Environmental impact of zebra mussels

DEFINITION: Endemic European freshwater bivalves that occur in North America as an exotic and invasive species

Zebra mussels are a source of concern in North America, where they are an invasive or exotic species, because of the mussels’ potential influence on aquatic systems. When zebra mussels colonize a body of water, they reduce the abundance and species diversity of native mussels, and they also reproduce in such density that they restrict water flow in pipes.

The zebra mussel (Dreissena polymorpha) is native to southern Russia and is thought to have been introduced into Lake Saint Clair—which lies between Michigan and Ontario, Canada—in 1986 via discharged ballast water. Since its introduction, the zebra mussel has become widely dispersed, occurring in all of the Great Lakes by 1990. By the mid-2020s, according to the US Fish and Wildlife Service, it had appeared in over thirty US states. This rapid dispersal is largely the result of the mussels’ ability to attach to boats that navigate these waters, as well as their ability at all life stages to survive overland transport (for example, living on the hulls of boats as the boats are transported between lakes). The invasive species also spreads through contaminated aquarium, pet, and garden supplies, such as Marimo moss balls.

It is expected that the species will continue to disperse and increasingly colonize North American inland lakes. However, in the second and third decades of the twenty-first century, some native ecosystems and the invasive species began to reach an emerging equilibrium that slowed their growth.

The shell sizes of zebra mussels average 25 to 35 millimeters (1 to 1.4 inches). Zebra mussels typically live three to five years, and females usually reproduce during their second year; each female can produce more than forty thousand eggs in one reproductive cycle. After fertilization, veliger larvae emerge within three to five days and are free-swimming for up to one month. Dispersal during this time is primarily caused by water currents. Larvae then settle to the bottom, where they crawl via foot, looking for suitable substrate (preferred to be hard or rocky). To attach themselves to the substrate, they secrete proteinaceous byssal threads from a byssal gland located in the foot.

From an ecological and environmental perspective, one of the most important concerns related to zebra mussel colonization of a body of water is that it reduces the abundance and species diversity of native unionid mussels. Because native unionid mussel beds provide the type of hard substrate that zebra mussels prefer, zebra mussels readily colonize such areas, negatively influencing the feeding, growth, locomotion, respiration, and reproduction of native unionids.

In addition, zebra mussels have an important influence on the environment because of their role as biofoulers. When they colonize pipes, they can restrict water flow, negatively affecting water supply to hydroelectric facilities, nuclear power plants, and public water supply plants. Zebra mussels can also attach to the hulls of boats, leading to increased drag, and their weight can cause navigational buoys to sink. Because zebra mussel densities have been measured as high as 700,000 mussels per 1 square meter (10.8 square feet), they can cause serious problems.

Despite their negative effects on aquatic systems, zebra mussels can have positive effects on water quality through their role as biofilters. An adult zebra mussel can filter phytoplankton from as much as 1 liter of water per day, significantly altering water quality. However, even this influence has potentially negative consequences in that it reduces the amount of food available for zooplankton and eventually for recruiting fish. This can also lead to a change in food webs from phytoplankton-dominated systems to macrophyte-dominated systems. Given their filtering ability, zebra mussels also tend to bioaccumulate substances, possibly increasing the concentration of toxic substances that are passed up the food web.

Bibliography

Blok, Andrew, and Sharon Oosthoek. "30 Years Later: Mussel Invasion Legacy Reaches Far beyond Great Lakes." Great Lakes Now, 2 Feb. 2021, www.greatlakesnow.org/2021/02/invasive-mussels-legacy-beyond-great-lakes. Accessed 24 Aug. 2025.

Creamer, David A., et al. “Identifying Lakes Critical to the Westward Spread and Establishment of Zebra Mussels.” Biological Conservation, vol. 302, 2025, doi:10.1016/j.biocon.2024.110931. Accessed 25 Aug. 2025.

"Invasive Zebra Mussels." National Park Service, 2 Apr. 2021, www.nps.gov/articles/zebra-mussels.htm. Accessed 24 Aug. 2025.

Johnson, Laura. "Zebra Mussels and Why We Should Care." SDPB, 23 May 2022, www.sdpb.org/environment/2022-05-23/zebra-mussels-and-why-we-should-care. Accessed 24 Aug. 2025.

Pimentel, David, editor. Biological Invasions: Economic and Environmental Costs of Alien Plant, Animal, and Microbe Species. CRC Press, 2002.

Van Driesche, Jason, and Roy Van Driesche. “Refuge for the Mussels: Biotic Integrity and Zebra Mussel Invasion in the Ohio River Basin.” Nature Out of Place: Biological Invasions in the Global Age. Island Press, 2000.

"What Are Zebra Mussels and Why Should We Care about Them?" USGS.gov, 19 Mar. 2025, www.usgs.gov/faqs/what-are-zebra-mussels-and-why-should-we-care-about-them. Accessed 24 Aug. 2025.

"Zebra Mussel." US Fish & Wildlife Service, www.fws.gov/species/zebra-mussel-dreissena-polymorpha. Accessed 24 Aug. 2025.