Invasive Zebra and Quagga Mussels in the Great Lakes: Status, Ecological Impact, and Control Efforts

Zebra mussels and quagga mussels, two closely related invasive species native to the Black Sea region of Eastern Europe, have fundamentally altered the ecology of the Great Lakes since their introduction in the late 1980s. Three decades after their arrival in ballast water discharged by transoceanic ships, these small but prolific mollusks continue to reshape water chemistry, native species populations, and the economics of water infrastructure across the basin.

Population Status Across the Great Lakes

The U.S. Geological Survey’s Great Lakes Science Center reports that quagga mussels have largely displaced zebra mussels in the deeper waters of all five Great Lakes. In Lakes Michigan, Huron, and Ontario, quagga mussel densities exceed 10,000 individuals per square metre on hard substrates in many locations. Lake Erie, with its shallower western basin and warmer temperatures, supports both species in significant numbers.

Lake Superior, long considered more resistant to invasion due to its colder water temperatures and lower calcium concentrations, has documented established zebra mussel populations in the Duluth-Superior harbour and several other nearshore locations since 2020. While Superior’s open waters remain largely mussel-free, researchers at the University of Minnesota’s Large Lakes Observatory caution that warming water temperatures could expand suitable habitat over the coming decades.

Ecological Consequences

The ecological impact of invasive mussels on the Great Lakes is well documented in peer-reviewed literature. A comprehensive review published in the Journal of Great Lakes Research in 2023 identified several cascading effects throughout the food web.

Filter feeding by invasive mussels has dramatically increased water clarity in several of the Great Lakes. In Lake Michigan, Secchi disk transparency measurements have more than doubled since the mid-1990s, from approximately 5 metres to over 12 metres in some offshore areas. While clearer water may appear to be a positive development, it represents a fundamental disruption of the lake’s nutrient cycling. The mussels intercept phytoplankton and nutrients before they can reach open-water food webs, redirecting energy from the pelagic zone to the nearshore benthic zone.

This “nearshore shunt” has contributed to declines in the population of Diporeia, a small native amphipod that once served as a critical food source for commercially valuable fish species including lake whitefish and several species of cisco. Diporeia populations have declined by more than 95 percent in Lake Michigan and Lake Huron since the mussel invasion, according to long-term monitoring data from NOAA’s Great Lakes Environmental Research Laboratory.

The fish community has responded to these changes. Lake whitefish, once the most valuable commercial fish species in the Great Lakes, have experienced significant declines in condition and recruitment in Lakes Michigan and Huron. The Ontario Ministry of Natural Resources and Forestry has reduced commercial whitefish quotas on Lake Huron by approximately 60 percent since 2000 in response to declining stocks.

Infrastructure and Economic Costs

Invasive mussels attach to virtually any hard surface submerged in water, including water intake pipes, lock structures, navigational buoys, and boat hulls. The Alliance for the Great Lakes estimates that mussel-related infrastructure damage and maintenance costs exceed 500 million dollars annually across the Great Lakes basin.

Municipal water utilities bear a significant portion of these costs. The City of Toronto’s water treatment facilities spend approximately 2.5 million dollars per year on mussel management, including chemical treatment of intake pipes, physical removal from infrastructure, and monitoring. Smaller municipalities along the Great Lakes shoreline face proportionally higher per-capita costs for mussel management.

Current Control and Prevention Efforts

No method currently exists to eradicate invasive mussels from the Great Lakes. Current management efforts focus on preventing their spread to uninfested water bodies and mitigating their impacts where they are already established.

Ballast water management regulations, implemented through Transport Canada’s Ballast Water Regulations and the U.S. Coast Guard’s ballast water management standards, require ships to treat or exchange ballast water before entering the Great Lakes. These regulations have been effective in preventing new introductions of invasive species through ballast water since their full implementation.

Research into biological control methods continues at several institutions. A team at the University of Cambridge has identified a natural parasite of quagga mussels that could potentially be used as a biological control agent, though any such intervention would require extensive environmental impact assessment before deployment in the Great Lakes.

For recreational boaters, the “Clean, Drain, Dry” protocol remains the most effective way to prevent spreading invasive mussels between water bodies. Ontario’s Invading Species Awareness Program provides identification guides and reporting tools at invadingspecies.com.