The impact of zebra mussel (Dreissena polymorpha) periostracum and biofilm cues on habitat selection by a Ponto-Caspian amphipod Dikerogammarus haemobaphes

Abstract

Dikerogammarus haemobaphes is one of several Ponto-Caspian gammarids invading Europe in recent decades. Previously, it exhibited active preferences for habitats associated with another Ponto-Caspian alien, zebra mussel. Now we tested gammarid preferences for living mussels and their empty shells with biofilm and/or periostracum present or absent, to find the exact cues driving gammarid responses. We observed a strong preference of gammarids for biofilmed shells, even if the biofilm was relatively young (2-day old). However, the biofilm quality, related to the substratum on which it had developed (shells with or without the periostracum, or coated with nail varnish) did not affect their behaviour. In the absence of biofilm, gammarids positively responded to the shell periostracum. Furthermore, they clearly preferred living zebra mussels over old empty shells, independent of the presence or absence of biofilm, confirming the importance of a periostracum-associated cue in their substratum recognition. On the other hand, shells obtained shortly after mussels’ death were preferred over living bivalves. Thus, the attractant is associated with fresh mussel shells, rather than with living mussels themselves. The ability of alien gammarids to locate sites inhabited by zebra mussels may contribute to their invasion success in novel areas inhabited by this habitat-forming bivalve.