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 Ob r( istvi (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 Brandys 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.Original Abstract: Au cours de nos recherches sur la biologie des populations d'ecrevisse invasive Orconectes limosus presentes en Republique tcheque, nous avons observe plusieurs cas d'epibioses par des macroinvertebres sur cette ecrevisse. (1) En 2001, nous avons observe un taux d'infestation eleve chez O. limosus par des vers (Annelida: Branchiobdellidae) dans l'Elbe a Ob istvi. Quatre especes europeennes de Branchiobdella ont ete recoltees et identifiees en examinant trois specimens d'ecrevisses: B. pentodonta (52 %), B. balcanica (24 %), B. parasita (18 %) et B. hexodonta (6 %). En 2003, une seule ecrevisse porteuse de Branchiobdella (5 specimens de la seule espece B. parasita) a ete trouvee dans la meme localite. Aucun Branchiobdellidae n'a ete trouve par la suite sur O. limosus. (2) La carriere de sable innondee de Lhota pres de Brandys nad Labem est la seule localite tcheque ou la fixation de Dreissena polymorpha (Mollusca, Bivalvia) sur le corps de O. limosus a ete observee. Les ecrevisses perdent les bivalves lors de la mue estivale mais de nouvelles moules se fixent sur leur cor