How does a restored oyster reef develop? An assessment based on stable isotopes and community metrics

Oyster reefs host complex food webs, as their three-dimensional biogenic structure provides habitat for a diverse range of invertebrates and fish. Oyster reefs have suffered severe degradation due to anthropogenic activities. Restoration projects aim to mitigate this habitat loss. We compared the development of a restored subtidal oyster reef to that of a natural reef for 29 months by assessing (1) community metrics (e.g., biomass, diversity), (2) the stable isotope composition of food sources and consumers, and ( 3) biomass-weighted isotopic diversity indices. A clear shift in restored reef community composition occurred 12-15 months after restoration, moving from a community dominated by opportunistic species to a more diverse and evenly distributed community, similar to that of the natural reef. Consumer stable isotope values indicated that the restored reef community was supported by similar food resources and had similar food chain length as the natural reef community by 5-month post-restoration. However, biomass-weighted isotopic diversity indices indicated that the magnitude of the main trophic pathways and characteristics of food web complexity in the restored reef did not recover to natural reef levels until 12-15 months after construction. The functional recovery of the restored reef community was driven by the homogenization of biomass distribution among trophic compartments as oysters and top predators increasingly colonized the reef. Results indicate that oyster reef restoration can support food web functions like those provided by natural reefs. We also demonstrate the importance of combining food web and community structure information in the study of ecological functioning.