THE FIRST TROPICAL ALIEN CRAYFISH SPECIES IN EUROPEAN WATERS: THE REDCLAW CHERAX QUADRICARINATUS (VON MARTENS, 1868) (DECAPODA, PARASTACIDAE)

A population of the tropical redclaw crayfish Cherax quadricarinatus (Von Martens, 1868) is reported here for the first time in Europe, despite some occasionally found released individuals found previously in some European countries. The redclaw population was first found in 2009 in the natural river oxbow lake Topla, with thermal hot water springs, in eastern Slovenia (Central Europe). The species is known to be invasive in tropical and subtropical regions, but this is the first record from the temperate climate zone. During intensive sampling with traps, 15 individuals were caught that seemed to belong to a sex- and age-structured population. The low abundance indicated that the population was still in the growth phase of colonization, or that habitat conditions for the species in the oxbow lake were suboptimal. The redclaw individuals were found at temperatures of up to 40 degrees C, but the bulk of the population with sexually mature individuals was restricted to regions between 21 and 31 degrees C. According to the modelled limits of annual water temperature fluctuation, further expansion of the redclaw is expected in the thermal oxbow lake, but invasion to adjacent rivers is less probable at least under current climatic conditions. As a rapidly growing large crayfish, the redclaw could pose a threat to local ecosystems in specific thermal water bodies with unique fauna and flora. Future studies are important to define threats of tropical invaders in specific thermal freshwater ecosystems in Europe.