The zebra mussel (Dreissena polymorpha), introduced to the Great Lakes in the late 1980s by ballast water discharged by cargo ships, is a major aquatic invasive species in Minnesota. Since its introduction, it has spread rapidly throughout North America, aided by natural dispersal and human activities such as boating.
Zebra mussels reproduce prolifically: females release millions of eggs for external fertilization, producing free-swimming larvae (veligers) that drift in the water column. Juveniles later settle on hard surfaces using byssal threads. Their small size, high reproductive output, efficient filter feeding, and lack of natural predators allow populations to grow quickly and spread throughout freshwater systems.
Zebra mussels have substantial ecological and economic impacts. They can displace native mussels and bioaccumulate pollutants such as mercury and heavy metals, increasing exposure risks for fish and humans. They also cause costly infrastructure damage by clogging power plants, water treatment facilities, boats, and dams. Although their filtration increases water clarity, it also removes large amounts of phytoplankton and zooplankton, disrupting food webs, reducing biodiversity, and decreasing ecosystem resilience.
While adult zebra mussels attach firmly to surfaces and are protected by hard shells, their larval stage is more vulnerable to environmental conditions. Rivers are highly dynamic systems characterized by flow, shear, and turbulence, which may impose mechanical stress on veligers and increase mortality. Despite this, zebra mussels disperse downstream over hundreds of kilometers, likely aided by areas of reduced turbulence such as impoundments, reservoirs, and lakes where survival conditions are more favorable.
To investigate these effects, we used a recirculating racetrack flume designed to simulate an effectively infinite river reach under controlled laboratory conditions. Turbulence was generated using roughness elements along the channel bed and walls. In the first experiment, zebra mussel larvae were exposed to turbulent flow for extended periods. Mortality was assessed microscopically by identifying cracked or open shells. On the other hand, live mussels were identified by moving organs or red coloring from absorbing the dye while feeding.
A second set of experiments examined adult mussels. Although their shells protect them from direct turbulence damage, turbulence may still influence their filter-feeding behavior. Gape sensors were used to monitor valve activity by detecting changes in shell opening and closing. Small magnets attached to each valve change their distance during movement, producing measurable voltage changes. Because zebra mussels filter feed while their valves are open, these voltage fluctuations provide a reliable proxy for feeding activity.
By integrating fluid dynamics with zebra mussel biological responses, this study examines how turbulence influences both larval survival and adult feeding behavior. Understanding these relationships may improve predictions of zebra mussel establishment and spread in freshwater ecosystems.