PARENT SESSION
Contributed Oral Session 35: Invasive Species: Great Lakes Area
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 524 B, Level 5, Palais des congrès de Montréal
Detecting long-term change in lake conditions with benthic invertebrate communities: the role of invasive species.
Wilson, Karen*,1, Howell, E. Todd2, Jackson, Donald1, 1 University of Toronto, Toronto, ON, Canada2 Ontario Ministry of the Environment, Toronto, ON, Canada
ABSTRACT- Lake Ontario has undergone several long-term, lake-wide changes since the late 1960s. Phosphorus-loading peaked in the early 1970s, decreased through the 1980s and has stabilized since the early 1990s. A succession of exotic species have been introduced to the lake, including zebra and quagga mussels (Dreissena spp.) first noticed in 1989. In 1981, the Ontario Ministry of the Environment initiated a study to determine whether large-scale changes in lake conditions would be reflected in the composition of nearshore benthic invertebrate communities and whether this information could augment ongoing monitoring of water quality. The 50 sites, located at depths of 5 and 10 m on hard and soft substrates, were revisited in 1991, and again in 2003. Over time, community composition has shifted dramatically, reflecting a decrease in nutrients from 1981 to 1991, and the domination of Dreissenid mussels on all substrate types in 2003. Even with Dreissenids removed from the analysis, invertebrate communities were significantly more similar in 2003 than in 1991 or 1981. Dreissenids, primarily D. bugensis, currently covered over 65% of the nearshore of Lake Ontario in 2003, and were only absent from extremely soft silt and shallow wave-swept sands. Dreissenids dominated the benthic invertebrate biomass, averaging 864 grams dry weight/m2, and represent a tremendous homogenization of the benthic habitat in Lake Ontario. Our results suggest that the utility of benthic invertebrate monitoring programs is compromised by the introduction of non-indigenous species that not only dominate in biomass, but also drastically modify the physical environment.
Key words: invasive species, benthic invertebrates, Lake Ontario, water quality