SOME CASES OF MACRO-EPIBIOSIS ON THE INVASIVE CRAYFISH ORCONECTES LIMOSUS IN THE CZECH REPUBLIC

Several cases of epibiosis by macro-invertebrates on Orconectes limosus were recorded during our research on the biology of populations of this invasive crayfish species in the Czech Republic. (1) In 2001, we observed a high infestation of O. limosus by native species of branchiobdellidan worms (Annelida: Branchiobdellidae) in the river Elbe at Obristvi (Central Bohemia). Four European Branchiobdella species were collected and identified from three crayfish specimens: B. pentodonta (52%), B. balcanica (24%), B. parasita (18%) and B. hexodonta (6%). In 2003, only a single crayfish was found bearing branchiobdellidans (5 specimens of B. parasita only) in the same locality. No branchiobdellidans on O. limosus have been confirmed since. (2) A flooded sandpit Lhota near Brandýs nad Labem is the only Czech locality where the settlement of Dreissena polymorpha (Mollusca, Bivalvia) on an O. limosus body was recorded. The crayfish lost the bivalves by moulting in summer; new mussels had settled by late summer and early autumn. (3) Females of the fish louse Argulus cf. foliaceus (Crustacea: Branchiura) lay egg-strings on any hard substrate, including the crayfish exoskeleton. Such egg-masses were found on up to 65% of O. limosus specimens in the above-mentioned sandpit. (4) Bryozoan colonies of Plumatella repens were found twice on crayfish in the rivers Elbe (Labe) and Cidlina.