Alien Crayfish in Europe: Negative and Positive Impacts and Interactions with Native Crayfish

Abstract

Worldwide, about 500 species of freshwater crayfish are known. Europe has only five, all of which belong to a single family, Astacidae, with two genera: Astacus astacus, A. leptodactylus and A. pachypus, and Austropotamobius pallipes and A. torrentium. The widespread elimination of native populations by crayfish plague, Aphanomyces astaci, and human intervention has led to the introduction of plague-resistant North American crayfish in an effort to restore Europe’s once highly profitable crayfish industry. Crayfish have also been imported to occupy a vacant niche, for aquaculture purposes, and for home aquariums and ornamental pools. The main alien species established in Europe are two cambarids, Orconectes limosus (introduced in the 1890s, currently in 15 countries) and Procambarus clarkii (1970s, 11 countries), and one astacid, Pacifastacus leniusculus (1960s, 25 countries). Recently, Orconectes immunis and Procambarus zonangulus have been released into natural waters in Germany. The main benefits of introductions have been new productive fishery in plague-stricken waters, new opportunities for crayfish culture and an additional source of food. The socio-economic aspects and recreational values are also important. The most disastrous impact has been on native crayfish populations. Alien species can be vectors of the plague fungus and thus present a persistent risk to native species. The fact that these species are highly competitive alien species — even without the plague — gives rise to detrimental competition and eventually replace native species when sympatric. Despite the increasing interest in conserving Europe’s unique native crayfish fauna and its biodiversity, the threat of crayfish plague, habitat changes, continuous expansion of the ranges of alien species by human activity and the removal of trade barriers hamper efforts to ensure the future of indigenous species.