Pathogen dispersal can lead to high exposure risk at European flat oyster restoration sites

Abstract Marine diseases threaten ecosystems and aquaculture, additionally harming endangered species including the European flat oyster (Ostrea edulis ). Although international restoration efforts follow biosecurity protocols, ocean currents may transport pathogens to restoration sites. Here, we used biophysical Lagrangian dispersal simulations to map upper-bound exposure risk of the oyster pathogen Bonamia ostreae across the North-West European shelf. We developed a workflow with pre-aggregated connectivity components allowing analyses of multiple scenarios without rerunning simulations. We found typical dispersal distances from 30 km for free pathogens to 50-60 km for infected larvae, with high spatial heterogeneity emphasizing the need for site-specific simulations. About 30% of restoration sites showed a continuously high potential exposure to pathogen arrival. We identified highly connected diseased sites that may drive transmission. We provide a scaling factor to calculate pathogen exposure at target locations and a tool for selecting low-risk sites. This transferable workflow supports site-specific spatial planning in restoration, aquaculture, and disease monitoring.