Search

Estimates of recreational fishing effort and catch are needed to inform fisheries management, but such estimates can be challenging to obtain. We combined a zig‐zag line transect survey of buoys, a fisheries enforcement survey and a drone survey to estimate recreational effort in the open‐access trap fishery for signal crayfish (Pacifastacus leniusculus) in the sixth largest lake in Europe, Lake Vättern, Sweden. Using supporting variables such as size of nearby ports and bathymetry, our model‐assisted estimate of total effort was 6400 (±4300 CI) buoys during the three‐weekend season. Using the frequency of buoys to traps as a constant, the total number of crayfish traps was estimated to be 25,500 (±17,000 CI). The sampling design and methods presented are useful for ecologists and resource managers to design future multi‐source surveys of recreational trap fishing effort. [ABSTRACT FROM AUTHOR]

Invasive Non-Native Species (INNS) are a principal threat to global biodiversity and the early detection of new introductions is key to facilitate a rapid response to limit the risk of establishment and spread. Related to this, there is growing interest in using environmental DNA (eDNA) for INNS detection. The applied use of eDNA in ecology is, however, in its relative infancy with few species for which regulator-approved methods are available. Here, laboratory trials were conducted to investigate the use of commercially available eDNA assays for detecting two high priority INNS in the UK, killer shrimp (Dikerogammarus villosus) and signal crayfish (Pacifastacus leniusculus), at different population densities. For killer shrimp, DNA of the expected fragment size was detected from all three trials where animals were maintained at a density of 1 per 1 L but species confirmation by Sanger sequencing was only possible for one of these replicates. Whilst capillary electrophoresis detected DNA of the expected fragment size in serially diluted samples down to a density of 1 shrimp in 100 L, this could not be confirmed by sequencing. Signal crayfish DNA was detected by qPCR in all four trials where animals were housed at a density of 1 per 10 L. Using serial dilutions, it was possible to detect signal crayfish in samples representing a density of 1 per 1,000 L, however this was unreliable. These results demonstrate the potential for using eDNA as a detection method for killer shrimp and signal crayfish but also highlights that detectability is species/assay specific and dependant on population density. The insights gained will help inform decisions surrounding the appropriateness of using these eDNA assays, and improve interpretation of any results generated. [ABSTRACT FROM AUTHOR]

Invasive species and river infrastructure are major threats to freshwater biodiversity. These stressors are commonly considered in isolation, yet the construction and maintenance of river infrastructure can both enhance and limit the expansion of invasive species. Spatial and temporal limitations of laboratory and field studies, coupled with little consideration of population‐level responses (e.g. invasion rate), have limited understanding of the efficacy of infrastructure for long‐term, catchment‐scale containment of invasive species.This study utilised an individual‐based model (IBM) to investigate the ability of a partial riverine barrier to contain the spread of invasive species at large spatio‐temporal scales, using American signal crayfish Pacifastacus leniusculus as a model species. The base model (no barrier) accurately recreated longitudinal expansion rates of signal crayfish reported in existing literature. A virtual riverine barrier was added to the base model, with passage at the structure parameterised using existing literature and the results of an experiment that demonstrated no clear relationship between crayfish density and passage efficiency at a Crump weir.Model outputs indicated a weir downstream of the release point had no effect on longitudinal expansion of crayfish, whereas an upstream barrier slowed the invasion rate for 6.5 years after it was first encountered. After the invasion rate had recovered to pre‐barrier levels, the invasion front was 2.4 km further downstream than predicted in the absence of a barrier, representing a 1.73 year delay in longitudinal range expansion.Synthesis and applications. Despite substantial negative impacts on native biodiversity, river infrastructure can also delay the spread of freshwater invasive species, representing a trade‐off. This demonstrates the need to consider positive ecological consequences of river infrastructure when designing prioritisation techniques for barrier removal and mitigation (e.g. selective fish passage), and suggests that in some cases barriers may provide a useful integrated pest management tool. [ABSTRACT FROM AUTHOR]

Microplastics are a globally pervasive pollutant with the potential to directly impact species and accumulate in ecosystems. However, there remains a relative paucity of research addressing their accumulation in freshwater ecosystems and a near absence of work in crayfish, despite their high ecological and economic importance. This study investigated the presence of microplastics in the invasive signal crayfish Pacifastacus leniusculus along a stream urbanization gradient. The results demonstrate a ubiquitous presence of microplastics in crayfish digestive tracts at all sites and provide the first evidence of microplastic accumulation in tail tissue. Evidence of a positive linear trend was demonstrated between microplastic concentration in crayfish and upstream urban area size in generalized linear models. Evidence for a positive effect of the upstream urban area and a negative effect of crayfish length on microplastic concentrations in crayfish was demonstrated in multiple generalized linear regression models. Our results extend the current understanding of microplastics presence in freshwater ecosystems and demonstrate their presence in crayfish in the wild for the first time. [ABSTRACT FROM AUTHOR]

Abstract Microplastics are a globally pervasive pollutant with the potential to directly impact species and accumulate in ecosystems. However, there remains a relative paucity of research addressing their accumulation in freshwater ecosystems and a near absence of work in crayfish, despite their high ecological and economic importance. This study investigated the presence of microplastics in the invasive signal crayfish Pacifastacus leniusculus along a stream urbanization gradient. The results demonstrate a ubiquitous presence of microplastics in crayfish digestive tracts at all sites and provide the first evidence of microplastic accumulation in tail tissue. Evidence of a positive linear trend was demonstrated between microplastic concentration in crayfish and upstream urban area size in generalized linear models. Evidence for a positive effect of the upstream urban area and a negative effect of crayfish length on microplastic concentrations in crayfish was demonstrated in multiple generalized linear regression models. Our results extend the current understanding of microplastics presence in freshwater ecosystems and demonstrate their presence in crayfish in the wild for the first time.

A new population of the non-indigenous signal crayfish, Pacifastacus leniusculus, was recorded from Lake Sugenuma in Gunma Prefecture, central Japan. A survey conducted in 2019 confirmed that the signal crayfish is established and widely distributed in the lake. Sathodrilus attenuatus(Annelida, Clitellata, Branchiobdellida)and Uncinocythere occidentalis (Arthropoda, Crustacea, Ostracoda)were newly recorded in the Prefecture, as ectosymbionts on the crayfish. The branchiobdellidan fauna suggests that the present crayfish and symbionts in Lake Sugenuma are derived from Hokkaido populations or their descendants. [ABSTRACT FROM AUTHOR]

Climate change is expected to alter impacts of invasive alien species (IAS). As omnivores and ectotherms, invasive crayfish species (ICS) can be particularly influenced by altered thermal regimes with possible impacts on native species and key ecosystem processes, such as leaf-litter breakdown. We performed a controlled study using a multi-trophic approach to assess the individual and combined effects between two ICS (Pacifastacus leniusculus and Procambarus clarkii) on leaf-litter breakdown under temperature increase (15 and 18 °C). We used aquaria with one or two species combinations of ICS (2-individuals per aquarium); each aquarium contained transparent cages with three individuals of a native invertebrate detritivore (Sericostoma sp.). All aquaria had a fine-mesh bag containing microbially-colonized oak leaves to assess direct and indirect impacts of crayfish on leaf-litter breakdown and fine particulate organic matter (FPOM) production. Leaf-litter breakdown driven by microbes and Sericostoma was affected by temperature. Increasing temperature enhanced leaf-litter breakdown and FPOM production by P. clarkii, but not by P. leniusculus. At 15 °C, leaf breakdown was lower in treatments with both ICS than the expected from their individual performances, which may suggest competitive interactions between crayfish species. FPOM production was significantly correlated with leaf-litter breakdown, but not in treatments with both ICS. Our results suggest that competitive interactions between ICS may occur and potentially attenuate their impacts on key ecological processes. However, predicted increases in temperature may change the performance of IAS and increase the magnitude of their combined effects. [ABSTRACT FROM AUTHOR]

The freshwater crayfish Pacifastacus leniusculus is among the most widespread invasive crayfish species in Europe. Pacifastacus leniusculus invaded Hungary around 1998 and here we investigated the recent expansion of this species and its impact on other aquatic macroinvertebrates. The colonization of watercourses throughout Europe by the signal crayfish resulted in negative impacts on the present aquatic communities. Our investigation (i.e. in Rába, Pinka, Gyöngyösstream, Répce, Arany-stream and Strém systems) revealed that the distribution range of signal crayfish is still in expansion in the western part of Hungary and in all likelihood impacting the aquatic communities in these watercourses. Our results obviously demonstrated that signal crayfish densities were highest in habitats with gravel or coarse particulate organic matter, which seems to reflect a species-specific habitat preference. Our investigation proved that the presence of P. leniusculus had negative effects on a number of protected species such as Calopteryx virgo and Onychogomphus forcipatus next to a significant negative effect on the Odonata and Trichoptera species richness as well as on the abundances of Ephemeroptera, Odonata and Trichoptera. Our study in Hungary supports the notion of the significant negative impact of signal crayfish on native freshwater invertebrate communities throughout Europe. In order to assess whether these impacts are restricted to fast flowing waters only, an adequate monitoring plan providing more knowledge on this species with respect to biotic and abiotic preferences and aquatic macroinvertebrate composition is required. [ABSTRACT FROM AUTHOR]

Predatory, non‐native fauna can influence biodiversity and trophic dynamics in invaded ecosystems. Signal crayfish (Pacifastacus leniusculus) are a highly successful invader, which have altered freshwater benthic communities, including bivalve populations. Bivalves are a keystone freshwater group in global in decline, partly due to invasion by alien bivalve and crayfish species. However, little is known about the predatory impacts of invasive crayfish within co‐occurring native and invasive bivalve populations. Mesocosm predation choice experiments considered relative signal crayfish predation rates between paired native (Anodonta anatina and Unio tumidus) and invasive (Dreissena polymorpha, D. bugensis, and Corbicula fluminea) bivalves, and between paired invasive bivalves. All bivalves were actively predated, but there was no consistent difference in the biomass of invasive versus native bivalves consumed. However, the effects of consumption were consistently different; 18.2% of invasive bivalves were lethally predated, with 100% of surviving individuals remaining undamaged, whereas 1.1% of native bivalves were lethally predated, but 100% of surviving individuals received nonlethal damage in the form of shell chipping, which could reduce long‐term bivalve fitness in natural environments. In experiments considering paired invasive species, D. polymorpha was more resistant to predation when compared to other invasive taxa tested. The majority of field research considering aquatic invasions considers purely lethal predation effects inferred from invertebrate presence/absence. These experiments demonstrate the need to better understand both the processes and impacts of predation by invasive species, which may include substantial nonlethal effects on the fitness and life history of endangered taxa. [ABSTRACT FROM AUTHOR]

Historically it has been assumed that abiotic forces dominate fluvial sediment dynamics. However, a growing body of work indicates that biological energy can also exert a significant control over sediment dynamics. The role that invasive species may play in altering fine sediment dynamics is particularly pertinent given that any influence may disrupt the natural equilibrium of the ecosystem. Here we investigated the effect of invasive signal crayfish (Pacisfastcus leniusculus) on the transport and storage of fine sediment in a densely populated river compared with a nearby control river without crayfish, over an 18‐week period. We observed clear evidence of diurnal fluctuations in turbidity associated with crayfish presence including periodograms with power peaks at a period of 1 day. Fine sediment fluxes indicated that crayfish contributed on average 18.5% extra to baseflow loads than would be likely under abiotic forcing alone. Temporal variations in suspended sediment concentrations were also observed at the control site but these were different in character and exhibited no clear temporal pattern or consistency as confirmed by periodogram analysis. Crayfish did not have an effect on sediment ingress rates relative to the control site and, at the crayfish site, the reach scale sediment budget was in net equilibrium during the sampling period. Our results provide further evidence that biological energy alters riverine fine sediment dynamics and warrants consideration in sediment dynamic models. [ABSTRACT FROM AUTHOR]

Abstract Biological invasions are a serious problem in natural ecosystems. Local species that are potential prey of invasive alien predators can be threatened by their inability to recognize invasive predator cues. Such an inability of prey to recognize the presence of the predator supports the naïve prey hypothesis. We exposed eggs of a damselfly, Ischnura elegans, to four treatments: water with no predator cue (control), water with a native predator cue (perch), water with an invasive alien predator cue (spinycheek crayfish) that is present in the damselfly sampling site, and water with an invasive alien predator cue (signal crayfish) that is absent in the damselfly sampling site but is expected to invade it. We measured egg development time, mortality between ovipositing and hatching, and hatching synchrony. Eggs took longer to develop in the signal crayfish group (however, in this group, we also observed high green algae growth), and there was a trend of shorter egg development time in the spinycheek crayfish group than in the control group. There was no difference in egg development time between the perch and the control group. Neither egg mortality nor hatching synchrony differed between groups. We suggest that egg response to signal crayfish could be a general stress reaction to an unfamiliar cue or an artifact due to algae development in this group. The egg response to the spinycheek crayfish cue could be caused by the predation of crayfish on damselfly eggs in nature. The lack of egg response to the perch cue could be caused by perch predation on damselfly larvae rather than on eggs. Such differences in egg responses to alternative predator cues can have important implications for understanding how this group of insects responds to biological invasions, starting from the egg stage.

Invasive alien species (IAS) are leading to the homogenisation of taxonomic and functional biodiversity, with negative consequences for key ecosystem processes in fresh water. Invasive signal crayfish (Pacifastacus leniusculus) is expected to disrupt detritus‐based food webs by affecting leaf breakdown and/or by decreasing invertebrate density and diversity through predation. The combination of per‐capita and abundance effects of P. leniusculus in invaded ecosystems is still largely unknown.A four‐week field experiment was established in Rabaçal and Tuela Rivers (NE Portugal) to assess effects of P. leniusculus on invertebrate taxonomic and functional diversity and leaf litter breakdown following a gradient of invasion. We controlled the presence and absence of crayfish by placing the animals and leaf litter inside cages at six sites (three sites per river) according to the crayfish in situ abundance (absent, low, high). Cages were covered with coarse‐ or fine‐mesh net to allow or prevent invertebrates from accessing the leaves.Results showed that higher crayfish in situ abundance led to a decrease in abundance, richness and Shannon diversity of invertebrates and to changes in the communities' structures. Higher crayfish abundance led also to a decrease in invertebrate functional redundancy and an increase in the percentage of invertebrate taxa with resistance forms. Leaf litter breakdown increased with crayfish presence and decreased at sites with higher crayfish abundance.Overall, signal crayfish changed the community structure of invertebrates, with potential severe long‐term effects on native communities and leaf litter breakdown. Given the widespread distribution of signal crayfish (and other crayfish species), their ecological impacts should be assessed carefully, especially in pristine freshwater ecosystems such as those described here. [ABSTRACT FROM AUTHOR]

Invasive species represent one of the greatest threats to freshwater biodiversity. The successful colonisation and establishment of populations of invasive predators in waterbodies may expose the pre‐existing fauna to novel predation strategies to which they are not pre‐adapted. Despite this, there is still a paucity of information on behavioural responses within biological invasion research.Here we present the results of a series of 24‐hr mesocosm experiments that examined the handling times and responses of four Gastropoda species (Radix balthica, Physa fontinalis, Gyraulus albus, Potamopyrgus antipodarum) exposed to physical and chemical cues associated with the invasive crayfish, Pacifastacus leniusculus. We specifically considered four physicochemical treatments: (1) control (no cue); (2) conspecific chemical; (3) crayfish chemical; and (4) physical presence (but confined). In addition, we considered the effect of previous predator experience of the gastropod (predator naïve or aware) and additonally assessed survivourship in encounter trials.Handling time was found to vary significantly between gastropod species with survivorship from predation mirroring handling times observed. P. fontinalis required the greatest handling time (average of 58 s) and had the highest survivorship rate. In marked contrast, P. antipodarum were rapidly consumed, with an average handling time of 6 s and no individuals surviving after 4‐hr in the encounter trials. Handling time varied by gastropod size but also shell morphology.The response to the physical and chemical cues varied between gastropod species. R. balthica and P. fontinalis demonstrated vertical avoidance behaviour most readily whilst P. albus and P. antipodarum displayed active migration only to the physical presence cue. In most instances, the response was immediate with vertical migration (above the reach of the crayfish at 15 cm on the mesocosm wall) evident within an hour.Predation regime was found to exert a significant effect on the avoidance response of the gastropods. This was particularly notable in relation to the crayfish chemical cue and to a lesser extent the injured conspecific chemical cue. Predator‐naïve populations reacted with strong vertical avoidance behaviour in response to the crayfish chemical cue, whilst, in the case of P. fontinalis, predator aware individuals reacted most strongly to the conspecific chemical cue.Our results highlight the multifaceted challenge of understanding predator–prey relationships, particularly in the face of novel invasive species, and provide much‐needed evidence to begin to tackle this complex process. Gaining a better understanding of such interactions is vital in order to underpin management strategies and to enable evolutionary trajectories in invaded ecosystems to be assessed. Previous predator experience in combination with species identity are important attributes in determining predation risk when gastropod populations are exposed to novel predators and their associated predation cues. [ABSTRACT FROM AUTHOR]

Biological invasions are a serious problem in natural ecosystems. Local species that are potential prey of invasive alien predators can be threatened by their inability to recognize invasive predator cues. Such an inability of prey to recognize the presence of the predator supports the naïve prey hypothesis. We exposed eggs of a damselfly, Ischnura elegans, to four treatments: water with no predator cue (control), water with a native predator cue (perch), water with an invasive alien predator cue (spinycheek crayfish) that is present in the damselfly sampling site, and water with an invasive alien predator cue (signal crayfish) that is absent in the damselfly sampling site but is expected to invade it. We measured egg development time, mortality between ovipositing and hatching, and hatching synchrony. Eggs took longer to develop in the signal crayfish group (however, in this group, we also observed high green algae growth), and there was a trend of shorter egg development time in the spinycheek crayfish group than in the control group. There was no difference in egg development time between the perch and the control group. Neither egg mortality nor hatching synchrony differed between groups. We suggest that egg response to signal crayfish could be a general stress reaction to an unfamiliar cue or an artifact due to algae development in this group. The egg response to the spinycheek crayfish cue could be caused by the predation of crayfish on damselfly eggs in nature. The lack of egg response to the perch cue could be caused by perch predation on damselfly larvae rather than on eggs. Such differences in egg responses to alternative predator cues can have important implications for understanding how this group of insects responds to biological invasions, starting from the egg stage. [ABSTRACT FROM AUTHOR]

Abstract As crayfish invasions continue to threaten native freshwater biota, a detailed understanding of crayfish distribution and population structure becomes imperative. Nonetheless, most current survey methods provide inadequate demographic data. The quantitative ‘Triple Drawdown’ (TDD) dewatering method has highlighted the importance of such data, yet practical constraints prevent its large‐scale application. Here, we introduce the ‘Pritchard Trap’, a novel passive sampling method that reliably generates quantitative crayfish population data while requiring substantially lower sampling effort than TDDs. This quadrat‐style sampler was extensively tested in headwater streams of North Yorkshire, England, along an invasion gradient for signal crayfish (Pacifastacus leniusculus) from well‐established sites to mixed populations of signal crayfish and native white‐clawed crayfish (Austropotamobius pallipes). The Pritchard Trap was trialled over several time intervals to determine the minimum required trap deployment time. TDDs at the same sites allowed for a robust evaluation of Pritchard Trap sampling accuracy in representing crayfish densities and population structure. The Pritchard Trap successfully sampled both invasive and native crayfish (8–42 mm carapace length). A minimum passive deployment time of 4 days was required. At low crayfish densities (0.5 individuals m−2), increased trapping effort was necessary to achieve accurate population density and size class distribution estimates. The Pritchard Trap required substantially less sampling effort (working hours) and resources than the TDD, whilst also posing less risk to non‐target species. The Pritchard Trap, for the first time, affords logistically simple, truly quantitative investigations of crayfish population demographics for headwater systems. It could be integrated into crayfish research and management, for example to explore density‐dependent ecological impacts of invasive crayfish and their management responses or to monitor populations and recruitment in native crayfish conservation initiatives.

Invasive species often co-occur in nature and positive or negative interactions among them can affect community structure and ecosystem functioning. Outcomes depend on the intrinsic traits of the species involved and on how species' performance is affected by the environmental conditions of the recipient ecosystem. Here, we investigated the impact of nitrate, a nutrient common in urban and agricultural sewage discharges, on two invasive crayfish species (Pacifastacus leniusculus and Faxonius virilis) co-occurring in a Nitrate Vulnerable Zone in the UK. Crayfish were exposed to two ecologically relevant nitrate concentrations (≤ 10 and 50 mg NO3−/l) and seven traits relating to foraging success and interspecific interactions were assessed. During monospecific experimental trials, elevated nitrate had a similar impact on the foraging efficacy of P. leniusculus and F. virilis, reducing their ability to sense and find food. However, during dyadic interspecific competition experiments, higher nitrate caused a greater reduction in the number of aggressive behaviours of F. virilis towards P. leniusculus. As such, changes in environmental nitrate regime may affect interactions between these invasive species in regions of sympatry with consequences for their respective invasion dynamics and the wider ecosystem. [ABSTRACT FROM AUTHOR]

The spread of non-indigenous crayfish species poses a threat to local populations of crayfish as well as to other fauna and flora across Europe and around the world. Several methods have been used in attempt to reduce their numbers and stop their further spread. Crayfish barriers are the best way to stop the non-anthropogenic spread of established invasive crayfish populations. Up to now there are very few published papers regarding crayfish barrier design and practical experience in construction. For the last seven years, we have optimised construction and functionality of crayfish barriers, tested various building materials and planned construction of many barriers across Switzerland. In this article, we highlight our experience, share the acquired knowledge and present the newest findings regarding considerations, which must be made when planning a barrier to stop the upstream movement of non-indigenous crayfish species. From our experience we conclude that crayfish barriers work in preventing the movement of invasive species if certain factors are taken into account. Barrier design and construction must be specific for each project, because the size of the watercourse, flow velocity, bank conditions, existing constructions and accessibility, all change the way a barrier should be set-up.

Freshwater crayfish can be successful invaders that threaten native biota and aquatic ecosystems in numerous countries worldwide. Nonetheless, the inability of conventional crayfish survey techniques like trapping and handsearching to yield quantitative population data has limited the understanding of crayfish invasion biology and associated ecological impacts.Here, we employed a novel 'triple drawdown' (TDD) method to sample invasive populations of signal crayfish Pacifastacus leniusculus in a headwater stream in Northern England. The method was compared with conventional techniques of trapping and handsearching.The TDD method proved to be an effective technique with high capture efficiency, reporting signal crayfish densities from 20.5 to 110.4 animals/m2 at our study sites. These numbers exceed any previous estimates for similar streams.The TDD showed the vast majority of individuals across all sites were juvenile or sub‐adult (<26 mm CL), with only 2.3% of the population large enough (≥35 mm CL) to be caught in standard traps.Synthesis and applications. The triple drawdown (TDD) method demonstrates strong inefficiencies and biases in conventional crayfish survey and management techniques. Trapping is not recommended for representative sampling or control of juvenile dominated populations. TDDs, which can be adapted and modified to operate in multiple habitat types and freshwater systems, generate robust quantitative data on invasive crayfish population demographics in situ. This can advance our understanding of the biology of an important invader of freshwater systems around the world. Obtaining this data prior and post‐intervention is fundamental to evaluate invasive crayfish management, and we recommend the TDD method to assess the effectiveness of future control measures. [ABSTRACT FROM AUTHOR]

Climate change and invasive species are among the biggest threats to global biodiversity and ecosystem function. Although the individual impacts of climate change and invasive species are commonly assessed, we know far less about how a changing climate may impact invading species. Increases in water temperature due to climate change are likely to alter the thermal regime of UK rivers, and this in turn may influence the performance of invasive species such as signal crayfish (Pacifastacus leniusculus), which are known to have deleterious impacts on native ecosystems. We evaluate the relationship between water temperature and two key performance traits in signal crayfish—feeding and burrowing rate—using thermal experiments on wild‐caught individuals in a laboratory environment. Although water temperature was found to have no significant influence on burrowing rate, it did have a strong effect on feeding rate. Using the thermal performance curve for feeding rate, we evaluate how the thermal suitability of three UK rivers for signal crayfish may change as a result of future warming. We find that warming rivers may increase the amount of time that signal crayfish can achieve high feeding rate levels. These results suggest that elevated river water temperatures as a result of climate change may promote higher signal crayfish performance in the future, further exacerbating the ecological impact of this invasive species. [ABSTRACT FROM AUTHOR]

Female crayfish stores male gametes after mating until the beginning of egg laying and fertilization. The aim of the present study was to investigate the duration of post-mating spermatophore storage as well as the timing and temperature of spawning in two crayfish species of economic importance, namely the signal crayfish Pacifastacus leniusculus and the noble crayfish Astacus astacus. Results showed that the average duration of the post-mating spermatophore storage is significantly (P

Invasive species represent one of the primary threats to global biodiversity. Despite acknowledged implications for taxonomic properties of ecological communities following invasion, functional measures remain poorly understood.We examined the long‐term implications of invasion by a crayfish species, Pacifastacus leniusculus, on functional alpha and beta diversity properties of lotic macroinvertebrate communities in three English regions. The dataset comprised 477 samples collected predominantly between 1990 and 2013. Unlike many invasion studies, we employed before and after invasion comparisons, in association with control rivers not invaded by crayfish.Functional richness and divergence metrics displayed the strongest responses to invasion, highlighting that P. leniusculus may alter the range of functional niches and extreme trait values (likely reflecting resistance and resilience mechanisms) displayed by macroinvertebrate communities. Interestingly, in one region, biodiversity gains seen in control rivers were not mirrored in invaded rivers, potentially suggesting that invasion inhibited ecological improvements.Invasion by signal crayfish resulted in functional compositional changes in two of the three English regions studied, with these rivers yielding greater ecological differences between pre‐ and post‐invasion periods relative to control rivers. This change was primarily driven by higher nestedness values in invaded rivers, with communities containing functional subsets relative to control rivers. The third region demonstrated no functional compositional changes or alterations in functional beta diversity associated with invasion.Our findings indicated that in most instances, the functional properties of macroinvertebrate communities responded to crayfish invasion and may therefore represent a complementary means to monitor the ecological condition of lotic ecosystems. Given their spatial transferability, functional traits could provide a platform to guide regional management practices in the face of biological invasions. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Ireland, being an island situated on Europe's western seaboard, has a fewer number of native species than mainland European Union Member States (MS). Increased numbers of vectors and pathways have reduced the island's biotic isolation, increasing the risk of new introductions and their associated impacts on native biodiversity. It is likely that these risks are greater here than they are in continental MSs, where the native biodiversity is richer. A horizon scanning approach was used to identify the most likely invasive alien species (IAS) (with the potential to impact biodiversity) to arrive on the island of Ireland within the next ten years. To achieve this, we used a consensus-based approach, whereby expert opinion and discussion groups were utilised to establish and rank a list of 40 species of the most likely terrestrial, freshwater and marine IAS to arrive on the island of Ireland within the decade 2017-2027. The list of 40 included 18 freshwater, 15 terrestrial and seven marine IAS. Crustacean species (freshwater and marine) were taxonomically dominant (11 out of 40); this reflects their multiple pathways of introduction, their ability to act as ecosystem engineers and their resulting high impacts on biodiversity. Freshwater species dominated the top ten IAS (seven species out of ten), with the signal crayfish (Pacifastacus leniusculus) highlighted as the most likely species to arrive and establish in freshwaters, while roe deer (Capreolus capreolus) (second) and the warm-water barnacle (Hesperibalanus fallax) (fifth), were the most likely terrestrial and marine invaders. This evidence-based list provides important information to the relevant statutory agencies in both the Republic of Ireland and Northern Ireland to prioritise the prevention of the most likely invaders and aid in compliance with legislation, in particular the EU Regulation on Invasive Alien Species (EU 1143/2014). Targeted biosecurity in both jurisdictions is urgently required in order to manage the pathways and vectors of arrival, and is vital to maintaining native biodiversity on the island of Ireland. [ABSTRACT FROM AUTHOR]

Invasive non‐native species (INNS) threaten biodiversity and ecosystem functioning globally. However, there remains a pressing need to understand the environmental factors controlling the dispersal, successful establishment and subsequent ecological impacts of INNS for receiving ecosystems. Here, we examine how region‐wide flow regime magnitudes facilitate the successful establishment of an invasive crayfish species (Pacifastacus leniusculus, signal crayfish) in England (UK). We also consider the interactive effects of invasive crayfish with flow regime variations on the structural and functional diversity of macroinvertebrate communities.Low‐flow magnitudes increased the likelihood of P. leniusculus establishment, with 80% of recorded invasion dates falling in years with flow magnitudes below average (low‐ and low‐moderate flow classes), whilst only 1.6% occurred in high‐flow years.Temporal trajectories of structural and functional macroinvertebrate responses in invaded rivers demonstrated reduced diversity compared to control rivers. Lower taxonomic and functional richness measures typically coincided with periods of low discharge in invaded rivers and were greatest during regionally high‐flows.Macroinvertebrate communities displayed significant structural and functional responses to the interaction between invasive crayfish and flow regime variations. Specifically, a number of low‐ and high‐flow indices yielded significant associations, highlighting the role of extreme hydrological events in shaping INNS effects on receiving ecosystems. We also detected greater ecological effects of invasive crayfish under hydrologically stable conditions. Importantly, and for the first time, we observed that invasive crayfish reversed macroinvertebrate community responses to flow regime cues (e.g. discharge fall rate and minimum flows in the preceding 180 days).Synthesis and applications. Results from this study indicate that low‐flow events facilitate the spread/establishment of invasive crayfish and correspond with greater ecological effects for receiving ecosystems. Given that low‐flow events are predicted to increase in intensity, duration and frequency over the 21st century, our results highlight the potential threat that invasive crayfish may pose under future hydroclimatic changes. Managing river flow regimes effectively (including maintaining higher flow events and flow variability) is likely to be vital in conserving ecological diversity following crayfish invasion. [ABSTRACT FROM AUTHOR]

The Louisiana red swamp crayfish is a pest species in California, unwanted because it is elbowing out native crayfish, snails, salamanders and frogs. Think of it as the Viking of the crayfish world–hearty, strong and aggressive, especially on foreign soil.

Biological invasions are among the leading causes of the loss of biodiversity worldwide. Although there are many hypotheses about traits of a good invader and characteristics of native communities that increase susceptibility to invasion, the realized success of an exotic species is likely a combination of both species and community traits. This dissertation takes a multi-stage approach to examine how behavioral traits of an invader, along with characteristics of invaded communities influence the distribution, establishment and impact of the signal crayfish (Pacifastacus leniusculus) in freshwater stream communities. I begin in chapter one by providing an overview of each stage of the invasion process along with invader traits and community characteristics important at each stage. I then describe the patterns of crayfish invasions and provide background on the systems studied in this dissertation. In chapter two, I evaluated how native species diversity, the presence of an ecologically similar species, prey availability and stream discharge influenced the distribution and abundance of signal crayfish at fine and broad spatial scales. In chapter three, I tested whether the presence of an ecologically similar species (e.g. native crayfish) influenced the aggressiveness, activity and voracity of signal crayfish. Finally, in chapter four I evaluated the consequences of high abundances of signal crayfish on native prey and the behavior of signal crayfish. Accumulated evidence suggests that signal crayfish possess the behavioral traits (e.g. a general aggression syndrome) to overcome many challenges faced during the invasion process, but that characteristics of the invaded community (e.g. prey availability and physical attributes of streams) provide some resistance against signal crayfish reaching high abundances. When native communities do not offer much resistance (i.e. abundant prey and low flood disturbances), signal crayfish often invade at high abundances that result in large impacts on native species. The patterns and results suggest that the communities with high prey availability and infrequent disturbances are most at risk of invasion, but that the aggressive nature of this invader makes most communities vulnerable to invasion.

Biological invasions are widely thought to have major negative impacts on native communities and ecosystems (Vitousek et al. 1996; Parker et al. 1999; Mack et al. 2000). Exotic species are the second most important cause of species extinctions (after habitat destruction) in the United States (Enserink 1999) and an important cause of losses in biodiversity worldwide (Sala et al. 2000). From an economic, resource management view, exotic species can have major direct and indirect impacts on commercially-important natural resources – e.g., fisheries, crops (Pimentel et al. 2000). Although exotic species can impact native species via various mechanisms (e.g., competition, spread of disease, hybridization), for aquatic animals, a key mechanism is clearly predation (Moyle and Light 1996; Gamradt and Kats 1996; Knapp et al. 2001). Thus an important goal on the interface between basic and applied ecology is to understand the ecology of potentially damaging invasive predators (including omnivores), in order to minimize their negative impacts.

The European noble crayfish Astacus astacus is threatened by crayfish plague caused by the oomycete Aphanomyces astaci, which is spread by the invasive North American crayfish (e.g. signal crayfish Pacifastacus leniusculus). Surveillance of crayfish plague status in Norway has traditionally relied on the monitoring survival of cage‐held noble crayfish, a method of ethical concern. Additionally, trapping is used in crayfish population surveillance. Here, we test whether environmental DNA (eDNA) monitoring could provide a suitable alternative to the cage method, and a supplement to trapping.We took advantage of an emerging crayfish plague outbreak in a Norwegian watercourse following illegal introduction of disease‐carrying signal crayfish, and initiated simultaneous eDNA monitoring and cage‐based surveillance, supplemented with trapping. A total of 304 water samples were filtered from several sampling stations over a 4‐year period. eDNA data (species‐specific quantitative real‐time PCR [qPCR]) for the presence of A. astaci, noble and signal crayfish within the water samples were compared to cage mortality and trapping.This is the first study comparing eDNA monitoring and cage surveillance during a natural crayfish plague outbreak. We show that eDNA monitoring corresponds well with the biological status measured in terms of crayfish mortality and trapping results. eDNA analysis also reveals the presence of A. astaci in the water up to 2.5 weeks in advance of the cage method. Estimates of A. astaci and noble crayfish eDNA concentrations increased markedly during mortality and vanished quickly thereafter. eDNA provides a snapshot of the presence, absence or disappearance of crayfish regardless of season, and constitutes a valuable supplement to the trapping method that relies on season and legislation.Synthesis and applications. Simultaneous eDNA monitoring of Aphanomyces astaci (crayfish plague) and relevant native and invasive freshwater crayfish species is well‐suited for early warning of invasion or infection, risk assessments, habitat evaluation and surveillance regarding pathogen and invasive/native crayfish status. This non‐invasive, animal welfare friendly method excludes the need for cage‐held susceptible crayfish in disease monitoring. Furthermore, eDNA monitoring is less likely to spread A. astaci than traditional methods. This study resulted in the implementation of eDNA monitoring for Norwegian crayfish plague and crayfish surveillance programmes, and we believe other countries could improve management strategies for freshwater crayfish using a similar approach. Simultaneous eDNA monitoring of Aphanomyces astaci (crayfish plague) and relevant native and invasive freshwater crayfish species is well‐suited for early warning of invasion or infection, risk assessments, habitat evaluation and surveillance regarding pathogen and invasive/native crayfish status. This non‐invasive, animal welfare friendly method excludes the need for cage‐held susceptible crayfish in disease monitoring. Furthermore, eDNA monitoring is less likely to spread A. astaci than traditional methods. This study resulted in the implementation of eDNA monitoring for Norwegian crayfish plague and crayfish surveillance programmes, and we believe other countries could improve management strategies for freshwater crayfish using a similar approach. [ABSTRACT FROM AUTHOR]

Animals are important drivers of sediment dynamics. Invasive signal crayfish (Pacifastacus leniusculus) have been shown to supply sediment to rivers by burrowing into riverbanks. Burrowing directly transfers excavated sediment into the river and also has an additional indirect affect by promoting riverbank failure. While previous research has isolated burrow densities at a point in time, rates of burrow construction and of burrow loss due to erosion are unknown, which introduces uncertainty into estimates of how much sediment burrows contribute to rivers. Here we report results from a 5-year study that evaluated the temporal dynamics of crayfish populations, rates of burrow loss due to erosion, and the mass of sediment directly supplied to rivers by burrow excavation. At ten reaches across five lowland streams in England, we estimated the mass of sediment displaced by 1861 new and previously constructed burrows. Both crayfish and burrow densities were variable over time, suggesting that burrows contribute temporally variable amounts of fine sediment to riverine systems. 42 % of observed burrows were constructed within the previous 365 days, and individual burrows lasted on average 461 days. Applying this to comparable historical data, an average of 2.0 t km−1 a−1 of sediment was excavated to construct burrows in the study reaches, which is eight times more than estimated in previous studies. Whilst total burrow densities in each year were not consistently correlated with contemporary crayfish densities, the mass of sediment excavated over the prior year was strongly correlated with contemporary crayfish densities. Current fine sediment management practices are largely aimed at controlling fine sediment delivery, predominately from agricultural activities, but biotic burrowing into riverbanks may represent an important and overlooked source of fine sediment supply. Incorporation of biotic processes in sediment dynamics would improve the accuracy of fluvial sediment budgets and enhance the knowledge base underpinning effective fine-sediment management practices. • Burrowing animals are important drivers of sediment dynamics. • Previously, animal burrows have largely been measured at one point in time. • 1443 crayfish burrows were monitored to calculate rates of construction and loss to erosion. • Crayfish supply eight times more sediment to rivers than previously recognised. • Burrow half-life was 15 months, with 58 % of burrows surviving more than one year. [ABSTRACT FROM AUTHOR]

[Display omitted] • Crayfish exoskeleton microbiomes were significantly affected by the environment. • Exoskeleton microbiomes of native and invasive crayfish shared a large proportion of taxa. • Composition and abundance of microbial taxa were species-specific. • Low loads of A. astaci and S. parasitica pathogens were detected on both crayfish species. Host-associated microbial communities are an important determinant of individual fitness and have recently been highlighted as one of the factors influencing the success of invasive species. Invasive hosts introduce their microbes into the new environment, and then both the host and its associated microbes enter into a series of interactions with the native macroscopic and microscopic biota. As these processes are largely unexplored, we aimed to compare the exoskeletal microbial communities of co-occurring and phylogenetically related crayfish: the native narrow-clawed crayfish Pontastacus leptodactylus and the invasive signal crayfish Pacifastacus leniusculus from the recently invaded Korana River, Croatia. The results of high-throughput 16S rRNA sequencing showed that the exoskeletal microbiome of both species is very diverse, significantly influenced by the local environment and dominated by low abundance bacterial families from the phylum Proteobacteria. Furthermore, the exoskeletal microbiomes of the crayfish species differed significantly in the composition and abundance of Amplicon Sequence Variants (ASVs), suggesting that they are to some extent shaped by species-specific intrinsic factors, despite sharing a common habitat. However, over 95% of the bacterial genera associated with the exoskeleton were detected in the exoskeleton samples of both native and invasive crayfish. We paid particular attention to two known crayfish pathogens, Aphanomyces astaci and Saprolegnia parasitica , and find that both species carry low amounts of both pathogens. On the side, we find that a non-standard ddPCR protocol outperforms standard qPCR test for A. astaci under low concentration conditions. Taken together, our results indicate the possibility of bidirectional mixing and homogenisation of exoskeleton microbiome. As such, they can serve as a baseline in future detangling of the processes that act together to shape the microbiomes of co-occuring native and invasive congeners during biological invasions. [ABSTRACT FROM AUTHOR]

Our study evaluates the distribution, habitat associations, and current conservation status of the Snake River pilose crayfish Pacifastacus connectens (Faxon, 1914) and pilose crayfish Pacifastacus gambelii (Girard, 1852), two little-studied and data-deficient species endemic to the western United States. We first developed a species distribution model (SDM) for the pilose crayfishes based on their historical occurrence records using boosted regression trees and freshwater GIS data layers. We then sampled 163 sites in the summers of 2016 and 2017 within the distribution of these crayfishes, including 50 where these species were observed historically. We next compared our field results to modeled predictions of suitable habitat from the SDM. Our SDM predicted 73 sites (45%) we sampled as suitable for the pilose crayfishes, with a moderate AUC value of 0.824. The pilose crayfishes were generally predicted to occur in larger streams and rivers with less extreme upstream temperature and precipitation seasonality. We found the pilose crayfishes at only 20 (12%) of the 163 total sites we sampled, 14 (20%) of the 73 sites predicted as suitable for them by our SDM, and 12 (24%) of 50 historical sites that we sampled. We found the invasive virile crayfish Faxonius virilis (Hagen, 1870) at 22 sites total and 12 (24%) historical sites for the pilose crayfishes, and we found the “native invader” signal crayfish Pacifastacus leniusculus (Dana, 1852) at 29 sites total and 6 (12%) historical sites for the pilose crayfishes. We subsequently used a single classification tree to identify factors associated with our high rate of false positives for contemporary pilose crayfish distributions relative to our SDM. This classification tree identified the presence of invasive crayfishes, impairment of the benthic community, and sampling method as some of the factors differentiating false positives relative to true positives for the pilose crayfishes. Our study identified the historical distribution and habitat associations for P. connectens and P. gambelii using an SDM and contrasted this prediction to results of contemporary field sampling. We found that the pilose crayfishes have seemingly experienced substantial range declines, attributable to apparent displacement by invasive crayfishes and impairment or change to stream communities and habitat. We recommend increased conservation and management attention to P. connectens and P. gambelii in response to these findings.

Successful establishment of non‐native species is strongly influenced, among other factors, by the genetic variation of founding populations, which can be enhanced by multiple introductions through admixture. Coexisting pathogens can also facilitate the establishment of non‐native species by detrimentally impacting on the native fauna acting as novel weapons. The signal crayfish (Pacifastacus leniusculus) is a highly invasive species, which has caused mass declines of native crayfish in Europe through displacement and transmission of the oomycete Aphanomyces astaci (crayfish plague), which is typically lethal to native European crayfish. However, whether Aphanomyces astaci may have facilitated the invasion of the signal crayfish is not known. We estimated the genetic diversity at microsatellite DNA loci, effective population size, and potential origins of seven infected and noninfected signal crayfish populations in Europe and one founder population in North America. Approximate Bayesian computation analysis and population structuring suggested multiple host introductions from diverse source populations, as well as higher heterozygosity among infected than uninfected populations, which could reflect a fitness advantage. Low effective population size, moderate heterozygosity, and lack of isolation by distance suggest that some invasive signal crayfish populations may not be fully established or that their genetic diversity may have been reduced by eradication attempts. Widespread invasive signal crayfish populations have low genetic diversity despite their diverse sources of origin, which could be due to founder effects or eradication attempts. However, plague carrier populations display the largest heterozygosity. Genetic screening during eradication attempts is needed to clarify their effects on the genetic diversity of the invaders and understand the role of disease transmission in their spread. [ABSTRACT FROM AUTHOR]

Our study evaluates the distribution, habitat associations, and current conservation status of the Snake River pilose crayfish Pacifastacus connectens (Faxon, 1914) and pilose crayfish Pacifastacus gambelii (Girard, 1852), two little-studied and data-deficient species endemic to the western United States. We first developed a species distribution model (SDM) for the pilose crayfishes based on their historical occurrence records using boosted regression trees and freshwater GIS data layers. We then sampled 163 sites in the summers of 2016 and 2017 within the distribution of these crayfishes, including 50 where these species were observed historically. We next compared our field results to modeled predictions of suitable habitat from the SDM. Our SDM predicted 73 sites (45%) we sampled as suitable for the pilose crayfishes, with a moderate AUC value of 0.824. The pilose crayfishes were generally predicted to occur in larger streams and rivers with less extreme upstream temperature and precipitation seasonality. We found the pilose crayfishes at only 20 (12%) of the 163 total sites we sampled, 14 (20%) of the 73 sites predicted as suitable for them by our SDM, and 12 (24%) of 50 historical sites that we sampled. We found the invasive virile crayfish Faxonius virilis (Hagen, 1870) at 22 sites total and 12 (24%) historical sites for the pilose crayfishes, and we found the ''native invader'' signal crayfish Pacifastacus leniusculus (Dana, 1852) at 29 sites total and 6 (12%) historical sites for the pilose crayfishes. We subsequently used a single classification tree to identify factors associated with our high rate of false positives for contemporary pilose crayfish distributions relative to our SDM. This classification tree identified the presence of invasive crayfishes, impairment of the benthic community, and sampling method as some of the factors differentiating false positives relative to true positives for the pilose crayfishes. Our study identified the historical distribution and habitat associations for P. connectens and P. gambelii using an SDM and contrasted this prediction to results of contemporary field sampling. We found that the pilose crayfishes have seemingly experienced substantial range declines, attributable to apparent displacement by invasive crayfishes and impairment or change to stream communities and habitat. We recommend increased conservation and management attention to P. connectens and P. gambelii in response to these findings. [ABSTRACT FROM AUTHOR]

Female crayfish stores male gametes after mating until the beginning of egg laying and fertilization. The aim of the present study was to investigate the duration of post-mating spermatophore storage as well as the timing and temperature of spawning in two crayfish species of economic importance, namely the signal crayfishPacifastacus leniusculus and the noble crayfishAstacus astacus . Results showed that the average duration of the post-mating spermatophore storage is significantly (P <0.05) longer in the noble crayfish (34.6 ± 1.7 days, range: 19 to 60 days) than the signal crayfish (3.9 ± 0.5 days, range: 1 to 18 days). The highest percentages of the post-mating spermatophore storage duration in the signal crayfish (46.5%) and the noble crayfish (44.5%) were 1 and 31 to 40 days, respectively. While there is an overlap in the timings of mating and egg laying in the signal crayfish, these two reproductive processes were not observed at the same days in the noble crayfish and there was at least 2 weeks interval between last mating and first egg laying individuals. Average mating and egg laying temperatures were significantly (P <0.05) higher in the signal crayfish than the noble crayfish. The average temperatures for mating in both species were significantly (P <0.05) higher than the temperatures that they utilized for egg laying. In conclusion, female noble crayfish stores post-mating spermatophores a longer duration compared with the signal crayfish. Also, the signal crayfish mates and lays egg in temperatures that are higher than the noble crayfish. Spawning season is shorter in the signal crayfish compared with the noble crayfish. The results of present study provide information contributing to the crayfish broodstock management in aquaculture. [ABSTRACT FROM AUTHOR]

Invasive alien species present a global threat to biodiversity, particularly where pathogens and symbionts are involved. Nonnative crayfish species can increase their impact on the host ecosystem through introductions of symbiotic fauna. Conversely, nonnative crayfishes could serve as hosts for native epibionts, thus substituting for disappearing native crayfishes as well. Here we report the presence of native branchiobdellids on naturalized populations of non-native crayfish Orconectes limosus and Pacifastacus leniusculus living in sympatry with native Astacus astacus. The native crayfish species probably served as a source of Branchiobdella spp. for non-native crayfishes. Two species of Branchiobdella (B. parasita and B. pentadonta) were found on P. leniusculus while only B. parasita was found on O. limosus. The level of colonization of inspected specimens and species was also evaluated. The mean number of branchiobdellids found on P. leniusculus and O. limosus was 26.0±15.9, and 64.8±27.7, respectively. Orconectes limosus was more heavily colonized by Branchiobdella despite being significantly smaller than P. leniusculus. Non-native species were corroborated as suitable to host the native epibionts. [ABSTRACT FROM AUTHOR]

Invasive alien species present a global threat to biodiversity, particularly where pathogens and symbionts are involved. Non-native crayfish species can increase their impact on the host ecosystem through introductions of symbiotic fauna. Conversely, non-native crayfishes could serve as hosts for native epibionts, thus substituting for disappearing native crayfishes as well. Here we report the presence of native branchiobdellids on naturalized populations of non-native crayfish Orconectes limosus and Pacifastacus leniusculus living in sympatry with native Astacus astacus. The native crayfish species probably served as a source of Branchiobdella spp. for non-native crayfishes. Two species of Branchiobdella (B. parasita and B. pentadonta) were found on P. leniusculus while only B. parasita was found on O. limosus. The level of colonization of inspected specimens and species was also evaluated. The mean number of branchiobdellids found on P. leniusculus and O. limosus was 26.0±15.9, and 64.8±27.7, respectively. Orconectes limosus was more heavily colonized by Branchiobdella despite being significantly smaller than P. leniusculus. Non-native species were corroborated as suitable to host the native epibionts.

The subject of the study was four populations of signal crayfish from Naryjska Struga River and lakes Pobłędzie, Mauda, and Staw Płociczno. The morphometric differentiation of female and male signal crayfish was studied with discriminant analysis. It was confirmed that both females and males from the Naryjska Struga River differ from the crayfish from the three lakes. The characters that best discriminated females were those associated with the cephalothorax and cheliped width, while in males they were those associated with the chelipeds and the abdomen.