Alien invasions are already taking place. That’s right. Our creeks, rivers and even the Bay are being invaded not by extraterrestrials from outer space but by plants, animals and microbes from other parts of the country or the globe.

Under natural conditions, the arrival of a new species into an area is a rare event. Natural barriers surround every ecosystem that tie certain animals and plants together, and exclude competitors and diseases that evolved elsewhere. However, increased mXbility and global trade have resulted in unprecedented invasion by non-native species.

Not all introductions are bad. For example, almost all of our economically important crops are of foreign origin. Popular sport fish, such as the rainbow trout and brown trout, were also introduced to U.S. waters. But approximately 675 (15 percent) of the 4,500 species that have established free-living populations in the United States cause significant ecological and economical damage.

Invasive organisms enter our waterways through many routes. Unintentional introductions into waterways occur mainly through boating and shipping activities.

Ballast water is a significant contributor of non-native aquatic organisms to coastal and freshwater inland ports. When ships unload cargo, they often fill their ballast tanks with water to provide balance for their return journey. Organisms in the water can be sucked up into the ballast tanks and emptied along with the water at the next port where the ship loads cargo. Some of the invasive species that have been established this way include the zebra mussel and ruffed and round gobies in the Great Lakes.

Once established, these organisms are spread by other boats. Barges have been known to carry zebra mussels on their hulls for thousands of miles up and down the Mississippi River. On a smaller scale, recreational boats can spread non-native species between local waterbodies when organisms become attached to hulls or propellers.

Another common form of introductions is aquarium and bait releases. Aquarium releases are responsible for the introduction of the invasive plant hydrilla.

Bait bucket releases and escapes are yet another pathway. Often, after fishing, an angler dumps unused live bait into the water, assuming it will be eaten.

The escape of fish and other aquatic animals from aquaculture facilities has also resulted in introductions.
What harm can these organisms do? Plenty. Invasive species threaten our native wildlife and local habitats.

They compete with native species for food, space and shelter. Others prey on native wildlife. They can also carry disease and parasites for which local wildlife have no natural immunity. Invasive plants and animals can even alter a habitat.

Over the past 100 years, the extinction of 27 species and 13 subspecies of North American fishes have been attributed to non-native species introductions. The sea lamprey was probably one of the first non-native fish species recognized as extremely harmful after it invaded Lake Erie and the upper Great Lakes via the Welland Canal. It caused the decline and near extinction of native lake trout in the Great Lakes.

Purple loosestrife, an ornamental plant imported from Eurasia in the early 1800s, is invasive in wetland areas, crowding out native plant communities that provide important habitat for waterfowl and other wildlife.

According to a 1998 Cornell University study, invasive species also hurt our economy, costing Americans $122 billion annually.

For example, the zebra mussel clogs water intake pipes and costs millions of dollars in cleanup and control measures.

Approximately $10 million is spent annually to control and research the sea lamprey. And nearly another $100 million is spent annually to control non-native aquatic weeds.

Here are just a few of the invasive species in the Chesapeake: nutria, rapa whelk, grass carp, phragmites, water chestnut, Eurasian watermilfoil and hydrilla.

What can you do?

  • The best way to limit the impacts of invasive species is to prevent them from being introduced in the first place. Each person can play an important role in preventing the introduction and spread of unwanted non-native species.
  • Never release unwanted pets or plants into the environment.
  • Never dump live fishing bait (worms or fish) into a waterbody. Dispose of bait in a trash bin on land.
  • Learn more about the bait you are using. If possible, use live bait that is native to your fishing area. Know your state’s laws concerning the use of live bait.
  • If you use a boat trailer, remove any aquatic plant or organisms found on your boat bottom, propeller or anchor. Dispose of them in a trash can.
  • Use native plants on your property.
  • Be aware of legislative and government programs that address incidental and accidental introductions of non-natives.
  • Educate others. The eradication of non-natives is nearly impossible, but we can prevent new species introductions by being aware of potential pathways.
  • Participate in community groups that either restore habitat and/or survey, remove and report sightings of invasive species.

For additional information, check out these web sites: