Differences in epifaunal ecological functioning between natural and artificial hard substrates with implications for offshore renewable energy development

Abstract The expansion of offshore renewable energy developments (ORED) has prompted increasing concerns regarding their potential impacts on the marine environment and repercussions for ecosystem functions. A comparative assessment of benthic invertebrate communities associated with natural versus artificial hard substrates could provide insights for assessing ecological changes following the installation of such structures. This study evaluated the ecological functionality of offshore wind turbine foundations, scour protection layers, and geogenic natural reefs through a trait-based approach. The analysis focused on two regions (which we called ‘Belgium’ and ‘Borkum’) selected based on the availability of high-resolution invertebrate taxonomic data, comprising natural and artificial substrates at nearby geographical locations. Taxonomic data were sourced from the BISAR database, while functional trait data were compiled through an extensive review of the scientific literature. A total of six functional traits, encompassing 29 modalities, were assessed. The resulting data were analysed to determine both taxonomic and functional differences between artificial and natural hard substrates. Functional analyses were performed using a combination of functional diversity indices and latent variable models to elucidate underlying patterns in trait distribution and community functioning. The results constitute evidence, demonstrating that geogenic natural habitats support higher levels of biodiversity and harbour functionally distinct communities when compared to artificial structures. Analyses of functional diversity indices revealed significant differences in functional evenness and divergence between natural reef communities and those associated with artificial structures. These differences illustrate that natural rocks exhibit greater functional resilience to environmental disturbances. Furthermore, the majority of trait modalities exhibited significant responses to at least one substrate type, and several taxa displayed effect sizes that were positively or negatively correlated with specific habitat types, indicating substrate-driven shifts in community functional composition. Given the pronounced differences in biodiversity and functional attributes between natural and artificial hard substrates, enhancing the ecological sustainability of ORED requires a shift towards ecologically informed design. Artificial structures could potentially be engineered to mimic the multidimensional and heterogeneous properties of natural substrates, facilitating the establishment of more resilient benthic communities. These results have conservation and management implications when planning the introduction of such structures over local and regional scales.