Mussel Facts

Distribution Maps

Zebra Mussels

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Invasive Zebra Mussel

Zebra mussels (Dreissena polymorpha) are small, fingernail-sized mussels native to the Caspian Sea region of Asia. Considered one of most damaging of the invasive species introduced to this country, zebra mussels were transported to the Great Lakes in the ballast water of transoceanic ships. Since that time, they have spread rapidly to all of the Great Lakes and waterways in many states, as well as Ontario and Quebec, and to southeast and western portions of the United States.

One of the zebra mussel’s most defining characteristics is its tendency to colonize hard substrates and surfaces (e.g., rocky bottoms and water intake structures) in high densities, with as many as tens of thousands living in a square yard.

Zebra mussels have had deleterious effects on local ecosystems. They reduce the amount of phytoplankton available for other organisms and increase water clarity, causing changes to the ecological structure of the lake community. In addition, zebra mussels accumulate contaminants within their tissues to levels greater than concentrations in the water column, increasing the exposure of wildlife to contaminants. Zebra mussel infestations also threaten native mussel populations by attaching to the native species and essentially smothering them.

Zebra mussels have caused a great deal of economic damage by clogging intake pipes of water treatment and power plants as well as boat engine cooling systems. Unfortunately, solutions to these problems are few and not highly effective, resulting in high costs for cleaning and control measures.

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Quagga Mussels

Quagga mussels (Dreissena bugensis) are fingernail-sized freshwater mollusks native to the Ukraine that attach to objects and other organisms.

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Invasive Quagga Mussel

Quagga mussels were first discovered in the Great Lakes in 1989 near Port Colborne of Lake Erie. They were found coexisting with dense populations of zebra mussels (Dreissena polyymorpha). Although these invasive mollusks are genetically and morphologically distinct, both have biological characteristics allowing their establishment and spread to watersheds across the United States.

While zebra mussels are generally limited to the colonization of hard substrates (e.g., rocky bottoms and water intake structures), quagga mussels are able to colonize soft substrate. This characteristic has allowed the quagga mussel to spread to areas of sand and sandy silt, such as the bottom of Lake Erie. Quagga mussels are also better able to flourish in low-food conditions than zebra mussels, allowing them to colonize less productive waters in much greater numbers.

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Comparison of invasive zebra mussel (l) and invasive quagga mussel (r)

Quaggas are extremely effective in filtering water for food, removing large amounts of phytoplankton and suspended particulate, decreasing the food supply for zooplankton and forage fishes, and thereby impacting the entire food web. Quagga mussel filtering has dramatically reduced primary production (photosynthetic production of chemical energy) in lakes Michigan and Huron. There have been significant impacts to the spring bloom of diatoms (silica based algae) by quagga infestations, disrupting the lower food web. Dreissenid mussels, including the quagga, have been implicated in the basin wide crash of populations of Diporeia, a bottom-dwelling invertebrate that once served as an important food source to many Great Lakes fishes. In addition to altering food webs, quagga mussels accumulate contaminants within their tissues, which can affect wildlife that feed on the species.

The quagga mussel also clogs water intake structures, such as pipes and screens, thereby reducing pumping capacity for power and water treatment plants and causing significant economic impacts to industries, companies, and communities.  Recreation-based industries and activities also have been impacted by the quagga mussel as docks, breakwalls, buoys, boats, and beaches all have been heavily colonized by this species.

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General Information


Images and distribution maps courtesy of USGS

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Erika Jensen
Great Lakes Commission
(734) 971-9135

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