The Zebra Mussel Invasion

Zebra Mussel (Dreissena polymorpha).

Zebra Mussel (Dreissena polymorpha).

High resolution (Credit: NOAA)

Nearly 20 years ago, non-native zebra mussels were discovered for the first time in North America. Believed to have been carried in the ballast tanks of ships from western European ports, these highly reproductive mussels were first found attached to the underwater surfaces of rocks, piers, and other structures in Lake St. Clair, which connects lakes Huron and Erie.

The arrival of this invasive animal and the damage they cause cities and ecosystems in the Great Lakes region has focused much attention on the ballast water of cargo ships as a major source for species introductions.

“Invasive species have been documented in the lakes since the early 1800s,” said David Reid, director, NOAA National Center for Research on Aquatic Invasive Species. “But the effect zebra mussels had on ecosystems, recreation, and commerce really raised national awareness about the adverse affects of aquatic invasive species.”

Concern Leads to Invasive Species Legislation

The invasion of zebra mussels led to changes in research throughout the nation. Invasion biology was only a minor discipline within the field of biology, but since the zebra mussel, interest has grown considerably. In 1990, Congress introduced the Nonindigenous Aquatic Nuisance Prevention and Control Act, the first U.S. legislation to provide significant focus on aquatic invasive species and ballast water.

Recent research has confirmed that salt water acts as a natural preventative against fresh water organisms that can be found in ballast water. Regulations implemented in 1993, and expanded in 2006, require that all ocean vessel operators flush ballast tanks with seawater, well before they enter the Great Lakes.

NOAA’s Invasive Species Monitoring and Research

NOAA-GLERL Divers.

NOAA-GLERL divers.

High resolution (Credit: NOAA)

NOAA’s Great Lakes Environmental Research Laboratory (GLERL) has monitored native mussel populations in Lake St. Clair since 1986. In the first survey, scientists found a diverse native mussel community consisting of 20 different species. In June 1988, researchers from the Universities of Windsor and Guelph, Ontario, Canada, discovered the invasive zebra mussel on small rocks in the southeastern portion of Lake St. Clair and within 10 years had entirely driven out native mussel species.

Additional research indicated that the invader had found its way downstream to western Lake Erie. And by 1989 had spread to Lake Ontario, the St. Lawrence River to the northeast, and continued to spread rapidly to all the Great Lakes, clogging intakes for urban water supplies and power plants.   

By the early 1990s, the mussels were found in many major river systems connected to the Great Lakes watershed via the Chicago Sanitary and Ship Canal, such as the Ohio, the Mississippi, and the Missouri Rivers.

Another invasive mussel species similar to the zebra mussel, the quagga mussel, was found in Lake Erie in 1989. It, too, has spread to all the Great Lakes and is replacing the zebra mussel as the predominant invasive mussel species. Both quagga and zebra mussels have recently been found west of the Continental Divide.

Risks Associated with Invasive Species

Zebra mussels cover a current meter in Lake Michigan.

Zebra mussels cover a current meter in Lake Michigan.

High resolution (Credit: NOAA)

There are now millions of these mollusks living in the Great Lakes system. They have an incredibly rapid reproductive growth and no natural predators in North America. And because mussels can attach to each other when they settle, large clusters occur in small areas. As many as 700,000 zebra mussels have been found in only one square yard of surface area on boats, pilings, and pipes.

Zebra mussels are efficient at filtering large volumes of water and as an adult may filter more than four quarts a day. This filtration process, although greatly improving water clarity, contributes to the explosive growth of harmful algal blooms in Saginaw Bay and other fresh bodies of water during the summer months.

The mussel is low in fat and its shell has no nutritional value causing fish to expend lots of energy crushing and digesting the mussel. The zebra and quagga mussels displace other more energy-rich food sources and leave fish and other aquatic species with fewer food options. As a result, fish stocks and conditions have declined in many of the Great Lakes. Of particular concern is a decline in lake whitefish, an important commercially-fished species.

In January 2007, quagga mussels were found in Lake Mead, Nev., and subsequently Lake Havasu, Ariz., as well as many of the reservoirs in California’s San Diego County. Recently, zebra mussels have been reported in at least one reservoir in San Bernardino County, Calif., and another near Pueblo, Colo. The mussels are now expected to infest most fresh water bodies throughout the west, making their distribution nationwide.

Help Prevent the Spread

Zebra mussels are transported from one lake or river system to another by hitch-hiking on boats, boat trailers, barges, sea planes and other aquatic equipment. Juvenile and adult mussels can attach to boat hulls, engines, anchors, and other submerged equipment, as well as to plant material that may get caught on boats and trailers. In their microscopic juvenile stage, they can also be carried in boat bilge water, live wells, bait buckets, and SCUBA gear.

By taking a few precautionary steps after boating and fishing, people living along or visiting the shoreline can prevent the spread of mussels.

There are no known methods for eliminating zebra mussels without severely damaging the ecosystem of the water body in which they’ve been found. Public assistance in preventing the spread of this highly invasive species and reporting new infestations is essential to help reduce their negative effects on the local environment and economy.

For more information, visit the NOAA National Center for Research on Aquatic Invasive Species. NOAA logo.