March of the Mussel: Is Atlantic Canada at risk of zebra mussel ( <i>Dreissena polymorpha</i> ) invasion?

The invasion of Atlantic Canadian (Eastern Quebec, New Brunswick, Nova Scotia, and Prince Edward Island) freshwater habitats by the zebra mussel ( Dreissena polymorpha) is currently in progress. Management of this ongoing invasion requires information on which areas have the highest invasion risk, which can be predicted using species distribution models (SDMs). Previous Canadian studies have focused on environmental suitability, with less use of information on potential pathways of introduction, and have tended to rely on single SDMs. In this study, the risk of Dreissena polymorpha spread in Atlantic Canada was explored using multiple SDM types, both separately and in combination via two ensemble modelling approaches, noting which approach increased SDM accuracy. Models were built using physico-chemical data coupled with spatially explicit information on human-mediated introduction pathways. Physico-chemical variables, and data relating to recreational fishing, were among the more important model variables. Model outputs identified several “higher-risk” areas for Dreissena polymorpha invasion that could be prioritized for future monitoring and management action. Of the trialed model types, random forest models were the most accurate.