Multinucleate Sphere X (MSX) is an important pathogen of the eastern oyster (Crassostrea virginica) on the east coast of North America. This parasite is currently not present in Prince Edward Island (PEI), but there are concerns that it will spread from Cape Breton, Nova Scotia, where it was recently identified. Introduction of MSX to PEI would cause direct losses to the shellfish industry and it would have long-term implications for exports of oysters. The main goal of this study was to assess the risk of introduction and dissemination of MSX, as estimated by the number of movements of commercial oysters from three data sources. The in-degree (incoming) and out-degree (outgoing) of the contact network among bays, estuaries, and rivers were used to quantify the risks. For a single location on PEI, identification of up to 55 incoming and up to 26 outgoing movements to and from different locations within PEI were recorded. This suggests that if MSX was introduced it could be disseminated quickly. Movements of shellfish (oysters and mussels) from New Brunswick and Nova Scotia, which pose additional risks of pathogen introduction to PEI, were also identified. Two locations (New London Bay and the East-North-West River complex) were consistently ranked in the top quartile of incoming movements by the three data sources. In addition, two other locations (Bideford Area and Conway Narrows) were classified in the same quartile by only two of the data sources, suggesting that these four areas can be considered at high risk for pathogen introduction. Similarly, two locations were classified in the top quartile of outgoing movements (East-North-West River complex and Orwell Area) by the three data sources, whereas Bideford Area and Foxley River were only identified by two of the three data sources in the same quartile. These results indicate not only risk areas for pathogen introduction or dissemination, but also those areas having both high risk of introduction and high risk of dissemination (e.g., East-North-West River complex). Results of this study illustrate the potential consequences of MSX should Haplosporidium nelsoni reach PEI. Findings also highlight the need for the development of a system that captures all shellfish movements, which will be essential to mounting an effective response to pathogen introduction and mitigation of disease dissemination.
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Vol. 34 • No. 3