Invasive species are animals and plants that are not native to their current habitat and have a negative effect on the ecosystem they invade. Invasive species negatively affect an ecosystem by encroaching on native species' food and/or habitat.
Invasive species are able to thrive in the ecosystems they invade because they lack the natural ecological controls — such as predators and disease — that keep the species in check in their native environment. Invasive species rank as one of the top threats to the country's native species, just after habitat destruction. About 42 percent of the native plants and animals listed as threatened or endangered in the United States are at risk of further decline because of invasive species.
Once an invasive species population is established it is unlikely to be completely eradicated. Controlling invasive populations uses millions of taxpayer dollars and requires extensive time, cooperation and commitment. That is why it is crucial to prevent non-native species from being introduced in the first place.
In the Chesapeake Bay region there are over 200 known or possible invasive species thought to cause serious problems. Forty-six of these were identified in 2001 as nuisance species, of which six pose the greatest threat to the Bay region’s ecosystem.
Mute swans are large white birds found in shallow waters such as ponds, creeks and marshes, particularly along Maryland’s Eastern Shore.
Mute swans are considered invasive because they destroy underwater bay grass beds while feeding and reduce the amount of food and shelter available to native wildlife. Because mute swans live in the Bay region the entire year and do not migrate like other waterfowl, they eat bay grasses throughout the summer. This reduces the amount of food available to native wintering waterfowl that rely on bay grasses for food during their yearly migrations.
On land, breeding mute swans are very territorial and protective of their nests. They will hiss at and chase away any intruders, including other birds, mammals or even humans. This can displace native wildlife from their feeding and nesting areas. Male mute swans have been known to attack other animals that come within six acres of their nests.
Nutria are prolific aquatic rodents native to South America. Their habit of digging out and feeding on the roots of marsh grasses causes marshes to quickly erode away and convert to open water.
Nutria invations have caused substantial wetland losses in Maryland, particularly at the Blackwater National Wildlife Refuge (NWR) on the Eastern Shore. Since their introduction, nutria have destroyed over 7,000 acres of marsh at the Blackwater NWR—nearly half of the refuge's marsh acreage.
Phragmites is an aggressive plant that grows in marshes and along river banks and shorelines throughout the Chesapeake Bay region. It is also common in disturbed and polluted areas such as ditches and roadsides.
Phragmites is invasive because it crowds out and replaces native wetland plants such as cattails and smooth cordgrass, which provide better food and shelter for wildlife. Phragmites grows so thickly that it does not allow other plants to grow, reducing the diversity of plant species in a marsh.
Today, the invasive strain of phragmites dominates many mid-Atlantic marshes. It is estimated to cover as much as one-third of the tidal wetland acreage in some states along the eastern U.S. coast. Only a few native phragmites populations still exist.
Purple loosestrife is an invasive wetland plant native to Eurasia. It grows in wet areas, including marshes, river banks, wet meadows and the edges of ponds and reservoirs.
Purple loosestrife is considered invasive because it crowds out native wetland plants, does not provide quality food and habitat for wildlife, and can disrupt water drainage and human recreational activities. It grows rapidly, produces many seeds and has no natural predators, allowing the plant to quickly establish itself in new areas. In some wetland communities, purple loosestrife has displaced more than 50 percent of native plant species. Native animals such as muskrats and bog turtles can’t live or raise their young in dense, impenetrable purple loosestrife stands.
Water chestnut is an aggressive, invasive aquatic plant native to Europe, Asia and Africa. Though it only occurs in isolated areas in the Bay region, water chestnut spreads rapidly and can reappear after several years, which has resulted in a series of costly eradication efforts.
Water chestnut is considered invasive because it blocks sunlight from reaching native underwater bay grasses, does not provide good habitat for aquatic life, and prevents nearly all water uses where it grows, including boating and swimming. Thick mats of water chestnut have also been known to become breeding grounds for mosquitoes and trap trash and pollution.
Zebra mussels are invasive freshwater bivalves native to Europe. The tiny mussels are easily introduced from one water body to another
Zebra mussels are invasive because they filter too much plankton out of the water, significantly reducing an important food source for native filter feeders. They also encrust boat hulls, buoys, docks and pipes, impeding navigation and clogging municipal water intakes.
Zebra mussel invasions have resulted in millions of dollars in damage to municipal and industrial facilities. It is estimated that zebra mussels cost the power industry more than $3.1 billion from 1993 to 1999.
Use this list to learn more about National Invasive Plant, Pest and Disease Awareness Month.
Blue and flathead catfish are two invasive species that threaten the Chesapeake Bay's rivers.
A team of scientists and trappers is working to eradicate nutria from the Chesapeake Bay by 2015.
Friends of Sligo Creek is a volunteer organization that has worked since 2001 to clean up this Potomac River tributary.
Weed Warriors is a program that trains and certifies volunteers to identify and remove invasive weeds.
Publication date: January 23, 2012 | Type of document: Adoption Statement | Download: Electronic Version
The Sustainable Fisheries Goal Implementation Team Executive Committee has concluded that the potential risk posed by blue catfish and flathead catfish on native species warrants action to examine potential measures to reduce densities and…
Publication date: May 12, 2001 | Type of document: Report
Recommendations on the reauthorization of the National Invasive Species Act specially dealing with Ballast Water Issues in Chesapeake Bay.