Introduced exotic plants and animals may harm native species by changing the
structure of the existing ecosystem. For example, non-native species
may compete with native species for resources such as water, food,
space, or light. However, an exotic species is not necessarily an
invasive species. A non-native species may become invasive if it does not have natural enemies, such
as predators or disease, in its new environment to help keep its population under
control. Without these controls, invasive species also often spread rapidly to areas other than where they were initially introduced.
For centuries, people introduced non-native species of plants and animals into the
Chesapeake Bay region for agricultural and aesthetic purposes.
Familiar products such as soy beans, wheat, dandelions, tulips, honey
bees, and cattle all have been introduced from other places. Many of
these introductions have been economically beneficial and not harmful
to the plants and animals that were already living here. However, some
introductions have had devastating effects on the existing ecosystem
because the introduced species has been able to out-compete the
native species for resources and have “taken over” the areas
where they are introduced. For example:
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The zebra mussel has spread throughout the Great Lakes and several major
river basins after being introduced into just one lake in Michigan
through the release of ship ballast water.
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The aquatic weed Hydrilla—a native of Asia—has been
found in 13 states, where it has out competed
native plants for space, and has caused fish kills by depleting
oxygen levels in the water.
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Another native of Asia, the snakehead fish, has been found in the Potomac
River and in rivers and ponds in several other states around the
country. Snakehead fish are sold in Asian food markets in the United
States, and it is believed that these food fish are the source of
the snakehead fish that have been released into the wild.
Scientists and resource managers have begun to learn our past mistakes, and regulations have been put in
place to try to control the negative effects of the introduction of
non-native species. Invasive species cause approximately $120 billion
dollars per year in environmental damage nationwide1. It
is not known if Crassostrea ariakensis, a non-native oyster, if introduced, would
become an invasive species or not. Even the possibility that it might
has scientists and policymakers cautious about going ahead with an
introduction. Before a non-native oyster can be introduced into the
Bay a Programmatic Environmental Impact Statement (PEIS) must be completed. A PEIS
describes the possible environmental effects of the proposed action,
and evaluates possible alternatives and their associated impacts.
A draft PEIS
for the proposed introduction of C. ariakensis was released for public comment in October 2008.
Below are some useful links to information about invasive species:
http://www.invasivespecies.gov/
is the gateway to federal efforts concerning invasive species. On this site
you can learn about the impacts
of invasive species and the federal government's
response, as well as read select
species profiles and find links to
agencies and organizations
dealing with invasive species issues. This is also the web site for
the National Invasive Species Council, which coordinates federal
responses to invasive species issues.
The following pages contain links to information about invasive species
on different scales:
Chesapeake Bay
National
International
1Pimentel, David, R. Zuniga and D. Morrison (2005).
Update on the environmental and economic costs associated with
alien-invasive species in the United States. Ecological Economics. 52(3):273-288.