Two species of decapods or malacostracans can be found in aquatic habitats in the Plitvice Lakes National Park; these are the stone crayfish (Austropotamobius torrentium) and the noble crayfish (Astacus astacus). Crayfish are a major component in biological systems.
Invasive alien species of crayfish mostly introduced from the North America present a great threat to the indigenous species of crayfish. These “American species” are more aggressive, more fertile and, most importantly, are carriers of a type of crayfish plague (a crayfish fungal disease) introduced with them from the American continent, but are themselves resistant to this plague. On the other hand, European species are not resistant to this type of disease so they die in great numbers in aquatic habitats that they share with alien species if they come into contact with the fungi that cause the disease.
Crayfish monitoring in the Park, carried out annually by the employees of the expert service in cooperation with the Croatian Biological Society for years, consists of monitoring the population status, the mortality of the indigenous species of crayfish and the presence of invasive alien species of crayfish as well as the detection of crayfish plague.