The crayfish plague agent, Aphanomyces astaci, has spread throughout Europe, causing a significant decline in native European crayfish. The introduction and dissemination of this pathogen is attributed to the spread of invasive North American crayfish, which can act as carriers for A. astaci. As native European crayfish often succumb to infection with A. astaci, determining the prevalence of this pathogen in non-native crayfish is vital to prioritize native crayfish populations for managed translocation. In the current study, 23 populations of invasive signal crayfish (Pacifastacus leniusculus) from the UK were tested for A. astaci presence using quantitative PCR. Altogether, 13 out of 23 (56·5%) populations were found to be infected, and pathogen prevalence within infected sites varied from 3 to 80%. Microsatellite pathogen genotyping revealed that at least one UK signal crayfish population was infected with the A. astaci genotype group B, known to include virulent strains. Based on recent crayfish distribution records and the average rate of signal crayfish population dispersal, we identified one native white-clawed crayfish (Austropotamobius pallipes) population predicted to come into contact with infected signal crayfish within 5 years. This population should be considered as a priority for translocation.

The microsporidian parasite Thelohania contejeani causes porcelain disease and has been implicated in mass mortalities in populations of the endangered European crayfish Austropotamobius pallipes. However, the route of parasite transmission is not known. This paper investigates the horizontal transmission of T. contejeani between A. pallipes hosts as well as its transmissibility to the invasive signal crayfish (Pacifastacus leniusculus). Field collected juvenile A. pallipes and P. leniusculus were assigned to 1 of 3 experimental treatments; fed heavily infected A. pallipes tissue, exposed to water from tanks housing heavily parasitized A. pallipes, and a control group to provide an estimate of the baseline infection levels in the field. After 26 weeks, abdominal muscle samples were screened by PCR for T. contejeani. Infection was significantly higher in the treatment groups (83% in the cannibalism treatment, 42% in the water exposure treatment) than in the control group (4%), providing evidence for horizontal transmission of the parasite between A. pallipes hosts. Cannibalism and scavenging are common amongst crayfish, providing transmission opportunities in the field. The study also provides the first direct evidence for transmission of the parasite from an indigenous European crayfish species to the invasive signal crayfish, with 50% of P. leniusculus in each treatment, and 8% of control animals infected. We discuss the possibility that high density populations of the invasive signal crayfish may serve either as reservoirs or sinks for the parasite.

Branchiobdellidans or crayfish worms are clitellate annelids and ectosymbionts of freshwater crayfish. An investigation of branchiobdellidan infestation was undertaken in a population of endangered white-clawed crayfish (Austropotamobius pallipes) in the river Aire, UK. Thirty two percent of animals were infested either by the adult parasite or their cocoons (n=107). Parasite burden increased with host size, but did not differ with sex. Observations of crayfish gill tissue revealed a strong positive relationship between melanization of filaments and parasite prevalence and burden. Taxonomic identification revealed that 1 species of branchiobdellidan was present, Branchiobdella astaci. The first sequences were generated for this species and phylogenetically analysed alongside published sequences for 5 other branchiobdellidan species in Europe. The position of B. astaci within the genus Branchiobdella was confirmed, and it was found to cluster as a sister group to B. parasita.

We studied the distribution patterns of the native European white-clawed crayfish (Austropotamobius pallipes) and the introduced signal crayfish (Pacifastacus leniusculus), and looked at the water chemistry in several streams in the north of the Iberian Peninsula (Cantabrian watershed). Fifty fluvial reaches which were currently or previously inhabited by crayfish and had physical attributes similar to the known habitat requirements of crayfish were sampled. P. leniusculus was the most common species encountered (54% of the samples), A. pallipes was found in 19% and neither species was recorded in the remaining reaches. In this paper we determine the relationship between crayfish presence and water chemistry. As neither species inhabits waters with the highest NO2– concentrations found, it seems both species are sensitive to NO2–. Mg+2 and SO4–2 concentrations are the factors separating sites with and without crayfish (crayfish inhabit water with higher concentrations of both cations). The main differences between reaches inhabited by native and signal crayfish lies in SO4–2 concentration: higher concentrations favour signal crayfish. Applications to management based on the river water chemistry are proposed.

If recovery programmes are to be initiated in England and Wales, it is very important to obtain information on how genetic variation is partitioned between the remaining populations for the endangered species Austropotamobius pallipes pallipes. A survey of the mtDNA genome, using 12 restriction enzymes revealed 3 haplotypes in 4 British populations. The study reveals a low level of genetic variation amongst four geographically distant populations. Moreover, the most widespread haplotype found in the British populations is also similar to those found in French populations; one of the rare haplotypes found in one English population is also widespread in French populations. Management of crayfish stocks may be possible at a national level however, a more extended study of mtDNA variation is needed to prove this conclusively.

Ce travail examine la distribution d'Autropotamobius pallipes (Ler.) et des caractéristiques abiotiques des écosystèmes aquatiques que cette espèce colonise en Bizkaia. 81 stations du réseau hydrographique de Bizkaia et 17 étangs situés dans une zone minière près de Bilbao ont été échantillonnés et leurs eaux analysées.On constate d'une part, la disparition de l'espèce dans la plupart des rivières et d'autre part, sa grande abondance dans les étangs. L'analyse des spectres écologiques permet de déterminer l'affinité écologique de l'écrevisse pour les eaux froides et dures et sa tolérance à l'eutrophisation.