Detachment rates of dreissenid mussels after boat hull-mediated overland dispersal

Introductions of the invasive zebra mussel ( Dreissena polymorpha ) and quagga mussel ( Dreissena rostriformis bugensis) into hydrologically isolated water bodies have been attributed to overland transport via (recreational) boat hulls. Before a boat becomes a successful vector, mussels must (1) attach to the hull, (2) survive air exposure during overland transport and (3) establish a viable population either after detachment or release of spat during launching or sailing. This study mimics these dispersal barriers and assesses the potential of boat hull-mediated release into a recipient environment for both species. Individuals were allowed to attach to aluminium and fibreglass plates. Hereafter, attached individuals were exposed to air and subsequently submerged again. Zebra mussels had a significantly higher attachment rate than quagga mussels. The percentage of attached dreissenid mussels that detached alive during rewetting ranged between 7.9 and 21.8%. No significant difference was found between species and hull materials. However, alive detachment during rewetting was significantly higher after 24 h compared to 48 h of air exposure. Our data allow modelling introduction pressure of lakes if quantitative data on overland boat movement and the density of attached mussels are available.