Subtidal temperate reefs in marginal seas enhance biodiversity, food web complexity, and ecosystem stability

Marine reefs are habitats that underpin key ecosystem services, including supporting diverse faunal communities. However, the ecological functioning of reefs in subtidal temperate waters has remained underexplored. Simultaneously, interest in restoring lost reefs is increasing due to the establishment of marine protected areas and the development of offshore wind farms. To explore the ecological importance of these reefs, we investigated how different subtidal temperate reef types affect faunal communities and their food web structures in the North Sea as an example of a temperate sea. We focused on the shallow nearshore Voordelta and the deeper offshore Borkum Reef Grounds in the Netherlands. Both sites hosted either geogenic (rocks) and/or biogenic (Lanice conchilega or bivalve) reefs, which we compared to a sandy non-reef reference. We sampled benthic macrofauna using box corers or grabs and mobile communities with baited traps and reconstructed food webs using stable isotope analysis and the literature. Results showed that reef presence enhanced benthic taxa richness, evenness, and abundance, with biogenic reefs creating intermediate communities between sand and rocks. Certain species of commercial interest (Cancer pagurus and Trisopterus luscus) were positively associated with the reefs. Reefs were found to increase food web complexity and connectivity, which are linked to the network’s stability and resilience to disturbances and influence the proportion of intermediate consumers. We conclude that temperate subtidal reefs enrich ecosystems and stabilise food webs, suggesting that their restoration and conservation could help mitigate anthropogenic impacts and enhance the overall health of marine ecosystems.