Date of Award

Winter 2014

Publication Type

Master Thesis

Degree Name



Great Lakes Institute for Environmental Research


Biological sciences, Health and environmental sciences, Aquatic plants, Biological invasion, Invasive species, Nonindigenous species, Water hyacinth, Water lettuce


MacIsaac, Hugh J.




Many macrophyte species sold in stores across Canada are perceived as unlikely to invade owing to climate mismatches. This does not account for climate change, which may make the Great Lakes more suitable to invaders. This study aimed to assess the invasion potential of two macrophytes ( Pistia stratiotes and Eichhornia crassipes ) that were recently discovered in the Great Lakes, and determine the mechanisms responsible for their persistence. I surveyed the Canadian shoreline of the Great Lakes to determine their current range, and tested three hypotheses that may account for their continued presence. Surveys conducted in 2010, 2011 and 2012 demonstrated that the species are recurring in some tributaries. I deployed enclosures to assess winter survival of experimental plants and results indicate that neither species can survive. However, water hyacinth produces seeds in the Great Lakes, and experiments indicate a germination rate of up to 67% under optimal conditions. Therefore, it is unlikely that water lettuce and water hyacinth are currently established in the area, though it may become an issue in the future.