Invasive Non-native Species

Photo: zebra mussels © Jim Moyes, Environment Canada
Zebra mussels

Great Lakes

Invasive non-native species are responsible for the loss of much of the original biotic community of the Great Lakes.9 The demise of Great Lakes native biota started with the opening of the Welland Canal in 1829, the accidental introduction of sea lamprey in 1920, and the subsequent collapse of lake trout. Non-native species now dominate the Great Lakes, with enormous ecological and economic consequences.10 One study estimated the economic loss caused by non-native invasive species in the Great Lakes to be as much as $5.7 billion annually.11

Trends in non-native species in the Great Lakes

Cumulative number of species
Graph: cumulative number of non-native species in the Great Lakes. Click for graphic description (new window).
Source: data from Great Lakes Aquatic Nonindigenous Species Information System (GLANSIS), 200912

As of 2008, over 185 non-native aquatic species had been reported to have reproducing populations in the Great Lakes. Of these, at least 10% are considered to be invasive.12 Examples of the impacts include the collapse of:

  • the deepwater amphipod, Diporeia, and 33% of native mussels, after the introduction of zebra and quagga mussels;
  • many lake fish after the introduction of alewife.13

Prevention of future introductions, such as Asian carps from the Mississippi Basin, is a critical challenge.13

Native Mussel Declines

Number of freshwater mussel species before and after zebra mussel invasion
Map and graph: native mussel decline in Lake Erie and Lake St. Clair. Click for graphic description (new window).
Note: no “before” data for Niagara River and East Lake St. Clair.
Source: adapted from Metcalf-Smith et al., 200214

Native freshwater mussels are ecologically important as natural biological filters, food for aquatic species, and indicators of good water quality.15 Nearly 72% of the 300 freshwater mussel species in North America are vulnerable to extinction or are already extinct.15 Native freshwater mussels were virtually extirpated from the offshore waters of western Lake Erie between 1989 and 199116 and from Lake St. Clair between 1986 and 1994.17 Their decline has been attributed to a number of human stressors such as pollution, overexploitation, and habitat destruction by dams,18 in addition to declining water levels, and competition with non-native species such as zebra and quagga mussels.15 Free-flowing rivers can provide a refuge for native mussel species by limiting zebra and quagga mussel colonization. However, non-native mussels can still establish in regulated rivers with reservoirs.15 In a 2004/2005 survey, zebra mussels were noted at all sites sampled downstream from the Fanshawe Reservoir in the lower Thames River, a system that has one of the most diverse freshwater mussel communities in Canada.19