Modling of the phsical environment and its effects on oyster disease in Delaware bay: past, present and future

Delaware Bay is important to a variety of ecological and economic processes including the production of oysters. For this Bay we develop, validate and apply a high-resolution hydro-dynamical model, hindcast its largely unknown physical environment, investigate the roles of the physical environment influencing oyster diseases, the Multinucleated Spheres of unknown origin (MSX), and inquire into the future fate of the Bay in response to climate changes. Model parameters are determined based on multiple experiments. Model validation against extensive in situ datasets shows that the model has significant skill in predicting variations in tracers and circulation. The model is applied to inquire into the relationships between water properties and the observed MSX prevalence (MSXP), and simulations of concurrent physical conditions are performed. Correlation analyses indicate that MSXP is significantly correlated with river flow, salinity, and the salty-warm area (SWA) index that combines the effects of temperature and salinity. The positive river flow/temperature and the negative river flow/salinity correlations determined a negative temperature/salinity correlation with relatively small SWA, helping control MSX. An effective upper Bay transport mechanism, via timely spreading MSX with a MSXP gradient often available, may also contribute to MSXP in the upper Bay. We inquire into the potential impacts on the physical environment in Delaware Bay arising from future climate change. Our sensitivity studies suggest that sea level rise (SLR) in 50-100 years may significantly change circulations and salinize the Bay mainly via weakened salinity gradient and salt advection, associated with intensified mixing induced by the widened Bay. Intensified river flow may not offset the SLR-induced salinization. Warmer surface air may significantly warm the shallow and thermally sensitive Bay. These new physical conditions would be generally unfavorable to oysters because they tend to promote oyster diseases (i.e., MXP and Dermo). By fixing the coastline the salinization induced by the SLR would be substantially mitigated. The avoidance of dredging in the lower Bay would also mitigate the salinization to some extent. Similar processes related to salinization and warming may occur in other similar estuaries.