Specimen of the Month: Racing Against Invasion

For those not familiar with zebra mussels, they are quite small. With a typical lengthwise measurement of less than one inch, one look at a singular specimen may persuade some to overlook its disastrous effects on other freshwater mussels and aquatic habitats. To that end, the Museum does not just have one zebra mussel on display this month--we have hundreds! 

Zebra mussels are small and inconspicuous invasive species
in many Midwestern water bodies.

Zebra mussels (Dreissena polymorpha) originally inhabited lowland lakes and rivers in areas around Russia and Ukraine but were unintentionally introduced to other areas worldwide via shipping routes. This small species clings to a variety of substrates but the hard, stable surface of native mussels, clams, and the hulls of boats provide an excellent area for it to build colonies. Since the 1980's they've literally invaded water bodies in the States, especially the Great Lakes area. 

Many native mussel and clam species have suffered due
to crowding of zebra mussels.

Zebra mussels have important traits of invasive species. They have high fecundity--females produce an estimated 30,000 to one million eggs in just one year! Larval dispersal rates are also high. Many small hairs projecting from a thin sheet of skin known as a velum allow zebra mussel larvae of the veliger stage to free-swim and draw in food particles. This makes them incredibly mobile. Furthermore, zebra mussels have high filtration capacity. Their dense clusters can remove over half of a lake's plankton biomass, which naturally provide a significant food source for many other creatures. 

As an important species to their native European water bodies, zebra mussels' filtering capacity contributes to the populations of neighboring species in two ways. One, they efficiently excrete particles eaten by many invertebrate species. This can nearly double invertebrate populations in areas with zebra mussels present. Two, as they clean up lake bottoms they help fish predators who rely largely on sight to catch prey. Take Lake Ontario for example, where salmon and their prey of alewife have both grown in size and population due to increased visibility when feeding on bottom-dwelling shrimp. Like any invasive species, zebra mussels contribute to a healthy biological balance in the right environment. 

When introduced to the wrong environment however, zebra mussels disrupt that balance. Many parts of the Great Lakes, Mississippi River, and notably Mille Lacs Lake in Minnesota host a staggering population of zebra mussels and have suffered. Divers in the Great Lakes are racing to document historical shipwrecks before they become encrusted by invasive zebra and quagga mussels. Visitors to picturesque beaches now share heartbreaking scenes of beaches blanketed with sharp zebra mussel shells. 

The Museum's Specimen of the Month allows visitors in August
to view and feel a bucket completely encased in zebra mussel shells.

Our aquatic landscapes are changing and as fellow creatures transforming the environment, we have the capacity and responsibility to approach this invasion with understanding. Individual action does not necessitate significant effort but it makes a significant impact as we hope to prevent zebra mussels from disrupting more habitats. Inspect, clean, and drain boating equipment between outings. Make note of the presence of zebra mussels and be sure to report sightings. Visit places to discover more about this species, including but certainly not limited to the Museum. After all, the more we learn about the world around us, the more capable we are of maintaining a healthy balance.