Insights into a native oyster restoration seascape: Genetic divergence between wild, foreign, and cultured Ostrea edulis populations

The European flat oyster (Ostrea edulis) is suffering population declines and the species is considered functionally extinct in southeastern parts of the North Sea. To conserve the flat oyster and protect its biogenic habitats, (inter)national restoration projects are implemented. In the Netherlands, this has resulted in a restoration seascape where foreign oysters, from Ireland or Norway, and cultured native oysters are used for restocking. However, their genetic connectivity to wild native oysters in the Netherlands remains unknown. Therefore, genetic population structure and connectivity between wild, foreign, and cultured O. edulis populations were investigated. Genotyping of 390 individuals, using a medium-density SNP array, demonstrated that foreign oysters from Ireland and Norway were genetically distinct from Dutch wild native oysters, questioning their suitability for restoration purposes. Cultured native oysters showed minimal genetic divergence from wild native oysters, however, exhibited higher kinship. As such, restoration of wild oyster populations by restocking with foreign or cultured native oysters requires careful consideration. Moreover, the recent establishment of two wild populations provided evidence for natural recolonization. Minimal founder effects suggest a rapid genetic recovery from a bottleneck, emphasizing the species’ capacity for genetic resilience. Collectively, our findings highlight the importance of integrating genetic monitoring in flat oyster restoration, providing valuable insights into the risks and opportunities associated with the translocation of non-native and cultured oysters for restoration purposes.