Zebra Mussel (Dreissenapolymorpha)

Zebra mussel (Dreissenapolymorpha)

Zebra mussels

Many zebra mussels attached to a native mussel.

Species and Origin:Zebra mussels are small, fingernail-sized animals that attach to solid surfaces in water. Adults are 1/4 to 1-1/2 inches long and have D-shaped shells, often with alternating yellow and brownish colored stripes. Female zebra mussels can produce 100,000 to 500,000 eggs per year. These develop into microscopic, free-living larvae (called "veligers") that begin to form shells. After two to three weeks, the microscopic veligers settle and attach to any firm surface using tiny fibers called "byssal threads." Zebra mussels are native to Eastern Europe and Western Russia and were brought over to the Great Lakes in the ballast water of ships. Populations of zebra mussels were first discovered in the Great Lakes in 1988.

Impacts:Zebra mussels can be a costly problem for cities and power plants when they clog water intakes. Zebra mussels also cause problems for lakeshore residents and recreationists; for example, they can:

• attach to boat motors and boat hulls, reducing performance and efficiency,
• attach to rocks, swim rafts and ladders where swimmers can cut their feet on the mussel shells, and
• clog irrigation intakes and other pipes.

Zebra mussels also can impact the environment of lakes and rivers where they live. They eat tiny food particles that they filter out of the water, which can reduce available food for larval fish and other animals, and cause aquatic vegetation to grow as a result of increased water clarity. Zebra mussels can also attach to and smother native mussels.

Status:Zebra mussels have spread throughout the Great Lakes, parts of the Mississippi River, and other rivers and inland lakes. They are established in Minnesota and were first found in the Duluth/Superior Harbor in 1989. See the infested waters list for more information on water bodies in Minnesota where zebra mussels have been found or water bodies that are closely connected to zebra-mussel-infested waters.

Control:The DNR, with partners, has used pesticides to treat zebra mussels in several Minnesota lakes since 2000. The DNR will consider permitting pilot projects to control zebra mussels in public waters with pesticides beginning in 2015.

• Fact sheet about zebra mussels
• Questions and answers about pilot projectsto control zebra mussels in public waters

How to prevent their spread:Mussels attach to boats, nets, docks, swim platforms, boat lifts, and can be moved on any of these objects. They also can attach to aquatic plants. Attached adult mussels can survive out of water and spread from one water body to another. Microscopic larvae (veligers) can survive in water contained in bait buckets, bilges, ballast bags or any other water moved from an infested lake or river. In Minnesota, you must take the following steps to prevent the spread of zebra mussels:

• cleanweeds and debris from your boats, and remove any attached zebra mussels,
• drainyour boat, livewells, and baitwells, and keep all drain plugs out while traveling,
• disposeof unwanted bait in the trash, and
• drydocks, lifts, swim rafts and other equipment for at least 21 days before placing equipment into another water body.

The Exotic Zebra Mussel

by Amy J. Benson

Zebra mussels have attached to this young Higgins eye pearlymussel, an endangered species found in the Mississippi river.
Photo by USFWS

The word "exotic" conjures up thoughts of faraway places where strange animals inhabit sun-drenched islands. But in the biological sciences realm, this word has come to be associated with unwelcome visitors to our shores. Over the past 500 years, more than 4,500 foreign species, including many harmful plants, vertebrates, invertebrates, and pathogens, have established populations in the United States.

One of these newcomers, the zebra mussel (Dreissenapolymorpha), poses widespread ecological and economic threats. This small freshwater mollusk originated in the Black, Caspian, and Azov seas region of the former Soviet Union. By the late 18th and early 19th centuries, the construction of extensive canal systems enabled the spread of zebra mussels to almost all major drainages of Europe.

In the United States, the first account of an established population occurred in 1988 from Lake St. Clair, located between Lake Huron and Lake Erie. By 1990, zebra mussels had been found in all five Great Lakes. Over the next two years they made their way out of the Great Lakes through canals and into the Illinois, Hudson, Arkansas, Cumberland, Hudson, Mississippi, Ohio, and Tennessee rivers. As of 2011, the following states had reported zebra mussels within, or in waters adjacent to, their borders: Alabama, Arkansas, California, Colorado, Connecticut, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New York, North Dakota, Ohio, Oklahoma, Pennsylvania, Tennessee, Texas, Utah, Vermont, Virginia, West Virginia, and Wisconsin. The mussels have also been documented in over 600 lakes and reservoirs in the United States.

Zebra mussels probably entered the Great Lakes when ships arriving from Europe discharged ballast water containing a variety of aquatic organisms, including zebra mussel larvae. The species rapid dispersal throughout the Great Lakes and major river systems was due to its ability to attach to boats navigating these waters. Zebra mussels have an even more troubling characteristic: the ability to stay alive out of water for several days under moist and reasonably cool conditions. Thus, overland dispersal is another possible means of range expansion. An increasing number of small lakes near, but not connected to, the Great Lakes are now inhabited by zebra mussels. Beginning in 1993, many trailered boats crossing into California and other western states were found to have zebra mussels attached to their hulls. These mussels, discovered at agricultural inspection stations by informed officials, were removed before the boats were allowed to continue.

Zebra mussels scooped from Lake Pepin where they form a deep carpet on the lake's bottom.
Photo by Minnesota Department of Natural Resources

Zebra mussels can grow to a maximum length of about 50 millimeters (1.9 inches) and live 4 to 5 years. Their common name was inspired by their dark, zebra-like stripes. Although they are freshwater animals, zebra mussels have recently been found living in brackish water with salinity levels of 1 to 2 parts per thousand. Females generally reproduce in their second year. More than 40,000 eggs can be laid in a reproductive cycle and up to 1 million in a spawning season. The larvae emerge within 3 to 5 days after the eggs are fertilized and are free-swimming for up to a month. Dispersal of larvae is normally passive downstream. The mussels begin their juvenile stage by settling to the bottom, where they crawl about by means of a foot searching for a suitable firm surface or substratum upon which to anchor. Although hard, calcareous materials, such as limestone, concrete, and the shells of other mussels are preferred substrates, they will attach to various surfaces, including water intake valves and pipes, and have even been found on vegetation. Juvenile zebra mussels attach themselves by an external organ called a byssus, which consists of many threads that adhere to a surface. Adults zebra mussels filter about 1 liter (2.1 pints) of water per day while feeding primarily on algae.

Most of the biological impacts of zebra mussels in North America may yet to be realized. However, they have the potential to harm native mussels by interfering with their feeding, growth, movement, respiration, and reproduction. Researchers are observing some of these effects as they study interactions between zebra mussels and native mussels in the Great Lakes. In one study, biologists found that where zebra mussel densities were highest, in Lake St. Clair and in the western basin of Lake Erie, native mussels had declined after only two years of zebra mussel colonization. Other studies have shown an inverse correlation between zebra mussel biomass and the density of native mussels. Scientists in the Great Lakes region are using models that may predict the degree of loss based on zebra mussel densities. Unfortunately, research shows zebra mussels prefer to attach to the shells of live mussels rather than to dead ones or to stones. Some native mussels have been found with more than 10,000 zebra mussels attached to them. Native species may not survive if zebra mussels continue to colonize Lake St. Clair.

Another exotic invader, the quagga mussel (Dreissenarostriformisbugensis), probably arrived at the same time as the zebra mussel. Although the quagga mussel closely resembles its cousin, it is not expected to have as great an impact on native mussels because it does not show a preference for using them as substrates. Hoever, in the Great Lakes, the quagga mussel appears to be outcompeting the zebra mussel to near exclusion. Quagga mussel were contained to primarily the Great Lakes until 2007 when a very large population was discovered in Lake Mead on the Colorado River in Nevada. Its appearance was mostly likely the result of a contaminated boat entering the lake coming from infested waters. This species is spreading in western states and overall has been reported from the following states: Arizona, California, Colorado, Illinois, Indiana, Michigan, Minnesota, Missouri, Nevada, New Mexico, New York, Ohio, Pennsylvania, Utah, and Wisconsin.

The rapid spread of both mussel species has researchers working together to help track this invading exotic. Many government and private organizations are cooperating with U.S. Geological Survey researchers at theSoutheast Ecological Science Centerin Gainesville, Florida, by reporting information on new sightings. This information becomes part of the Nonindigenous Aquatic Species Information System, which distributes general information available to government agencies, private groups, and the public. The system also provides sound scientifc information to State and Federal agencies responsible for the management of public lands. It is available at By working together, it may be possible to control the continued spread of non-native pests like the zebra mussel.

Zebra Mussel- Protect Your Waters ()

What do zebra mussels look like?

Zebra mussels get their name from the striped pattern of their shells. However, the pattern varies greatly to where there are no stripes, only dark or light colored shells. Zebra mussels can grow to a maximum length of about 50 mm (5-10 mm in the first year) and live four to five years.

Why are zebra mussels considered to be a nuisance?

Ecological Impacts - Zebra mussels have disrupted the traditional aquatic food chains of many inland lakes. Regardless of their size, inland lakes represent unique ecological systems. When zebra mussels enter into these fragile systems, their voracious filter feeding depletes the availability of microscopic organisms that play a critical part in each lake's ecological food web. As a result, valued sportfish are impacted. Zebra mussels consume considerable amounts of these beneficial microscopic organisms and this creates less food for larval and juvenile fishes that support sport and commercial fisheries.

Biological Impacts - Zebra mussels are similar to other mussel species because they attach themselves to hard surfaces. However, unlike other species, zebra mussels will readily attach themselves to native mussels. This behavior is known as bio-fouling and with the spread of zebra mussels, native mussel populations have been severely reduced. Some native mussels are more tolerant than others, but even for these resistant species, becoming covered by zebra mussels makes them more vulnerable to environmental stressors, such as extreme water temperatures, lack of food, or parasites and disease. As zebra mussels spread, biologists are concerned that populations of native mussels will decline, and perhaps some of the rarer species may be completely eliminated.

Economic Impacts - The zebra mussel attaches to hard surfaces located at moderate depths. This affinity for hard surfaces has made water intake structures, like those used for power and municipal water treatment plants, susceptible to colonization. Since 1989, some plants located in areas of extensive zebra mussel colonization have reported significant reductions in pumping capabilities and occasional shutdowns.

Human Health Impacts – As significant filter feeders, zebra mussels may increase human and wildlife exposure to organic pollutants (PCBs and PAHs). Early research shows that zebra mussels can rapidly accumulate organic pollutants within their tissues to levels more than 300,000 times greater than concentrations in the environment. They also deposit these pollutants in their pseudofeces. These contaminants can be passed up the food chain so that any fish or waterfowl consuming zebra mussels will also accumulate these organic pollutants. Likewise, human consumption of these same fish and waterfowl could result in further risk of exposure.

How do zebra mussels affect recreational users?

Boaters - Recreation-based industries along Lake Erie have been impacted by zebra mussels. Unprotected docks, breakwalls, boat bottoms, and engine outdrives were rapidly colonized beginning in 1989. Consequently, there were numerous reports of boat engines overheating due to colonies of zebra mussels clogging cooling water inlets and mussels colonizing boat hulls.

Swimmers - Beaches are also affected by zebra mussels. The sharp-edged mussel shells along swimming beaches can be a hazard to unprotected feet. By autumn of 1989, extensive deposits of zebra mussel shells were on many Lake Erie beaches. The extent of these deposits varied with successive periods of high wave activity.

SCUBA Divers – One of the things that attract people to dive underwater are the many features such as shipwrecks, various fish species and underwater landscapes. Since zebra mussels attach to hard surfaces, many of the features are at risk of becoming obscured.

Where are Zebra Mussels currently found?

As a native to Russia, zebra mussels were introduced into the Great Lakes in 1985 or 1986, when one or more transoceanic ships discharged ballast water into Lake St. Clair. Being a temperate, freshwater species, the zebra mussels found the plankton-rich Lakes St. Clair and Erie to their liking. Since this time, zebra mussels have spread throughout the Great Lakes, the Ohio River Basin and the Mississippi River Basin. Colonies have been found as far west as Oklahoma and live zebra mussels have been found attached to recreational boats transported to Washington state. As of 1994, the following states had reported records of zebra mussels within their borders or in water bodies adjacent to their borders: Alabama, Arkansas, Illinois, Indiana, Iowa, Kentucky, Louisiana, Michigan, Minnesota, Mississippi, Missouri, New York, Ohio, Oklahoma, Pennsylvania, Tennessee, Vermont, West Virginia, and Wisconsin. More recently, Connecticut has been added to the list of states where zebra mussels have been found.

What is the potential for zebra mussels to spread elsewhere in U.S.?

The potential for zebra mussels to spread is very high. In fact, several bills are in front of Congress that focus on preventing the westward spread of zebra mussels. These hitchhikers can spread to other inland waters either in their immature form known as veligers transported in water or as adults attached to boat hulls, engines, aquatic weeds, or other surfaces. Veligers are small-about the size of the period at the end of this sentence-and may be able to survive in any residual water source.

Adult mussels are very hardy and can survive out of water for extended periods depending upon temperature, humidity, wind, and sunlight. Maximum out-of-water survival time in ideal conditions is about 10 days for adults and 3 days for newly-settled juveniles.

Originally, when zebra mussels entered Lake Erie, the public saw the positive impacts of their filter feeding that cleaned up the lake. Zebra mussels contributed to the improvement of Lake Erie's water clarity. Research shows that in the early ‘70s, water clarity was approximately 3 feet. It improved to 6 to 10 feet in the 1980s after a decade of reduced phosphorus inputs, and improved again to 10 to 17 feet in the early 1990s, after zebra mussels colonized the area. However, while the water may have better clarity, the negative impacts outweigh this one positive benefit. One result of clearer water is increased vegetative growth, which may not be the best thing for anglers, boaters, swimmers and other aquatic recreation users.

Examine boat exterior for mussels if it has been docked in infested waters; if mussels are found or exterior is heavily fouled by algae, either clean fouled surfaces or leave boat out of the water for at least 5 days before entering uninfested waters.