Invasive zebra mussel colonisation of invasive crayfish: a case study

We investigated the interaction between two invasive invertebrate species in a shallow Central European flooded sandpit: the epibiosis of Ponto-Caspian zebra mussels Dreissena polymorpha on the American crayfish Orconectes limosus. Between 2004 and 2005, we followed the seasonal variation in number and size of the mussels attached to crayfish bodies, and microhabitats preferred by mussels. The proportion of crayfish colonised by mussels varied seasonally: in spring and early summer it was consistently over 75%, afterwards it dropped temporarily due to loss of bivalves during the crayfish moult, and later increased again due to re-colonisation by often relatively large juvenile mussels. Three different pathways of mussel settlement on crayfish hosts are likely: (1) primary settlement of free-swimming pediveliger larvae; (2) secondary settlement of plantigrade mussels and juveniles; (3) active re-attachment of grown mussels from the substrate to crayfish. This epibiosis was promoted by lack of suitable substrates at the studied locality. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.