Aquatic Invasive Species
Invasive species have had an enormous impact in the waters of Ontario. In the Great Lakes watershed, the entire ecosystem has been restructured by invasive species; in the period since construction of the St. Lawrence Seaway, a new invasive species was introduced to the Great Lakes every nine months, on average.
The introduction of fish species such as parasitic sea lamprey, which is much larger than native lamprey species and more destructive, and alewife, which produces a substance that inhibits reproduction in many native fish species and feeds on native fish eggs and larvae, have created havoc in native fish communities, effectively driving some populations to extinction.
Invasive invertebrates have also had serious effects. Zebra and quagga mussels, which feed on very small food items they filter from the water, have led to major changes in the food web structure of the Great Lakes. Invasive plants such as Eurasian water milfoil and invasive Phragmites have caused substantial restructuring of wetland ecosystems.
Invasive species affect aquatic ecosystems and alter food webs by preying on and competing with native fish, invertebrates and plants.
Natural expansion of species beyond their historical range typically occurs over long periods of time; however, humans can and do contribute to the rapid spread of invasive species. Some of the most damaging impacts on our lakes and streams have been the result of introductions of invasive species from other parts of North America. Invasives can be introduced and spread in a variety of ways including ship ballast water, movement of bait, the aquarium and water garden trade, live food fish, unauthorized deliberate introductions and canals and water diversions.