Musician pedals around Lake Superior
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If you live on the Great Lakes or in a similar coastal area, you've no doubt heard of zebra mussels or sea lamprey. Chances are you've also seen patches of purple loosestrife growing in your community or on the side of a local highway. You might not have recogized this attractive flowering plant as a non-native species, but it is. Although pretty to look at, these purple stalks are choking out native plant species by overtaking and altering their habitat.
These are just three of the more than 140 nonindigenous, or invasive, species that have become established in and around the Great Lakes since the 1800s. In fact, due in large part to increases in the volume of shipping traffic, the introduction of new "exotic" species has increased dramatically over the past 50 years. More than 87 nonindigenous aquatic species have been accidentally introduced into the Great Lakes in the 20th Century alone. Once introduced, invasive species must be managed and controlled, as they are virtually impossible to eradicate.
While many non-native species have no serious ecological impact, the introduction of a single key species can, as in the example of the sea lamprey, cause a sudden and dramatic shift in the entire ecosystem's structure. New species can significantly change the interactions between existing species (and between those species and their non-living environment), creating ecosystems that are unstable and unpredictable.
Graphic: Sea Lamprey shown attached to a lake trout. Courtesy U.S. Fish & Wildlife Service.