A risk assessment of the golden mussel, Limnoperna fortunei (Dunker, 1857) for Ontario, Canada

The golden mussel, Limnoperna fortunei, is an epibenthic mytilid native to freshwaters of China and south-eastern Asia. It became established in Hong Kong in 1965, in Japan in the 1990's and South America in 1991 through ballast water discharge into the La Plata River basin in Argentina. It has since expanded to Bolivia, Paraguay, Uruguay, and Brazil in South America. Populations have steadily increased in these countries since their first reported incidence. The golden mussel is not yet present in North America. A Risk Assessment of golden mussel for the Province of Ontario, Canada was performed using a four step process, developed by the Ontario Ministry of Natural Resources and Forestry: While the potential impacts of an invasion of golden mussel in the Great Lakes has been well documented, the likelihood of a wide spread invasion (i.e., the likelihood of arrival, survival, establishment and spread) was further investigated. Uncertainty for each of the four stages of invasion was also estimated. The risk assessment ranked ballast water exchange of Atlantic transoceanic vessels from South America as the primary potential pathway for introduction of golden mussel directly into the Great Lakes. A back door entry into the Great Lakes was also considered via overland dispersal (e.g. trailered boats) following a ballast water exchange introduction by transoceanic vessels from Asia to the Pacific coast of North America. However, the overall probability of arrival through these two pathways was ranked low. The probability of survival, establishment, and spread of golden mussel in Ontario was deemed to be low, primarily because of its physiological intolerance of cold, winter waters. The level of uncertainty was considered moderate as there has been no golden mussel invasion reported from lakes that freeze over in Asia or South America for at least two months. Based on the current distribution of golden mussel being limited mostly to waters with minimum temperatures of 10 degrees C to 12 degrees C at 36 degrees latitude, the Climatch analysis, and the number of degree days required for reproduction and establishment, the level of risk for invasion into Ontario waters is low and the level of uncertainty is moderate. This would likely apply to all of Canada and most of the USA north of the 36th parallel that is covered by snow or where lakes have ice cover for at least two months of the year. An analysis of the impact of climate change on golden mussel in Ontario suggests that summer temperatures in Lake Erie could rise to levels that would support reproduction and establishment by 2040. However, the lowest temperature reported to support establishment of mussels is 5 degrees C and it is estimated it would likely take more than 200 years to reach and maintain this temperature in Lake Erie.