Migration and fouling potential of macrophyte-attached zebra mussels (Dreissena polymorpha)

The success and impact of invading species can often be attributed to their life history traits and behaviours in relation to their environment. A key trait contributing to the invasive spread and impact of the zebra mussel Dreissena polymorpha (Pallas 1771) is its ability to attach to solid surfaces using byssal threads. In lakes, common substrates for attachment are aquatic macrophytes such as Eurasian watermilfoil (Myriophyllum spicatum Linnaeus 1753), which can support enormous numbers of newly settled zebra mussels. A question remaining to be resolved is the fate of zebra mussels attached to macrophytes that senesce before winter. We experimentally showed that macrophyte-attached zebra mussels (juveniles and adults, 2–18 mm shell length) migrated to other benthic substrates during senescence of Eurasian watermilfoil. We tested whether migrating zebra mussels exhibited preferences for alternative substrates, including living unionid mussels Elliptio complanata (Lightfoot 1786), intact empty unionid shells, rocks, and sand. After three weeks, densities of migrated zebra mussels were equally highest on living unionids, empty shells, and rocks. Zebra mussel translocation from macrophytes can thus contribute to biofouling on unionid mussels, which has caused rapid local declines in unionid populations.