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Non-native crayfish can have impacts on stream communities that are highly variable. A possible explanation for this variability is that crayfish are responding in a context-dependent manner to variation in environmental factors. Among the most critical environmental factors in streams is current velocity. Moving water defines lotic ecosystems and many benthic organisms, including crayfish, respond to its influence. To examine how current velocity affected the impacts of non-native Orconectes rusticus crayfish on benthic communities, we conducted a cage-enclosure experiment in a Wisconsin stream. We hypothesized that current velocities > 50 cm s−1 would decrease the effects that O. rusticus had on community composition (macroinvertebrate richness and numbers) and physical structure (sediment accumulation). Three cage enclosure treatments (open, closed crayfish and closed control) were grouped into eight replicate blocks divided equally among streambed regions of slow (< 50 cm s−1) and fast (> 50 cm s−1) current. Open cages allowed resident crayfish access, closed crayfish cages contained one O. rusticus, and closed controls had no crayfish. After three weeks, crayfish cages had lower macroinvertebrate abundance and richness and less sediment accumulation. Current velocity showed a positive relationship to macroinvertebrates in general, and a negative relationship to sediment build-up. The most common macroinvertebrates were hydropsychid caddisflies that responded to O. rusticus in a context-dependent manner such that cages containing crayfish had decreased hydropsychid numbers in fast current, but not in slow. Open cage treatments showed a similar pattern, suggesting that natural crayfish densities in the stream were also sufficient for lowering hydropsychid numbers in fast current. Our study demonstrates that current velocity may provide an important context for understanding the effects that O. rusticus have on benthic communities, not just in terms of what these crayfish do, but how the benthic communities respond to their presence.

Non-native crayfish can have impacts on stream communities that are highly variable. A possible explanation for this variability is that crayfish are responding in a context-dependent manner to variation in environmental factors. Among the most critical environmental factors in streams is current velocity. Moving water defines lotic ecosystems and many benthic organisms, including crayfish, respond to its influence. To examine how current velocity affected the impacts of non-native Orconectes rusticus crayfish on benthic communities, we conducted a cage-enclosure experiment in a Wisconsin stream. We hypothesized that current velocities > 50 cm s−1 would decrease the effects that O. rusticus had on community composition (macroinvertebrate richness and numbers) and physical structure (sediment accumulation). Three cage enclosure treatments (open, closed crayfish and closed control) were grouped into eight replicate blocks divided equally among streambed regions of slow (< 50 cm s−1) and fast (> 50 cm s−1) current. Open cages allowed resident crayfish access, closed crayfish cages contained one O. rusticus, and closed controls had no crayfish. After three weeks, crayfish cages had lower macroinvertebrate abundance and richness and less sediment accumulation. Current velocity showed a positive relationship to macroinvertebrates in general, and a negative relationship to sediment build-up. The most common macroinvertebrates were hydropsychid caddisflies that responded to O. rusticus in a context-dependent manner such that cages containing crayfish had decreased hydropsychid numbers in fast current, but not in slow. Open cage treatments showed a similar pattern, suggesting that natural crayfish densities in the stream were also sufficient for lowering hydropsychid numbers in fast current. Our study demonstrates that current velocity may provide an important context for understanding the effects that O. rusticus have on benthic communities, not just in terms of what these crayfish do, but how the benthic communities respond to their presence. [ABSTRACT FROM AUTHOR]

The impact of nonconsumptive effects (NCEs) in structuring predator-prey interactions and trophic cascades is a prominent area of ecological research. For NCEs to occur, prey need to be able to detect the presence of predators through sensory mechanisms. The investigation of the role of different sensory modalities in predator detection has lagged behind the development of NCE-based theories. This study aimed to determine whether a hierarchy in the reliance upon sensory modalities exists in the rusty crayfish ( Orconectes rusticus (Girard, 1852) = Faxonius rusticus (Girard, 1852)) for predator detection and if this hierarchy is altered across different sensory environments (flowing and nonflowing environments). Rusty crayfish were exposed to largemouth bass ( Micropterus salmoides (Lacépède, 1802)) odor in either a flowing or nonflowing arena where behavior was recorded under different sensory lesions. Linear mixed models were conducted to determine the impact of lesions, flowing environments, and the interactive effects of lesions and flowing environments on the rusty crayfish ability to respond to predatory stimuli. Results from this study support the significance of sensory multimodality in the rusty crayfish for accurately detecting and assessing predatory threats. Results from this study also suggest a hierarchy in the reliance upon sensory modalities in the rusty crayfish that is dependent upon the environment and the location of rusty crayfish within an environment. [ABSTRACT FROM AUTHOR]

Inherent difficulties of tracking and observing organisms in the field often leave researchers with no choice but to conduct behavioral experiments under laboratory settings. However, results of laboratory experiments do not always translate accurately to natural conditions. A fundamental challenge in ecology is therefore to scale up from small area and short-duration laboratory experiments to large areas and long durations over which ecological processes generally operate. In this study, we propose that stable isotope analysis may be a tool that can link laboratory behavioral observations to past field interactions or function of individual organisms. We conducted laboratory behavioral assays to measure dominance of invasive rusty crayfish, Orconectes rusticus, and used stable isotope analysis to hindcast trophic positions of these crayfish under preceding natural conditions. We hypothesized that more dominant crayfish in our assays would have higher trophic positions if dominance were related to competitive ability or willingness to pursue high-risk, high-reward prey. We did not find a relationship between crayfish dominance and trophic position, and therefore infer that laboratory dominance of crayfish may not necessarily relate to their ecology in the field. However, this is to our knowledge the first attempt to directly relate laboratory behavior to field performance via stable isotope analysis. We encourage future studies to continue to explore a possible link between laboratory and field behavior via stable isotope analysis, and propose several avenues to do so.

Parasites can alter communities by reducing densities of keystone hosts, but few studies have examined how trait-mediated indirect effects of parasites can alter ecological communities. We test how trematode parasites ( Microphallus spp.) that affect invasive crayfish ( Orconectes rusticus) behavior alter how crayfish impact lake littoral communities. O. rusticus drive community composition in north temperate lakes, and predatory fish can reduce crayfish activity and feeding. In laboratory studies, Microphallus parasites also alter O. rusticus behavior: infected O. rusticus eat fewer macroinvertebrates and are bolder near predatory fish than uninfected individuals. We used a 2 × 2 factorial experiment to test how predatory fish and parasites affect O. rusticus impacts in large mesocosms over 4 weeks. We predicted (1) that when predators were absent, infected crayfish would have lower impacts than uninfected crayfish on macrophytes and macroinvertebrates (as well as reduced growth and higher mortality). However, (2) when predators were present but unable to consume crayfish, infected crayfish would have greater impacts (as well as greater growth and lower mortality) than uninfected crayfish because of increased boldness. Because of its effect on crayfish feeding behavior, we also predicted (3) that infection would alter macrophyte and macroinvertebrate community composition. In contrast to our first hypothesis, we found that infected and uninfected crayfish had similar impacts on lower trophic levels when predators were absent. Across all treatments, infected crayfish were more likely to be outside shelters and had greater growth than uninfected crayfish, suggesting that the reduced feeding observed in short-term experiments does not occur over longer timescales. However, in support of the second hypothesis, when predatory fish were present, infected crayfish ate more macroinvertebrates than did uninfected crayfish, likely due to increased boldness. We also observed a trend for greater macrophyte consumption associated with infection and a trend indicating infection might alter macroinvertebrate community composition. Our results suggest that parasites can alter aquatic communities in mesocosms merely by modifying host behavior. [ABSTRACT FROM AUTHOR]

This laboratory study examined the effects of the specific serotonin reuptake inhibitor fluoxetine on growth following molting and on a range of behaviors in the crayfishOrconectes rusticus. For growth experiments, male Form I and Form II crayfish were weighed and measured and placed individually in water containing 0–500 μg/L of fluoxetine. They were held in fluoxetine or control water until they molted and were reweighed two weeks post-molt. In behavior experiments, juvenile and adult animals were held individually in 0, 2, 200, or 500 μg/L of fluoxetine for 10 days and tested in an open field arena to assess locomotion, thigmotaxis, sheltering, and habituation to a novel environment. Under our laboratory conditions, crayfish exposed to fluoxetine at 500 μg/L showed significantly enhanced growth: post-molt Form I animals had greater body weight and post-molt Form II animals had greater carapace length, relative to controls. In open field tests, juvenile crayfish exposed to 2 and 500 μg/L fluoxetine displayed significantly reduced locomotion compared to controls. The results indicate that crayfish growth and locomotion can be manipulated by short-term exposure to ambient fluoxetine, suggesting that this means of exposure may offer a useful and noninvasive way to examine drug effects in freely moving animals. However, effects were only observed at concentrations well above fluoxetine levels currently reported in the environment. This suggests thatO. rusticusmay be relatively resistant to this form of pharmaceutical pollution but whether effects would occur following long-term exposure to lower concentrations is unknown. [ABSTRACT FROM AUTHOR]

Linkages between habitats can strongly affect ecosystem function through exchange of energy and materials. In lake food webs, large piscivorous fishes integrate littoral and pelagic energy sources through the consumption of smaller fishes and macroinvertebrates. We tested the hypothesis that the introduction of the invasive rusty crayfish (Orconectes rusticus) decouples littoral and pelagic food webs by reducing the abundance of small fish and noncrayfish benthic macroinvertebrates, thereby shifting diets of large fish to increased dependence on littoral energy sources (i.e., crayfish). We used stable isotope ratios of C (δ13C) and N (δ15N) to examine differences in resource use between lakes with high abundance of O. rusticus (invaded) and lakes with native crayfish only or with low abundance of nonnative crayfish (uninvaded). The trophic position of juvenile crayfish was lower in invaded than in uninvaded lakes, results suggesting decreased availability of, and reliance on, macroinvertebrate prey and greater dependence on detritus and algae. In invaded lakes, diets of piscivorous fishes relied more strongly on littoral energy sources, and Walleye (Sander vitreus), an obligate piscivore, had a lower trophic position than in uninvaded lakes, results suggesting reduced availability of fish prey. In agreement with another recent stable-isotope study and observations from many smaller-scale but more mechanistic mesocosm and enclosure experiments, these results support the hypothesis that invasion by O. rusticus causes a reduction in the abundance of benthic macroinvertebrates and small fishes and consequently reduces trophic position and increases littoral dependence of large fishes. [ABSTRACT FROM AUTHOR]

Increasing levels of anthropogenic chemicals within an aquatic ecosystem may inhibit animals from extracting information from chemical signals. We investigated whether antennular flicking, a behavioral mechanism involved in chemically-mediated behaviors of the rusty crayfish, Orconectes rusticus, was altered following a sublethal copper exposure (450 µg/L). Crayfish exposed to copper exhibited lower flicking rates than control crayfish and were significantly less successful in their ability to orient to a food odor. Copper was then eliminated from the housing tanks, providing a recovery period. Groups of crayfish were assayed for antennular flicking rates and orientation success three times over the course of the 21 day recovery period. Crayfish demonstrated significant increases in rates of successful localization of odors and antennular flicking during this portion of the experiment. These results indicate that the mechanism by which copper impairs chemoreception in the rusty crayfish is reversible if elevated levels of copper concentrations are eliminated from aquatic ecosystems contaminated by runoff from agricultural or aquacultural chemicals. [ABSTRACT FROM AUTHOR]

Parasites can have profound effects on host behaviour and species interactions, but the consequences of these impacts are inadequately understood. Three common crayfish in northern Wisconsin and Michigan (native Orconectes virilis, non-native O. propinquus and non-native and invasive O. rusticus) are intermediate hosts for trematode parasites, Microphallus spp. Some species in the genus Microphallus alter host behaviour, increasing their predation risk, but the effects of microphallids on crayfish are unknown. Orconectes propinquus replaces O. virilis in most lakes where they are introduced, and O. rusticus replaces both. These species replacements have major effects on macrophytes, macroinvertebrates and fish. Therefore, differential parasite impacts on crayfish could have community-level effects if competitive outcomes are altered., We examined the shelter affinity of infected and uninfected individuals of all three species in laboratory experiments in the presence and absence of a conspecific. We also observed behaviour during agonistic interactions, and measured boldness by quantifying how quickly crayfish emerged from shelter with a predatory fish present., Infection with Microphallus substantially altered crayfish shelter affinity, shelter competition and boldness, though infection affected each species differently. Infection reduced shelter affinity in O. propinquus and the ability of O. virilis to compete for shelter against uninfected conspecifics. Infected crayfish were bolder in the presence of a predatory fish., Our results suggest that infection with Microphallus alters crayfish behaviour so that all three species are more vulnerable to predation. Orconectes propinquus is likely to suffer the greatest increase in predation when infected, due to a reduced affinity for shelter coupled with increased boldness. In lakes where crayfish species coexist, O. rusticus will probably be less affected by the parasite than either congener. Therefore, crayfish parasites could alter crayfish abundance and species composition in north temperate lakes via behavioural modifications. [ABSTRACT FROM AUTHOR]

Modeling of invasive species' potential distributions is critical for preventing new invasions. Distribution models use environmental characteristics of observed distributions to determine the suite of conditions that allows invasion. Some variables are directly related to species' biological needs, while others are surrogates that do not directly influence distributions. For aquatic invasive species (AIS) with calcified shells and exoskeletons, one common limiting factor is the chemical restriction on forming calcium carbonate (CaCO), which is usually represented by conductivity or dissolved calcium. We predicted that conductivity and calcium would not serve as accurate surrogates for CaCO saturation state, which is more directly linked to calcification potential. To test this prediction, we fit classification trees to field surveys of northern Wisconsin lakes for three calcifying AIS-rusty crayfish ( Orconectes rusticus), banded mystery snail ( Viviparus georgianus), and Chinese mystery snail ( Cipanguladina chinensis). Along with lake area, variables associated with calcification were the best predictors of species distributions. Even though saturation state is the most biologically mechanistic variable, it did not improve model predictions or explain more variability in species presence than its surrogates. Overall, surrogates are sufficient for species distribution modeling in these lakes that exhibit a wide range of chemical states. [ABSTRACT FROM AUTHOR]

Before reaching concentrations that are high enough to cause mortality, elevated levels of chemical pollution can significantly alter a keystone indicator species’ ability to extract sensory information. To organisms that rely on chemical signals to make crucial ecological decisions, increased amounts of a pollutant may impact chemoreceptive abilities by altering the perception of the sensory landscape or impairing the functioning of sensory organs. Heavy metal pollutants entering an aquatic ecosystem are of increasing concern due to discernible effects on chemoreception in many ecologically and economically important species. In order to determine the effects of sublethal copper toxicity on chemically mediated behavior, male and female rusty crayfish, Orconectes rusticus , were exposed to ecologically relevant concentrations of copper (4.5, 45, and 450 µg/l) for 120 h. Following exposure, crayfish were allowed to orient toward a food odor stimulus. During orientation trials, select crayfish oriented under a point or nonpoint source copper background pollutant at the same concentration as the exposure period. Orientation trials were videotaped and analyzed using EthoVision XT 8.5 (Noldus Information Technology, The Netherlands) for differences in overall success in locating the food source and orienting parameters. Significant differences were found in the overall orientation ability of O. rusticus to locate an odor source when previously exposed to copper in combination with a source of pollution in the background of orientation trials. Crayfish exposed to copper in any capacity during the experiment (regardless of concentration or background during trials) showed slower walking speeds toward the source, decreased turning angles, increased heading angles toward the source, and decreased upstream heading angles. Results from this experiment support that copper impairs the ability of crayfish to detect, process, and/or respond appropriately to chemosensory information in order to successfully localize a food odor source. [ABSTRACT FROM AUTHOR]

In situ seed banks are a promising avenue for restoration of plant communities damaged by anthropogenic changes. The invasive rusty crayfish (Orconectes rusticus) has had well documented effects on macrophytes in north temperate lakes. To understand mechanisms of macrophyte recovery from the seed bank, we examined seed banks from lakes with different durations of exposure to O. rusticus and compared these findings to longterm macrophyte surveys. We cored littoral-zone sediments at sediment depths of 0-5, 5-10, and 10-15 cm to test whether deeper layers hold viable seeds that can be used to restore macrophytes. The seed bank in uninvaded lakes contained a higher number and richness of viable seeds than did the seed bank in invaded lakes. Number and richness of viable seeds decreased with sediment depth in all lake categories, and most seeds were found in the top 10 cm. Among all lakes, at most, 33% of the species recorded in field surveys of standing vegetation were represented in the seed bank. We conclude that the seed bank has only modest potential to contribute to natural recovery. Natural regeneration of the macrophyte community is more likely to rely upon vegetative propagules from remnant stands in invaded lakes, especially from very soft-bottom areas avoided by crayfish. Our results emphasize the importance of preventing destruction of macrophytes, especially in lakes without habitats likely to constitute a refuge for macrophytes. [ABSTRACT FROM AUTHOR]

Habitat alteration and species introductions have contributed to the decline of native crayfish in Ontario. Although lake populations of crayfish in Ontario are monitored, there is no corresponding program for streams. We used removal-based sampling to evaluate the efficacy of three sampling techniques (backpack electrofishing, hand capture, and seining) to characterize native and non-native crayfish populations in six streams in the Kawartha Lakes region and five streams in the Muskoka/Haliburton Lakes region. All types were effective at detecting non-native Rusty Crayfish (Orconectes rusticus). Rusty Crayfish were collected from 65% of samples, constituted 90% of the total catch, and were the only species present in 30% of streams. Compared with other methods, electrofishing was more likely to capture additional crayfish species. Removal-based sampling was not a reliable approach for estimating capture probability and population size. Failure of the removal model was due to increases in the number of crayfish captured after the first pass or too few individuals collected. Mean capture probabilities for electrofishing (0.30) and hand capture (0.31 ) did not result in reliable population estimates. Compared with seining, electrofishing and hand capture resulted in more sexually active males (fewer sexually inactive males) and more small (< 25 mm carapace length) individuals. For each method, there were differences in capture probability among length classes. A combination of electrofishing and seining (with multiple passes) would maximize species detection, permit sampling of a range of habitat types, and be easily integrated into existing stream fish surveys. [ABSTRACT FROM AUTHOR]

Despite increasing recognition of the importance of invertebrates, and specifically crayfish, to nearshore food webs in the Laurentian Great Lakes, past and present ecological studies in the Great Lakes have predominantly focused on fishes. Using data from many sources, we provide a summary of crayfish diversity and distribution throughout the Great Lakes from 1882 to 2008 for 1456 locations where crayfish have been surveyed. Sampling effort was greatest in Lake Michigan, followed by lakes Huron, Erie, Superior, and Ontario. A total of 13 crayfish species occur in the lakes, with Lake Erie having the greatest diversity (n = 11) and Lake Superior having the least (n = 5). Five crayfish species are non-native to one or more lakes. Because Orconectes rusticus was the most widely distributed non-native species and is associated with known negative impacts, we assessed its spread throughout the Great Lakes. Although 0. rusticus has been found for over 100 years in Lake Erie, its spread there has been relatively slow compared to that in lakes Michigan and Huron, where it has spread most rapidly since the 1990s and 2000, respectively. 0. rusticus has been found in both lakes Superior and Ontario for 22 and 37 years, respectively, and has expanded little in either lake. Our broad spatial and temporal assessment of crayfish diversity and distribution provides a baseline for future nearshore ecological studies, and for future management efforts to restore native crayfish and limit non-native introductions and their impact on food web interactions. [ABSTRACT FROM AUTHOR]

As the main witnesses of the ecological and economic impacts of invasions on ecosystems around the world, ecologists seek to provide the relevant science that informs managers about the potential for invasion of specific organisms in their region(s) of interest. Yet, the assorted literature that could inform such forecasts is rarely integrated to do so, and further, the diverse nature of the data available complicates synthesis and quantitative prediction. Here we present a set of analytical tools for synthesizing different levels of distributional and/or demographic data to produce meaningful assessments of invasion potential that can guide management at multiple phases of ongoing invasions, from dispersal to colonization to proliferation. We illustrate the utility of data-synthesis and data-model assimilation approaches with case studies of three well-known invasive species--a vine, a marine mussel, and a freshwater crayfish--under current and projected future climatic conditions. Results from the integrated assessments reflect the complexity of the invasion process and show that the most relevant climatic variables can have contrasting effects or operate at different intensities across habitat types. As a consequence, for two of the study species climate trends will increase the likelihood of invasion in some habitats and decrease it in others. Our results identified and quantified both bottlenecks and windows of opportunity for invasion, mainly related to the role of human uses of the landscape or to disruption of the flow of resources. The approach we describe has a high potential to enhance model realism, explanatory insight, and predictive capability, generating information that can inform management decisions and optimize phase-specific prevention and control efforts for a wide range of biological invasions. [ABSTRACT FROM AUTHOR]

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 metaanalysis 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Conditions fostering coexistence of native species with invasive species have received little attention in invasion biology, especially for closely related invasive and native species. We used long-term datasets on multiple replicate invasions to define conditions under which native virile crayfish ( Orconectes virilis) can coexist with invasive rusty crayfish ( O. rusticus). We examined multiple drivers of coexistence involving habitat use and predation at between-lake and within-lake scales to derive predictions that could guide prioritization efforts to prevent future introductions of rusty crayfish and mitigate impacts of existing invasions. Lakes in which native species persisted for many years had significantly less cobble and sand habitats, and significantly more vegetated habitats compared to lakes from which native crayfish have been displaced. In the presence of rusty crayfish, virile crayfish alter their habitat use to vegetated habitats relative to habitat use in the absence of rusty crayfish. Such vegetated habitats had greater plant standing crop, plant species richness, and sediment percent organic matter compared to vegetated sites occupied by rusty crayfish. Our results suggest that low abundance of cobble habitat and altered habitat use allows native crayfish to coexist with the rusty crayfish invader. At the within-lake scale, virile crayfish persist by escaping predation in the vegetated habitats, despite suboptimal abiotic conditions. By understanding these abiotic and biotic conditions that promote coexistence, managers could enhance native crayfish persistence by targeting high cobble lakes for efforts to prevent the introduction of invasive crayfish, and targeting vegetated habitats for protection in already invaded lakes. [ABSTRACT FROM AUTHOR]

Rapid transitions in ecosystem structure, or regime shifts, are a hallmark of alternative stable states (ASS). However, regime shifts can occur even when feedbacks are not strong enough to cause ASS. We investigated the potential for ASS to explain transitions between dominance of an invasive species, rusty crayfish (Orconectes rusticus), and native sunfishes (Lepomis spp.) in northern Wisconsin (USA) lakes. A rapid transition from Lepomis to rusty crayfish dominance occurred as rusty crayfish invaded Trout Lake, and the reverse transition resulted from an eight-year experimental removal of rusty crayfish from Sparkling Lake. We fit a stage-structured population model of species interactions to 31 years of time-series data from each lake. The model identified water level as an important driver, with drought conditions reducing rusty crayfish recruitment and allowing Lepomis dominance. The maximum-likelihood parameter estimates of the negative interaction between rusty crayfish and Lepomis led to ASS in the model, where each species was capable of excluding the other within a narrow range of environmental conditions. However, uncertainty in parameter estimates made it impossible to exclude the potential that rapid transitions were caused by a simpler threshold response lacking alternative equilibria. Simulated forward and backward transitions between species dominance occurred at different environmental conditions (i.e., hysteresis), even when the parameters used for simulation did not predict ASS as a result of slow species responses to environmental drivers. Thus, ASS are possible, but by no means certain, explanations for rapid transitions in this system, and our results highlight the difficulties associated with distinguishing ASS from other types of threshold responses. However, whether regime shifts are caused by ASS may be relatively unimportant in this system, as the range of conditions over which transitions occur is narrow, and under most conditions, the system is predicted to exist in only a single state. [ABSTRACT FROM AUTHOR]

Over the last three decades, the rusty crayfish ( Orconectes rusticus (Girard, 1852)) has been expanding its range northward via human-mediated dispersal. If this species is to continue expanding its range northward, it will move onto the Canadian Shield, where calcium (Ca) availability is low and is predicted to decline further in the future. Dissolved Ca is a vital functional component of mollusc and crustacean physiology, important for exoskeletal condition and strength, as well as metabolic activity. However, some organisms are able to compensate for reduced structural integrity by modifying their behaviour. In this study, we asked if the invasive O. rusticus can survive low levels of ambient Ca and, if it can, whether it exhibits modified antipredator behavior in response to the physiological limitations imposed by low [Ca]. We found that, under reduced Ca levels, O. rusticus reduced the frequency of standard activities (such as grooming and foraging) and was more likely to engage in vigilance and (or) escape behavior. We also found that some individuals, in extremely low [Ca], died while molting. This study suggests that Ca limitation on the Shield, especially where predators are present, may limit the northward expansion of O. rusticus beyond their current range limit. [ABSTRACT FROM AUTHOR]

The pereiopods (walking legs) of crustaceans have been shown to have both mechano- and chemosensory functions including: detecting various odors, mechanical stimuli, as well as being used for grooming of gills and brood care. Using scanning electron microscopy, we examined the pereiopods of reproductive male (form I) and reproductive female (glair) crayfish Orconectes rusticus Girard, 1852 and found that the distal portion (dorsal surface) of the propodus of pereiopods 2 through 5 contain smooth, ptumose, serrate and cuspidate setae. Various studies have implicated both smooth and serrate setae as being important for grooming; therefore, we used scanning electron microscopy to examine and compare the distribution of smooth and serrate setae on the pereiopods of reproductive male and female crayfish in order to determine if there were differences between sexes. We found that there were no differences in the number of tufts (pockets) or number of smooth setae on the second and third pereiopods (chelipeds) between male and female crayfish. Further, the second and third pereiopods of both male and female crayfish had significantly more smooth setae than the fourth and fifth pereiopods. When the distribution of serrate setae was compared, we found that reproductive female crayfish possess significantly more serrate setae on their fifth pereiopods than their fourth pereiopods and both pereiopods 4 and 5 of form I male crayfish. Overall, increases in serrate setae on the fifth pereiopods of reproductive female crayfish are significant. We suggest that female crayfish may use serrate setae of the fifth pereiopods extensively for grooming eggs and brood care during reproduction. [ABSTRACT FROM AUTHOR]

Crayfish form social hierarchies through agonistic interactions. During formation of social hierarchies, individual crayfish establish dominance by signalling status through olfaction, vision and touch. Our study investigated which of these three sensory modalities played the most important role in establishing dominance in rusty crayfish (Orconectes rusticus). Olfaction, vision and touch were systematically impaired in staged triadic and dyadic agonistic interactions to determine the relative contribution of each sensory input. Our results suggest that olfaction is the most important sensory modality during the initial formation of dominance hierarchies in rusty crayfish. Using olfaction alone, crayfish were capable of communicating social status with sensory competent crayfish; without full olfactory ability crayfish were unable to effectively establish dominance. Vision and touch were also found to play practical roles in reducing unnecessary risk; with antennae for touch, functionally reducing the number of fight initiations, and vision allowing a crayfish under imminent attack to ready itself, strike first, or retreat. [ABSTRACT FROM AUTHOR]

Habitat fragmentation and nonindigenous species are 2 of the leading causes of species loss globally. Thus, scientific information is needed to assess their interactive effects on the biota of lotic ecosystems. We tested the hypothesis that culverts (i.e., pipes) at road-stream intersections elevate flow velocities and differentially slow upstream locomotion of native relative to nonindigenous crayfishes. We: 1) mapped culvert locations and measured their flow; 2) quantified movement of (native) in culverts with velocities of 2, 31, and 42 cm/s; 3) compared the movement of (nonindigenous), , and (native) in a culvert with velocity of 30 cm/s; and 4) used a recirculating flume to determine the water velocity that impeded upstream movement (impedance velocity) of each species. Culverts had higher velocities than upstream riffles during baseflow conditions. moved upstream in culverts with flows >30 cm/s, but individuals slipped more frequently and traveled slower than those tested at 2 cm/s. moved upstream faster in culverts and had an impedance velocity ∼6 cm/s faster than (34.0 ± 1.2 cm/s, mean ± 1 SE) and ∼8 cm/s faster than (32.0 ± 1.1 cm/s). Culverts impeded crayfish upstream movement differently among species. Nonindigenous species tolerated higher flows, so culverts may create a filter that favors the spread of invasive species. Culverts should be designed to keep water velocity <30 cm/s to mitigate flow effects on crayfish passage, thereby minimizing the possible combined effects of fragmentation and nonindigenous species introductions. [ABSTRACT FROM AUTHOR]

The article presents a study that assesses the vulnerability of the ecosystem to invasive rusty crayfish, Orconectes rusticus. The study utilizes the freshwater-rich landscapes of Wisconsin to develop a model for invasive rusty crayfish. It also provides stakeholders with flexibility to prioritize sites for prevention efforts given a maximum level of acceptable risk or based on budgetary or time restrictions.

Competing group members tend to arrange in a social order that governs who will likely submit to whom. In many species the spatial distribution of individuals often reflects social status: dominants tend to occupy central locations while subordinates are often found along the group's periphery. This article explores the emergence of spatial consequences as a result of social rank differentiation. Rather than orienting centripetally, the movements of crayfish (Orconectes rusticus) primarily indicated a tendency to remain close to arena walls. Spatial locations were affected by the location of group members; but, rather than actively aggregating or clustering, individuals maintained a minimum distance. Previously established social rank did not affect spatial distributions. High population densities in the field are likely attributed to habitat constraints, rather than any social or centripetal tendencies of individual crayfish. [ABSTRACT FROM AUTHOR]

Canadian water bodies are presently experiencing fluctuations in orconectid crayfish ranges largely as a result of human activities. The range of Orconectes virilis, Canada’s most widespread crayfish, is expanding westward into previously uninhabited water bodies of Alberta. This species is also set to re-colonize watersheds in the eastern extent of its range as post-acidification recovery of aquatic ecosystems continues. In addition, the non-native Orconectes rusticus has invaded Central Canada. This species has the potential to rapidly invade boreal water bodies and out-compete native congeners, including O. virilis. Both these crayfish species are known to affect benthic ecosystems and their invasions may have adverse consequences for Canadian water bodies if left unchecked. Here we review the current documented distribution of O. virilis and O. rusticus in Canada, and identify the potential impacts that their invasion may have on boreal aquatic ecosystems. Finally, we consider options that resource managers might consider to contend with these invasions. [ABSTRACT FROM AUTHOR]

In 2004, we revisited a Michigan stream invaded by rusty crayfish (Orconectes rusticus) to determine if this species continued to expand its downstream range and negatively impact the stream food web. Compared to a 1992 study, we predicted that rusty crayfish would increase in density and downstream distribution from a small lake, resulting in further reduction of in-stream resources such as organic matter, benthic invertebrates, and periphyton. To determine current crayfish distributions and impacts, we conducted a longitudinal survey of crayfish abundance, ran a 28-d leaf breakdown experiment, and sampled benthic substrates. Leaf packs of sugar maple (Acer saccharum) leaves were placed at three sites with differing crayfish densities (high, intermediate, and none). Breakdown rates were compared across the three sites and for two treatments (closed leaf bags excluding crayfish and open bags allowing crayfish access). Benthic invertebrates were sampled from leaf bags and invertebrates and periphyton were sampled from cobbles. In contrast to 1992, we found that the maximum downstream distance of rusty crayfish declined from 4 km to less than 3 km downstream from the lake. Leaves in open bags decayed significantly faster (k = 0.143) than did leaves in closed bags at all sites (k = 0.079) (p = 0.0005). The site lacking crayfish had significantly higher densities of invertebrates compared to both high and intermediate crayfish density sites (p = 0.005). Although we found that rusty crayfish reduced standing stocks of leaves and invertebrates, we did not detect measurable changes in periphyton biomass. Therefore, rusty crayfish have not dispersed further downstream since 1992, but where present, these omnivores significantly reduce resource availability via the consumption of leaf material and benthic invertebrates. [ABSTRACT FROM AUTHOR]

Preventing the invasion of freshwater aquatic species is the surest way to reduce their impacts, but it is also often expensive. Hence, the most efficient prevention programs will rely on accurate predictions of sites most at risk of becoming invaded and concentrate resources at those sites. Using data from Vilas County, Wisconsin (U.S.A.), collected in the 1970s, we constructed a predictive occurrence model for rusty crayfish (Orconectes rusticus ) and applied it to an independent data set of 48 Vilas County lakes to predict which of these were most likely to become invaded between 1975 and 2005. We nested this invasion model within an economic framework to determine whether targeted management, derived from our quantitative predictions of likely invasion sites, would increase the economic value of lakes in the independent data set. Although the optimum expenditure on lake protection was high, protecting lakes at this level would have produced net economic benefits of at least $6 million over the last 30 years. We did not attempt to determine the value of nonmarket benefits of protection; thus, our results are likely to underestimate the total benefits from preventing invasions. Our results demonstrate that although few data are available early in an invasion, these data may be sufficient to support targeted, effective, and economically rational management. In addition, our results show that ecological predictions are becoming sufficiently accurate that their application in management can produce net economic benefits. [ABSTRACT FROM AUTHOR]

In many species, social interactions play a key role in deciding resource allocation. Aggression is one mechanism by which crayfish become dominant, which, in turn, enables them to acquire higher-quality resources. In crayfish, hierarchies and dominance structures are formed by dyadic interactions. In natural habitats, crayfish have agonistic interactions that often take place with other crayfish in the vicinity. There is a possibility for observers to gain information about potential future opponents. We were interested in examining the impact of observing agonistic interactions on the social behaviour of a bystander crayfish. Bystanders were visually exposed to one of four treatments followed by an agonistic interaction with a naïve individual. Treatments consisted of: (1) two size-matched crayfish fighting (fight treatment); (2) two size-matched crayfish not fighting (visual control); (3) an empty fight arena with a retractable wall (motion control); or (4) an empty tank with no retractable wall (handling control). The second interaction, where the bystander crayfish was fought against a naïve size-matched individual, or tester crayfish, was analysed by a person, blind to treatment, for initiation, winner–loser and temporal dynamics of escalation. Our results indicate that bystander crayfish exposed to the fight treatment lost significantly more often to tester crayfish than bystander crayfish subjected to control treatments. In addition, there were changes in the fight dynamics for the bystander crayfish. These results show that observations of interactions by a third crayfish have implications for hierarchies and social behaviour in natural settings. [Copyright &y& Elsevier]

1. Invasive species frequently have adverse impacts on native communities and ecosystems. Management options are often limited. Our goal is to evaluate the effect of intensive trapping and fish predation on the population dynamics of an invasive crayfish. 2. From 2001 to 2005, we removed invasive rusty crayfish ( Orconectes rusticus) by trapping in Sparkling Lake in northern WI. In addition, the Wisconsin Department of Natural Resources restricted harvest of fish species known to consume crayfish, thereby increasing predation on crayfish that are too small to trap. 3. After an initial increase, catch rates of rusty crayfish declined by approximately 95%, from 11 crayfish per trap per day in 2002 to 0.65 in 2004. The catch rate in 2005 remained low at 0.5 crayfish per trap. Females comprised nearly 50% of the catch from 2002 to 2004. Unlike rusty crayfish in Sparkling Lake, catch rates of O. rusticus and Orconectes propinquus in three nearby lakes increased or remained relatively constant over the 5-year removal period. 4. We also examined the influence of habitat and temperature on crayfish catch rates. Catch rates were highest at water temperatures between 20 and 25 °C and on cobble, log or macrophyte habitats that may serve as refuge from fish predation. 5. Five summers of intensive trapping and fisheries management practices reduced abundances, but did not extirpate rusty crayfish in Sparkling Lake. To determine the potential of trapping as a management option for invasive crayfishes, these methods must be tested in other systems. [ABSTRACT FROM AUTHOR]

Our study examined the effect of dominance on feeding, mating behaviour, and shelter use in the crayfish, Orconectes rusticus. In three different experiments, dominance and resource use were recorded in male populations, mixed-sex populations, and when crayfish were alone. Crayfish established dominance status in populations or through status conditioning and had access to variable resources (food, mates, and/or shelters) in each experiment. Subsequent resource use was quantified and compared to dominance rank. Our results did not match conventional predictions that dominance would confer increased access to resources. Top ranked dominant crayfish occupied shelter significantly less than lower ranks. This differential shelter use may be due to dominant motivation to reinforce status, as dominants also participated in the most agonistic interactions. When dominant crayfish had access to resources in the absence of conspecifics, dominant crayfish occupied shelter significantly more than subordinate and naïve crayfish. This result illustrates that present social context has a significant impact on behavioural decisions in crayfish. Social history and social context interact to determine shelter occupancy in this case. Feeding and mating was unaffected by social status in our populations. This is a surprising result given current views on the role of dominance and aggression in many animal systems. The consequences of dominance for resource use in crayfish do not follow our current understanding of resource holding potential. We hypothesize that these consequences vary due to changing behavioural motivations in different social contexts. Future studies should examine under which conditions dominance may impact feeding and mating and whether differential resource use results in differential reproductive success. [ABSTRACT FROM AUTHOR]

The major chelae have been found to be important structures used for breeding and reproduction in crustaceans; however their role in the detection of conspecific sex odours is unknown. We implemented a behavioural bioassay to test whether male reproductive (form I) and nonreproductive (form II) crayfish (Orconectes rusticus) use their major chelae to detect reproductive female odours. We videotaped and analysed the behavioural reactions of form I and form II males to four different odour treatments: reproductive female-conditioned water, male-conditioned water, filtered fish homogenate (food odour; positive control), and water (negative control) delivered from an air stone (N = 20 per treatment). In addition, all males were under two sensory conditions: intact or blocked chelae. Chelae were chemosensory-blocked by coating their dorsal surface with super glue. Normalized odour source handling time was measured, along with time spent handling the odour source between differing groups of sensory appendages: major chelae/first walking legs and maxillipeds/first walking legs. Our results indicate that both form I and II, intact and blocked, male crayfish significantly handled the odour source after a food stimulus was introduced. These results indicate the efficacy of the behavioural assay and sensory-blocks. Only intact form I males handled the odour source significantly when a reproductive female odour was delivered. Sensory-blocking of the chelae of form I males eliminated this difference. Intact and blocked form II males showed no differences when presented with reproductive female odours. Intact form I male crayfish spent more time handling the reproductive female-conditioned water source with their major chelae/first walking legs than those crayfish exposed to food odours. These results strongly suggest that the major chelae contain necessary chemosensory structures needed for female odour source recognition. [ABSTRACT FROM AUTHOR]

1. Biological invasions are widely recognised as a significant component of human-caused environmental change and a primary threat to native biodiversity. The negative impacts of species invasions are particularly evident for freshwater crayfish faunas. 2. This study provides novel insight into the ecological effects of native and non-native crayfish on zoobenthic communities (with emphasis on the non-native rusty crayfish, Orconectes rusticus) across broad scales by combining a meta-analysis of small-scale experimental studies with a long-term observational study conducted over a 24 year period in Sparkling Lake, Wisconsin, U.S.A. (46°00′N, 89°42′W). 3. The meta-analysis summarised quantitatively the results of cage experiments for seven species of crayfish spanning four continents. We found that total zoobenthos densities (primarily Gastropoda and Diptera) were significantly lower in treatments containing crayfish relative to controls; a result that was significant for non-native crayfish but not for crayfish in their native range, perhaps owing to a small sample size. In contrast to other species, rusty crayfish were also negatively associated with Ephemeroptera. 4. Results from the time series analysis comparing temporal trends in rusty crayfish and invertebrate abundances from Sparkling Lake were consistent with the findings from the meta-analysis. Rusty crayfish were negatively correlated with the abundance of total zoobenthos, Diptera, Ephemeroptera and Odonata, as well as families of Trichoptera. 5. By coupling the results from short and long-term research, our study offers greater insight into the nature of crayfish-invertebrate interactions in aquatic systems, revealing consistent effects of invasive crayfish on native fauna. The control and management of invasive species is facilitated by the knowledge that well executed small-scale studies may be extrapolated to understand larger-scale ecological interactions. [ABSTRACT FROM AUTHOR]

Aquatic organisms may use different mechanisms to locate an odour source, including odour-gated rheotaxis and chemotaxis. However, the effects of spatial and temporal information contained within odour signals in guiding orientation are under debate. In nature, turbulence and plume meandering give rise to signal intermittency, which organisms must overcome to locate an odour source successfully. In this study, crayfish were presented with odour plumes formed by a continuously released jet or a pulsed jet ranging from 0.5 to 3Hz. Crayfish oriented significantly differently in pulsed odour plumes differed significantly from than in a continuously released jet plume. In a continuous odour plumes, crayfish walked faster, had more accurate heading and turning angles, and stopped less often. The results suggest that crayfish are able to orient in a pulsed odour plumes, but that the spatial and temporal complexity of a continuous released odour plume allowed them to be more successful to find the odour source. [ABSTRACT FROM AUTHOR]

Global homogenization of biota is underway through worldwide introduction and establishment of nonindigenous (exotic) species. Freshwaterecologists should devote more attention to exotic species for two reasons. First, exotics provide an opportunity to test hypotheses aboutwhat characteristics of species or habitats are related to successful establishment or invasibility, respectively. Second, predicting which species will cause large ecological change is an important challenge for natural resource managers. Rigorous statistical relationships linking species characteristics to probability of establishment or ofcausing ecological impacts are needed. In addition, it is important to know how reliable different sorts of experiments are in guiding predictions. We address this issue with different spatial scales of experiments testing the impact of two predators on native snail assemblages in northern Wisconsin USA lakes: an exotic crayfish, the rusty crayfish (Orconectes rusticus); and a native fish predator, the pumpkinseed sunfish (Lepomis gibossus). For the crayfish, laboratory experiments, a field cage experiment, and a snapshot survey of 21 lakes gaveconsistent results: the crayfish reduced abundance and species richness of native snails. Laboratory and field experiments suggested thatpumpkinseed sunfish should have a similar impact, but the lake survey suggested little impact. Unfortunately, no algorithms exist to guide scaling up from small-scale experiments to the whole-lake, long~term management scale. To protect native biodiversity, management of freshwater exotic species should be targeted on lakes or drainages that are both vulnerable to colonization by an exotic, and that harbour endemic species. Management should focus on preventing introduction because eradication after establishment is usually not possible. [ABSTRACT FROM AUTHOR]