Environmental factors associated with the distribution of non-native starry stonewort (Nitellopsis obtusa) in a Lake Ontario coastal wetland

Starry stonewort (Nitellopsis obtusa) was likely introduced to the Laurentian Great Lakes via ballast water in the late 1970s. Since its introduction, little research has been conducted to determine the extent of its spread throughout the Great Lakes basin or to explore the environmental variables associated with its distribution. This is partly because, outside of its native range, N. obtusa is not often differentiated from other native Characeae. Here, we document the spatial distribution of N. obtusa in Presqu'ile Bay, Lake Ontario and identify physical and chemical environmental factors that predict the presence of N. obtusa. In Presqu'ile Bay, N. obtusa was primarily clustered along the north-shore and tended to be at locations with higher conductivity, water hardness, and nitrate–nitrite and lower exposure to wind and wave action. The best predictors of N. obtusa presence, based on a boosted regression tree model, included high density of docks within a 1km radius, high conductivity, short distance to the nearest marina, and low fetch. These results support the notion that N. obtusa can be transported via boating activity, and the findings can be used by management agencies to focus search efforts when attempting to determine N. obtusa presence. Given the paucity of knowledge regarding both the distribution of N. obtusa in the Great Lakes and how its introduction has influenced native flora and fauna, it is hoped that this study will spur future research.