A COUPLED BENTHIC-CIRCULATION MODEL FOR DERMO DISEASE IN THE EASTER OYSTER Crassostrea virginica  

The understanding of waterborne microparasitic disease transmission in bivalve filter feeders requires consideration of both biological and hydrodynamic processes. The dose of infective cells received by a filter feeder depends on the concentration of these particles in the water column, which is affected by the relative rates of supply and removal due to decay, advection and diffusion as well as production and removal of particles through filtration by benthic organisms. Here, we combine a circulation model, the Regional Ocean Modeling System (ROMS), with a benthic organism Dermo-disease model for eastern oyster Crassostrea virginica, parameterized using experimental results and literature data, to determine the relative contribution of the hydrodynamic and biological processes to disease transmission.

We simulate disease transmission in idealized simplified estuaries to examine how estuarine circulation moves and/or retains infectious particles. Different freshwater/river inflow scenarios are imposed to generate different estuarine circulations which will affect estuarine residence time and thereby, the development or reduction of disease prevalence. Each case includes an oyster metapopulation distributed among reefs oriented along the axis of the estuary. The simulations are evaluated using the concentration of infectious particles in the water column along the estuary and intercepting benthic populations. We also track evolution in time of particles, and susceptible, infected, and dead infected individuals in each population.

The model, by reproducing the hydrodynamics and disease dynamics, permitted simulation of the spatial-temporal evolution of disease spread over the reefs and the rate of development of disease in populations that are remote from initially infected populations, thereby providing estimates of the transfer of disease between populations and the mechanisms that foster transmission. The model detects the effect of flow particle availability, low oyster density, reef size, and relative location of reefs on disease transmission and spread.