Pleurocerid snails are a common element of the benthos in rivers and streams throughout the Appalachian highlands from Virginia to Georgia on both sides of the continental divide. Yet their dispersal capabilities are so limited today that significant gene frequency differences have been demonstrated over a scale of meters. We obtained mitochondrial cytochrome oxidase c subunit I (COI) sequence data from 3 individual snails sampled from each of 13 populations of pleurocerids representing 3 species—Leptoxis carinata (4 populations), Goniobasis (“Elimia”) catenaria (4 populations), and Goniobasis (“Elimia”) proxima (5 populations). To these data we added previously published COI sequences from 3 other G. proxima populations. Levels of intrapopulation sequence divergence were strikingly high, ranging up to 21.9% within populations and 22.6% between populations within species. A neighbor-joining analysis revealed 3 loose clusters corresponding to the species, but featured numerous extreme outliers. Wilcoxon rank-sum tests returned no evidence that the Continental Divide (as it presently stands) makes any contribution to mean levels of interpopulation sequence divergence, nor that simple geographic distance (regardless of modern drainage) has an effect. We suggest that populations of pleurocerid snails inhabiting the Older Appalachians might date to such an age that all geographic signal in the divergence of our test gene has been lost. We review additional lines of evidence from other genetic studies and from ecology, life history, continental biogeography, and the fossil record that suggest that our pleurocerid populations might be living fossils from the Paleozoic uplift of the Appalachians.

The species composition of lentic communities often shifts along hydroperiod gradients, in part because temporary-habitat specialists replace closely related permanent-habitat specialists. These replacements reflect tradeoffs between traits that facilitate coexistence with permanent-habitat predators and those that prevent desiccation. The evidence for species replacements and the underlying tradeoffs is considerable in North America, but few studies have explored this pattern in other regions. We compared benthic communities in permanent and temporary habitats on the South Island of New Zealand. Ordination across 58 sites showed that community composition was distinctly different between the 2 types of habitats. Assemblages in permanent habitats had >2× the number of species as those in temporary habitats. We found little evidence for temporary-habitat specialists; i.e., species in temporary communities were a nested subset of those in permanent communities. Quantitative sampling at 12 intensively studied sites revealed that chironomids, water bugs, beetles, and crustaceans accounted for 90% of the biomass in temporary, but only 14% of the biomass in permanent habitats, which were dominated by mollusks, annelids, caddisflies, and odonates. Damselflies, dragonflies, caddisflies, and several other large-bodied taxa common in permanent habitats were absent from most temporary habitats. We propose 2 explanations for the absence of species replacements in these groups in the New Zealand habitats that we studied. First, drying is unpredictable within and between years, perhaps precluding the evolution of temporary-habitat specialization. Second, fish predation on benthic invertebrates, a driver for phylogenetic diversification in North America, appears to be comparatively weak in New Zealand. Comparative studies across a range of climates and faunas will be needed to identify the ecological and phylogenetic contexts that favor evolution of generalists vs specialists along permanence gradients.

We evaluated how benthic algal assemblages that vary in composition, richness, and other diversity metrics remove NO₃-N from the water column of a mountain stream. Ecological theory and empirical studies suggest that ecosystem process rates should increase as richness increases because of niche separation or activity of dominant taxa. Accordingly, we predicted that algal assemblages with highest richness would show the highest rates of NO₃-N uptake. To test this prediction, we transplanted 225 rocks representing 3 patch types (green, yellow, and brown) that differed macroscopically in algal composition from a lake outflow stream to a lake inflow stream where an experimental release of ¹⁵N-NO₃ was ongoing. We measured ¹⁵N uptake in each patch type during the stable isotope release. Benthic algal richness varied from 28 genera in the green patch type and 26 genera in the yellow patch type to 22 genera in the brown patch type. Without accounting for differences in chlorophyll a content, NO₃-N uptake (2.1–3.3 × 10⁻⁴/d) was highest in the green patch type, lowest (0.3–0.6 × 10⁻⁴/d) in the yellow patch type, and intermediate (1.2–1.5 × 10⁻⁴/d) in the brown patch type. NO₃-N uptake normalized to chlorophyll a increased in concert with algal richness in the 3 patch types. This result supports the hypothesis that increased assemblage diversity leads to higher rates of community processes. Aside from diversity differences per se, lower rates of NO₃-N uptake in the brown patch type might be the consequence of differences in functional characteristics of the taxa present. Approximately 29% of algal biovolume in the brown patch type consisted of taxa capable of N₂-fixation, a result that suggests that algae in this patch type might be capable of meeting N needs via N₂-fixation rather than via removal from the water column.

Leaf litter inputs and retention play an important role in ecosystem functioning in forested streams. We examined colonization of leaves by microbes (bacteria, fungi, and protozoa) and fauna in Fuirosos, an intermittent forested Mediterranean stream. Black poplar (Populus nigra) and plane (Platanus acerifolia) leaf packs were placed in the stream for 4 mo. We measured the biomasses and calculated the densities of bacteria, fungi, protozoa, meiofauna, and macroinvertebrates to determine their dynamics and potential interactions throughout the colonization process. Colonization was strongly correlated with hydrological variability (defined mainly by water temperature and discharge). The 1^st week of colonization was characterized by hydrological stability and warm water temperatures, and allocation of C from microbial to invertebrate compartments on the leaf packs was rapid. Clumps of fine particulate organic matter (FPOM) were retained by the leaf packs, and enhanced rapid colonization by microfauna and meiofaunal collector-gatherers (ostracods and copepods). After 2 wk, an autumnal flood caused a 20-fold increase in water flow. Higher discharge and lower water temperature caused FPOM-related fauna to drift away from the packs and modified the subsequent colonization sequence. Fungi showed the highest biomass, with similar values to those recorded at the beginning of the experiment. After 70 d of postflood colonization, fungi decreased to nearly 40% of the total C in the leaf packs, whereas invertebrates became more abundant and accounted for 60% of the C. Natural flood occurrence in Mediterranean streams could be a key factor in the colonization and processing of organic matter.

The physical structure of vegetation influences diversity, interactions, movement, and thermoregulation of animals. Vegetation structure might be a good indicator of habitat requirements of generalist predators, such as dragonflies and damselflies (order Odonata), and thereby affect species diversity. Odonates use aquatic and terrestrial habitats during larval and adult life stages, respectively, but the relative importance of vegetation in these habitats is poorly understood. We compared how aquatic and riparian habitat variables affected odonate larvae from 41 sites (each 30 m in shoreline length) on 17 lakes in northern Wisconsin. We used principal components analyses to reduce multiple habitat variables to 2 lake-level axes (lake size and development, lake wetlands and predators), 2 site-level littoral axes (littoral macrophytes, littoral muckiness), and 2 site-level riparian axes (riparian structural complexity, riparian tall wetland plants). Most (61.6%) of the variance in larval species richness occurred at the site level. Density of the most abundant family, Gomphidae, was positively related to riparian tall wetland plants, whereas species richness was positively correlated with abundance of littoral macrophytes (on the basis of multiple linear regression with an information theoretic approach). Surveys in 18 paired littoral microsites in 9 lakes indicated that larvae from the clasper and sprawler behavioral guilds were most abundant in microsites with submerged macrophytes. However, predation risk, assessed by tethering larvae in patches of submerged macrophytes, did not differ between habitats with and without macrophytes. We tested whether shoreline plants affected recruitment from the adult stage by comparing adult odonate behaviors in response to 2 riparian vegetation treatments. Adult damselfly abundance was higher where we placed potted wetland plants than at manicured lawns without tall vegetation. Our results indicate that odonate larvae might be influenced by vegetation structure in both aquatic and riparian habitats and demonstrate how animals with complex life histories link aquatic and terrestrial communities.

We explored N₂ fixation and alkaline phosphatase activity (APA) in periphyton from a N-limited stream ecosystem by coupling measurements of these processes with nutrient diffusion substrata (NDS) experiments. We measured periphyton biomass accumulation (as ash-free dry mass [AFDM] and chlorophyll a [CHLA]), N₂ fixation, and APA to evaluate the relative importance of N₂ fixation as an N source to the periphyton community and APA as an indicator of P deficiency in a seemingly N-limited system. We used fritted-glass-disc NDS and estimated AFDM, CHLA, N₂ fixation, and APA on days 6, 18, and 29 after deployment. Periphyton AFDM steadily increased on NDS over time, but was not influenced by nutrients. CHLA was elevated in the N treatment on days 18 and 29, indicating autotrophic N limitation. Consistent with N limitation, N₂ fixation was high but not different in the control and P treatments and was virtually undetectable on the N treatment. N₂ fixation in control and P treatments was detectable in both light and dark incubations, and dark rates were 4 to 73% of the light rates on days 18 and 29. The average contribution of total N₂ fixation to periphyton in control and P treatments was 0.93 mg N/m² on day 18 and 1.0 mg N/m² on day 29. APA was significantly elevated on the control and was highest in the N treatment despite no apparent P limitation of periphyton biomass accumulation. P enrichment always decreased APA. Measurable N₂ fixation and the change in CHLA suggest that autotrophs were primarily N limited. However, APA observed in controls demonstrated that some portion of the periphyton community was experiencing P deficiency. This result suggests that periphyton metabolism was related to both N and P availability, but that biomass accumulation might have been limited primarily by N. One explanation for these findings is that different organisms, perhaps occupying different trophic positions within the community, might have been limited by different elements.

Ecological responses to dam construction are poorly understood, especially for downstream benthic algal communities. We examined the responses of benthic algal communities in downstream reaches of a tributary of the Xiangxi River, China, to the construction of a small run-of-river dam. From February 2003 to August 2006, benthic algae, chemical factors, and habitat characteristics were monitored upstream and downstream of the dam site. This period spanned 6 mo before dam construction and 37 mo after dam construction. Benthic algal sampling yielded 199 taxa in 59 genera that belonged to Bacillariophyta, Chlorophyta, and Cyanophyta. Some physical factors (flow velocity, water depth, and channel width) and 3 algal metrics (diatom species richness, Margalef diversity, and % erect individuals) were significantly affected by the dam construction, whereas chemical factors (e.g., NH₄-N, total N, SiO₂) were not. Nonmetric multidimensional scaling (NMS) ordinations showed that overall algal assemblage structure downstream of the dam sites was similar to that of upstream control sites before dam construction and for 1 year after dam construction (p > 0.05). However, sites belonging to upstream and downstream reaches were well separated on NMS axis 1 during the 2^nd and 3^rd years after dam construction. Our results suggest that impacts of dam construction on benthic algal communities took 2 to 3 y to emerge. Further development of a complete set of indicators is needed to address the impact of small-dam construction. Our observations underscore the need for additional studies that quantify ecological responses to dam construction over longer time spans.

Channel reconfiguration is a popular but controversial approach to river restoration, and ecological responses to channel reconfiguration have not been rigorously assessed. We compared physical-habitat variables, taxonomic and functional-trait diversities, taxonomic composition, and functional-trait abundances between 24 pairs of upstream (control) and downstream reconfigured (restored) reaches in 3 catchment land uses (urban, agricultural, rural) across the North Carolina Piedmont. We asked how environmental filters and functional species traits might provide insight to biological responses to restoration. Taxonomic and functional-trait differences between control and restored reaches suggest that restoration affected aquatic assemblages only in agricultural and rural catchments. Our results highlight 2 important aspects of channel reconfiguration as a restoration practice. First, responses to restoration differ between agricultural/rural and urban catchments, possibly because of modified hydrological regimes caused by urbanization. Second, we find evidence that channel reconfiguration disturbs food and habitat resources in stream ecosystems. Taxa sensitive to disturbance were characteristic of control reaches, whereas insensitive taxa were characteristic of restored reaches. Abundances of traits related to reproduction (voltinism, development, synchronization of emergence, adult life span), mobility (occurrence in drift, maximum crawling rate, swimming ability), and use of resources (trophic and habitat preferences) differed significantly between control and recently restored reaches. Our results suggest that taxa in restored habitats are environmentally selected for traits favored in disturbed environments. Our work suggests how functional-trait approaches could benefit the practice of river restoration when used to target restoration activities and to develop informed expectations regarding recovery following restoration activities.

We experimentally manipulated mussel community structure and observed mussel burrowing behavior in mesocosms held in a greenhouse. Vertical positions, vertical movements, and horizontal movements of Actinonaias ligamentina, Amblema plicata, Fusconaia flava, and Obliquaria reflexa were recorded during five 11-d trials. Community structure was manipulated by constructing communities with 11 different diversity treatments crossed with 3 different density treatments. Vertical positions, vertical movements, and horizontal movements of mussels differed significantly among diversity treatments, and vertical movements differed among density treatments. Differences among diversity treatments were caused by differences in species composition because the burrowing activity of mussels in multispecies communities could be predicted additively from single-species communities. The species used in our study vary in body size, but differences among species were still significant after accounting for body length. We think that differences in species burrowing behavior might be a result of niche partitioning of vertical space, might be a result of differing effects of temperature between species, or might be related to mechanisms to avoid dislodgement during high flows. The burrowing behavior of freshwater mussels has implications for mussel sampling protocols, the sensitivity of mussels to zebra mussel attachment, and how mussels influence benthic ecosystems.

Capture and quantitative analysis of the motion of organisms is a powerful tool that can be used in diverse biological fields including physiology, behavior, kinematics, and ecology. A number of high-end commercial motion capture and analysis systems that offer a wide array of features and image capture and analysis capabilities are available. However, few, if any, such systems are low cost and could be used for projects with small budgets or by researchers interested in collecting pilot data before upgrading to an expensive motion capture and analysis system. Our paper describes a low-cost (<$US1000, not including the cost of the computer) motion capture and analysis system that simultaneously captures live video from 5 digital video cameras (Unibrain Fire-i FireWire [IEEE 1394]) using standard security camera software (SecuritySpy 1.3.1). The video analyses are carried out using a combination of standard spreadsheet software (Microsoft Excel) and a freeware image-analysis program (NIH Image J), with one of the available particle-tracking plugins. Tests using New Zealand mudsnails (Potamopyrgus antipodarum) demonstrated that the system could record and accurately track the movement of small (4 mm) targets. Recommendations for designing similar project-specific systems are provided.

Anthropogenically increased sediment loads are one of the most pervasive pollution pressures on surface waters and carry major ecological implications for biota. We conducted an experiment in artificial streams to quantify the response of 4 common macroinvertebrate taxa (Rithrogena semicolorata, Baetis rhodani, Asellus aquaticus, and Glossosoma boltoni) and benthic algae to doses of inorganic sediment that differed in maximum concentration and exposure time. Relatively minor disturbances (maximum concentration 250 mg/L) decreased % organic content of epilithon significantly after the first 24 h of exposure. However, algal biomass (measured as chlorophyll a) was reduced significantly only in the most prolonged exposure time (7 d). Epilithic nutrient stoichiometry (as indicated by molar organic C:N ratios) was not affected by sediment addition. Invertebrate drift was affected strongly by exposure time, and all taxa exhibited statistically significant responses within the first day under all concentrations. However, concentration interacted significantly with exposure time in its effects on the drift of both mayfly species. Macroinvertebrate survival was high or complete for all treatments. Therefore, the differing relative and interactive effects of concentration and exposure time suggest that the common prediction of severity of effect based on a constant relationship between these factors can produce considerable overestimates or underestimates of environmental risk. Biological effects derived from increased sediment loads should be assessed on the basis of their overall dose and on the basis of the specific relationship between the concentration and exposure time that make up the dose.

We sampled macroinvertebrate assemblages in the littoral benthos and on the surface of snags in the Upper Mississippi, Missouri, and Ohio rivers. Snag assemblages differed from benthic assemblages. Tubificids, Caenis, Tanytarsus, Cryptochironomus, Limnodrilus, and Chironomini were consistently more abundant in the benthos; Nais, Cricotopus/Orthocladius, Nematoda, and Rheotanytarsus were consistently more abundant on snags. Filterers were more abundant and gatherers were less abundant on snags than in the benthos. Snag assemblages differed among rivers and among reaches within rivers. Variation among reaches was the result of direct and indirect effects of high-dam reservoir impoundments (upper vs lower Missouri River) and low-dam impoundment for navigation (impounded vs free-flowing Upper Mississippi River). The maximum relative abundance of filterers in the lower Missouri River, which was the only long unregulated reach we studied, was related to particulate organic C and sestonic chlorophyll a concentration, which increased with distance downriver from the lowest main-stem dam. Snag diameter, snag-surface characteristics, and water depth did not affect the composition of snag assemblages, but the dominant taxa on snags in fast-velocity locations were different from the dominant taxa on snags in slow-velocity locations. Relatively few taxa showed strong longitudinal patterns in relative abundance within a reach, and only on the Missouri River. We hypothesize that the many navigation dams on the Ohio and Upper Mississippi rivers suppress the development of environmental gradients and inhibit the formation of longitudinal patterns in macroinvertebrate assemblages. Snag assemblages were dominated by a few taxa (genus-level and higher), a characteristic that might constrain the sensitivity of the assemblages to some human impacts. Sampling snag assemblages has potential for great-river bioassessment, but further research is necessary on sampling methods and sensitivity of assemblages to stressors.

Despite the prevalence and importance of intermittent streams, few studies have examined their use by crayfishes. We documented persistence in an intermittent stream and use of the hyporheic zone by 2 imperiled crayfishes, Orconectes williamsi and Orconectes meeki meeki, upon stream drying. During 2005 to 2007, we monitored summer flows and crayfish densities in 10 riffles in a Missouri (US) Ozark stream to document stream drying and crayfish persistence. Stream drying variables were riffle wetted area (m²) and current velocity (m/s). Crayfish density estimates were obtained with a quadrat sampler. We sampled monthly (May–August 2006) to examine crayfish response to decreased flows, and excavated dry quadrat samples (to 30 cm depth) after surface flows ceased. Over 2 periods during summer 2007, we used baited traps in the stream and a downstream reservoir where the stream terminates to examine whether crayfish migrated from the stream to permanent water in response to drying. Riffles dried significantly by July, few had surface water present by August, and all were rewetted by the following June. Annual June densities of O. williamsi remained stable throughout the study, whereas densities of O. m. meeki were lower in 2007 than 2005. Both species burrowed to the hyporheic zone during drying, and crayfish densities were similar to those estimated in riffles before drying. We found no evidence that either species migrated to permanent water in the reservoir during drying. Use by crayfish of the hyporheic zone during drying and interannual persistence in intermittent streams suggests that hyporheic habitats are important for conservation of these crayfishes. Our study contributes to the increasing body of knowledge that indicates the importance of intermittent streams for conservation of freshwater biodiversity.

The construction of salmon redds represents a localized but intense disturbance to benthic substrate and associated flora and fauna. Pink salmon (Oncorhynchus gorbuscha) have a fixed 2-y life cycle. Thus, their spawning run in Wolf Point Creek, a 1^st-order coastal stream in southeast Alaska, alternates between high-density (odd years) and low-density (even years) returns. During July and August 1996 and 1998, counts of returning fish were low (<2000 fish) with little evidence of streambed disturbance by redd construction, whereas in 1997, counts of returning fish were >10,000 fish, and streambed disturbance was extensive. Coarse particulate organic matter and macroinvertebrate density and taxonomic richness were significantly lower in the main channel in 1997 than in 1996 or 1998. Macroinvertebrate densities and taxonomic richness were similar in all years in areas unsuitable for salmon redds (refugium habitat: margins, boulders, shallows). Macroinvertebrate drift density increased during the 1997 spawning run. Several taxa demonstrated circadian drift behavior, but the peak in redd construction activity coincided with an absence of nocturnal peaks for most macroinvertebrate taxa. Simulation of the abrasion and settling of material excavated during redd construction caused a modest but significant increase in total macroinvertebrate drift density compared with unmanipulated reference sites. Drift density declined after the cessation of experimental disturbance, a result suggesting that entombment and mortality associated with abrasion and settling was high and indicating that excavation, rather than abrasion and settling, was the most important process causing overall increase in drift density during redd construction. River habitat structure is a critical feature mediating the effects of disturbance associated with spawning salmon. Redd construction displaces macroinvertebrates and opens habitable space. Thus, it is an important determinant of community structure and function and could influence the course of community succession.

Shredders appear to be scarce in many tropical streams, but few data are available about their abundance or role in litter breakdown in these systems. Shredder species richness, abundance, and biomass were investigated in 10 small streams (5 shaded, 5 unshaded) in Hong Kong as a step toward understanding the role of shredders in tropical Asian streams. In addition, breakdown of Liquidambar formosana (Hamamelidaceae) leaves was investigated to determine if breakdown rates changed in response to shredder species richness, abundance, or biomass in these 10 streams. Shredders were scarce in terms of species richness (a total of 6 obligate shredders and 2 facultative shredders) and abundance (mean = 2.0%, range = 0–7.7% of total macroinvertebrate abundance). Obligate shredder biomass was not high across the 10 streams (mean = 13% of total biomass), and it was variable in shaded streams (0.6–38.7%); all high values were attributable to the presence of a few large individuals (<0.2% of total abundance). Relative abundance and biomass of obligate shredders were higher in shaded than in unshaded streams (abundance: 1.9% vs 0.1%; biomass: 22.3% vs 4.3%). Shading did not affect the densities or relative abundances of functional feeding groups (FFGs) other than shredders. Litter breakdown rates did not vary in response to species richness, abundance, or biomass of shredders among the 10 streams. However, when the 2 moderately nutrient-enriched streams were excluded, breakdown rates were positively related to obligate shredder densities, indicating a possible contribution of shredders to litter breakdown. The potential importance of microbes was indicated by a relationship between breakdown rates and stream PO₄ concentrations.

Many freshwater ecosystems receive allochthonous resource subsidies from adjacent terrestrial environments. In eastern North American forests, geographic broods of periodical cicadas emerge every 13 to 17 y to breed, and local abundances can sometimes be >300 individuals/m². Most individuals avoid predation, senesce after breeding, and become a resource pulse for forest ecosystems; some cicada carcasses enter freshwater ecosystems where they represent a detrital resource pulse. Here, we present a 2-part study in which we examined the deposition of cicada detritus into woodland ponds and low-order streams in southwestern Ohio during the emergence of Brood X periodical cicadas. We compared the deposition of nutrients associated with periodical cicada detritus and terrestrial leaf litter into small woodland ponds and low-order streams. We used a laboratory experiment to compare patterns of decomposition and nutrient release of adult periodical cicada carcasses and sycamore leaf litter. Input of periodical cicada detritus to woodland streams and ponds was a function of local cicada emergence densities. Organic C loading to woodland aquatic ecosystems from cicada detritus was substantially less than that from terrestrial leaf litter; however, the higher mass-specific N and P content of cicada material made cicada detritus a relatively important nutrient input. N and P deposited in cicada detritus represented 0.2 to 61% of the N and 0.3 to 50% of the P deposited into woodland aquatic ecosystems via terrestrial leaf litter. Decomposition experiments indicated that cicada detritus was of much higher quality than was sycamore leaf litter; female and male cicada carcasses lost mass at significantly faster rates than sycamore leaves (female k = −0.05/d, male k = −0.04/d, sycamore leaf k = −0.002/d). Release rates of C, N, and P from cicada carcasses were 4, 39, and 150× greater, respectively, than release rates from sycamore leaves. Our study indicates that periodical cicada detritus can represent a substantial allochthonous resource pulse to forested aquatic ecosystems and that cicada detritus is of substantially higher quality than is terrestrial leaf litter. These results suggest that deposition and decomposition of periodical cicada detritus can affect the productivity and dynamics of woodland aquatic ecosystems and that the role of animal-derived resource pulses to ecosystems requires further exploration.

Skutzia epleri sp. n. from USA, S. inthanonensis sp. n. from Thailand, and S. quetzali sp. n. from Panama and Mexico are described and figured as male imagines, and S. gaianii Andersen is recorded from Trinidad and Tobago. The genus now consists of 6 species. In addition to the species mentioned above, S. inopinata Reiss from Canada and S. bahiensis Reiss from Brazil are included. Skutzia is placed in the subtribe Zavreliina of the tribe Tanytarsini, but because the immatures are not known, this placement must be regarded as tentative. The distribution of the genus, previously known only from the Nearctic and the Neotropical regions, is expanded to include the Oriental region, indicating a Beringian connection. An emended diagnosis and a key to the males of Skutzia are provided.

Densely spawning salmon (Oncorhynchus spp.) affect macroinvertebrates negatively through redd construction and positively through nutrients released during spawning and carcass decomposition. We investigated the long-term characteristics of this interaction by measuring density, biomass, and C and N sources in benthic macroinvertebrates over 1 y. Total macroinvertebrate community biomass decreased during spawning and redd construction. However, the percentage of macroinvertebrate biomass derived from salmon increased. The highest percentage (56%) and biomass (2.71 g/m²) of salmon-derived tissue in the macroinvertebrate community occurred 3 mo after spawning. Shredders accumulated the most salmon-derived biomass per individual; however, collector-filterers, scrapers, and predators accumulated the most salmon-derived biomass at the population level, a result that suggests multiple pathways of salmon nutrient acquisition. Salmon-derived macroinvertebrate biomass was never <22% of macroinvertebrate community biomass in the spawning reach, but 6 mo after spawning, no clear density or biomass differences were found between reaches with and without salmon. This pattern held true at all scales examined, from whole community to functional feeding group to individual taxa in prespawning samples from both years. These results suggest that increased macroinvertebrate production from the nutrient and energy subsidy from salmon was restricted to the recovery period following the disturbance of redd construction and might have been obscured by emergence and transfer to higher trophic levels.

Demand for water is increasing in many parts of the world, but removal of significant volumes of water from streams for irrigation, industry, and municipal supply has the potential to affect aquatic biota. Protecting the ecological value of streams is of increasing interest to water managers and the public. However, few experimental studies address the impacts of flow reduction on stream habitat condition and biota. We reduced discharge by 80 to 95% in 3 small, stony-bottomed streams (<4 m width), using weirs and diversion channels/pipes and quantified diel patterns of density of naturally drifting macroinvertebrates before and during a 2-mo period of continuous reduced flow. We also measured artificially induced passive invertebrate drift distance in control and impact reaches to determine the impact of flow reduction on drift distance. We measured the head capsule width of common drifting taxa to determine if larval size interacted with discharge to influence drift distance. Drift density of several taxa increased dramatically in the days following flow reduction, but drift returned to prereduction levels for the remainder of the reduced-flow period. Drift density of some taxa was elevated throughout the reduced-flow period. Few individuals drifted >1 or 2 m under reduced-flow conditions. Larval size influenced drift distance only for the mayfly Coloburiscus humeralis. We concluded that some taxa respond to the stress of reduced flow by drifting. Whether animals actively entered the drift or increased drift density was caused by increased benthic activity (i.e., invertebrates moving more) that, in turn, initiated increased passive drift entry, is unclear. Reduced discharge limits the distance an individual can travel in the water column. In small, shallow streams, drifting is unlikely to be a viable strategy for rapid escape of unfavorable conditions as a result of reduced discharge through flow abstractions.

Several species of amphidromous shrimp play important roles in the food webs of Neotropical freshwater stream ecosystems. We quantified the timing and magnitude of the upstream migration of 3 genera of amphidromous shrimp on the Rio Espiritu Santo in northeastern Puerto Rico. We then used multiple regression analyses to identify potential environmental factors that affected our observed migration rates. We also conducted artificial stream experiments to assess which potential physical and chemical factors affect migratory behavior. Shrimp post-larvae migration patterns and the environmental factors affecting those patterns were species specific. The migration rates of Xiphocaris elongata and Macrobrachium spp. were more affected by environmental conditions than were those of Atya spp. The migration rates of X. elongata and Macrobrachium spp. were negatively affected by high stream discharge. Atya spp. made up most of the total post-larvae migration; however, Macrobrachium spp. migration was highly seasonal and made up a large proportion of the total shrimp migration in late summer. Migration rates of all post-larvae were uniformly distributed throughout the night. Experimental increases in turbidity had a negative effect on the migratory behavior of Atya spp. and X. elongata post-larvae, as did the presence of fish predators. Our results confirm evolutionary hypotheses regarding migration cues and dynamics of diadromous species. Flow variables provide reliable cues for upstream migration pathways and allow colonization of island habitats, whereas predator-related cues (fish and light) are recognized and avoided, a pattern that suggests adaptation to predation.

Chironomidae spatial distribution was investigated at 63 near-pristine sites in 22 catchments of the Iberian Mediterranean coast. We used partial redundancy analysis to study Chironomidae community responses to a number of environmental factors acting at several spatial scales. The percentage of variation explained by local factors (23.3%) was higher than that explained by geographical (8.5%) or regional factors (8%). Catchment area, longitude, pH, % siliceous rocks in the catchment, and altitude were the best predictors of Chironomidae assemblages. We used a k-means cluster analysis to classified sites into 3 major groups based on Chironomidae assemblages. These groups were explained mainly by longitudinal zonation and geographical position, and were defined as 1) siliceous headwater streams, 2) mid-altitude streams with small catchment areas, and 3) medium-sized calcareous streams. Distinct species assemblages with associated indicator taxa were established for each stream category using IndVal analysis. Species responses to previously identified key environmental variables were determined, and optima and tolerances were established by weighted average regression. Distinct ecological requirements were observed among genera and among species of the same genus. Some genera were restricted to headwater systems (e.g., Diamesa), whereas others (e.g., Eukiefferiella) had wider ecological preferences but with distinct distributions among congenerics. In the present period of climate change, optima and tolerances of species might be a useful tool to predict responses of different species to changes in significant environmental variables, such as temperature and hydrology.