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Defending Against Invasive Mussels

Columns of mussels covering hydro equipment.
Invasive quagga mussels covering hydro dam equipment. Photo Washington Invasive Species Council. 


The Columbia River Basin spans an area the size of France, that includes portions of seven states and parts of Canada. It is the only major river basin in the United States that hasn’t been impacted by invasive quagga or zebra mussels (WDFW, 2019). Dr. Stephen Bollens, who co-directs the WSU Aquatic Ecology Lab in Vancouver with Dr. Gretchen Rollwagen-Bollens, are working on developing strategies to prevent new introductions, quickly detect new arrivals, and help control the bivalves’ spread. It’s not an easy task since female bivalves can produce a million eggs a year and the size of larvae are measured in microns. Even as adults, the mussels can easily be overlooked, since they’re just a little more than one inch in size.

Three larger zebra mussels and four quagga mussels with a scale.
Zebra and quagga mussels with scale. Photo Wen Baldwin.

Zebra and quagga mussels, collectively called dreissenid mussels, are non-native, freshwater mollusks. They were first discovered in the US in the Great Lakes in the 1980s; they apparently hitched a ride in ballast water from ships that came from the Caspian and Black Seas in Eurasia. Since then, they have invaded fresh waterbodies and estuaries across North American, causing extensive economic and environmental damage. They’re responsible for clogging pipes and mechanical systems of industrial plants, water and sewer utilities, locks and dams, as well as causing serious environmental damage to native aquatic species and habitats.

Keeping the harmful bivalves from colonizing and damaging infrastructure and ecosystems in the Columbia River is a high priority. If they take hold in Washington, officials estimate it could cost more than $100 million annually to keep the state’s power and water infrastructure maintained (Washington Invasive Species Council 2017).

2019). The mussels could also undo decades of restoration work on salmon fisheries.

Although neither zebra or quagga mussels have yet been found in Washington waters, they have been found on boats transported across state lines. The Washington Department of Fish and Wildlife have intercepted more than 50 boats with mussels attached to them in the past two years. In fact, recreational boats are considered a primary cause of invasive mussel spread in the United States. See How Boaters Can Help sidebar at the end of this article for how to clean your boat.

A three-prong approach of detection, control, and prevention is used to ensure the mussels don’t get a hold in the Columbia. Early detection and rapid response are key to successfully control the mollusks and minimize their impacts. Control or eradication efforts are only possible when population densities are low and restricted to small areas. Prevention is much less expensive than trying to control or eradicate the mussels, especially after populations have become well established. The appropriate amount of response is critical, though. Counihan and Bollens (2017) found that the current level of effort being expended in the Columbia and Snake rivers is not sufficient to mitigate the risk through early detection measures.

Three people in a boat using bottom sampling equipment.
Summer Henricksen, Salvador Robb-Chavez, and Mariah McCleskey using a PONAR grab (bottom sampler) during shipboard monitoring for Asian clams on the Columbia River.

To address this, Bollens’ team is working to enhance monitoring and early detection through new technologies such as the FlowCam and environmental DNA (eDNA). The FlowCam is an automated microscope and imaging system used to identify and count particles (such as plankton) suspended in fluids such as river water (Hassett et al. 2017). eDNA is organismal DNA that can be found in the environment and can be used to monitor for aquatic invasive species. Bollens and Aquatic Ecology Lab colleagues are collaborating with the U.S. Geological Survey’s Upper Midwest Environmental Sciences Center on deploying this technology.

The Aquatic Ecology Lab has mapped access points and routinely samples for larval mussels on the mainstem Columbia River to better understand the potential risk for introductions. If mussels do invade the Columbia, the researchers are working on effective strategies that would minimize the impact to hydroelectric, irrigation and urban water facilities.

In following the old saying about knowing your enemy, the Lab is also delving into the interrelations between different aquatic invasive species and their habitats. Recent research revealed a high abundance of larval Asian clams in several mainstem Columbia River reservoirs (Hassett et al.,2017). Asian copepods (small crustaceans) have also invaded several Pacific Northwest rivers, including the Columbia River (Dexter et al. 2020a,b). Could these invasive species, or something in its host environment be playing a role in keeping dreissenid mussels at bay, or might these current invaders actually make it easier for new invaders to colonize Pacific Northwest waters? Stay tuned for more findings from Bollens and his colleagues.
To learn more about the WSU Aquatic Ecology Lab in Vancouver.

How Boaters Can Help

Here are some tips for ensuring your boat doesn’t have any hitchhiking invasive species:

Man in orange protective suit sprays a metal boat on a trailer.
Boat being decontaminated. Photo WDFW.

Clean: When leaving the water, clean all equipment that touched the water by removing all visible plants, algae, animals, and mud. This includes watercraft hulls, trailers, shoes, waders, life vests, engines and other gear. It’s not just powerboats that can give bad bivalves a ride. Kayaks, rafts, and rowboats can have stowaways, too.

Drain: Drain any accumulated water from watercraft or gear, including live and transom wells, before leaving the water access area.

Dry: If transporting watercraft from outside Washington State, be sure to clean and dry everything. Once home, let everything fully dry before using it again in a different water body.

Remember, the penalty for transporting aquatic invasive species in Washington State can range from a $500 fine to a class C felony. Call the Aquatic Invasive Species hotline at 1-888-WDFW-AIS (1-888-933-9247) for more information or visit WDFW’s website.

For more clean boating tips see WSU’s Shore Steward Newsletter.


Counihan, T. D. and S. M. Bollens. 2017. Early detection monitoring for larval dreissenid mussels: How much plankton sampling is enough? Environmental Monitoring and Assessment, 189: 98. DOI: 10.1007/s10661-016-5737-x.

Dexter, E., S. M. Bollens, J. Cordell, and G. Rollwagen-Bollens. 2020a. Zooplankton invasion on a grand scale: Insights from a 20-year time-series across 38 Northeast Pacific estuaries. Ecosphere,11(5):e03040.

Dexter, E., S. M. Bollens, and G. Rollwagen-Bollens. 2020b. Native and invasive zooplankton show differing responses to decadal-scale increases in maximum temperatures in a large temperate river. Limnology and Oceanography Letters, In Press.

Hassett, W., S. M. Bollens, T. D. Counihan, G. Rollwagen-Bollens, J. Zimmerman, and J. Emerson. 2017. Veligers of the invasive Asian clam Corbicula fluminea in the Columbia River Basin: Broadscale distribution, abundance and ecological associations. Lake and Reservoir Management, 33: 234-248. DOI: 10.1080/10402381.2017.1294218.

McMahon, Robert F. Quagga/Zebra Mussel Life History. The University of Texas at Arlington.

Washington Department of Fish and Wildlife. 2019. Federal, state, and tribal governments join forces to practice emergency response should invasive mussels infest Washington. Waters.

Washington Invasive Species Council. 2017.  Economic Impact of Invasive Species to Washington State.