Modeling seasonal variation of mud-blister worm infestation in oysters using a stage-structured ordinary differential equation framework

Predicting the seasonal dynamics of shell-boring polychaete infestations remains a challenge for oyster aquaculture and restoration. We developed a stage-structured ordinary differential equation (ODE) model to describe the infestation dynamics of Polydora websteri in the eastern oyster (Crassostrea virginica), using empirical prevalence data from the Herring River Estuary (Cape Cod, Massachusetts). The model partitions the host population into uninfested, latent, and visibly infested compartments, incorporating multiple latent stages to represent the developmental delay between larval recruitment and visible shell damage. The model was validated through data fitting, and model parameters were estimated using numerical integration and a bounded quasi-Newton optimization algorithm approach alongside the monthly prevalence data. Simulations accurately reproduced the observed seasonal lag, with infestation peaking in fall and winter despite larval recruitment being restricted to spring and summer. The best fit occurred when six latent compartments were included, consistent with gradual within-host progression. This framework provides a novel mechanistic description of Polydora infestation dynamics and offers a predictive tool to identify low-risk harvest periods and anticipate parasite responses to environmental change. More broadly, it illustrates how stage-structured ODE models can link life-history processes to seasonal parasite dynamics in marine host–parasite systems.