Early detection, dispersal, and maturation of zebra mussels (Dreissena polymorpha) in the Marais des Cygnes River and Melvern Lake, Kansas

Abstract

The zebra mussel (Dreissena polymorpha) is an aquatic invasive mollusk brought to North America via cargo ships from the Black and Caspian seas in 1986. A biofouling species, zebra mussels not only cause damage to submerged manmade materials but also outcompete native mussels, many of which are already critically endangered. Zebra mussels also destroy ecosystems by disrupting native food webs. The objectives of my study were to determine: 1) the best method for early detection of a zebra mussel infestation; 2) the distribution pattern of zebra mussels in the Marais des Cygnes River; and 3) stages of gametogenesis achieved by zebra mussels in the Marais des Cygnes River and Melvern Lake, Kansas. From June–November 2013 and May–November 2014, I investigated the invasion of zebra mussels in the Marais des Cygnes River from a source population in Melvern Lake, downstream 196 river-km. I used 30-minute inspection of shoreline, settlement structures, cross-polarized light microscopy (CPLM)

iii of plankton, and detection of environmental DNA (eDNA) to determine which of these methods would provide the earliest indication of a zebra mussel infestation. I chose 12 sites of three site types (lake, free-flowing river, and lowhead dam) to determine whether lowhead dams influenced the dispersal and distribution of zebra mussels downstream from the source lake. I also performed histological analysis to determine whether zebra mussels entered a mature stage of gametogenesis in the river and sought to determine whether increased veliger densities were due to instream recruitment or simply accumulation from the upstream source population. CPLM of water samples taken via plankton net tows gave the earliest indication of infestation at previously non documented sites. The density of zebra mussels (both settled recruits and veligers) decreased with distance from the source lake, with peaks of densities at lowhead dam sites. Zebra mussels achieved sexual maturity, with correlative likelihood of reproduction, at both free-flowing and inundated (dammed) sites, consistent with the downstream–march model of dispersal.