Date of Award


Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Biological Sciences (MS)

Administrative Home Department

Department of Biological Sciences

Advisor 1

Casey Huckins

Committee Member 1

Amy Marcarelli

Committee Member 2

Chris Webster


The invasion of Eurasian watermilfoil (Myriophyllum spicatum) can influence littoral zone communities within lakes. Its formation of dense mats at the water surface can suppress native macrophyte growth and impact fish diets and community structure, as well as invertebrate assemblages. However, in the colder waters of the upper Great Lakes region, Eurasian watermilfoil is patchily distributed and integrates more with the native macrophyte community. In order to identify the associations of invasive Eurasian watermilfoil and the littoral communities of the Keweenaw Waterway of Michigan’s Upper Peninsula, we sampled invertebrates, fish, and macrophytes at sites that represented a gradient of Eurasian watermilfoil abundance, as well as habitats with dense and sparse native vegetation. We hypothesized that areas dominated by Eurasian watermilfoil would exhibit less rich and diverse communities of native macrophytes, fish, and invertebrates. We also hypothesized that invertebrate abundances would be greatest in more invaded habitats as a result of reduced predation, but that fish would be more abundant at moderate invasion levels due to optimal foraging efficiency. Our results indicate that, overall, the more vegetated habitats supported more abundant and rich fish and invertebrate communities. However, while habitats with more abundant Eurasian watermilfoil tended to support more abundant fish communities, the most invaded habitats supported fewer fish, and reduced species richness and diversity. While invertebrate abundance also increased along with Eurasian watermilfoil abundance, more of the variation in invertebrate abundance was explained by native macrophytes. At the abundances observed in the Keweenaw Waterway, Eurasian watermilfoil appears to have little impact on invertebrate taxa richness and diversity. Overall, Eurasian watermilfoil appears to provide useful habitat to fish and invertebrates where it integrates more with the native macrophtye community. Yet, if Eurasian watermilfoil is left unmanaged and continues to spread, these effects may intensify over time, leading to reductions in fish abundance and biomass.