Counting on resilience: understanding biodiversity and functional diversity in temperate reef restoration

Active biodiversity restoration is gaining global attention, with the European Restoration Law (2024) signaling its mainstream acceptance. Habitat restoration typically assumes improvements in biodiversity and environmental resilience, which are critical for securing corporate and governmental support. While biodiversity assessments are well‐studied in conservation management, concepts like resilience and functional redundancy are rarely tested in marine habitat restoration. This study is the first to compare functional and biodiversity traits between a wild oyster reef and one under restoration. Using a wild oyster bed recovering from fishing as an analogy, two European native oyster reefs were compared: one from an established wild fishery and another undergoing restoration after local extinction. The 4‐year‐old restoration site was contrasted with the wild site, which had been fished 4 years prior. Results showed significantly higher species richness and biodiversity in the wild reef, indicating slower development at the restoration site. However, both reefs exhibited similar functional diversity and inferred ecological resilience, though the restored reef's functional diversity relied on fewer species and individuals. These findings suggest that while biodiversity indices are important for guiding restoration, generalizations about resilience may not always apply in biodiversity restoration, particularly in temperate biogenic reefs. Despite similar functional diversity, the restored reef shows potential for further biodiversity growth, raising questions about the use of resilience as a metric in restoration policy and management.