National aquatic invasive species (AIS) risk assessment for Zebra Mussel (Dreissena polymorpha) and Quagga Mussel (Dreissena rostriformis bugensis), April 2022

Abstract

Since being introduced into the Laurentian Great Lakes region in the 1980s, Zebra (Dreissena polymorpha) and Quagga (Dreissena rostriformis bugensis) Mussels have spread throughout North America and have had significant ecological impacts to freshwater ecosystems. In Canada, Zebra Mussels have subsequently spread to certain waterbodies in Manitoba and southern Quebec, while Quagga Mussels have only spread within the Laurentian Great Lakes region. Compared to the 2012 risk assessment, this new assessment was conducted at a higher spatial resolution. It included all provinces and territories, new and updated environmental data and species occurrence information, and two different habitat suitability models. The ecological risk for both Zebra and Quagga Mussels was assessed by integrating metrics related to introduction, establishment, and ecological impact. This new assessment did not evaluate the risk to individual waterbodies. Rather, it provided an ecological risk assessment at 9,260 m x 9,260 m grid cell resolution across Canada. As a result, risk and impacts may differ at smaller spatial scales where conditions may be more or less favourable. Introduction was assessed based on a proxy of human activity (Human Footprint Index) and proximity to invaded waterbodies (connectivity metric). Establishment was assessed using two modeling approaches to characterize habitat suitability (Calcium-based model and MaxEnt-based model). Since Zebra and Quagga Mussel have significant and well documented negative ecological impacts, the impact to Canadian freshwater aquatic ecosystems was determined to be very high. For both Zebra and Quagga Mussel, all provinces and territories contain watersheds that have Moderate or High Ecological Risk. Higher ecological risk areas are distributed along the southern reaches of Canada ranging from Nova Scotia to southern Alberta and British Columbia. The ecological risk presented here represents current conditions. As Zebra and Quagga Mussel invasions continue and environmental drivers change, the risk to Canadian freshwater aquatic ecosystems may change and will need to be reassessed. Data limitations resulted in a number of uncertainties related to the characterisation of risk in this assessment. Improved and expanded geospatial data (e.g., environmental, species, and introduction vectors) will improve future risk assessments.