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Crayfish are ecologically important in freshwater systems worldwide and are imperiled in North America and globally. We sought to examine landscape- to local-scale environmental variables related to occupancy and detection probability of a suite of stream-dwelling crayfish species. We used a quantitative kickseine method to sample crayfish presence at 102 perennial stream sites with eight surveys per site. We modeled occupancy (psi) and detection probability ( P ) and local- and landscape-scale environmental covariates. We developed a set of a priori candidate models for each species and ranked models using (Q)AICc. Detection probabilities and occupancy estimates differed among crayfish species with Orconectes eupunctus , O. marchandi , and Cambarus hubbsi being relatively rare (psi < 0.20) with moderate (0.46–0.60) to high (0.81) detection probability and O. punctimanus and O. ozarkae being relatively common (psi > 0.60) with high detection probability (0.81). Detection probability was often related to local habitat variables current velocity, depth, or substrate size. Important environmental variables for crayfish occupancy were species dependent but were mainly landscape variables such as stream order, geology, slope, topography, and land use. Landscape variables strongly influenced crayfish occupancy and should be considered in future studies and conservation plans.

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.

Despite the widespread introduction of nonnative species and the heterogeneity of ecosystems in their sensitivity to ecological impacts, few studies have assessed ecosystem vulnerability to the entire invasion process, from arrival to establishment and impacts. Our study addresses this challenge by presenting a probabilistic, spatially explicit approach to predicting ecosystem vulnerability to species invasions. Using the freshwater-rich landscapes of Wisconsin, USA, we model invasive rusty crayfish ( Orconectes rusticus ) as a function of exposure risk (i.e., likelihood of introduction and establishment of O. rusticus based on a species distribution model) and the sensitivity of the recipient community (i.e., likelihood of impacts on native O. virilis and O. propinquus based on a retrospective analysis of population changes). Artificial neural networks predicted that ∼10%% of 4200 surveyed lakes ( n == 388) and ∼25%% of mapped streams (23 523 km total length) are suitable for O. rusticus introduction and establishment. A comparison of repeated surveys before vs. post-1985 revealed that O. virilis was six times as likely and O. propinquus was twice as likely to be extirpated in streams invaded by O. rusticus , compared to streams that were not invaded. Similarly, O. virilis was extirpated in over three-quarters of lakes invaded by O. rusticus compared to half of the uninvaded lakes, whereas no difference was observed for O. propinquus . We identified 115 lakes (∼3%% of lakes) and ∼5000 km of streams (∼6%% of streams) with a 25%% chance of introduction, establishment, and extirpation by O. rusticus of either native congener. By identifying highly vulnerable ecosystems, our study offers an effective strategy for prioritizing on-the-ground management action and informing decisions about the most efficient allocation of resources. Moreover, our results provide the flexibility for stakeholders to identify priority sites for prevention efforts given a maximum level of acceptable risk or based on budgetary or time restrictions. To this end, we incorporate the model predictions into a new online mapping tool with the intention of closing the communication gap between academic research and stakeholders that requires information on the prospects of future invasions.

Environmental DNA (eDNA) is a powerful method for assessing the presence and distribution of invasive aquatic species. We used this tool to detect and monitor several invasive crayfishes Procambarus clarkii, Orconectes limosus and Pacifastacus leniusculus present in, or likely to invade, the ponds of the Brenne Regional Natural Park. A previous study showed that the eDNA method was not very efficient in detecting P. clarkii. In the present study, we explored new improvements in the detection of invasive crayfish. We designed specific primers for each crayfish species, and set up an experimental mesocosm approach to confirm the specificity of the primers and the sampling protocol. We analysed samples taken from ponds in 2014 and 2015. We compared two qPCR protocols involving either SybrGreen or TaqMan assays. Using these same primers, we were able to detect crayfish eDNA with both assays during the mesocosm experiment. However, crayfish from field samples could only be detected by performing qPCR with a SybrGreen assay. We successfully monitored the presence of three invasive species of crayfish using eDNA. This method is a powerful tool for establishing the presence or absence of invasive species in various freshwater environments.

The ultrastructure of spermatozoa in three species of cambarid crayfish, Cambarus robustus , Orconectes propinquus , and Orconectes rusticus , were studied and compared with eight previously studied species from different crayfish families using morphological features and biometrical data. The ultrastructure of spermatozoa show a generally conserved pattern including an acrosome and nucleus in the anterior and posterior parts of the cell, respectively, radial arms that wrap around the nucleus, and the whole cell is enclosed by an extracellular capsule. The most outstanding morphological feature in spermatozoa of three studied cambarid crayfish is the crest-like protrusions in the anterior part of the acrosome that can be used as one of the features for distinguishing the members of this family. Results of biometrical data reveal that acrosome size in the representatives of Parastacidae are the smallest, while representatives of Astacidae show the biggest acrosome. The acrosome size in species belonging to Cambaridae occupy an intermediate position between the two other families of freshwater crayfish. In conclusion, a combination of morphological features and biometrical data of spermatozoa can help distinguishing different species of the freshwater crayfish.

Ecological applications of stable isotope analysis are dependent on knowing consumer-diet discrimination factors ( Delta ) and consumer metabolic turnover rates (m). We used an 80-day laboratory experiment to test for differences in the delta super(13)C, delta super(15)N and m of two species of crayfish (Orconectes rusticus and O. virilis) fed one of two diets (algae wafers and bloodworms). Over the course of the experiment, the delta super(13)C and delta super(15)N signatures of the crayfish approached equilibrium with those of their diets. We fit our data to a growth-based model and found delta super(13)C, delta super(15)N, and m to be largely indistinguishable between species, except in the case of delta super(15)N and m of crayfish on the algae diet. We thus pooled parameters to calculate Delta super(13)C (algae diet: 1.57ppt [95% confidence interval: 0.86-2.35]; bloodworm diet: 0.8ppt [0.14-1.55]) and Delta super(15)N (bloodworm diet: 1.2ppt [0.32-2.11]), and used species-specific data to calculate Delta super(15)N for the algae diet (O. rusticus: 2.54ppt [2.06-3.08]; O. virilis: 3.35ppt [2.53-4.51]). Our results provide values of stable isotope Delta and m for applications to crayfish, and offer a rare comparison of these values between two closely related species and to commonly used literature values.

Early detection is invaluable for the cost‐effective control and eradication of invasive species, yet many traditional sampling techniques are ineffective at the low population abundances found at the onset of the invasion process. Environmental DNA (eDNA) is a promising and sensitive tool for early detection of some invasive species, but its efficacy has not yet been evaluated for many taxonomic groups and habitat types. We evaluated the ability of eDNA to detect the invasive rusty crayfish Orconectes rusticus and to reflect patterns of its relative abundance, in upper Midwest, USA, inland lakes. We paired conventional baited trapping as a measure of crayfish relative abundance with water samples for eDNA, which were analysed in the laboratory with a qPCR assay. We modelled detection probability for O. rusticus eDNA using relative abundance and site characteristics as covariates and also tested the relationship between eDNA copy number and O. rusticus relative abundance. We detected O. rusticus eDNA in all lakes where this species was collected by trapping, down to low relative abundances, as well as in two lakes where trap catch was zero. Detection probability of O. rusticus eDNA was well predicted by relative abundance of this species and lake water clarity. However, there was poor correspondence between eDNA copy number and O. rusticus relative abundance estimated by trap catches. Synthesis and applications. Our study demonstrates a field and laboratory protocol for eDNA monitoring of crayfish invasions, with results of statistical models that provide guidance of sampling effort and detection probabilities for researchers in other regions and systems. We propose eDNA be included as a tool in surveillance for invasive or imperilled crayfishes and other benthic arthropods.

Invasive crayfishes have a strong negative effect on multiple trophic levels, including other crayfishes. However, documentation of the spread of non-native crayfish species and their impact on native crayfishes could be improved, particularly over large spatial scales in stream ecosystems. We collected crayfish and quantified habitat at 461 stream sites throughout Michigan in 2014–2016 and compared our collections to a historical account of crayfish collections published in 1975. Our objectives were to: (1) quantify the change in non-native rusty crayfish (Faxonius rusticus) and native species distributions from 1975 to 2014–2016; (2) quantify how rusty crayfish affect the habitat associations of native species in Michigan streams; and (3) determine the effectiveness of dipnets, our primary sampling method. We found all species in more watersheds compared to 1975, likely due in part to increased sampling. However, we found rusty crayfish in 22 more HUC-8 watersheds than in 1975, a larger increase than all other species. Habitat associations of native species also shift in the presence of rusty crayfish. In instances where native species co-occurred with rusty crayfish, most obligate aquatic native species were found in less-preferred habitat such as sand or macrophytes compared to cobble substrate when the species is in isolation. Our results indicate a broad range expansion by rusty crayfish over the last 40 years, suggesting that surveys of crayfish diversity and habitat occupancy should be more routine to inform management of native crayfish species.

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 sub(3)), which is usually represented by conductivity or dissolved calcium. We predicted that conductivity and calcium would not serve as accurate surrogates for CaCO sub(3) 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.

Pyrethroid insecticides are highly toxic to many aquatic organisms. The aim of this study was to evaluate the toxicity of the commercial products Cyperkill 25 EC (active compound 250 g/l cypermethrin) and Decis Mega (active compound 50 g/l deltamethrin) for European non-indigenous marbled crayfish Procambarus virginalis, red swamp crayfish Procambarus clarkii, signal crayfish Pacifastacus leniusculus, spiny-cheek crayfish Orconectes limosus and yabby Cherax destructor. These data will provide a baseline for potential programmes to eradicate alien crayfish from Europe (EU Regulation No. 1143/2014; Commission Implementing Regulation No. 2016/1141) and are also relevant globally. The 96hLC50 values of Cyperkill 25 EC were 0.09, 0.17, 0.18, 0.19 and 0.30 µg/l for spiny-cheek crayfish, red swamp crayfish, marbled crayfish, signal crayfish and yabby, respectively. In the same order, the 96hLC50 values of Decis Mega were 0.76, 0.16, 0.21, 0.03 and 0.27 µg/l. The toxicity of the insecticides was similar and species-specific, possibly reflecting the size difference of the tested animals. This study shows that cypermethrin and deltamethrin are highly toxic to the tested crayfish species at low concentrations. This high sensitivity, along with the low accumulation in the food chain and short-term persistence in the aquatic environment, suggests that they are suitable biocides for eradicating crayfish in the wild. Stagnant, closed water bodies with newly emerging invaders are ideal sites for possible application, although local conditions must be considered.