Building a Risk Assessment Framework for Dermo Disease (Perkinsus marinus) in Nova Scotian Oyster Farms

Abstract

In Nova Scotia, oyster farming is a valuable industry, supporting local revenue and coastal livelihoods. However, the current and future sustainability of the oyster farming sector is threatened by the recent detection of Perkinsus marinus, the parasite responsible for causing dermo disease in eastern oysters (Crassostrea virginica). Dermo disease can negatively affect growth and reproduction leading to an increase in oyster mortality, with temperature and salinity as key environmental drivers of P. marinus proliferation. This research examines the potential risk dermo disease poses to Nova Scotia’s current oyster farming operations. A parasite proliferation model for P. marinus was developed based on Ragone Calvo et al. (2001) and forced with local temperature and salinity data. Numerical experiments were conducted using a full factorial design, altering initial parasite load (IPL), parasite transmission (PT), the temperature threshold for parasite growth (PG(T)), the high and low temperature threshold for parasite mortality (PM (HT)) and (PM(LT)), respectively. A sensitivity analysis identified the most influential parameters of the model to be the initial parasite load (IPL) and the temperature threshold for parasite growth (PG(T)). Simulation results were interpreted under best- and worst-case scenarios. Sites along the North Shore of Nova Scotia exhibited higher parasite loads and increased mortality compared with sites along the Eastern and South Shores. These findings highlight the importance of understanding the contribution of local conditions influencing P. marinus dynamics and the need for continued research to minimize the potential risk that dermo disease poses to oyster aquaculture in Atlantic Canada.