Crayfish Plague Research Articles

Mapping 15 years of crayfish plague in the Iberian Peninsula: The impact of two invasive species on the endangered native crayfish

Crayfish plague, caused by the pathogen Aphanomyces astaci, is one of the main factors responsible for the decimation of the native European crayfish species Austropotamobius pallipes. In Spain, two North American freshwater crayfish species, Procambarus clarkii and Pacifastacus leniusculus, were intentionally introduced during the 1970s for aquaculture and fishery purposes. Since then, incidences of crayfish plague have been continually reported. In this work, we evaluated more than 50 diagnosed cases of crayfish plague that have occurred in the Iberian Peninsula since 2004 by performing a microscopic examination of infected specimens and by molecularly identifying and haplotyping the pathogen. Our results showed that (i) the pathogen A. astaci has been active 45 years since the first introductions of the invasive North American crayfish species in the Iberian Peninsula, and (ii) P. clarkii and P. leniusculus are chronic reservoirs of the crayfish plague pathogen. Moreover, our data confirmed a correspondence between pathogen origin and spread and the specific haplotypes carried by the North American invasive crayfish located in the vicinity of each outbreak. We generated a crayfish plague incidence map of the Iberian Peninsula that shows (i) a northern area, mainly inhabited by alien P. leniusculus, where crayfish plague cases are associated with the b-haplotype specific to P. leniusculus, and (ii) southern, central and eastern areas that are basically inhabited by alien P. clarkii, where crayfish plague cases are associated with the d1- and d2-haplotypes specific to P. clarkii. The results presented here are evidence of the long standing and negative impact of the two invasive crayfish species on the native species, indicating the need for more extensive control measures.

Habitat separation of the crab potamon potamios and the crayfish pontastacus leptodactylus in Lake eğirdir, Turkey

Freshwater decapods rarely co-occur. The crab Potamon potamios and the narrow-clawed crayfish Pontastacus leptodactylus complex usually do not share the same pond even if they live in sympatry. An exception, however, is Lake Eğirdir (Turkey), where both species are present. The aim of our study was to analyze the distribution patterns of the two species in this large lake in more detail, to better understand their ecological roles and possible interaction patterns. Our study indicated a strong segregation between the species, with crabs almost exclusively inhabiting the lake’s shore area. Although the crab populations seem to have diminished recently (the reason is still unclear), they still defend this region against crayfish. More than half of the crayfish specimens and more than one quarter of the crabs had at least one melanized spot, which could be a symptom of the crayfish plague (Aphanomyces astaci). Measures are needed to guarantee the survival of indigenous crabs, which are impacted by several threats.

The signal crayfish (Pacifastacus leniusculus) in Lake Tahoe (USA) hosts multiple Aphanomyces species

The genus Aphanomyces (Oomycetes) comprises approximately 50 known species of water molds in three lineages. One of the most notorious is Aphanomyces astaci, the causative agent of crayfish plague. In this study, fresh isolates of Aphanomyces were collected from 20 live specimens of the signal crayfish Pacifastacus leniusculus (Dana, 1852) from Lake Tahoe, California, providing 35 axenic cultures of A. astaci as well as two apparently undescribed Aphanomyces spp. isolates. Based on the results of ITS-, chitinase-, mitochondrial rnnS- and rnnL-sequences and microsatellite markers combined, the Lake Tahoe A. astaci isolates were identical to isolates of A. astaci B-haplogroup commonly detected in Europe, and infection experiments confirmed their high virulence towards noble crayfish. One of the two undescribed Aphanomyces spp. isolates was highly similar to an Aphanomyces lineage detected previously in crustacean zooplankton (Daphnia) in Central Europe, while the other was distinct and most closely related (ITS sequence similarity of 93%) to either A. astaci or to Aphanomyces fennicus isolated recently from Astacus astacus in Finland. Neither of the two Aphanomyces spp. isolates caused crayfish mortality under experimental conditions. Our results indicate that the populations of North American signal crayfish can act as carriers of both pathogenic and non-pathogenic Aphanomyces at the same time. Furthermore, considering that a limited number of crayfish individuals from a single location yielded multiple distinct Aphanomyces isolates, our results suggest that substantial species diversity within this genus remains undescribed.

Sustainable Aquaculture Futures

Sustainable Aquaculture Futures

Invasive rusty crayfish (Faxonius rusticus) populations in North America are infected with the crayfish plague disease agent (Aphanomyces astaci)

The American rusty crayfish, Faxonius rusticus, is an invasive species in parts of North America where it displaces native crayfish species. In Europe, various invasive North American crayfish species are carriers of the crayfish plague disease agent Aphanomyces astaci that causes devastating population declines of European crayfish. Little is known about either the presence or the influence of A. astaci in North America where it originates. Here, we attempted to isolate A. astaci from North American F. rusticus for the first time and compare it to the strains detected in Europe. We tested the infection status of 84 F. rusticus samples from 10 different locations in the midwestern United States that are outside of the F. rusticus native distribution range. We used quantitative real-time PCR (qPCR) to assess the infection status in each individual, and we determined the mitochondrial haplotypes and multilocus microsatellite genotypes when it was possible. We detected A. astaci DNA in 9 individuals from 4 out of 10 locations. Analyses of the axenic culture isolates and the crayfish tissue samples by sequence analyses, haplotyping, and genotyping confirmed the results and revealed a novel A. astaci microsatellite genotype. Our results clearly identify F. rusticus as a host of A. astaci in North America. The threat of these strains to endangered crayfish species in North America remains unknown, but the potential of A. astaci infections should be considered when developing and implementing invasive species management plans for conservation purposes.

A new bunya-like virus associated with mass mortality of white-clawed crayfish in the wild

We report the discovery of a new enveloped, spherical virus belonging to the Phenuiviridae family of negative ssRNA viruses associated with a massive outbreak in a French population of the endangered white-clawed crayfish Austropotamobius pallipes. We call this virus Bunya-like Brown Spot Virus (BBSV) and characterize it using transmission electronic microscopy, genome sequencing and clinical signs. Infected specimens show discolored brown spots on the cuticle. Using RNA-seq data we assembled a partial sequence for the L, M and S genome segments of BBSV. Phylogenetic analyses using all three segments show this virus is closely related to the Wenling crustacean virus 7 (China) and to a bunya-like virus found in feces of the European otter. Our survey of the mass mortality event indicates the virus is less virulent than the crayfish plague caused by Aphanomyces astaci. Overall, the discovery of BBSV provides a new important asset to monitor A. pallipes populations.

Monitoring a Norwegian freshwater crayfish tragedy: eDNA snapshots of invasion, infection and extinction

Abstract 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.

Improved method for genotyping the causative agent of crayfish plague (Aphanomyces astaci) based on mitochondrial DNA.

Aphanomyces astaci causes crayfish plague, which is a devastating disease of European freshwater crayfish. The likely first introduction of A. astaci into Europe was in the mid-19th century in Italy, presumably with the introduction of North American crayfish. These crayfish can carry A. astaci in their cuticle as a benign infection. Aphanomyces astaci rapidly spread across Europe causing the decline of the highly susceptible indigenous crayfish species. Random amplified polymorphic DNA-PCR analysis of A. astaci pure cultures characterized five genotype groups (A, B, C, D and E). Current A. astaci genotyping techniques (microsatellites and genotype-specific regions, both targeting nuclear DNA) can be applied directly to DNA extracted from infected cuticles but require high infection levels. Therefore, they are not suitable for genotyping benign infections in North American crayfish (carriers). In the present study, we combine bioinformatics and molecular biology techniques to develop A. astaci genotyping molecular markers that target the mitochondrial DNA, increasing the sensitivity of the genotyping tools. The assays were validated on DNA extracts of A. astaci pure cultures, crayfish tissue extractions from crayfish plague outbreaks and tissue extractions from North American carriers. We demonstrate the presence of A. astaci genotype groups A and B in UK waters.

Ecological plasticity and commercial impact of invasive marbled crayfish populations in Madagascar

BackgroundThe marbled crayfish (Procambarus virginalis) is a monoclonal, parthenogenetically reproducing freshwater crayfish species that has formed multiple stable populations worldwide. Madagascar hosts a particularly large and rapidly expanding colony of marbled crayfish in a unique environment characterized by a very high degree of ecological diversity.ResultsHere we provide a detailed characterization of five marbled crayfish populations in Madagascar and their habitats. Our data show that the animals can tolerate a wide range of ecological parameters, consistent with their invasive potential. While we detected marbled crayfish in sympatry with endemic crayfish species, we found no evidence for the transmission of the crayfish plague pathogen, a potentially devastating oomycete. Furthermore, our results also suggest that marbled crayfish are active predators of the freshwater snails that function as intermediate hosts for human schistosomiasis. Finally, we document fishing, farming and market sales of marbled crayfish in Madagascar.ConclusionsOur results provide a paradigm for the complex network of factors that promotes the invasive spread of marbled crayfish. The commercial value of the animals is likely to result in further anthropogenic distribution.

A tentative new species Aphanomyces fennicus sp. nov. interferes with molecular diagnostic methods for crayfish plague.

Several isolates of an unknown oomycete resembling the genus Aphanomyces were obtained into laboratory culture from samples of noble crayfish (Astacus astacus) in 2016-2017. The crayfish were kept in cages in connection with a study on an eventually persistent crayfish plague infection in a small Finnish lake, following an acute episode of the disease in 2010. Despite the close resemblance of the isolates to the causative agent of crayfish plague, Aphanomyces astaci, and the positive results obtained in OIE recommended A.astaci-specific ITS-based conventional PCR and qPCR molecular assays, the isolates can be distinguished from A.astaci by morphological features concerning hyphal structure and chlamydospore formation, as well as using the randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) method, microsatellite-based genotyping, the pathogenicity test and phylogenetic analysis based on ITS sequencing. The name Aphanomyces fennicus sp. novum is proposed for this close relative of A.astaci. The detection of this tentative novel species giving false-positive results in existing diagnostic assays for the crayfish plague highlights the importance of careful interpretation of the results from molecular methods, especially concerning crayfish with low-level infections, excluding the possibility to verify the results from clinical or sequencing data.

Estimating the population size of the endangered white-clawed crayfish Austropotamobius pallipes using mark-recapture at three Special Areas of Conservation (SACS)

The white-clawed crayfish, Austropotamobius pallipes, is the sole native freshwater crayfish species found in Ireland, with Irish populations being considered the most substantial and important in Europe. At present, the size of the majority of Irish crayfish populations is unknown. Recent outbreaks of the crayfish plague Aphanomyces astaci in Ireland amplify the need to acquire accurate population estimates. The Schnabel estimator and closed population model, the Mth model, were employed in this study to estimate the adult A. pallipes population sizes from three specific sites. All adult individuals captured using both hand-search and baited trap methods were marked by ablation and released back into the sampling area in close proximity to suitable refuges. Both methods provided similar population estimates, although the Mth model appears to be the most precise. The estimated adult crayfish population size using the Mth model method was 214 individuals at the River Abbert, 1392 at the River Manulla, 18,153 at Lough Owel Site 1 and 27,325 at Lough Owel Site 2. A significant relationship was found between baited trap CPUE and population estimate, indicating that with further research a CPUE value could be used to generate a rough estimate of population size. Mark-recapture data and population estimate results indicate abundant populations of A. pallipes are present at each site.

The Red Alien vs. the Blue Destructor: The Eradication of Cherax destructor by Procambarus clarkii in Latium (Central Italy)

Cherax destructor is a crayfish endemic to south-eastern Australia and one of the last alien crayfish to be introduced in Italy. In the Laghi di Ninfa Natural Reserve (Latium region, Central Italy), the species was probably introduced in 1999, but only reported for the first time in 2008. Nearby this area, the most widespread alien crayfish is the red swamp crayfish Procambarus clarkii. In the Natural Reserve, between 2008 and 2013 and during spring and summer, crayfish sampling was carried out with baited traps to assess the distribution of C. destructor and its possible relationship with P. clarkii. Cherax destructor was first recorded in 2008; few P. clarkii were detected in the cultivation ponds where C. destructor was present in 2012 and 2013. Moreover, crayfish plague analyses evidenced a positive result in two out of the 12 sampled P. clarkii. Cherax destructor is now completely absent from the Natural Reserve, while P. clarkii has spread in the area and was probably responsible for this eradication since C. destructor is vulnerable to crayfish plague which was also detected in the area. An ecosystem restoration project in the area favoured the spread of. P. clarkii; the implications of this intervention are discussed.

EDNA-based crayfish plague detection as practical tool for biomonitoring and risk assessment of A. astaci-positive crayfish populations

While environmental DNA (eDNA) approaches have the potential to revolutionize biodiversity research and monitoring, most aquatic biomonitoring and management programs still rely on conventional monitoring methodologies. Here we evaluated the suitability and robustness of an eDNA-based approach for the detection of the crayfish plague agent Aphanomyces astaci and assessed the capacity of this new method as practical tool for bioassessments in freshwater. The approach was examined in three case studies: case study A tested its use as biomonitoring tool to determine the range and density of A. astaci- infected crayfish populations in three different water systems. Case study B focussed on the identification of possible A. astaci infection sources, here an aquafarm. For case study C we assessed a migration front of infected crayfish near a native crayfish area. The eDNA-based detection allowed to infer local patterns and distribution limits of crayfish plague occurrence. Spore estimates in eDNA samples correlated significantly with catch per unit effort values and pathogen loads of captured A. astaci- positive crayfish obtained from trapping in running waters. We also showed that spore concentrations are detectable up to three kilometres downstream from hot spot areas of infected crayfish. By identifying a possible A. astaci entry point and migration front eDNA proved suitable for the detection of A. astaci spores at low population densities and/or pathogen levels of infected crayfish. The study provides conclusive evidence for the suitability of the eDNA approach as a tool for risk assessment and large-scale monitoring of A. astaci for a wide range of practical conservation issues of indigenous crayfish species.

Procambarus clarkii (Girard, 1852) and crayfish plague as new threats for biodiversity in Indonesia

Abstract Numerous freshwater crayfish species are known to become successful invaders when introduced to new territories. One of the most invasive species in this group is the red swamp crayfish, Procambarus clarkii (Girard, 1852). In addition to other characteristics facilitating its invasiveness, it is also a vector of crayfish plague, a disease mostly lethal to crayfish of non‐North American origin. Procambarus clarkii, at present the most widespread crayfish species globally, is popular in many countries both for human consumption and as an ornamental animal. An established population of this species was documented for the first time within Indonesia, representing the first record for maritime Southeast Asia. The species is also common in the local ornamental pet trade. Infection by the crayfish plague pathogen Aphanomyces astaci Schikora was confirmed both in the outdoor population of P. clarkii and in one of the surveyed pet shops. Furthermore, A. astaci was detected in specimens of freshwater crab and shrimp species coexisting with P. clarkii. Local climatic conditions and the species temperature requirements suggest a high probability of the establishment of P. clarkii in Indonesia. Its further spread could irreversibly damage populations of many native endemic crustaceans in the country (as well as elsewhere in the region), and the thriving local aquacultures of the redclaw crayfish Cherax quadricarinatus (von Martens, 1868) may also be threatened. The total ban of P. clarkii and other crayfish species of North American origin in Indonesia is strongly recommended, especially considering that aquaculture and trade with Australasian species is a viable alternative option.

Italian acacia honey exhibits lytic effects against the crayfish pathogens Aphanomyces astaci and Fusarium avenaceum.

This study purpose was to evaluate the invitro inhibitory properties of Italian acacia honey extracts against pathogenic aquatic oomycete/fungal isolates that cause different diseases in crayfish, resulting in an elevated mortality rate. The antimycotic activity of acacia honey aqueous extracts was evaluated against the strain UEF88662 of Aphanomyces astaci (oomycete) and the strain SMM2 of Fusarium avenaceum (fungus). The extracts preparation was carried out with water by a cheap, not complex and organic solvent-free procedure, with low environmental impact and the higher possibility of large-scale reproducibility. The anti-oomycete and antifungal activities were quantitatively evaluated by growth, survival and sporulation microbiological assays. The extracts displayed a dose-dependent inhibitory efficacy on oomycete and fungal growth and survival, as well as on the production of oomycete and fungal spores. Supported by future invivo studies, our results encourage the use of natural extracts like honey as innovative tools to counteract mycotic infections. SIGNIFICANCE AND IMPACT OF THE STUDY: The continuous spread of aquatic fungal disease as the 'crayfish plague' and the 'burn spot disease' has severe ecological and commercial repercussions. Critical factor to prevent further spread is the availability of effective antifungals possibility derived from local natural resources to use in innovative strategies of control and eradication of these diseases. This study provides relevant information about the invitro anti-oomycete and antifungal activity of Italian acacia honey aqueous extracts against two highly infectious and dangerous pathogenic species, Aphanomyces astaci and Fusarium avenaceum, that are responsible for important crayfish diseases.

Aphanomyces astaci genotypes involved in recent crayfish plague outbreaks in central Italy.

The oomycete Aphanomyces astaci is the causative agent of crayfish plague in native European freshwater crayfish. Molecular analyses showed that several distinct genotype groups of this pathogen, apparently associated with different original host taxa, are present in Europe. Tracking their distribution may contribute to understanding the introduction pathways of A. astaci. We used microsatellite markers to genotype the pathogen strains involved in 7 mass mortalities of the endangered indigenous crayfish Austropotamobius pallipes that occurred between 2009 and 2016 in the Abruzzi and Molise regions, central Italy. Three A. astaci genotype groups (A, B, and D, with the latter represented by 2 distinct multilocus genotypes) were identified, suggesting the existence of multiple infection sources even in a relatively small area. Most crayfish plague episodes were due to genotype groups associated with the North American host species Pacifastacus leniusculus and Procambarus clarkii, although these crayfish are not widespread in the study area. A. astaci genotype group A was detected not only in crayfish plague outbreaks but also in apparently healthy Astacus leptodactylus imported for human consumption from Armenia and kept alive in an aquaculture facility. Imports of chronically infected A. leptodactylus from Armenia, Turkey, and possibly Eastern Europe are an underestimated introduction pathway for A. astaci. Although we cannot exclude the presence of latently infected native populations of A. pallipes in the region, A. astaci infections in legally imported crayfish species considered vulnerable to crayfish plague may represent further reservoirs of A. astaci; this should be reflected in the policies regulating the trade of live crayfish.

Genetic diversity and parasite facilitated establishment of the invasive signal crayfish (Pacifastacus leniusculus) in Great Britain.

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.

New genotyping method for the causative agent of crayfish plague (Aphanomyces astaci) based on whole genome data.

The oomycete Aphanomyces astaci causes crayfish plague, the most important disease of European freshwater crayfish species. Presumably introduced into Europe 150 years ago with the import of North American crayfish, A. astaci is highly pathogenic to European crayfish species. Five genotypes (A, B, C, D, and E) have been defined based on random amplified polymorphic DNA analysis (RAPD-PCR) from A. astaci pure cultures. The distinction of genotypes is an essential tool to conduct molecular epidemiological studies on crayfish plague and it has been used to clarify and better understand the history and spread of this disease in Europe. Whereas RAPD-PCR requires DNA from pure culture isolates, the development of genotyping tools that can be applied to DNA extracted from clinical samples allows a much wider application of genotyping studies, including revisiting historic samples. In this study, we present a new approach that adds to currently available methods for genotyping A. astaci strains directly from clinical crayfish samples. Whole-genome sequencing of A. astaci strains representing all currently known genotypes was employed, genomic regions unique to the respective genotype identified, and a PCR-based genotyping assay designed, which focuses on the presence/absence of PCR product after amplification with the genotype-specific primers. Our diagnostic methodology was tested using DNA extracts from pure A. astaci cultures, other Aphanomyces species and additional oomycetes, samples from a recent Italian crayfish plague outbreak and additional historical samples available in the Centre for Environment, Fisheries and Aquaculture Science laboratory. The new markers were reliable for pure culture and clinical samples from a recent outbreak and successfully discriminated genotype A, B, D, and E. The marker for genotype C required an additional sequencing step of the generated PCR product to confirm genotype.

Hidden sites in the distribution of the crayfish plague pathogen Aphanomyces astaci in Eastern Europe: Relicts of genetic groups from older outbreaks?

The crayfish plague agent Aphanomyces astaci is one of the world's most threatening invasive species. Originally from North America, the pathogen is being imported alongside American crayfish species, which are used for various purposes. In this study, we investigated the marginal, currently known distribution area of the pathogen in Eastern Europe by sampling narrow-clawed crayfish (Astacus leptodactylus) and spiny-cheek crayfish (Orconectes limosus) populations. In addition, using specific real-time PCR, we tested several marine decapod species, which also occur in brackish waters of the Danube at the West coast of the Black Sea and the Dniester River basin. By sequencing the nuclear chitinase gene, mitochondrial rnnS/rnnL DNA and by genotyping using microsatellite markers, we identified the A. astaci haplogroups of highly infected specimens. The A. astaci DNA was detected in 9% of the investigated A. leptodactylus samples, both in invaded and non-invaded sectors, and in 8% of the studied O. limosus samples. None of the marine decapods tested positive for A. astaci. The results revealed that narrow-clawed crayfish from the Dniester River carried the A. astaci B-haplogroup, while A. astaci from the Danube Delta belonged to the A- and B-haplogroups. In the invaded sector of the Danube, we also identified the A-haplogroup. Microsatellite analysis revealed a genotype identical to the genotype Up. It might be that some of the detected A. astaci haplogroups are relics from older outbreaks in the late 19th century, which may have persisted as a chronic infection for several decades in crayfish populations.

Simultaneous detection of invasive signal crayfish, endangered white-clawed crayfish and the crayfish plague pathogen using environmental DNA

Aquatic invasive species (AIS) are important vectors for the introduction of novel pathogens which can, in turn, become drivers of rapid ecological and evolutionary change, compromising the persistence of native species. Conservation strategies rely on accurate information regarding presence and distribution of AIS and their associated pathogens to prevent or mitigate negative impacts, such as predation, displacement or competition with native species for food, space or breeding sites. Environmental DNA is increasingly used as a conservation tool for early detection and monitoring of AIS. We used a novel eDNA high-resolution melt curve (HRM) approach to simultaneously detect the UK endangered native crayfish (Austropotamobius pallipes), the highly invasive signal crayfish (Pacifastacus leniusculus) and their dominant pathogen, Aphanomyces astaci (causative agent of crayfish plague). We validated the approach using laboratory and field samples in areas with known presence or absence of both crayfish species as well as the pathogen, prior to the monitoring of areas where their presence was unknown. We identified the presence of infected signal crayfish further upstream than previously detected in an area where previous intensive eradication attempts had taken place, and the coexistence of both species in plague free catchments. We also detected the endangered native crayfish in an area where trapping had failed. With this method, we could estimate the distribution of native and invasive crayfish and their infection status in a rapid, cost effective and highly sensitive way, providing essential information for the development of conservation strategies in catchments with populations of endangered native crayfish.