Invasive Species
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.
The mute swan is an invasive, non-native species that was introduced to the Bay region for its ornamental value; however, the birds have had an increasingly disruptive effect on the ecology of the Bay.
Nutria are prolific aquatic rodents native to South America. Their habit of digging out and feeding on the roots of marsh grasses has caused substantial wetland losses on Maryland's Eastern Shore.
An invasive strain of phragmites, or the common reed, that was introduced from Eurasia has limited the growth of native phragmites and many other marsh plants that support wildlife and a balanced marsh ecosystem.
Purple loosestrife is a perennial wetland plant native to Eurasia. It spreads rapidly in disturbed wetland areas, crowding out native, wildlife-supporting plant species and threatening the health of the Bay ecosystem.
Water chestnut is an aquatic plant native to Europe, Asia and Africa. Though it only occurs in isolated areas in the Bay region, it spreads rapidly and can reappear after several years, requiring costly eradication efforts.
The zebra mussel (Dreissena polymorpha) is an invasive freshwater bivalve that is native to Europe. Zebra mussels are easily introduced from one water body to another, altering the ecosystem of their invaded habitat and costing millions in damage to municipal and industrial facilities.