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.