Introduced, invasive, non-native, nonindigenous, exotic – all of these terms are used to describe organisms found outside of their native watershed, state, country, or continent. Species introductions are a global problem affecting both terrestrial and aquatic habitats, and have become so widespread that introduced species may comprise up to 20% of the flora and fauna in a give region. While some organisms, like the armadillo and the opossum, are naturally expanding their range, most have had help from us.

We have introduced all types of organisms into aquatic ecosystems including amphibians, reptiles, fish, mammals, mollusks, crustaceans, plants, algae, bacteria, viruses and parasites. Whether accidental or intentional, we have played a key role in introducing species. When we humans first started moving around, we started moving organisms with us. Since we have developed the ability to move farther faster, the number of introduced organisms has greatly increased. For example, over the past 200 years over 150 aquatic organisms have been introduced into the Great Lakes – 1/3 of these introductions have occurred since 1959, when the St. Lawrence Seaway opened. Introductions into aquatic environments have occurred through the release of ballast water from ships, recreational boating, sport fish stocking, aquarium trade, and bait buckets.

While not all species introductions are harmful, some have had severe ecological and economic consequences. Invasive species may cause habitat alteration or loss, changes in food webs and alteration of ecosystem processes such as primary production and decomposition. Any of these may cause a reduction in the biodiversity or even the complete extinction of native species. Invasions have also resulted in loss of revenue to the industries of aquaculture, recreation and tourism.

One exotic species threatening the state of Missouri is the zebra mussel. The zebra mussel was released into the St. Lawrence Seaway in 1986 from the ballast water of a ship. The first population of zebra mussels was detected in Lake St. Clair in 1988, and by 1993 it had spread to all of the Great Lakes as well as lakes and rivers in 18 states. The invasion of zebra mussels has negatively impacted fisheries, and disrupted aquatic ecosystems. Zebra mussels have the unique ability to attach to surfaces, causing the extinction of many native species by literally growing over them. The mussels will attach to anything, including each other, resulting in the clogging of power plants, water intakes, the cooling systems of boats, and the sinking of navigational buoys. Cities and power companies have already spent millions of dollars trying to control zebra mussels; however, the economic impacts over the next ten years are expected to be in the billions of dollars. Zebra mussels will also attach to boats, anchors, trailers, and wetsuits, facilitating their spread since they can live for up to two weeks out of the water.
The zebra mussel was first reported in Missouri in 1991, at sites on the Mississippi river. The mussel was not reported elsewhere in the state until 1999, when it was detected in the Missouri River, and the lower Meramec River. The zebra mussel thrives in lakes and rivers, and has the potential to spread to all of Missouri’s waters. Once established, the zebra mussel is difficult to manage and nearly impossible to eliminate. The prevention of their spread throughout the state of Missouri is the best management plan. This can only be done if boaters diligently inspect their boats and trailers, particularly after being in waters known to be infested with zebra mussels.

Once introduced, a species can have a tremendous impact on the invaded system. The impacts of invasion may be far reaching, causing economic problems as well as ecologic ones. There is little that we can do to un-introduce a species once it has been established. The best we can do is educate ourselves about them, and take care not to move them around.

Jennifer Graham

Zebra mussels are 1 - 1 ½ inches, and have a very distinctive striped pattern on their shell. They are also the only freshwater mussel in North America that can attach to surfaces. If you believe you have located a population of zebra mussels please contact the Missouri Department of Conservation.

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