gammarus fasciatus. However, crayfish at densities of 20.8 individuals ·m-2 still reduced non-Dreissena macroinvertebrate biomass and Gammarus densities by 33 and 37%, respectively, relative to crayfish exclosures. Crayfish had negligible effects on Dreissena densities or shell length frequency distribution. Because crayfish and amphipods are prey for several fish species, trophic interactions among Dreissena, amphipods, and crayfish may be important in channeling energy from Dreissena to higher trophic levels in the Great Lakes.

Quantitative descriptions of interactions between zebra mussels (Dreissena polymorpha) and other organisms are needed for an understanding of zebra mussel effects on energy flow and community dynamics in North American freshwater ecosystems. We used a field experiment to quantify effects of 2 potential mechanisms for increasing benthic macroinvertebrate biomass and densities in the Great Lakes following the zebra mussel invasion: 1) habitat created by zebra mussel shells, and 2) habitat and food provided by increases in benthic organic matter. Macroinvertebrate biomass, macroinvertebrate densities, and organic matter mass (hereafter termed organic matter) were measured on substrates (tiles without zebra mussels, with zebra mussel shells, and with live zebra mussels) that were held in western Lake Erie for 37 d. Organic matter was 3×-5× greater on tiles with live mussels than on plain tiles or tiles with shells, demonstrating that filter-feeding zebra mussels increased organic matter on benthic substrates....

Of the approximately 140 non-indigenous species that have invaded the Great Lakes since the early 1800s, few have had greater effects on this ecosystem than the zebra and quagga mussel (Dreissena polymorpha and D. bugensis, respectively). In this study the effects of these bivalves on macroinver-tebrates inhabiting hard substrates in western Lake Erie were quantified. Biomass, densities, diversity of macroinvertebrates, and paniculate organic matter mass were measured on bricks with high and low Dreissena densities that were held at a depth of 3.5 mfor 49 days in 1996. Total macroinvertebrate densi ties and biomass (excluding Dreissena) were two and five times greater on substrates with high Dreissena densities than when Dreissena were rare. These differences were largely attributed to the amphipod Echinogammarus ischnus, itself an invading species, which constituted 29 and 31% of total macroinvertebrate densities and biomass, respectively, on Dreissena-dominated substrates. Dreissena also stimulated increased macroinvertebrate diversity, causing a shift from a community dominated by the chironomid Dicrotendipes neomodestus to an assemblage characterized by increased densities and equitability of hydroids (Hydridae), the flatworm Dugesia tigrina, tubificid oligochaetes, leeches (Alboglossiphonia het-eroclita and immature Erpobdellidae), limpets (Ancylidae), snails (Physella integra and Amnicola limosa), Echinogammarus, the microcaddisfly Hydroptila ?waubesiana, and the chironomid Micro-tendipes pedellus. No taxon responded negatively to Dreissena in this study. In addition, particulate organic matter mass, an important food and habitat resource for benthic invertebrates, was two times greater on Dreissena-dominated substrates than on bricks with few Dreissena. Our results support hypotheses that Dreissena have strong effects on community dynamics and energy flow pathways in the Great Lakes.

Changes in benthic macroinvertebrate communities inhabiting natural cobble and artificial reef substrates in southwestern Lake Ontario were quantified following invasion of zebra mussels (Dreissena polymorpha) and “quagga” mussels (Dreissena sp.). Post-Dreissena invasion data (1991–1992) were compared with pre-invasion data (1983) from the same sites. In 1991–1992, Dreissena comprised 79% and 93% of macroinvertebrates collected at cobble and artificial reef sites, respectively, replacing the amphipod Gammarus fasciatus as the numerically dominant taxon at both sites. Total abundance of non-Dreissena macroinvertebrates was significantly greater at both sites in 1991–1992 than in 1983. Taxa showing the greatest increases in abundance at the cobble site included the annelids Manayunkia speciosa, Spirosperma ferox, and unidentified tubificids; the gastropods Helisoma anceps, Physa heterostropha, Stagnicola catascopium, Valvata tricarinata, Goniobasis livescens, and Amnicola limosa; the amphipod Gammarus fasciatus; and the decapod Orconectes propinquis. At the artificial reef site, significant population increases of Physa heterostropha, Valvata tricarinata, Goniobasis livescens, Amnicola limosa, Gammarus fasciatus and the trichopteran Polycentropus were observed. No taxon was less abundant in 1991–1992 than 1983. Comparisons of macroinvertebrate community similarity in 1983 and 1991–1992 by Morisita's Index, excluding Dreissena, indicated that previously established taxa did not change substantially between 1983 and 1991–1992 at either site. Although many factors may have contributed to the changes observed, our results support theories that Dreissena is facilitating energy transfer to the benthos through pseudofecal/fecal deposition, and that mussel colonies are providing additional habitat for other invertebrate taxa.