Hitchhikers on dead shells: an unanticipated pathway of alien species invasion associated with discarded seafood remains at oyster tasting sites

Shellfish mariculture, particularly of oysters, poses a significant risk for the introduction of non-native species into marine ecosystems. This study investigates the diversity of invertebrate species colonizing live and discarded oyster shells originating from a farm and oyster bar in the Tylihul Estuary, a region with active oyster farming. Advanced molecular techniques identified several invasive species associated with the discarded shells, including Semibalanus balanoides , Austrominius modestus and Monocorophium insidiosum . These taxa have not been previously documented in the region. Our findings indicate that macrofaunal composition differs between live and discarded oyster shells, and that the richness of invasive invertebrates associated with oyster shells is higher than expected. The discarded shells not only act as a substrate for colonization but also serve as potential vectors for biological invasions. We performed a Species-related Risk Assessment to identify the potential ecological impacts on local biodiversity and ecosystems of the invasive species associated with oysters. Our study proposes management strategies aimed at mitigating the risks associated with shells discarded by oyster bars. Our recommendations include informing recreational travellers and retailers about the implications of discarding shells into the water and advocating for the control of risks related to the use of shells as a construction material.