Crayfish plague pathogen detected in the Danube Delta – a potential threat to freshwater biodiversity in southeastern Europe

Anne Schrimpf,Denis Copilaș-Ciocianu,Lucian Pârvulescu,Adam Petrusek,Ralf Schulz

doi:10.3391/ai.2012.7.4.007

Anne Schrimpf, Denis Copilaș-Ciocianu + Show 3 more

Open Access

https://doi.org/10.3391/ai.2012.7.4.007

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Abstract

The crayfish plague, caused by the oomycete Aphanomyces astaci, is probably the most significant reason for declines in European freshwater crayfish species. One of its hosts, the North American spiny-cheek crayfish Orconectes limosus, extends its range in the river Danube and recently reached the territory of Romania. We used highly sensitive A. astaci-specific real-time PCR to test if the native narrowclawed crayfish Astacus leptodactylus in the highly protected Danube Delta about 970 km downstream of the current invasion front of American crayfish is a carrier of the crayfish plague. Thirteen out of 40 analysed native A. leptodactylus tested positive for the crayfish plague pathogen, infected individuals were found at both sampled localities within the Danube Delta. Therefore A. astaci has a much wider range in this river than assumed. The pathogen seems to persist in local populations, as neither crayfish mass mortalities nor alien crayfish species have been reported from the region. Aphanomyces astaci may have reached the Delta by long-range passive dispersal of infected hosts or pathogen spores, or by gradually infecting populations of native crayfish in upstream regions of the Danube in a stepping-stone manner. Alternatively, the crayfish plague may have persisted in the Danube Delta as chronic infection from an old plague wave in the 19th century. In any case, the presence of this pathogen in the lower Danube may become a threat to conservation of European crayfish and to freshwater biodiversity in many regions of southeastern Europe, at present considered “crayfish plague-free”.

Highlights

The distribution of freshwater organisms is affected by varying climatic cycles and topographic features and in the last centuries to a high degree by direct and indirect human impacts
It has been believed that all native crayfish from Europe are highly susceptible to crayfish plague, and that infection by the plague pathogen generally leads to their death
40 individuals of narrow-clawed crayfish were collected in the Danube Delta, 37 from the Chilia Channel and three from Merhei Lake

Summary

Introduction

The distribution of freshwater organisms is affected by varying climatic cycles and topographic features (e.g. changes in river flow) and in the last centuries to a high degree by direct and indirect human impacts (e.g. by species translocations, habitat alterations, and anthropogenic pollution). The oomycete Aphanomyces astaci Schikora, the causative agent of this disease, had been most probably introduced from North America to Europe in the late 1850s together with some of its original hosts, North American freshwater crayfish species (Alderman 1996) This aggressive pathogen is listed among the worlds. A few recent studies reported that native crayfish populations may persist for several years or even decades with certain levels of infection by A. astaci (Jussila et al 2011; Kokko et al 2012; Svoboda et al 2012) Despite these exceptional cases, crayfish plague poses a high risk to waters not yet affected by the disease, especially in eastern European countries where it is less widespread (Holdich et al 2009)

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