Investigations of predator–prey dynamics have largely focused on quantifying predation rates, yet achieving an appropriate sample to quantify predation is difficult when prey populations are small and individuals are rare. Moreover, quantifying rates of predation does not necessarily provide solutions for protecting threatened populations from predation. We used predator abundance and fine-scale predator–prey spatial overlap to identify trends in predation risk from cormorants, Phalacrocorax, to adults of the endangered Macquarie Perch, Macquaria australasica, in Cotter Reservoir, Australia. We made observations of cormorants at Cotter Reservoir between February 2008 and July 2009 to estimate abundance and spatial distribution. We used radiotelemetry to locate adult Macquarie Perch. Cormorant abundance was highest in spring and summer. Increased cormorant abundance corresponded with an increase in the fine-scale overlap of the distributions of Macquarie Perch and cormorant within the reservoir. Overlap was highest in the upstream section of the reservoir, which is characterized by shallow water (<5 m depth). Increased overlap corresponded with congregation of Macquarie Perch in the upper reservoir and movement toward the source river for spawning. Our results provide valuable insight into when and where predation is most likely to occur, thereby allowing conservation efforts to be tailored to protect this threatened fish population effectively.

Whole-ecosystem metabolism is an important indicator of the role of organic matter, C cycling, and trophic structure in rivers. Ecosystem metabolism is well studied in small streams, but less is known about metabolism in large rivers. We estimated daily whole-ecosystem metabolism over 2 y for 1 site each at the Mississippi and Chattahoochee Rivers in the USA to understand factors influencing temporal patterns of ecosystem metabolism. We estimated rates of gross primary production (GPP), community respiration (CR), and net ecosystem production (NEP) with a curve-fitting approach with publicly available discharge (Q), dissolved O₂, temperature, and photosynthetically active radiation (PAR) data. Models were run for week-long blocks, and power analyses suggested that rates should be established at least once for each 10-wk period throughout the year to characterize annual rates of metabolism accurately in these 2 rivers. We analyzed weekly rates averaged over 10-wk periods with Spearman rank correlation to identify potential drivers and with path analyses to identify interactions among variables driving GPP, CR, and NEP. Both rivers had an overall negative NEP, and the Mississippi River had stronger seasonal trends. In the Mississippi River, CR was strongly positively correlated with Q, which suggests variation in seasonal availability of allochthonous C. In the Chattahoochee, CR was most strongly positively correlated with GPP, whereas GPP was negatively correlated with Q, which suggests that autochthonous processes and water-column light attenuation played important roles in C dynamics. Our results suggest that these large rivers were net heterotrophic at annual time scales but autotrophy can be important seasonally.

The periphyton of stony hard substrates in the littoral zone of lakes is inhabited by an abundant and diverse algae and meiofauna assemblage that is regulated by grazing. The objective of our study was to examine the effect of macroinvertebrate grazers on periphytic algae and meiofaunal organisms at different depths in the littoral zone of Lake Erken (Sweden). To this end, a 2-factorial field experiment was carried out in which macrofaunal access to the periphyton was manipulated at 3 different water depths (30, 70, and 200 cm). Grazing effects on algal biomass varied among depths and were highest in both deeper zones. Compared to algal biomass, the abundance of meiofaunal organisms was less affected by grazing because macrograzers significantly reduced meiofauna only at the 200-cm depth. The organism mainly responsible for the depth-dependent differences in grazer effects was the snail Theodoxus fluviatilis, which dominated macrofaunal assemblage at depths where grazing effects were the strongest (70 and 200 cm). The abundance of T. fluviatilis was positively correlated with the proportions of reduced algal biomass and reduced meiofaunal abundance. Meiofaunal groups and individual nematode species responded differently to grazing, so our results further revealed that grazing macroinvertebrates affected the composition of the meiofaunal assemblage. However, meiofaunal and nematode assemblages differed more across depths than across grazing treatments, suggesting that other depth-related factors (e.g., hydrodynamics or light) also were important for structuring periphytic meiofaunal assemblages.

Evaluators of aquatic systems often use benthic macroinvertebrates because they are central components in the food chain and useful for water-quality assessments and management decisions. More than 44 sampling devices are commonly used to collect benthic macroinvertebrates. Bitter Lake National Wildlife Refuge in New Mexico, USA, is a unique habitat with a complex of aquatic sinkholes. Morphometry, water chemistry, and biology differ vastly among sinkholes, creating challenges when deciding how to sample appropriately for benthic macroinvertebrates. We evaluated 5 sampling methods commonly used in lentic habitats: aquatic net (epibenthic sled), artificial substrate (Hester–Dendy multiplate [H-D] sampler), light trap, grab (Ponar grab), and suction sampler (pump sampler). We compared total number of taxa, % taxa detected, and total number of individuals collected among the 5 methods with a mixed-model incomplete block analysis of variance. The light trap caught the most taxa and yielded the highest % taxa detected. It also caught the most specimens. H-D samplers and Ponar grabs added taxa that were not commonly found in light traps, especially gastropods. We were unable to deploy the pump sampler and the epibenthic sled in all sinkholes, and they contributed little additional information. We recommend combined use of light traps, H-D samplers, and a Ponar grab to obtain a good representation of benthic invertebrates over a wide variety of environmental conditions in sinkholes and other lentic habitats. Together these methods detected 84 to 100% of taxa in each sinkhole.

Nutrient enrichment affects bacteria and fungi associated with detritus, but little is known about how biota associated with different size fractions of organic matter respond to nutrients. Bacteria dominate on fine (<1 mm) and fungi dominate on coarse (>1 mm) fractions, which are used by different groups of detritivores. We measured the effect of experimental nutrient enrichment on fungal and bacterial biomass, microbial respiration, and detrital nutrient content on benthic fine particulate organic matter (FPOM) and coarse particulate organic matter (CPOM). We collected FPOM and CPOM from 1 reference and 1 enriched stream. CPOM substrates consisted of 2 litter types with differing initial C:nutrient ratios (Acer rubrum L. and Rhododendron maximum L.). Fungal and bacterial biomass, respiration, and detrital nutrient content changed with nutrient enrichment, and effects were greater on CPOM than on FPOM. Fungal biomass dominated on CPOM (∼99% total microbial biomass), whereas bacterial biomass dominated on FPOM (∼95% total microbial biomass). These contributions were unchanged by nutrient enrichment. Bacterial and fungal biomass increased more on CPOM than FPOM. Respiration increased more on CPOM (up to 300% increase) than FPOM (∼50% increase), indicating important C-loss pathways from these resources. Microbial biomass and detrital nutrient content were positively related. Greater changes in nutrient content were observed on CPOM than on FPOM, and changes in detrital C:P were greater than changes in detrital C:N. Threshold elemental ratios analyses indicated that enrichment may reduce P limitation for shredders and exacerbate C limitation for collector-gatherers. Changes in CPOM-dominated pathways are critical in predicting shifts in detrital resource quality and C flow that may result from nutrient enrichment of detritus-based systems.

Presence/absence sampling designs are commonly used approaches for documenting the occurrence of benthic invertebrates, but these methods often provide biased indices of occupancy or abundance. Unionids are particularly susceptible to bias associated with nondetection because of their generally low abundance and burrowing behavior. We present a case study in which we used an occupancy-modeling approach that incorporates estimation of detection probability to assess the occurrence of unionids at 39 locations along a 119-km reach of Flint River, Georgia. We fitted models relating site- and reach-level variables to detection and occupancy for 3 species of conservation concern and contrasted inferences drawn between models accounting for variable imperfect detection and models assuming constant imperfect detection. We collected 20 unionid species among 39 sites. Among species, detection probabilities averaged 0.25 and ranged from 0.01 to 0.69, and estimated occupancy averaged 0.56 and ranged from 0.03 to 1.00. Estimated occupancy across all species was, on average, 25.78% greater than naïve occupancy (i.e., proportion of sites without accounting for incomplete detection). Detection probabilities varied by species, time, macrohabitat, and searcher experience. Inferences regarding factors affecting species occupancy differed among models contrasting detection as variable or constant but imperfect. The occupancy-modeling approach was a useful and efficient method to assess the distribution and habitat relationships of unionids in the lower Flint River. We think that detection probability is an underused but necessary parameter that should be evaluated during sampling to provide a measure of confidence in benthic invertebrate data and to account for potential sources of bias.

Salamanders are abundant consumers in many temperate streams and may be important recyclers of biologically essential nutrients, but their ecological role is poorly understood. The ecological significance of nutrient recycling by salamanders may vary spatially and seasonally because of their potentially patchy distribution in streams and the dynamic nature of stream hydrology and other nutrient fluxes. We examined the spatial and seasonal variation of salamander-driven nutrient recycling in 3 headwater streams in the southern Appalachian Mountains. We quantified the aggregate areal excretion rates of N (NH₄ -N) for the larvae of the 2 most abundant salamander species in these steams before and after leaf fall to examine spatial and seasonal variation in the supply of nutrients from salamanders. We used short-term nutrient additions in each stream to examine temporal heterogeneity in the ecosystem demand for NH₄ -N. Before leaf fall, salamanders were capable of meeting ∼10% of the ecosystem demand for NH₄ -N and could turn over the ambient nutrient pool in ∼3 km. The significance of this contribution declined to ∼3% after leaf fall and the turnover length increased 7×. The ecological significance of salamander nutrient excretion varied by as much as 17× within streams and was as high as 30% of the nutrient demand in some stream sections, a result suggesting that salamanders may create biogeochemical hotspots in these nutrient-limited ecosystems. Thus, salamanders appear to be capable of contributing substantially to stream nutrient cycles through the excretion of limiting nutrients and may be underappreciated members of headwater stream ecosystems, particularly at small spatial scales. However, this contribution varied substantially seasonally and spatially.

The abundance and distribution of aquatic mesograzers may be regulated by both top-down (i.e., predator-mediated) and bottom-up (i.e., producer-mediated) effects. Under predation by fish, these herbivores may experience differential survivorship among different types of resource patches. Prey may attempt to maximize fitness by integrating information on predation risk and patch quality into foraging decisions. The freshwater amphipod Hyalella azteca occupies mats of the toxic cyanobacterium Lyngbya wollei and the green alga Rhizoclonium hieroglyphicum in lotic water bodies throughout the southeastern USA. We tested the hypotheses that Lyngbya is an effective refuge from Bluegill Sunfish (Lepomis macrochirus) predation and that predator cues modify habitat selection by amphipods. In no-choice assays, amphipods exposed to fish predation showed higher survivorship on Lyngbya than on Rhizoclonium. In choice assays, we observed greater proportions of amphipods on Lyngbya in tanks containing either predators or waterborne predator cues compared to control tanks containing only freshwater. These results suggest that Lyngbya is an effective refuge from predation for amphipods. Furthermore, predatory fish may indirectly influence the relative abundance of algae and cyanobacteria by reducing amphipod abundance on highly palatable species and restricting these mesograzers to less palatable species.

Human activity has significantly increased dissolved inorganic N (DIN) availability and has modified the relative proportion of NO₃⁻ and NH₄ species in many streams. Understanding the relationship between DIN concentration and DIN uptake is crucial to predicting how streams will respond to increased DIN loading. Nonetheless, this relationship remains unclear because of the complex interactions governing DIN uptake. We aimed to evaluate how biofilms from 2 streams differing in background DIN concentration would respond to increases in availability and changes in speciation (NO₃⁻ or NH₄ ) of DIN. We measured DIN uptake by biofilms in artificial flumes in each stream, using separate ¹⁵N-NO₃⁻ and ¹⁵N-NH₄ additions in a graded series of increasing DIN concentrations. The ambient uptake rate (U) was higher for NO₃⁻ than for NH₄ in both streams, but only U for NH₄ differed between streams. Uptake efficiency (U_N-specific) at ambient conditions was higher in the low-N than in the high-N stream for both DIN species. A Michaelis–Menten model of uptake kinetics best fit the relationship between uptake and concentration in the case of NH₄ (for both streams) but not in the case of NO₃⁻ (neither stream). Moreover, saturation of NH₄ uptake occurred at lower rates (lower U_max) in the low-N than in the high-N stream, but affinity for NH₄ was higher (lower K_s) in the low-N stream. Together, these results indicate that the response capacity of biofilm communities to short-term increases of DIN concentration is determined primarily by the ambient DIN concentrations under which they develop. Our study also shows that DIN uptake by benthic biofilms varies with DIN availability and with DIN speciation, which often is modified by human activities.

Native freshwater mussels are a diverse but imperiled fauna and may be especially sensitive to increasing water temperatures because many species already may be living near their upper thermal limits. We tested the hypothesis that elevated water temperatures (20, 25, 30, and 35°C) adversely affected the survival and physiology of 2-mo-old juvenile mussels (Lampsilis abrupta, Lampsilis siliquoidea, and Megalonaias nervosa) in 28-d laboratory experiments. The 28-d LT50s (lethal temperature affecting 50% of the population) ranged from 25.3 to 30.3°C across species, and were lowest for L. abrupta and L. siliquoidea. Heart rate of L. siliquoidea was not affected by temperature, but heart rate declined at higher temperatures in L. abrupta and M. nervosa. However, for both of these species, heart rate also declined steadily during the experiment and a strong temperature × time interaction was detected. Juvenile growth was low for all species in all treatments and did not respond directly to temperature, but growth of some species responded to a temperature × time interaction. Responses to thermal stress differed among species, but potential laboratory artifacts may limit applicability of these results to real-world situations. Environmentally relevant estimates of upper thermal tolerances in native mussels are urgently needed to assess the extent of assemblage changes that can be expected in response to global climate change.

Research on how N is retained and removed from stream networks has focused on microbial metabolic pathways, such as denitrification. An alternative pathway for N to escape streams is in the form of emerging aquatic insects, and unlike denitrification, previous studies suggest that this pathway may be stimulated by increased availability of P. We tested the hypothesis that the flux of N exported from streams through insect emergence increases relative to flux through denitrification with increasing levels of stream P. We measured emergence and denitrification rates at 7 lowland stream sites in Costa Rica that differ in dissolved P levels and substrate characteristics. Emergence N flux ranged from 2.0 to 16.3% of measured denitrification rates and was not related to any measured physical or chemical variables. Sediment redox conditions were the best predictor of denitrification rates. Our emergence results suggest that most invertebrate biomass production in these streams is consumed by in-stream predators, keeping this N in the stream ecosystem. Nevertheless, our findings indicate that in streams with low denitrification rates, emergence should be considered as an additional pathway of N removal from stream ecosystems.

River landscapes are increasingly viewed as a collection of nested geomorphic features, the hydrological effects of which juxtapose to create a mosaic of aquatic habitat conditions. We examined how the combined hydrological influences of stream reaches and gravel bars affect the composition of hyporheic invertebrate assemblages along the longitudinal and vertical dimensions of river landscapes. We worked in 12 braided-river valley segments of tributaries to the Rhône River, France. Valley segments were bounded downstream by geological knickpoints so that bedform-induced exchange flows beneath gravel bars and riffles were predictably embedded in exchange flows occurring at the valley-segment scale. In upstream reaches (UR) and downstream reaches (DR) of each valley segment, we collected invertebrates at the heads and tails of gravel bars in the hyporheic zone and at the upstream and downstream ends of riffles in surface channels adjacent to the bars. Patterns of vertical hydraulic gradient and specific conductance and the resulting spatial heterogeneity of temperature, dissolved O₂, and particulate organic C suggested that DR were points of flow convergence and water mixing. Specific conductance increased and temperature decreased more steeply along gravel bars in DR, indicating that water from long hyporheic flow paths or lateral aquifers was discharging at the tails of bars in DR. Density hotspots for insect larvae corresponded to hyporheic patches at the heads of bars in DR, which received the highest organic matter inputs from localized downwelling of surface water and were not affected by inputs of cold water from hyporheic flow paths or lateral aquifers. Density of epigean taxa at the tails of bars decreased more steeply with depth in DR than in UR, and density of hypogean taxa increased more steeply. Viewing local hyporheic assemblages as the outcome of a series of environmental filters operating over multiple exchange flows induced by nested geomorphic features provides a general framework that may foster our understanding of biodiversity patterns in river landscapes.

Freshwater mussels perform critical ecosystem functions and provide many valuable ecological services. However, anthropogenic effects have severely decreased mussel diversity and abundance at both local and regional scales. Understanding how human disturbances, particularly landuse change, and fish assemblages are related to mussel assemblages is essential for effective conservation and restoration. We used Random Forests (RF) regressions, a data-mining technique, to examine how mussel species richness, total abundance, and abundances of individual species were related to land use at different spatial scales and to fish species richness and abundance in east central Illinois, USA. Mussel richness increased with % wetlands, % open water, % grassland in the riparian zone, and total fish abundance; decreased with % urban land in the riparian zone; but responded poorly to fish species richness and fish Index of Biotic Integrity (IBI) scores. Total mussel abundance mainly increased with total fish abundance and decreased with both % urban land in the riparian zone and road density. Of 8 mussel species modeled, the abundances of 3 were strongly related to total fish abundance or fish-host abundance, 3 with both fish abundance and land use, and 2 with land use and other physical variables. These findings can help researchers and resource managers explain the spatial variation of mussel assemblages and choose abiotic and biotic variables to monitor or manipulate for maintaining or restoring overall mussel diversity or the populations of individual species.

Terrestrial sources of dissolved organic C (DOC) provide energy for stream microbial heterotrophs. Hydrologic conditions alter flow paths to the stream and influence terrestrial source quantity and quality. We used bioreactors to measure biodegradable DOC (BDOC) in water from soils, shallow wells, and spring seeps under baseflow conditions, overland flow during storms, and a stream during base flow and storm flow. Stream DOC concentrations ranged from 0.7 to 15.5 mg C/L and total BDOC ranged from 0.1 to 8.7 mg C/L. Under baseflow conditions, DOC was generally <2 mg C/L and BDOC was <0.7 mg C/L. BDOC made up 37.8% of DOC (8.2% labile and 29.6% semilabile constituents) and most DOC (62.2%) was recalcitrant. Storms increased DOC concentrations 6- to 12-fold and selectively mobilized BDOC increasing concentrations 8- to 27-fold. Labile and semilabile constituents increased 2-fold to 17.3% and 55.4%, respectively, so that storm flow DOC was largely biodegradable (73%). Terrestrial DOC concentrations declined from 2.15 mg C/L in soil water to 1.78 mg C/L in shallow wells to 1.26 mg C/L in spring seeps, and labile BDOC concentrations declined from 0.1 mg C/L in soil water to 0.04 mg C/L in shallow wells but increased to 0.13 mg C/L in spring seeps. Overland flow waters had elevated DOC (11.0 mg C/L) and labile BDOC (1.7 mg C/L) concentrations. Peak storm concentrations for 2 biological reactivity classes were coincident during 2 storms but divergent during another storm, suggesting temporal variation in hydrologic pathways. Our results demonstrate that storms deliver increased BDOC loads to a headwater stream and reveal the temporal variability of labile and semilabile BDOC constituents. Storms increase stream depth and velocity, resulting in increased uptake lengths for BDOC constituents, exporting them from the basin and probably providing a downstream subsidy.

The US Environmental Protection Agency (USEPA) conducted a National Lakes Assessment (NLA) in the conterminous USA in 2007 as part of a national assessment of aquatic resources. The EPA used the National Hydrography Dataset (NHD) as the basis for the sample frame for the NLA. The target population was all lakes >4 ha, excluding the Laurentian Great Lakes and the Great Salt Lake. An unequal probability survey design was used to select 4472 candidate lakes for potential sampling. The unequal selection depended on 5 lake area classes and 9 aggregated Omernik level III ecoregions. In all, 2034 candidate lakes were evaluated for inclusion in the target population, and 1309 lakes (representing ∼68,000 lakes in the sample frame) met the criteria. A total of 1028 lakes (of 1309) were sampled and represented ∼50,000 lakes. The remaining lakes (231, representing ∼18,000 lakes) could not be sampled because of access denial or physical inaccessibility. The target population included natural (41 ± 2% [SE]) and man-made lakes (59 ± 2%). All target lakes in the Southern Appalachian region and >90% of the target population in the Southern Plains and Xeric regions were man-made. In the Upper Midwest region, 97 ± 1% of the target population were natural lakes. Small lakes (4–10 ha) made up 47 ± 2% of the target population, and lakes >50 ha made up ∼15% of the target population. The results raise 2 issues that have implications for current and future NLA projects: 1) the cost and effort required to identify lake features in the sample frame that do not meet the criteria for inclusion in the target population (∼50% in NLA 2007), and 2) the potential for biased estimates of the size and condition of the target population caused by lakes that cannot be sampled. Future NLA efforts involve refining the survey design to include smaller lakes and resampling lakes from previous NLAs. We offer approaches for addressing both issues, including use of a high-resolution version of NHD as the basis for developing the NLA sample frame. Developing a master sample frame of lakes would provide a consistent basis of lake numbers (or surface area) from which to estimate extent or assess ecological condition.

Scenario analysis has the potential to improve management of aquatic systems throughout the Mountaintop Removal–Valley Fill mining (MTR–VF) region of central Appalachia. However, the extent to which surface mining interacts with other landuse stressors (i.e., cumulative effects) is unclear, and this limits our ability to predict the effects of new mines on physical, chemical, and biological conditions downstream. We tested for additive and interactive effects of landuse change (surface mining, deep mining, and residential development) on water quality (specific conductance and Se), habitat quality, and benthic macroinvertebrates via a uniquely designed watershed-scale assessment of the Coal River, West Virginia (USA). We derived equations for predicting in-stream response to landscape changes and predicted the outcome of a realistic future scenario involving development of 15 permitted mines. Elevated Se concentrations were directly correlated with incremental increases in surface-mining extent. Surface mining, deep mining, and residential development had additive effects on elevated specific conductance and reduced biological condition. We found evidence of a positive interactive effect (stressor antagonism) of deep mining and residential development on biological condition, presumably caused by stream-flow augmentation from deep mines. Landscape context influenced predicted impacts from construction of 15 new mines because of additive and interactive effects of landuse change. New surface mines increased the number of receiving streams exceeding chemical and biological criteria, but a greater proportion of receiving streams exceeded chemical and biological criteria at equivalent levels of new mine development when pre-existing stressors were present. When surface mining was the only stressor, ≥30 or 40% increases in surface mining caused 100% of streams to exceed chemical or biological standards, respectively, whereas in streams stressed by deep mining and residential development, ≥10% additional surface mining caused 100% of streams to exceed chemical and biological standards. Continued progress in this area will require a better understanding of how landuse change affects aquatic systems in the rest of the MTR–VF mining region, where watershed-to-watershed variation in landuse patterns probably causes variability in ecological response.

Raised bog pools are extremely nutrient poor and rich in humic substances, and these features limit primary production. To assess the base of the invertebrate food web in bog pools we measured the stable-isotopic signatures of primary producers, dead organic matter, and invertebrates, and the composition and stable-C-isotope ratio of their phospholipid-derived fatty acids (PLFAs). The stable-isotopic signatures showed the presence of multiple trophic levels and differential use of basal food sources by the invertebrates among and within species, individuals, and size classes. Carnivorous and omnivorous invertebrates assimilated polyunsaturated fatty acids (PUFAs) derived from algae, and possibly macrophytes, and fatty acids that are specific for methane-oxidizing bacteria (MOB). Part of the bacterial biomass conveyed to higher trophic levels in the bog pools originated from MOB. Pelagic zooplankton appeared to rely more on bacteria, whereas insects relied more on algae. Periphyton, a primary algal food source, was the basal food source most depleted in ¹³C and was inferred to sustain ≥½ the invertebrate food web. The relatively depleted δ¹³C values of PUFAs in invertebrates suggest a role for methane-derived C. We argue that the CO₂ assimilated by the algae could be derived from MOB. Therefore, depleted δ¹³C values of invertebrates do not necessarily indicate a direct pathway between MOB and these invertebrates because algae may form an intermediate level.

Life-history knowledge is central to basic and applied ecology, but recent reviews show that knowledge of life histories of many freshwater invertebrates is incomplete because of difficulty in conducting such studies or a general decline of interest in natural-history research. We review and summarize published life histories for crayfishes native to the USA and Canada. We document the rate of accumulation of crayfish life-history knowledge and biases and gaps in life-history knowledge by taxonomic group, geography, habitat preference, and conservation status. A total of 78 published studies (59 papers; several included life-history information for multiple species) covering 42 (12%) of the 347 USA and Canadian crayfishes recognized as of 2007 met our criteria for crayfish life-history studies. Life-history studies were lacking for crayfishes of conservation concern and stygobitic or primary burrowing-habitat specialists. Life-history knowledge is relatively complete for low-diversity freshwater ecoregions of northern and western North America, but lacking for high-diversity freshwater ecoregions of the southeastern USA. From 1972 to 2007, an average of 3.40 new crayfish species/y were described, whereas 0.63 species/y were added to the list of crayfishes with published life-history studies. Thus, taxonomic knowledge is expanding faster than ecological or life-history knowledge of these same species, inevitably limiting our ability to manage and conserve them. We conclude with suggestions for increasing publication of crayfish life-history studies, and priorities for regions, taxonomic groups, and life-history traits that require urgent attention. We also present a database of existing crayfish life-history studies for researchers interested in life-history questions and to provide a foundation for traits-based inquiries into crayfish macroecology and applied questions in conservation like the prediction of extinction and invasion risk.

We used radio telemetry to track the daily movements of Cambarus chasmodactylus (New River Crayfish) in Anthony Creek, West Virginia, to help us better understand the daily activity and habitat preferences of cambarid crayfish. We fitted ten 0.8-g transmitters to the chelae of C. chasmodactylus (6 form I males/3 form II males/1 female) and released them at their initial point of capture. We tracked animals for 5 consecutive days, after which we initiated a 20-d noninteraction period followed by 6 more days of tracking. After locating an individual, we noted water depth, current velocity, and substrate type at the individual's position and recorded distance traveled over the previous 24 h. The ephemeral home range concept applied to most movement patterns, a result indicating that individual C. chasmodactylus have multiple home ranges over the course of their lives. Beginning in July, form I males maintained more permanent territories under slab boulders, a behavior theorized to be mediated by reproductive receptivity of females. Smaller adults moved longer distances and more frequently than larger adults. Habitats preferred by C. chasmodactylus had moderate (0.25–0.75 m) water depth and flow velocity (0–1.9 m/s) and slab boulders. Adult C. chasmodactylus appear to be habitat specialists that use slab boulders exclusively as daily retreats. Our results demonstrate the utility of telemetry as a means to obtain data about habitat and ecological associations of crayfishes, knowledge that is currently lacking for many species.

One of the best studied freshwater predator–prey interactions is arguably that between crayfish and gastropods. In many ecosystems, crayfish limit populations of thin-shelled snails and induce changes in snail traits. However, the connection between these 2 phenomena and, therefore, the mechanism by which crayfish have population-dynamic effects on snails, has been little studied. I examined the population-level effects of 2 procambarid crayfish (Procambarus alleni and Procambarus fallax) on a 2-species assemblage of snails (physids: Hatia cubensis, planorbids: Planorbella duryi) in experimental mesocosms. Observations early in the experiment suggested that both snail species were responding behaviorally to the crayfish, especially to P. alleni. At the end of the study (8 wk), both species of crayfish had reduced filamentous periphyton by 50% and snail density by >95%. The 2 crayfish species had quantitatively similar effects on both trophic levels. Physids laid eggs early in the study, but they had no size refuge and were almost completely eliminated from the crayfish treatments by the end of the study. Large planorbids had a size refuge and persisted with crayfish, but almost no recruitment occurred in the presence of crayfish. Per-capita egg-laying rates on bottom substrates at the end of the experiment were equal between treatments, results indicating that planorbids persisted in laying eggs and that crayfish continued to consume the hatchlings. The observations from this experiment suggest that crayfish limit snail populations primarily by direct consumptive effects.

Commonly referred to as keystone species, crayfish are ecologically important for their ability to transfer energy efficiently to higher trophic levels in aquatic food webs. They also are ecosystem engineers, modifying substrate and influencing distribution of other benthic invertebrates. However, crayfish have yet to be examined as potential predators of benthic fish in lotic systems. We examined a possible relationship between crayfish and benthic fish populations by quantifying natural densities of both groups and by using enclosure/exclosure and laboratory experiments to test for crayfish predation on benthic fish. Data obtained by sampling Illinois streams showed that increased crayfish density was correlated with decreased fish density, and this relationship was not influenced by habitat variables. Data from in-stream enclosure/exclosure experiments showed predation by crayfish (Orconectes sp.) on darters (Etheostoma sp.) in all treatments. The highest overall fish mortality occurred in the low-density crayfish treatment. We ran controlled tank experiments to seek formal evidence that crayfish are capable of killing and consuming benthic fish. Our study provides evidence that crayfish predation on benthic fish may have an influence on benthic fish populations, and this interaction could be of particular importance in streams with the invasive crayfish Orconectes rusticus.

Dams and impoundments, both large and small, affect downstream physicochemical characteristics and up- and downstream biotic communities. I tested whether small dams and their impoundments altered downstream crayfish assemblages in northern Mississippi. I sampled crayfish and measured physicochemical variables at 4 sites downstream of impoundments (outlet sites) and 4 sites not influenced by impoundments (undammed sites) in August, September, and November 2004. In November 2010, I sampled 7 undammed, 6 outlet, and 3 intermediate sites (influenced by beaver activity or ∼1 km downstream of an impoundment). Crayfish assemblages differed between undammed and outlet sites. Catch-per-unit-effort (CPUE) of Orconectes (Trisellescens) sp. was higher in undammed than outlet sites in both years. Procambarus (Pennides) spp. CPUE was lower in undammed than outlet sites in November 2010 and nearly so in November 2004. In 2004, Procambarus (Ortmannicus) hayi was common in autumn at outlet sites but virtually absent from undammed sites, but in 2010, P. hayi CPUE did not differ between categories. Cambarus striatus CPUE, which was low overall, did not differ between categories in 2004 but was higher in undammed sites in 2010. Seasonal differences among taxa in reproductive timing were important to understanding impoundment effects. The most consistent difference in habitat was that undammed sites had significantly higher width:depth ratios than did outlet sites. Based on the number of mapped small impoundments and a conservative estimate that each impoundment influenced crayfish assemblages over 2 km, I estimated that impoundments probably affect crayfish assemblages in >284 km of stream in the upper Little Tallahatchie River subbasin. Extrapolated to the entire Gulf Coastal Plain, impoundments may influence crayfish assemblages over thousands of stream kilometers.

Burrowing crayfish are potentially important ecological links between terrestrial and aquatic systems, but little is known about what drives their local distribution patterns. We investigated potential mechanisms underlying the patchy local distribution of the devil crayfish (Cambarus diogenes Girard) in a stream floodplain ecosystem of the coastal plain of Alabama. We used a series of field surveys and laboratory trials to: 1) quantify local distributions and soil-type associations, 2) identify soil preferences of juveniles and adults, 3) examine the effects of biotic (adult occupancy) and abiotic (soil compaction) factors on juvenile burrowing preferences, and 4) investigate the role of floodplain connectivity on burrow density. Juvenile crayfish were more abundant in sandy streamside soils, whereas adults were more abundant in clay-based floodplain soils. In laboratory preference trials in artificial burrowing chambers, adults and juveniles showed affinity for floodplain over streamside soils, a result suggesting that factors other than soil preference influence field patterns. When juveniles were presented with situations where adults were established, they initiated burrows in association with the adult burrows regardless of soil type. Soil compaction did not influence juvenile burrowing preference, but did result in smaller burrows in laboratory trials. Adult burrow density in the floodplain was negatively related to stream bank angle and top-of-bank height. Juvenile C. diogenes took longer to climb banks with high bank angles than those with low bank angles, a result suggesting increased risk of predation and desiccation associated with disconnected floodplain conditions. Local distribution of C. diogenes burrows in stream/floodplain systems appears to be a product of interacting physical and biological factors rather than of soil-type preferences. Stream–floodplain connectivity may affect recruitment and population viability of burrowing crayfish.

Astacoidean crayfishes serve as hosts to obligate ectosymbiotic annelids called branchiobdellidans. Branchiobdellidans can act either as mutualistic cleaners or as ectoparasites and can have strong effects on crayfish growth and survivorship. This potentially vital aspect of crayfish biology has gone largely unexplored until recently. We reviewed the current state of knowledge regarding this symbiosis and examined factors that contribute to variability in the effects of branchiobdellidans on crayfish. We show that branchiobdellidans affect crayfish in various ways depending on branchiobdellidan species, abundance, and ecological context. We also discuss evidence for regulatory controls that crayfish exert over their symbionts and symbiont–host preferences. Last, we evaluate the utility and challenges of using the crayfish–branchiobdellidan association as a model system for ecological and evolutionary research and point to promising areas for future study. Further investigations of the complex interactions between crayfish and their ectosymbionts will greatly advance the field of crayfish biology and offer many exciting opportunities for the study of symbioses.

In cleaning symbioses, colonization of hosts by parasites and other epibionts often varies across habitats, and this variability could influence the net effect of cleaners on host fitness. We investigated how variation in environmental fouling (i.e., epibiont colonization and accumulation of particulate matter) influenced symbiont populations and partner regulation in a crayfish–branchiobdellidan worm cleaning symbiosis. We manipulated initial worm density and environmental fouling in a laboratory experiment. We monitored the number of worms (both stocked, large worms and juvenile worms born during the experiment) and the number of worm cocoons deposited on the crayfish for 8 wk. Initial worm density and fouling potential of the environment significantly affected removal of large worms by crayfish. Loss of large worms was higher in the high-initial-density and the low-fouling treatments during the 1^st wk of the experiment, after which the density of large worm numbers did not differ among treatments. Cocoon production did not differ among treatments, but cocoon production ceased early in the low-fouling treatment with high initial densities. Number of juvenile worms was higher in the high- than in the low-fouling treatments by the end of the experiment, probably because of increased availability of epibiotic resources. Fouling treatment had a greater effect on total branchiobdellidan population size (initial worms plus juveniles) than did initial worm density. These results demonstrate that initial symbiont density and environmental context can influence partner regulation by the host and cleaner reproduction and abundance in a cleaning symbiosis.

Nonnative crayfish have been widely introduced and are a major threat to freshwater biodiversity and ecosystem functioning. Despite documentation of the ecological effects of nonnative crayfish from >3 decades of case studies, no comprehensive synthesis has been done to test quantitatively for their general or species-specific effects on recipient ecosystems. We provide the first global meta-analysis of the ecological effects of nonnative crayfish under experimental settings to compare effects among species and across levels of ecological organization. Our meta-analysis revealed strong, but variable, negative ecological impacts of nonnative crayfish with strikingly consistent effects among introduced species. In experimental settings, nonnative crayfish generally affect all levels of freshwater food webs. Nonnative crayfish reduce the abundance of basal resources like aquatic macrophytes, prey on invertebrates like snails and mayflies, and reduce abundances and growth of amphibians and fish, but they do not consistently increase algal biomass. Nonnative crayfish tend to have larger positive effects on growth of algae and larger negative effects on invertebrates and fish than native crayfish, but effect sizes vary considerably. Our study supports the assessment of crayfish as strong interactors in food webs that have significant effects across native taxa via polytrophic, generalist feeding habits. Nonnative crayfish species identity may be less important than extrinsic attributes of the recipient ecosystems in determining effects of nonnative crayfish. We identify some understudied and emerging nonnative crayfish that should be studied further and suggest expanding research to encompass more comparisons of native vs nonnative crayfish and different geographic regions. The consistent and general negative effects of nonnative crayfish warrant efforts to discourage their introduction beyond native ranges.

Competitive exclusion is a commonly cited mechanism of species replacement in nonindigenous crayfish introductions. However, even when it seems highly plausible, it may not be the driving mechanism. We sought to identify competition-driven habitat shifts in populations of native St Francis River crayfish Orconectes quadruncus and invasive woodland crayfish Orconectes hylas. Crayfish were tagged with passive integrated transponder (PIT) tags at locations where the 2 species were sympatric and where the native was allopatric. Information was collected on crayfish habitat use, habitat availability, and habitat associations during multiple seasons. Discrete choice analysis and model selection results indicated that both species selected large, concealing substrate and slower current velocities. We observed no significant shifts in habitat use by the native species when sympatric with the invasive species. A high degree of space-use overlap between the species and few differences in how species used or selected habitats indicated a high potential for competition and provided no evidence that competitive exclusion had occurred. No solid explanation for species replacement exists, but it appears that competitive exclusion for space and habitat does not occur or occurs slowly at some sympatric localities.

Phenotypic plasticity of ecologically relevant traits relating to physiology, behavior, morphology, and life history is widespread and can affect the ecology and evolution of organisms. In streams, phenotypic plasticity in morphology and corresponding differences in performance have been documented for fishes and, to a lesser extent, for macroinvertebrates. Morphological plasticity in crayfish has not been addressed but, if present, has the potential to interact with behaviorally plastic traits to affect performance in high water velocities. Lake and stream invasions of rusty crayfish, Orconectes rusticus, provide excellent opportunities to examine morphological variation in habitats differing in water velocity. Spread of O. rusticus and displacement of resident species in lakes has been attributed to larger mean body and chelae sizes than for native species, but larger body and chelae sizes may not be advantageous in high-velocity environments. We examined populations of male O. rusticus (form I and II) from lakes, low-velocity streams (LVS ≈ 25 cm/s), and high-velocity streams (HVS ≈ 50 cm/s) to test the hypothesis that size and shape are affected by water velocity. We analyzed scanned images of chelae and body with geometric morphometrics. Body size differed significantly between HVS populations and LVS and lake populations, which did not differ in size or shape. Shape tended to differ between HVS populations and LVS and lake populations. Chelae of form I but not of form II crayfish were significantly smaller in HVS than in LVS and lake populations. Chelae (form I and II) in HVS populations were broader and stunted relative to chelae in LVS and lake populations. Chelae may help deflect water over the bodies. Morphological plasticity in crayfish adapted to HVS may alter invasion rate or success with subsequent effects on stream ecosystems.

The stone crayfish, Austropotamobius torrentium, is one of the oldest freshwater crayfish species in Europe. Most Carpathian populations are in Romania, with a distribution clustered in 2 compact metapopulations in the western part of the country. Our goal was to understand if this pattern is the result of a coincidence or a complex set of restrictive circumstances. Romania is an ideal place to analyze crayfish distributions because they have not been disturbed by species translocations or massive loss of populations. We recorded the presence/absence of crayfish and measured 15 habitat variables at 428 randomly chosen headwater sampling sites, and analyzed the crayfish distribution pattern with a boosted regression tree model. Our results show that most of the Romanian territory is ecologically suited to support stone crayfish under current conditions. The most important influences on probability of presence were water velocity, conductivity, altitude, river size, and dissolved O₂. When included as a supplementary predictor in the model, the distance from karst became the strongest variable accounting for the probability of presence and explaining the current distribution of the stone crayfish. We propose the hypothesis that at least one cycle of Pleistocene glaciation shaped the current distribution pattern by causing massive extinction in the Carpathians, except in karstic underground water bodies that offered ecological refuges. After the glaciations, stone crayfish expanding from these refuges competed with colonizing noble crayfish Astacus astacus, restricting stone crayfish to insular areas.