Zebra Mussel (Dreissena polymorpha) Habitat Associations in Four West-Central Minnesota Lakes

In 1989, zebra mussels (Dreissena polymorpha) were first documented in the land of ten thousand lakes in the Lake Superior Basin at Duluth. Zebra mussels are successful invaders because the species attaches to substrates with byssal threads, can adapt to a wide range of environmental conditions, and has a free-swimming veligers that are easily transported. Although invasive mollusks pose a range of economic and ecological threats to inland waters, our understanding of zebra mussels in Minnesota lakes remains limited. To gain additional information regarding zebra mussel ecology in lake systems, I conducted research in four west-central Minnesota lakes that were colonized prior to 2009. The objectives of this study were to 1) evaluate the relationship between zebra mussel distribution and substrate size, 2) assess the potential associations zebra mussels may have with organic biomass and individual plant species, and 3) survey the zebra mussel infested study lakes for native mussels and develop research questions about the zebra mussel and native mussel interactions. In the summer of 2014, mussel, vegetation, and substrate surveys were completed via SCUBA at five 0.25 m2 quadrats spread 10-m apart along six 50-m transects in each lake. Substrate was categorized using phi (φ) values. Zebra mussels were enumerated and measured to determine density and size structure. Vegetative cover (%) was estimated and organic biomass was separated by type and dried to determined density (g/m2 dry weight). The majority (73%) of the quadrats had a phi value of 0-1, indicating small particulate substrates were available for zebra mussel attachment. Underlying geologic substrate was not a statistically significant predictor of zebra mussel density (r2=0.32, P=0.054) in this chain of lake system, however, biological importance may be present. The study showed minimal variation in particle size among lakes within the chain-of-lake system therefore, should be considered as one unit when analyzing zebra mussel density. Significantly more zebra mussels were found attached to algaes (filamentous and Chara spp.) than macrophyte taxa, including Potamogeton spp. (P=0.001). Additionally, juvenile zebra mussels were found more on organic substrates than adults (P\u3c0.001). Lastly, two species of native mussels were found in the study area, including fatmucket (Lampsilis siloquoidea) and giant floater (Pyganodon grandis). Future research assessing the factors that facilitate Unionid species success in their native range, compared to their introduced ranges, may help clarify the ecological mechanisms and impacts of zebra mussel naturalization