Many unwittingly helping the spread of invasive species
Gruesome-looking invasive species like the northern snakehead fish and nuclear worm recently caught the attention of the public and media.
These creatures didn’t emerge on their own — they were introduced, either intentionally or accidentally, by people.
The possibility of these animals multiplying rampantly in our waters — and eating, displacing or infecting our native aquatic life — is a real concern to natural resources managers and anglers alike.
What make a species invasive?
All living things have evolved to live and thrive in specific areas. Local climate, geology, soil, available water and other natural factors influence which plants and animals can live in a particular ecosystem. Species that have evolved in a particular place are native to that place.
Non-native plants or animals are those that have been introduced from other continents or states, as well as other habitats.
Not all non-native plants and animals are invasive. Invasive species are aggressive spreaders and/or prolific reproducers. They also adapt to a variety of conditions; move about easily, either on their own or by hitching a ride on wind, water, wildlife, or people or their equipment; have few natural controls, such as predators or diseases to keep them in check; and are difficult to control or eliminate once they become established in the wild.
Why are invasive species a problem?
Invasive species damage natural systems by upsetting the balance — they disrupt the intricate web of life for native plants, animals and microorganisms, many of which are already rare.
Invasive animals eat native animals, compete with natives for food and space, and may spread parasites or pathogens to wildlife or people.
Once they’ve consumed all the food sources or destroyed the habitat, they move on to the next suitable site.
Invasive plants crowd out native plants or crops; are often of little value to wildlife compared with native plants; eliminate native host plants needed by native insects; and cause a general decline in the diversity of life on which we depend.
How do they get here?
Dumping unwanted aquarium fish and plants, releasing unused live fish bait and expelling ballast water from ships are some of the ways invaders are introduced into waterways. In the Bay watershed, many plants and animals introduced either accidentally or intentionally are causing problems.
Some aquatic organisms, such as the zebra mussel, a problem in the Great Lakes region that may soon become problematic here, and hydrilla, an aquatic plant known for its ability to clog waterways, spread from one area to the next by attaching to boat bottoms or motors and later dropping off in a different location.
The green crab, a ravenous predator of clams, oysters, mussels and other aquatic life, competes with shorebirds for food. Arriving in the 1800s from Europe and northern Africa by clinging to boat hulls or as stowaways in ship ballast, the green crab made itself at home in Atlantic coastal bays from New Jersey to Cape Cod, but has since spread north and to the West Coast in packing material with lobsters and bait.
Nutria, which are large, voracious South American rodents, were brought here in the 1930s for the fur trade and accidentally released into the wild.They have chewed their way through wetlands, accelerating the loss of thousands of acres of marshland in the nation’s richest and largest estuary.
Another accidental introduction is the Eurasian mute swan. Attractive yet aggressive birds, mute swans have taken over shoreline areas and ponds, vital feeding and breeding areas for native waterfowl and colonial waterbirds.
Could you be part of the problem?
You’re probably thinking that you’re not part of the invasive species problem. After all, you’ve never released anything invasive into the wild. Many people don’t realize that invasive exotic plants can be just as damaging. They are the second greatest threat to natural areas (after direct habitat destruction), and many unsuspecting citizens may be harboring invasive plants on their own properties.
Most people are familiar with destructive “weeds” such as phragmites, Japanese honeysuckle, Canada thistle and kudzu. What they don’t know is that many commonly used ornamental plants can also escape cultivation and become much more than a nuisance.
A 1997 study by the Brooklyn Botanic Garden found that 50 percent of the most serious plant invaders were brought into the United States for horticulture, livestock forage, erosion control and other uses. More than 400 invasive plant species threaten our forests, wetlands, prairies and other natural areas nationwide; nearly 300 of these are a threat in mid-Atlantic states.
What are the costs?
Once an invasive species — plant or animal — has a foothold, the cost in terms of degraded natural areas, lost agriculture, and control efforts can be astronomical. An estimated 4,600 acres of public natural areas alone are daily lost to invasive species.
According to the National Invasive Species Council, invasive plants cover more than 100 million acres in the United States and are spreading across an additional 3 million acres each year. The estimated cost of invasive species to the U.S. economy is approximately $137 billion per year.
In addition, other economic resources and lifestyle choices are lost because of the spread of exotic species. Recreational activities, such as fishing, hunting, boating, bird or wildlife-watching are affected, as are sources of income associated with these activities, such as the seafood industry; outdoor equipment and clothing retailers, hunting and fishing licenses and guide services; travel and tourism; and gasoline for boats and automobiles.
What is being done?
The recent concerns highlighted by the snakehead fish have led to a proposal by the secretary of the Department of Interior that the fish be banned from sale and importation into the United States and across state lines.
This is not an unusual solution — many dangerous invaders have been similarly banned either nationwide or in individual states. Purple loosestrife, a garden favorite that has literally taken over expansive wetlands in all 48 contiguous states, has been banned from a number of states.
Federal laws and various state laws similarly regulate the importation of, or interstate commerce in, harmful non-native species.
What can you do to help?
For plants: Become familiar with invasive plants and don’t plant them.
Ask for native plant alternatives at your nursery. Obtain a list of native plants from your state natural resources agency or the U.S. Fish and Wildlife Service Chesapeake Bay Field Office at: www.fws.gov/r5cbfo/BayScapes.
Carry these lists to nurseries when selecting plants. If you already have invasive plants on your property, consider removing them and replacing them with native alternatives.
When visiting a natural area, be alert for invasive plants. If you see any, notify the agency or organization responsible for the land.
If you visit another state, region or country, make sure you do not bring back any hitchhikers. Brush seeds from clothing and rinse off boats and trailers before leaving the area.
For animals: Before acquiring an exotic pet, be sure that the animal or the species was legally imported into the country.
Never release any pets, live bait or other unwanted live animals into the wild. Rinse off boats and trailers before leaving the area. Report sightings of exotic animals to your state wildlife agency. Learn about and participate in the public process involved in developing wildlife management regulations.
Information on Invasive Species
For information on invasive species, check out these web sites:
- U.S. Fish and Wildlife Service
- Chesapeake Bay Field Office
- U.S. National Park Service
- U.S. Department of Agriculture Animal & Plant Health Inspection Service
- National Biological Information Infrastructure & The National Invasive Species Council
- Plant Conservation Alliance, “Weeds Gone Wild”
- Mid-Atlantic Exotic Pest Plant Council
- Maryland Department of Natural Resources
- Virginia Department of Conservation and Recreation
- Pennsylvania Department of Conservation & Natural Resources
- Delaware Department of Natural Resources & Environmental Control
Common Potentially Invasive Plants
Exotic bamboos (Bambusa species)
Purple loosestrife (Lythrum salicaria)
Japanese silver grass (Miscanthus sinensis)
Japanese barberry (Berberis thunbergii)
Butterfly bush (Buddleia davidii)
Winged burning bush (Euonymus alata)
Norway maple (Acer platanoides)
Mimosa or silk tree (Albizia julibrissin)
Bradford pear (Pyrus calleryana ‘Bradford’)
English ivy (Hedera helix)
Periwinkle (Vinca minor)
Asian wisterias (Wisteria floribunda & W. sinensis)
These species and others will be presented in the educational publication, “Plant Invaders of Mid-Atlantic Natural Areas,” along with suggested control measures and native plant alternatives for use in landscaping. National Park Service and U.S. Fish and Wildlife Service, September 2002.
For a copy contact: National Park Service, Center for Urban Ecology at 202-342-1443 or U.S. Fish and Wildlife Service, Chesapeake Bay Field Office at 410-573-4500.
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