Lowhead dams and the downstream dispersal of zebra mussels

In rivers of the upper Neosho basin, Kansas, USA, lowhead dams influence the downstream dispersal of zebra mussels (Dreissena polymorpha). We quantified density of planktonic zebra mussel larvae and abundance of recruited individuals at 13 sites in this river–reservoir system to examine potential effects of four lowhead dams on dispersal dynamics of this invasive species. Density and abundance declined downstream from reservoir sources but repeatedly increased at sites inundated by lowhead dams compared to free-flowing areas, with colonization extending 189 river-km. The pattern of zebra mussel dispersal in these rivers is best described by the downstream-march model, with lowhead dams acting as stepping stones. Even though these zebra mussel populations are likely not self-recruiting behind lowhead dams, reproduction at these dams could lead to recruitment downstream. Thus, in rivers with lowhead dams, control of zebra mussel metapopulations may not be accomplished solely by limiting source–sink dynamics from upstream infested lakes.