Non-indigenous Crayfish Species Research Articles

The Crayfish Plague Pathogen Aphanomyces astaci in Ireland.

Crayfish plague is a devastating disease of European freshwater crayfish and is caused by the oomycete Aphanomyces astaci (Ap. astaci), believed to have been introduced to Europe around 1860. All European species of freshwater crayfish are susceptible to the disease, including the white-clawed crayfish Austropotamobius pallipes. Ap. astaci is primarily spread by North American crayfish species and can also disperse rapidly through contaminated wet gear moved between water bodies. This spread, coupled with competition from non-indigenous crayfish, has drastically reduced and fragmented native crayfish populations across Europe. Remarkably, the island of Ireland remained free from the crayfish plague pathogen for over 100 years, providing a refuge for A. pallipes. However, this changed in 1987 when a mass mortality event was linked to the pathogen, marking its introduction to the region. Fortunately, crayfish plague was not detected again in Ireland until 2015 when a molecular analysis linked a mass mortality event in the Erne catchment to Ap. astaci. Since then, the pathogen has appeared across the island. Between 2015 and 2023, Ap. astaci was detected in 18 water catchments, revealing multiple genotypes. Intriguingly, the pathogen in Ireland is present without its natural host species. The uneven distribution of various genetic lineages strongly suggests the human-mediated transport of zoospores via contaminated water equipment as a primary cause of spread. This review details the timeline of these events, Ap. astaci's introduction into Ireland, and its rapid spread. As well, this review references the genotypes that have been determined, and discusses the issue of non-indigenous crayfish species in Ireland and management efforts.

Distribution of Non-Indigenous Crayfish Species in Estonia and Their Impacts on Noble Crayfish (Astacus astacus L.) Populations

Invasive non-indigenous crayfish species (NICS) are a major threat to the existence of native crayfish populations in European freshwater ecosystems. The discovery of signal crayfish Pacifastacus leniusculus, marbled crayfish Procambarus virginalis, and spiny-cheek crayfish Faxonius limosus in Estonia has increased the risk of extinction of Estonia’s only native crayfish species, the noble crayfish Astacus astacus. The aim of this study was to give an overview of the status, distribution, and impacts of P. leniusculus, F. limosus, and Procambarus virginalis on A. astacus populations and assess the effect of trapping on NICS abundance. Annual monitoring of crayfish has been carried out since 2008 as part of A. astacus conservation and the NICS eradication plan. In this study, we present data from nine sampling locations monitored from 2010 to 2022. The spread of NICS continues to increase beyond their distribution areas, and in two sampling locations P. leniusculus and A. astacus live in sympatry. Our results suggest that trapping has a limited effect on population abundance, as NICS have already caused the extinction of two A. astacus populations. However, intensive trapping should continue simultaneously with sensitive molecular techniques to monitor the spread of NICS.

Long-term trends in crayfish invasions across European rivers

Europe has experienced a substantial increase in non-indigenous crayfish species (NICS) since the mid-20th century due to their extensive use in fisheries, aquaculture and, more recently, pet trade. Despite relatively long invasion histories of some NICS and negative impacts on biodiversity and ecosystem functioning, large spatio-temporal analyses of their occurrences are lacking. Here, we used a large freshwater macroinvertebrate database to evaluate what information on NICS can be obtained from widely applied biomonitoring approaches and how usable such data is for descriptions of trends in identified NICS species. We found 160 time-series containing NICS between 1983 and 2019, to infer temporal patterns and environmental drivers of species and region-specific trends. Using a combination of meta-regression and generalized linear models, we found no significant temporal trend for the abundance of any species (Procambarus clarkii, Pacifastacus leniusculus or Faxonius limosus) at the European scale, but identified species-specific predictors of abundances. While analysis of the spatial range expansion of NICS was positive (i.e. increasing spread) in England and negative (significant retreat) in northern Spain, no trend was detected in Hungary and the Dutch-German-Luxembourg region. The average invasion velocity varied among countries, ranging from 30 km/year in England to 90 km/year in Hungary. The average invasion velocity gradually decreased over time in the long term, with declines being fastest in the Dutch-German-Luxembourg region, and much slower in England. Considering that NICS pose a substantial threat to aquatic biodiversity across Europe, our study highlights the utility and importance of collecting high resolution (i.e. annual) biomonitoring data using a sampling protocol that is able to estimate crayfish abundance, enabling a more profound understanding of NICS impacts on biodiversity.

Investigation of the first recent crayfish plague outbreak in Ireland and its subsequent spread in the Bruskey River and surrounding areas

White-clawed crayfish (Austropotamobius pallipes) is a keystone species found in western European freshwater bodies, where it has suffered drastic declines due to pathogens, competition with non-indigenous crayfish species (NICS) and habitat deterioration. In Ireland, populations of (naturalised) A. pallipes have been considered healthy and abundant mainly because no diseases or NICS have been reported in the past decades. The present study investigated a sudden mass mortality event that occurred in the Erne catchment in 2015. Molecular analysis confirmed that the cause of the event was infection by the oomycete Aphanomyces astaci (the causative agent of the crayfish plague). While in 2015 the spread of the pathogen appeared to remain confined to the outbreak’s epicentre and nearby upstream waters, follow up surveys using conventional methods and environmental DNA (eDNA) approaches indicated that by a year later (2016), the pathogen was still present and had spread downstream beyond Lough Gowna. No NICS were detected during the surveys conducted. This crayfish plague outbreak is of grave concern to Irish white-clawed crayfish and associated ecosystems.

First Record of the Alien Species Procambarus virginalis Lyko, 2017 in Fresh Waters of Sardinia and Insight into Its Genetic Variability.

In the fresh waters of Sardinia (Italy), the non-indigenous crayfish species Procambarus clarkii has been reported from 2005, but, starting from 2019, there have been several reports of a new non-indigenous crayfish in southern and central areas of this Mediterranean island, and its morphology suggests that this species may be the marbled crayfish Procambarus virginalis. Forty-seven individuals of this putative species were analyzed, using the mitochondrial gene Cytochrome c Oxidase subunit I as molecular marker to identify this crayfish and investigate the level of genetic variability within the recently established population. Phylogenetic and phylogeographic analyses were carried out on a dataset including sequences from the Sardinian individuals and from all congenerics available in GenBank. Results showed that the new Sardinian crayfish belong to the species P. virginalis. All the sequences belonging to P. virginalis from European countries are identical, with only few exceptions found among Sardinian individuals. In conclusion, this paper highlights the occurrence of a new further alien species in the Sardinian fresh waters, which are already characterized by the high presence of non-indigenous species.

Barriers against invasive crayfish species in natural waters and fish passes - Practical experience

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.

A review of the use of physical barriers to stop the spread of non-indigenous crayfish species

Invasive non-indigenous crayfish species (NICS) are a global threat to local flora and fauna. Total eradication of an entire population of invasive NICS is a difficult task; several methods have been tested and are still being used, with varying success. Most methods reduce population size and control the species within the targeted area but do not majorly prevent further spread of NICS. However, construction of crayfish barriers can stop the spread of NICS and can therefore, be used to protect indigenous crayfish species (ICS). There are currently very few published scientific papers about this topic. This review reflects current knowledge on how to stop migration when NICS are established and provides useful information for the construction of barriers. The most important findings related to building a crayfish barrier are: the need for a vertical wall with an overhanging lip above the water surface; smooth sections to prevent crayfish from walking or climbing over the obstacle, combined with flow velocities of 0.65 m/s act as a barrier within the waterbody. Additionally, modifications to existing structures, bridges, culverts and dams reduce costs and increase effectiveness in stopping upstream migration of NICS. Barriers can negatively impact certain aquatic species, mainly benthic and slow swimming fish by preventing their migration and genetic exchange. However, they can have positive impacts for ICS and other indigenous organisms against the negative effects of NICS. Local legislation should support barrier construction to prevent the spread of invasive crayfish and other aquatic invaders to protect ark sites for ICS.

Continuing expansion of non-indigenous crayfish species in Northern Europe: first established spiny-cheek crayfish Faxonius limosus (Refinesque, 1817) population in Estonia

Continuing expansion of non-indigenous crayfish species in Northern Europe: first established spiny-cheek crayfish Faxonius limosus (Refinesque, 1817) population in Estonia

Acute toxicity of two pyrethroid insecticides for five non-indigenous crayfish species in Europe

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.

Recent changes in distribution pattern of freshwater crayfish in Croatia − threats and perspectives

Analysis of Croatian freshwater crayfish populations, aiming to gather new distributional data and complement previous surveys (2005–2011), was performed during 2014–2016, within the frame of Natura 2000 Integration Project. The research included different waterbodies across the whole of Croatia, harbouring both indigenous and non-indigenous crayfish species (ICS and NICS, respectively). Field work was conducted in 117 grid squares with dimensions 10 × 10 km, and up to four waterbodies were surveyed per grid square, making a total of 450 studied sites. Out of those, crayfish were not recorded in 368 sites. In the sites with crayfish presence (i.e., 82), the most frequently observed ICS was Astacus astacus (registered in 33 sites) followed by Austropotamobius pallipes (16 sites), Austropotamobius torrentium (12 sites), and Astacus leptodactylus (5 sites). Concerning NICS, the majority of records were for Orconectes limosus (13 sites), followed by Pacifastacus leniusculus (2 sites), whereas Procambarus fallax f. virginalis was registered in only one locality. Comparisons of obtained data with those from previous surveys showed that NICS are progressively spreading and displacing ICS, as recorded for A. leptodactylus that was almost completely displaced by O. limosus in waterbodies of the east Croatia. Existing ICS populations are under growing anthropogenic preassure, frequently fragmented and isolated. Moreover, this survey showed that in the last decade 55% of A. astacus and 67% of A. pallipes populations disappeared mainly as a consequence of anthropogenic influence onto their habitats. Further monitoring and conservation actions for ICS should be urgently applied to mitigate negative impacts of both NICS and anthropogenic influence.

Cambarellus patzcuarensis in Hungary: The first dwarf crayfish established outside of North America

AbstractIn 2017, a new non-indigenous crayfish species was found established in Europe. The captured individuals were identified as an orange morph of the Mexican dwarf crayfish

A crayfish survey of the fishing creek watershed in northeastern Pennsylvania suggests widespread prevalence of a nonindigenous species and the absence of a native congener

Abstract Introduction of nonindigenous crayfish species impacts freshwater ecosystems and can result in displacement of native crayfish. The crayfish Orconectes limosus and Cambarus bartonii are native to the Susquehanna River drainage in Pennsylvania. However, several nonindigenous crayfish have become established in this drainage. No comprehensive survey exists on crayfish species within the Fishing Creek watershed. Historic records report O. limosus and C. bartonii in this watershed; however, recent point surveys have documented the presence of the nonindigenous crayfish O. obscurus. We sampled crayfish in 15 sites from the lower reaches of Fishing Creek through its headwaters and major tributaries. We collected a total of 484 crayfish, representing the species O. obscurus and C. bartonii. We found O. obscurus within much of Fishing Creek and some tributaries, but absent from the upper reaches of the watershed, possibly due to a series of dams. C. bartonii were primarily found in the upper portions of the Fishing Creek watershed, but also found at low abundance with O. obscurus in the central portions of the watershed and in a small, first order tributary. We collected no O. limosus specimens in our samples, suggesting local extirpation via displacement by O. obscurus, as has been reported elsewhere.

Ecosystem of Caspian Sea threatened by pet-traded non-indigenous crayfish

Freshwater ecosystems are particularly vulnerable to biological invasions; the aquatic animal pet trade has been recognized as a significant pathway of introductions. Crayfish are considered a model group of traded organisms with a series of highly successful species already established in the wild, having the potential to negatively influence both indigenous crayfish species (ICS) as well as alter occupied ecosystems. Eastern Europe includes the entire native ranges of indigenous Astacus leptodactylus sensu lato and A. pachypus. This region has been largely overlooked and considered relatively safe from the adverse impacts of non-indigenous crayfish species (NICS). In this study, we evaluated the crayfish pet trade in the Lower Volga Region with special emphasis on Astrakhan, the biggest city of Russian Federation in the region located just in the delta of Volga River, thus being a potential gateway of introductions to the Caspian Sea and adjacent freshwaters. The local pet trade involves 12 NICS. Considering their origin, availability, probability of establishment, invasiveness and further aspects, Procambarus fallax f. virginalis, P. clarkii and Cherax destructor are considered potentially the most problematic, including transmission of diseases like crayfish plague caused by Aphanomyces astaci or white spot syndrome virus. Taking this information as a whole, the availability of NICS with a high probability of overlapping the entire range of European ICS means that attention is warranted. Further research is needed to corroborate the abilities of NICS and their associated diseases to withstand specific conditions of the Caspian Sea as well as the adjacent Black and Azov Seas, all possessing different degrees of elevated salinity.

Freshwater crayfish distribution update and maps for Greece: combining literature and citizen-science data

Crayfish are charismatic creatures of high interest to humans, among others playing key roles in freshwater ecosystems. Considering the significance of indigenous crayfish species (ICS) as well as the risks posed by non-indigenous crayfish species (NICS) that may dissemite a crayfish plague pathogen Aphanomyces astaci , astacological research has advanced particularly in Europe. In this context, crayfish distribution patterns are of fundamental importance. Focused on all crayfish established in the Greek wild, we provide an updated distribution and maps, combining extensive review of existing literature as well as newly emerging sources, largely represented by increasingly important citizen-science data. Obtained results demonstrate that ICS, mainly the Astacus astacus and Austropotamobius torrentium , remain relatively well settled in the country. The last ICS, Astacus leptodactylus , was translocated in few places outside its native range, leading to the formation of new flourishing populations and at least in one case it sustains commercial exploitation. Concerning NICS, a single population of Pacifastacus leniusculus is also established in the artificial lake Agra (Region of Central Macedonia) and keeps spreading. Unfortunately, there are only few methods under a very narrow range of conditions making successful eradication of unwanted NICS populations feasible. This option is even more difficult as this population is commercially exploited and traded. Since further potentially problematic NICS are also pet-traded in the country, educating public and communicating highlighted issues are the most effective ways limiting their releases and consecutive establishment in the wild.

In this issue

IN THIS ISSUE Bruce Osborne Plant traits and soil processes Whilst soils are considered to be largely a consequence of the weathering of parent material, their ultimate characteristics and biological complexity are inextricably linked with the presence of vegetation. There is almost a symbiotic relationship between soil processes and the associated vegetation, with plants providing labile carbon, for instance, which supports microbial activity and the microbial populations , in turn, providing access to the essential nutrients required by plants. However, this is only one of many examples of the interactions that occur between vegetation and soils. Although many of these interactions are well known, much less is understood about how particular plant or vegetation characteristics or traits specifically impact on soil functioning, and this is the focus of a new Praeger Review, by Richard Bardgett, in this issue. There is now a significant body of evidence linking aboveground traits to soil microbial communities and soil carbon, but less is known about linkages with belowground traits. How do root traits, in particular, impact on soil processes and to what extent are variations in root traits linked to modifications in soil functioning? Whilst the development of new technologies has made these assessments more tractable, there are still major technical difficulties in measuring belowground traits, particularly in field settings. Identification of causal or functional links between shoot or root traits and soil processes is also a significant challenge. Not only is this information important for a fundamental understanding of the interrelationships between soil processes and vegetation , it could also provide potentially significant practical and environmental benefits through improved resource acquisition and greater nutrient retention in agro-ecosystems. Ain’t no barricade high (or wide) enough Enforcing any restriction on the movement of goods or organisms is beset by problems even when physical barriers are used. We have been lucky in Ireland that the movement of many unwanted organisms has been prevented because we are separated from both the UK and continental Europe by natural water barriers. Whilst natural barriers to free movement are important these can still be circumvented often through trade-related, humanassisted transportation. Remarkably, Ireland has no populations of non-indigenous crayfish, although the native white clawed crayfish is widespread. But, as Zen Faulkes points out in this issue, four non-indigenous crayfish species available through the pet trade in Ireland pose a significant risk if they are introduced into natural habitats. Although these risks of these crayfish have not been assessed, their success in the wild may be limited by low temperatures , although one, Cambarellus patzcuarensis, could still have an indirect impact on native populations because it is a potential vector for crayfish plague. Whilst legislation will limit the import of non-native crayfish into Ireland, there still seems to be a thriving crayfish trade within the country that should cause some concern. It is also possible that projected increases in temperature might also increase the chances of naturalised crayfish populations in the future. Perhaps there is a message here*that the implementation of any barrier to the movement of an unwanted species is always likely to be too late*and that such a move has to be combined with an appropriate follow-up management plan? Mealybugs Mealybugs are a group of plant-sucking insects with around 2,000 species, all of which are covered by a powdery wax material that resembles finely ground ‘meal’, hence their name. In many countries they are a common pest of greenhouses, where they can have a significant impact on the growth of plants, particularly ornamentals and succulents. Colonisation of the exudate produced by mealybugs by ascomycetes is also common, leading to secondary fungal infections. In some parts of the world, particularly the tropics and sub-tropics, where they are widely distributed, mealybugs can also be a common pest of fig and mango orchards. With increasing pressure to reduce pesticide use, alternative ways to controlling mealybugs are being examined. Moniruzzaman et al., in this issue, report on the effectiveness of two plant extracts, obtained from Jatropha ( Jatropha curcas) and neem (Azadirachta indica), together with conventional applications of the pesticide malathion, in controlling mealybugs in fig orchards. Their results indicate that both Jatropha and neem can...

In this issue

IN THIS ISSUE Bruce Osborne Plant traits and soil processes Whilst soils are considered to be largely a consequence of the weathering of parent material, their ultimate characteristics and biological complexity are inextricably linked with the presence of vegetation. There is almost a symbiotic relationship between soil processes and the associated vegetation, with plants providing labile carbon, for instance, which supports microbial activity and the microbial populations , in turn, providing access to the essential nutrients required by plants. However, this is only one of many examples of the interactions that occur between vegetation and soils. Although many of these interactions are well known, much less is understood about how particular plant or vegetation characteristics or traits specifically impact on soil functioning, and this is the focus of a new Praeger Review, by Richard Bardgett, in this issue. There is now a significant body of evidence linking aboveground traits to soil microbial communities and soil carbon, but less is known about linkages with belowground traits. How do root traits, in particular, impact on soil processes and to what extent are variations in root traits linked to modifications in soil functioning? Whilst the development of new technologies has made these assessments more tractable, there are still major technical difficulties in measuring belowground traits, particularly in field settings. Identification of causal or functional links between shoot or root traits and soil processes is also a significant challenge. Not only is this information important for a fundamental understanding of the interrelationships between soil processes and vegetation , it could also provide potentially significant practical and environmental benefits through improved resource acquisition and greater nutrient retention in agro-ecosystems. Ain’t no barricade high (or wide) enough Enforcing any restriction on the movement of goods or organisms is beset by problems even when physical barriers are used. We have been lucky in Ireland that the movement of many unwanted organisms has been prevented because we are separated from both the UK and continental Europe by natural water barriers. Whilst natural barriers to free movement are important these can still be circumvented often through trade-related, humanassisted transportation. Remarkably, Ireland has no populations of non-indigenous crayfish, although the native white clawed crayfish is widespread. But, as Zen Faulkes points out in this issue, four non-indigenous crayfish species available through the pet trade in Ireland pose a significant risk if they are introduced into natural habitats. Although these risks of these crayfish have not been assessed, their success in the wild may be limited by low temperatures , although one, Cambarellus patzcuarensis, could still have an indirect impact on native populations because it is a potential vector for crayfish plague. Whilst legislation will limit the import of non-native crayfish into Ireland, there still seems to be a thriving crayfish trade within the country that should cause some concern. It is also possible that projected increases in temperature might also increase the chances of naturalised crayfish populations in the future. Perhaps there is a message here*that the implementation of any barrier to the movement of an unwanted species is always likely to be too late*and that such a move has to be combined with an appropriate follow-up management plan? Mealybugs Mealybugs are a group of plant-sucking insects with around 2,000 species, all of which are covered by a powdery wax material that resembles finely ground ‘meal’, hence their name. In many countries they are a common pest of greenhouses, where they can have a significant impact on the growth of plants, particularly ornamentals and succulents. Colonisation of the exudate produced by mealybugs by ascomycetes is also common, leading to secondary fungal infections. In some parts of the world, particularly the tropics and sub-tropics, where they are widely distributed, mealybugs can also be a common pest of fig and mango orchards. With increasing pressure to reduce pesticide use, alternative ways to controlling mealybugs are being examined. Moniruzzaman et al., in this issue, report on the effectiveness of two plant extracts, obtained from Jatropha ( Jatropha curcas) and neem (Azadirachta indica), together with conventional applications of the pesticide malathion, in controlling mealybugs in fig orchards. Their results indicate that both Jatropha and neem can...

Salinity tolerance of marbled crayfishProcambarus fallaxf.virginalis

Eastern Europe comprises a significant part of the native ranges for indigenous crayfish species (ICS) belonging to the genus Astacus . This region has been largely overlooked by astacologists and considered relatively immune to the impacts of non-indigenous crayfish species (NICS). The recent discovery of two marbled crayfish Procambarus fallax f. virginalis populations in Ukraine has changed this view. Increased propagule pressure (mainly due to pet trade) has raised concerns of NICS which may negatively impair the ecosystems of Azov, Black and Caspian Seas and their tributaries inhabited by ICS. In this study, we provide the first insight into salinity tolerance of marbled crayfish. We performed a 155-day experiment using 5 different salinities (6, 9, 12, 15, and 18 ppt) and a freshwater control. Evaluation of survival, growth and reproduction suggests that marbled crayfish have a lower salinity tolerance than other crayfish species, which may limit their invasive potential in brackish environments. However, its ability to survive for more than 80 days at 18 ppt opens up the possibility of gradual dispersion and adaptation to brackish conditions. Our study highlights the need for further studies elucidating the potential for marbled crayfish to negatively impair these ecosystems.

Predictions of marbled crayfish establishment in conurbations fulfilled: Evidences from the Czech Republic

AbstractThe marbled craynsn (

The bad and the super-bad: prioritising the threat of six invasive alien to three imperilled native crayfishes

Multiple species invasions and limited resources for management require prioritisation of deleterious effects of invaders on imperilled native species. This study prioritises the threat of six non-indigenous crayfish species (NICS) to three indigenous crayfish species (ICS) in southwestern Germany, a European region with high diversity of crayfish species and freshwater habitats. Using multivariate statistical analyses and niche-based species distribution models, the (1) contemporary and potential range overlap, (2) habitat overlap, and (3) rate of spread of the nine species were assessed. Predicted and contemporary range overlap with ICS was consistently the highest for the alien signal crayfish. Environmental niches of ICS tended to be associated with cooler temperatures (except for white-clawed crayfish), lower Human Influence Index, and higher terrain slope than that of alien Orconectes and Procambarus species, but were mostly similar to that of signal crayfish. Habitat overlap was found to be the highest between signal crayfish and ICS. In contrast to Orconectes and Procambarus species, signal crayfish also invade headwaters, where the most ICS populations occur. Range expansion during the past 15 years was the highest for signal crayfish, followed by Orconectes species. Because of the great potential to invade as-yet isolated refuge areas and spread at a high rate, signal crayfish is of the highest concern for conservation of ICS and should be primarily targeted by prevention and control measures. However, it merely represents the ‘worst of the worst’, since all NICS of North American origin are natural reservoirs of crayfish plague, a fatal disease of ICS.

East European crayfish stocks at risk: arrival of non-indigenous crayfish species

An increasing number of non-indigenous crayfish species (NICS) of apparently pet trade origin have become established particularly in Europe. Especially alarming are recent confirmation of two distantly separated marbled crayfish Procambarus fallax f. virginalis populations in Ukraine and indications of more North American cambarids present in the local pet market. The present study aimed to investigate crayfish species availability within the Ukrainian pet trade together with the climate match and risk they represent to the freshwater ecosystems generally and indigenous crayfish species in particular. Altogether, 15 NICS belonging to all three crayfish families were detected. Considering their origin, availability, probability of establishment, invasiveness and further aspects, marbled crayfish and red swamp crayfish Procambarus clarkii appear to be potentially the most troubling. Available information obtained from the pet trade in ornamental crayfish as a whole demonstrates that the broad availability of NICS most probably overlaps the vast majority of European indigenous crayfish species distribution, including the endemic thick-clawed crayfish Astacus pachypus , which occupies only a limited area that is situated critically close to established marbled crayfish populations. Negative effects of NICS on freshwater ecosystems as a whole can be also expected.