Detrital processing in streams exposed to acidic precipitation in the Central Appalachian Mountains

Continuing high rates of acidic deposition in the eastern United States may lead to long-term effects on stream communities, because sensitive catchments are continuing to lose anions and cations. We conducted a two-year study of the effects of pH and associated water chemistry variables on detrital processing in three streams with different bedrock geology in the Monongahela National Forest, West Virginia. We compared leaf pack processing rates and macroinvertebrate colonization and microbial biomass (ATP concentration) on the packs in the three streams. Breakdown rates of red maple and white oak leaf packs were significantly lower in the most acidic stream. The acidic stream also had significantly lower microbial and shredder biomass than two more circumneutral streams. Shredder composition differed among streams; large-particle detritivores dominated the shredder assemblages of the two circumneutral streams, and smaller shredders dominated in the acidic stream. Within streams, processing rates for three leaf species were not significantly different between the two years of the study even though invertebrate and microbial communities were different in the two years. Thus, macroinvertebrate and microbial communities differed both among streams that differed in their capacity to buffer the effects of acidic precipitation and among years in the same stream; these differences in biotic communities were not large enough to affect rates of leaf processing between the two years of the study, but they did significantly affect processing rates between acidic and circumneutral streams.The Unit is jointly sponsored by the National Biological Service, the West Virginian Division of Natural Resources, West Virginia University, and the Wildlife Management Institute.The Unit is jointly sponsored by the National Biological Service, the West Virginian Division of Natural Resources, West Virginia University, and the Wildlife Management Institute.     

<Emphasis Type="Italic">Encentrum (Parencentrum) walterkostei</Emphasis> n. sp., a new dicranophorid rotifer (Rotatoria: Monogononta) from the high alpine zone of the Central Alps (Austria)

Leaf litter processing rates and fungal biomass on leaf detritus were compared in four streams of different water chemistry. The streams drained catchments underlain by different bedrock types and varied in mean pH from 4.3 to 7.5 and in mean alkalinity from 0.0 to 35.8 mg CaCO₃ l^–1. Processing rates were fastest in WS3 and WS4, which had a pH of 6.0; slowest in SFR, which had a pH of 4.3; and intermediate in HSR which had a pH of 7.5. Fungal biomass as measured by the fungal sterol, ergosterol, was similar in WS3, WS4, and HSR but was much lower in SFR. These results suggest that reduced processing rates in SFR were associated in part with reduced fungal biomass on the leaves, whereas reduced processing rates in HSR were not related to differences in fungal biomass on the leaves.The Unit is jointly sponsored by the U.S. Fish and Wildlife Service, the West Virginia Division of Natural Resources, West Virginia University, and the Wildlife Management Institute.     

Fish assemblages of the central Appalachian Moutains: an examination of trophic group abundance in nine West Virginia streams

Synopsis We used multivariate ordination techniques to examine patterns of trophic group abundance among fish assemblages in nine West Virginia streams. These patterns were examined in relation to habitat and water chemistry gradients. The first two components from a principal components analysis (PCA) explained 71% of the variation in trophic group abundance. The first two axes from a PCA of habitat data accounted for 75% of the total variation. Generalized insectivores and insectivore-piscivores were the predominant trophic groups in stable, pool environments. Benthic insectivores and herbivores-detritivores were most abundant in shallow, temporally variable environments. We attributed the presence of generalized insectivores in deep, pool environments to the effects of a severe drought. The predominance of benthic insectivores in shallow environments was attributed to an abundance of benthic stream fishes and a depauperate catostomid assemblage. The Unit is jointly sponsored by the Wildlife Service, the West Virginia Division of Natural Resources, West Virginia University, and the Wildlife Management Institute.     

Comparison of three zooplankton samplers: a taxon-specific assessment

We compared densities of zooplankton captured by three commonzooplankton samplers during 24 h. A tube sampler generally yieldedzooplankton densities equal to or greater than those from avertical net tow or a Schindler-Patalas trap. Exceptions includedherbivorous rotifers and Diaphanosoma. Because rotifer densityusually was greatest in the deepest stratum sampled (i.e. nearthe bottom of the tube), water loss with lifting probably accountedfor reduced rotifer capture. Why the tube and the Schindler-Patalastrap were less efficient than the net for Diaphanosoma remainsunclear. Because tubes sample the entire water column, providingzooplankton densities comparable with traditional gear, theyare a time-saving alternative for zooplankton sampling in shallowlakes and weedy littoral zones. ²The Unit is sponsored jointly by The United States Fish andWildlife Service, Ohio Department of Natural Resources, TheOhio State University and the Wildlife Management Institute.     

Food selection by brook trout in a subalpine stream

The diet and food selection of brook trout (Salvelinus fontinalis) and macroinvertebrate drift are described for a high altitude stream (3 205 m above mean sea level) adjacent to the alpine zone on the Snowy Range in the Medicine Bow National Forest, Wyoming. Diet composition differed between brook trout of two length classes, 150 mm and > 150 mm in total length. The number of prey organisms per stomach generally declined and the proportion of terrestrial prey items increased from July to September, 1985. Fish of both length classes selected for Trichoptera and Coleoptera over the three sampling months, and fish > 150 mm also selected for terrestrial insects in August and September.The Unit is jointly supported by the University of Wyoming, the Wyoming Game and Fish Department, and the US Fish and Wildlife ServiceThe Unit is jointly supported by the University of Wyoming, the Wyoming Game and Fish Department, and the US Fish and Wildlife Service     

Habitat use by bluegill in laboratory pools: where is the refuge when macrophytes are sparse and alternative prey are present?

Synopsis In northern clear-water systems, bluegill, Lepomis macrochira, select habitats based on relative reward rates and risk of predation. However, because freshwater systems to the south are often turbid, and their resident fish species different, bluegill habitat use patterns may differ from those found in northern clear-water systems. Here I examine the effects of elimination of the inshore macrophyte refuge (an indirect effect of turbidity), and decreased pelagic predation rates on bluegill due to the presence of gizzard shad, Dorosoma cepedianum, in laboratory pools. Bluegill used depths 20 cm more often with largemouth bass, Micropterus salmoides, than without them; the presence of a preferred alternate prey, gizzard shad, did not affect this behavior. Though bluegill did not alter their habitat use in response to bass activity, they did school more as predator activity increased. Even in the presence of a preferred alternate prey without macrophytes, bluegill continue to use shallow littoral areas to avoid predation.This Unit is sponsored jointly by The United States Fish and Wildlife Service, Ohio Department of Natural Resources, The Ohio State University, and the Wildlife Management Institute.     

The role of leaf litter macroinvertebrates in stream-floodplain dynamics

The floodplain has been viewed as a transitional system or ecotone between aquatic and terrestrial habitats. This research has evaluated the role of floodplain macroinvertebrates in the degradation of leaf litter in a Michigan woodland floodplain, and examined the interrelationships among floodplain-stream macroinvertebrates, microbial colonization and selected environmental factors. Although taxonomically different decomposer groups operate in both systems, their functional roles as leaf litter detritivores are basically the same. Leaf litter processing rates were compared and contrasted between the stream and adjacent floodplain using leaf packs and litter bags, respectively. In the stream, the major time period for detritus processing by invertebrates is in the fall and winter, while in the floodplain it is during the spring. Therefore, the sequence of events involved in processing are similar, yet the timing and rate of these events are strikingly different. An understanding of the significant ecological processes linking the stream and floodplain as complementary systems is discussed within the context of watershed management.     

Complex predator-prey interactions and predator intimidation among crayfish,piscivorous fish,and small benthic fish

Summary Predator-prey interactions were studied among a small prey fish (the johnny darter Etheostoma nigrum) and two predators (crayfish Orconectes rusticus and smallmouth bass Micropterus dolomieui) with complementary foraging behaviors. When only smallmouth bass were present, darters reduced activity to 6% of control rates and spent most of the time hiding under tile shelters. When only crayfish were present, darter activity and shelter-use were similar to controls. When both crayfish and bass were present, an interaction occurred. Darters, normally inactive in the presence of bass, were often forced to move by approaching crayfish and thus activity increased to 19% of control rates. Also, darters were often evicted from shelters by intruding crayfish. Thus, crayfish increased the vulnerability of small fish to bass by evicting them from shelters and causing increased activity. Conversely, bass increased the vulnerability of small fish to crayfish by forcing these fish to seek cover under shelters occupied by crayfish. Intimidation effects of bass on darters last for some time. After a 30-min exposure to bass, darters showed reduced activity and increased shelter use lasting at least 24 h after the bass was removed. Thus predators, throught intimidation, can influence prey behavior even though the predators are no longer present.The Unit is sponsored jointly by the United States Fish and Wildlife Service, the Ohio Department of Natural Resources, and The Ohio State University     

Bluegill growth as modified by plant density: an exploration of underlying mechanisms

Summary Bluegill (Lepomis macrochira) growth varies inconsistently with plant density. In laboratory and field experiments, we explored mechanisms underlying bluegill growth as a function of plant and invertebrate density. In the laboratory, bluegills captured more chironomids (Chironomus riparius) than damselflies (Enallagma spp. and Ischnura spp.), but energy intake per time spent searching did not differ between damselfly and chironomid treatments. From laboratory data, we described prey encounter rates as functions of plant and invertebrate density. In Clark Lake, Ohio, we created 0.05-ha mesocosms of inshore vegetation to generate macrophyte densities of 125, 270, and 385 stems/m² of Potamogeton and Ceratophyllum and added 46-mm bluegill (1/m²). In these mesocosms, invertebrate density increased as a function of macrophyte density. Combining this function with encounter rate functions derived from laboratory data, we predicted that bluegill growth should peak at a high macrophyte density, greater than 1000 stems/m², even though growth should change only slightly beyond 100 stems/m². Consistent with our predictions, bluegills did not grow differentially, nor did their use of different prey taxa differ, across macrophyte densities in the field. Bluegills preferred chironomid pupae, which were relatively few in numbers but vulnerable to predation, whereas more cryptic, chironomid larvae, which were associated with vegetation but were relatively abundant, were eaten as encountered. Bluegills avoided physid snails, which were abundant. Contrary to previous work, vegetation did not influence growth or diet of bluegill beyond relatively low densities owing to the interaction between capture probabilities and macroinvertebrate densities.The unit is sponsored jointly by the United States Fish and Wildlife Service, Ohio Department of Natural Resources, The Ohio State University, and The Wildlife Management Institute     

Geographic variation in patterns of nestedness among local stream fish assemblages in Virginia

Nestedness of faunal assemblages is a multi-scale phenomenon, potentially influenced by a variety of factors. Prior small-scale studies have found freshwater fish species assemblages to be nested along stream courses as a result of either selective colonization or extinction. However, within-stream gradients in temperature and other factors are correlated with the distributions of many fish species and may also contribute to nestedness. At a regional level, strongly nested patterns would require a consistent set of structuring mechanisms across streams, and correlation among species tolerances of the environmental factors that influence distribution. Thus, nestedness should be negatively associated with the spatial extent of the region analyzed and positively associated with elevational gradients (a correlate of temperature and other environmental factors). We examined these relationships for the freshwater fishes of Virginia. Regions were defined within a spatial hierarchy and included whole river drainages, portions of drainages within physiographic provinces, and smaller subdrainages. In most cases, nestedness was significantly stronger in regions of smaller spatial extent and in regions characterized by greater topographic relief. Analysis of hydrologic variability and patterns of faunal turnover provided no evidence that inter-annual colonization/extinction dynamics contributed to elevational differences in nestedness. These results suggest that, at regional scales, nestedness is influenced by interactions between biotic and abiotic factors, and that the strongest nestedness is likely to occur where a small number of organizational processes predominate, i.e., over small spatial extents and regions exhibiting strong environmental gradients.The Virginia Cooperate Fish and Wildlife Research Unit is jointly sponsored by United States Geological Survey, Virginia Polytechnic Institute and State University, and Virginia Department of Game and Inland Fisheries.     

Effects of atmospheric N deposition on coarse organic matter in a headwater stream

Input, storage, export potential, and system-level processing of coarse organic matter were investigated in the intermittent streams that drain the Bear Brook Watershed in Maine (BBWM). BBWM is a paired catchment study investigating ecosystem effects of atmospheric N and S deposition. We predicted that the increased N loading to the treatment catchment would elevate input of organic matter, result in higher levels of coarse organic matter biomass, and increase litter processing rates in the treatment stream relative to the reference stream. We found that the streams draining BBWM did not have statistically different coarse organic matter input, biomass, or processing rates and we found only modest differences in export potential. System-level processing rates for maple (Acer spp.) litter were similar to rates previously quantified using litterbag methods. However, system-level processing rates for American beech (Fagus grandifolia) litter were an order of magnitude faster than rates measured with litterbags. This difference was likely due to movements of these leaves from riffle/runs and pools into debris dams, rather than differences in measurements of leaf tissue processing rates between methods. Organic matter dynamics of the intermittent streams at BBWM were similar to other forested, headwater streams. Our results indicate that the long-term N manipulation experiment at BBWM has not altered input, storage or processing of coarse organic matter in the treatment stream. Physical characteristics of these stream ecosystems appear to regulate organic matter dynamics rather than differences in nutrient chemistry.     

Spatiotemporal variability of stream habitat and movement of three species of fish

Relationships between environmental variability and movement are poorly understood, due to both their complexity and the limited ecological scope of most movement studies. We studied movements of fantail (Etheostoma flabellare), riverweed (E. podostemone), and Roanoke darters (Percina roanoka) through two stream systems during two summers. We then related movement to variability in measured habitat attributes using logistic regression and exploratory data plots. We indexed habitat conditions at both microhabitat (i.e., patches of uniform depth, velocity, and substrate) and mesohabitat (i.e., riffle and pool channel units) spatial scales, and determined how local habitat conditions were affected by landscape spatial (i.e., longitudinal position, land use) and temporal contexts. Most spatial variability in habitat conditions and fish movement was unexplained by a site’s location on the landscape. Exceptions were microhabitat diversity, which was greater in the less-disturbed watershed, and riffle isolation and predator density in pools, which were greater at more-downstream sites. Habitat conditions and movement also exhibited only minor temporal variability, but the relative influences of habitat attributes on movement were quite variable over time. During the first year, movements of fantail and riverweed darters were triggered predominantly by loss of shallow microhabitats; whereas, during the second year, microhabitat diversity was more strongly related (though in opposite directions) to movement of these two species. Roanoke darters did not move in response to microhabitat-scale variables, presumably because of the species’ preference for deeper microhabitats that changed little over time. Conversely, movement of all species appeared to be constrained by riffle isolation and predator density in pools, two mesohabitat-scale attributes. Relationships between environmental variability and movement depended on both the spatiotemporal scale of consideration and the ecology of the species. Future studies that integrate across scales, taxa, and life-histories are likely to provide greater insight into movement ecology than will traditional, single-season, single-species approaches. The Virginia Cooperative Fish and Wildlife Research Unit is jointly sponsored by the US Geological Survey, Virginia Polytechnic Institute and State University, Virginia Department of Game and Inland Fisheries, and Wildlife Management Institute.     

Shifts in leaf litter breakdown along a forest–pasture–urban gradient in Andean streams

Tropical montane ecosystems of the Andes are critically threatened by a rapid land‐use change which can potentially affect stream variables, aquatic communities, and ecosystem processes such as leaf litter breakdown. However, these effects have not been sufficiently investigated in the Andean region and at high altitude locations in general. Here, we studied the influence of land use (forest–pasture–urban) on stream physico‐chemical variables (e.g., water temperature, nutrient concentration, and pH), aquatic communities (macroinvertebrates and aquatic fungi) and leaf litter breakdown rates in Andean streams (southern Ecuador), and how variation in those stream physico‐chemical variables affect macroinvertebrates and fungi related to leaf litter breakdown. We found that pH, water temperature, and nutrient concentration increased along the land‐use gradient. Macroinvertebrate communities were significantly different between land uses. Shredder richness and abundance were lower in pasture than forest sites and totally absent in urban sites, and fungal richness and biomass were higher in forest sites than in pasture and urban sites. Leaf litter breakdown rates became slower as riparian land use changed from natural to anthropogenically disturbed conditions and were largely determined by pH, water temperature, phosphate concentration, fungal activity, and single species of leaf‐shredding invertebrates. Our findings provide evidence that leaf litter breakdown in Andean streams is sensitive to riparian land‐use change, with urban streams being the most affected. In addition, this study highlights the role of fungal biomass and shredder species (Phylloicus; Trichoptera and Anchytarsus; Coleoptera) on leaf litter breakdown in Andean streams and the contribution of aquatic fungi in supporting this ecosystem process when shredders are absent or present low abundance in streams affected by urbanization. Finally, we summarize important implications in terms of managing of native vegetation and riparian buffers to promote ecological integrity and functioning of tropical Andean stream ecosystems.     

Effects of agricultural development on processing of tussock leaf litter in high country New Zealand streams

1. We compare the rates and mechanisms of processing of tussock (Chionochloa spp.) leaf litter in six New Zealand streams draining grassland catchments that contrast in the extent to which they have been developed for pasture. 2. Rates of processing, measured as rate of weight loss of leaf packs and rate of leaf softening, were at the slow end of the spectrum for vascular plant processing. Processing was faster at developed sites, mediated mainly through the influence of oxidized nitrogen concentration on microbial activity. 3. Few invertebrate shredders colonized leaf packs and it is unlikely that invertebrates had an appreciable effect on leaf processing in our study streams, which do not effectively retain leaf litter. Very small headwater tributaries appear to retain leaf litter and possess a more abundant shredder community. 4. Measures of leaf processing in our six streams were significantly correlated with Petersen's (1992) RCE score of stream condition. We discuss the potential for using rate of leaf litter processing as a method of bioassessment. 5. Even the most degraded stream in our study is classed as ‘good’ using the RCE inventory system. Human impact in the Taieri River is relatively small compared with the degradation observed in some parts of the world.     

A Comparative Study of Leaf Breakdown of Three Native Tree Species in a Slowly‐Flowing Headwater Stream in the Colombian Andes

The dynamics of leaf breakdown in a headwater Colombian stream were evaluated for the native tree species Myrsine guianensis, Cupania latifolia and Nectandra lineatifolia using coarse and fine mesh litter bags. Ten bags of each species (five of each mesh size) were retrieved from the stream at 1, 8, 15, 30, 60 and 120 days. k values ranged from 0.0008 to 0.0058 day^–1 and density of macroinvertebrates from 35 to 55 individuals per leaf bag, peaking at day 8. Myrsine guianensis degraded more rapidly than the other species for both coarse and fine mesh bags. This species and Nectandra lineatifolia presented differences in k values between coarse and fine mesh bags, suggesting that macroinvertebrates influenced the decay rate. Despite the low densities of macroinvertebrates found, shredders represented 12.7% of individuals and 50 to 68% of the invertebrate biomass in bags, indicating that this functional feeding group was an important component of fauna associated with litter breakdown in this first order tropical stream. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Production of a stream shredder, Peltoperla maria (Plecoptera: Peltoperlidae) in disturbed and undisturbed hardwood catchments

SUMMARY. (1) The average benthic density of Peltoperla maria in an undisturbed southern Appalachian stream was more than twice that of a nearby stream draining a previously clear-cul catchment in its tenth year of natural secondary succession.
(2) Peltoperla production estimates, using three methods, do not show a significant difference in production between streams draining the two catchments. We attribute these results to quicker growth and slightly higher densities of larger nymphs in the disturbed stream. Production estimates for the disturbed stream ranged from 498 to 560 mg (ash free dry weight) m⁻²y⁻¹ while those for the undisturbed stream were 41–4–515 mg m⁻² y⁻¹.
(3) Our results reinforce the view that conclusions based solely upon numerical densities may lead to erroneus interpretations about the roles organisms play in ecosystems.
(4) Annual frass production by this shredder is about 20 times (10 g m⁻² y⁻¹) the secondary production of P. maria.     

Nest defense and aggressive interactions between a small benthic fish (the johnny darter Etheostoma nigrum) and crayfish

Synopsis Aggression by nest-guarding male johnny darters, Etheostoma nigrum, against intruding crayfish was investigated in laboratoy experiments and field observations. In the laboratory, darter success in chasing crayfish, Orconectes rusticus, from the nest site was inversely related to crayfish size. Small crayfish (less than 15 mm carapace length) were routinely evicted from the nest area by nips directed at the posterior end of the abdomen. Although such aggressive behavior was less successful against larger crayfish, even the largest crayfish tested (carapace length 30–32 mm) were chased from the nest area in 33% of the trials. Those large crayfish that entered nests often remained despite repeated attacks by the male johnny darter and egg predation was observed. In a small Ohio stream, openings to johnny darter nests were generally between 7 and 13 mm. Thus crayfish with a carapace height greater than 13 mm (corresponding to a carapace length greater than 29 mm) would not be able to enter johnny darter nests. In field observations, male Johnny darters successfully defended nests against another crayfish species (Orconectes sanborni, carapace length 12–29 mm). Together, aggressive behavior and small size of nest entrances allow the johnny darter to successfully reproduce in areas with abundant crayfish. The Unit is sponsored jointly by the United States Fish and Wildlife Service, The Ohio Department of NaturalResources, and The Ohio State University.     

Pine afforestation changes more strongly community structure than ecosystem functioning in grassland mountain streams

In the past decades, afforestation of grassland landscapes has gained importance both as an economic activity and a mechanism to mitigate anthropogenic carbon emissions. This study evaluates the effect of pine afforestation on grassland streams analyzing changes in two integrative ecological indicators: leaf litter breakdown and primary production. We compare those results with changes in structural attributes of benthic biota (primary producers and invertebrates). Six contiguous first-order streams were selected in the upper basin of the Ctalamochita river (Córdoba, Argentina): three reference streams draining grasslands and three streams draining Pinus elliottii afforestations. Two in situ experiments were performed to compare leaf litter breakdown and primary production between grassland and afforested streams. Additionally, invertebrate assemblages in leaf litter and riffles, and periphyton standing stock were sampled and assessed. Nine out of 26 structural indicators showed differences between stream types but indicators measuring changes at the basal level of the food web (i.e. detritus and primary producers) were less sensitive than those recording changes in consumers. Our attempt to measure direction and magnitude of changes on stream functioning following afforestation was halted by our simple implemented methodology (i.e. leaf pack method for leaf litter decay and biofilm accrual on natural stone substrates for primary production assessments); only 1 out of 4 indicators differed. We argue that the lack of strong differences in elemental measurements of primary production and needle decay between afforested and grassland streams resulted from compensating opposing forces controlling such processes, i.e. higher grazing vs. higher sunlight in grassland streams and higher shredding vs. lower microbial decomposition mediated by lower temperature in afforested streams. Attributes related to the invertebrate compartment showed the highest sensitivity to afforestation, emphasizing their value as biological indicators of stream ecological integrity.     

Processing of leaf litter in two northern jarrah forest streams,Western Australia: II. The role of macroinvertebrates and the influence of soluble polyphenols and inorganic sediment

The long-term processing of jarrah (Eucalyptus marginata) leaves was examined in a small forest stream to determine the role played by macroinvertebrates and the influence of soluble polyphenols in the leaves. The widely used exponential model of litter processing was inadequate in describing the fate of jarrah leaves. Decomposition occurred in three distinct phases and was best described by a quadratic model. After a substantial and rapid loss due to leaching, processing was virtually inhibited during summer and autumn, with no associated increase in the organic nitrogen content. Macroinvertebrates played a significant role in the latter part of the year, processing approximately 25% of the initial leaf mass.High levels of soluble polyphenols in the leaves had an inhibitory effect on the microbial colonization of jarrah leaves, as indicated by the organic nitrogen content. However, pre-leaching of these compounds had no effect on the rate of decomposition nor on the leaf bag fauna. Polyphenols released into the stream during summer, when flows are low, may reach high concentrations and contribute to the slow processing at this time. Leaf litter processing in a nearby sedimented stream was compared with that in the undisturbed stream. Sediment disrupted litter processing, virtually eliminating the contribution made by invertebrates. Smothered leaf bags became anoxic, restricting microbial activity and reducing leaf quality. The low processing rate of leaves in the sedimented stream was attributed to differences in the leaf bag fauna. Leaf bags in the sedimented stream had more animals but shredders were poorly represented and predators were the most abundant feeding group. The low density of shredders was more likely to be a result of the reduced availability of detritus rather than selective predation. Whatever the reason, invertebrates in the sedimented stream were denied access to an important source of energy. Inorganic sediment can have a profound effect on stream function by interfering with the shredder-CPOM pathway.     

Predation by rock bass on other stream fishes: experimental effects of depth and cover

Synopsis Effects of water depth and cover availability on predation rates by adult rock bass, Ambloplites rupestris, on juvenile central stoneroller, Campostoma anomalum, pumpkinseed, Lepomis gibbosa, and fantail darter, Etheostoma flabellare, were measured in a laboratory stream. A predation rate experiment and a prey activity experiment were conducted. In the first experiment, each prey type shared experimental chambers with predatory rock bass under all combinations of two depths (shallow and deep) and two cover levels (absent and present). Predation rates after 72 h were greater in deep (35–38 cm) than in shallow (7–10 cm) water for fantail darter and two sizes of central stoneroller, but not for pumpkinseed. Presence of cover (opaque plastic tubes) on the stream bottom had no direct effect on predation rates, which were higher for pumpkinseed and small stoneroller (35–64 mm total length) than for fantail darter and large stoneroller (70–89 mm total length). In the second experiment, diel patterns of small stoneroller activity were monitored under all combinations of two water depths and three levels of predation risk. Small stonerollers were more active during the day and in the absence of rock bass, but were not affected directly by water depth. My results suggest that effects of habitat features (e.g., depth, cover) on predator-prey interactions vary according to the natural history and behavior of particular prey and predators. Future research should integrate habitat-specific responses of prey to predation risk into models that predict the distribution of prey among available habitats.The unit is jointly supported by the U.S. Fish and Wildlife Service, the Virginia Department of Game and Inland Fisheries, the Wildlife Management Institute, and Virginia Polutechnic Institute and State University.