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Invasive Species

A seemingly innocuous invader, the zebra mussel, has devastated fisheries and industries in its host lands. Source: USGS

The invasive snakehead. Source: USGS, Artist: Susan Trammell

Invasive species are non-native species that have been introduced to a waterway and that have been able to establish themselves in that ecosystem at the expense of other species. Increase in invasive species is correlated with a decrease in overall biodiversity and loss of ecosystem services and is a major concern in coastal ecosystems (Worm et al, 2006). Invasive species often upset the entire ecosystem balance, driving less competitive species into extinction and fundamentally altering the food web. High profile examples include the proliferation of zebra mussels in the Great Lakes--which have caused the decline in many native species and caused many industrial problems--and the Nile perch, which caused the extinction of hundreds of aquatic species in Lake Victoria. Invasive species are listed as the second greatest source of species extinctions (Wilcove et al, 1998).The figures at the right illustrate the interrelations between biodiversity, ecosystem services, and risks;species invasions is shown at the far right under "risks."

Invasive species are often transported via the ballast water ships sometimes carry to help keep them level. Water is taken from the starting point of a journey and then released at the end point--along with any organisms living inside. High risk ballast in regards to transport of invasives is water taken onboard in a freshwater or estuarine port as those organisms have a high chance of surviving in their new environment (Portland University, 2006). Invasives are also released intentially-as with unwanted pet release or through aquarium dumping--such as the release of the red-eared slider in the United States.

An important aspect of the invasive species problem is that once an invasive is present in an estem, it is often impossible to remove it; thus, it is essential to prevent invasive species from arriving in the first place.