More than 180 non-native aquatic species such as plants, animals, fish and microorganisms have entered the Great Lakes to date, and the impact of many of these introduced species can be catastrophic for native ecosystems. When the spread of a non-native species risks damage to the environment, human economy or human health, they are called invasive.
Invasive species can alter the food web, affect the cycling of essential nutrients or even remove these nutrients from the food web altogether, dramatically altering or even destroying water quality. They can also change or destroy coastal habitat.
As a result, native flora and fauna can be decimated as the invasive species crowd out, displace and eventually replace the natural inhabitants and their position in the food web. Further, changes at one level of the food chain have a ripple effect on all the other creatures and organisms, as all levels are highly inter-dependent. This can permanently alter the biodiversity of coastal wetlands.
Invasive species are able to do this effectively because they travel to areas outside their natural environment. They typically can establish themselves quickly and reproduce even faster, often with extremely rapid expansion. With few natural predators in the new area, there is little natural control of their population and its spread. This is why invasive species are considered one of the largest threats to the health of the Great Lakes ecosystem.