What are Zebra Mussels?
The zebra mussel (Dreissena Polymorpha) is an invasive species that originated in western Asia and eastern Europe. They are small, freshwater mollusks, measuring from 1/4 inch up to 2 inches in length, and are named for the pattern of dark and light stripes on their shells.
Zebra mussels were introduced into US waters when they were transported in the ballast water of oceangoing ships. They were first detected in 1988 in Lake St. Clair, located on the US-Canadian border between Lake Huron and Lake Erie. They quickly spread, and within a decade they were found in all five of the Great Lakes and throughout the Ohio, Hudson, Mississippi and Tennessee River basins. They have been reported in states ranging from Canada to the Gulf of Mexico, and have even been detected on the west coast. Since they attach to any solid surface, zebra mussels can be transported by recreational boats, fishing boats and diving gear. Adult zebra mussels can survive out of water for up to ten days, and juveniles can survive for 3 days.
Zebra mussels live for about 4-5 years. The females begin to reproduce at two years of age, and can lay up to a million eggs per year. The eggs hatch into a larval stage called veligers.
Ecological Impact of the Zebra Mussel
Zebra mussels are very efficient filter feeders, and each mussel can process up to a gallon of water per day. They clear the water column of algae and microscopic organisms, either by eating the particles or coating them with mucus and ejecting them, after which they sink to the bottom of the river or lake. Clearing the water of microorganisms affects the ecosystem by removing food that is needed by native species such as invertebrates and fish larvae. Zebra mussel infestations have caused declining populations of some native species. Unionid clams, native to Lake St. Clair and western Lake Erie, have been driven to near extinction in the short period of time since zebra mussels have become established there.
Zebra mussels attach to any solid surface, including the shells of crustaceans, turtles, snails and larger native mollusks. This can harm or kill the animals to which the mussels are attached.
Zebra mussels themselves provide food for a number of species. Birds and migrating ducks as well as various fish species including sturgeon, sunfish, catfish and yellow perch feed on zebra mussels. Clearing the water of particles allows more light to penetrate and causes increased growth of aquatic plants. These plants provide food and cover for young fish and other aquatic animals.
Efforts to Control Zebra Mussels
In addition to the ecological impact of zebra mussels, this invasive species also causes problems by clogging water intake pipes and attaching to boats and underwater structures. Zebra mussels cannot be eradicated once they have become established. Measures to control their growth with chemicals have been ineffective and harmful to other species. People who use infested rivers and lakes for boating, fishing and diving are urged to take precautions to prevent the spread of zebra mussels to un-infested areas. Some steps to take after fishing and boating in infested waters include:
- Clean all vegetation and mud off of boats, trailers, and equipment that was in the water, and allow to dry for 2 days before using in un-infested water
- If the boat has been docked in infested water for a long period of time, clean off all mussels and algae, and allow it dry for at least 5 days before using it in un-infested water.
- Flush out the bilge, live wells and engine cooling system with tap water; if possible, use hot water
- Do not reuse bait
For more information, see the ANS Task Force website, Protect Your Waters.
USGS Great Lakes Science Center, Zebra Mussels
ANS Task Force, Protect Your Waters, Harmful Aquatic Hitchhikers
Image source: D. Jude, Wikimedia Commons