Laying out the foundations: Assessing the spatial extent and drivers of offshore wind turbine artificial reef effects on soft sediments

Abstract

With the rapid expansion of offshore energy, numerous artificial structures are being installed on the seabed, including wind turbine foundations. This study investigates the “artificial reef” (AR) effect of bottom-fixed offshore wind farms (OWFs) on soft sediment benthic communities. While previous studies have focused on distances ≥30 m from turbines, in this study, sediment and macrobenthic samples were collected at shorter distances (1 m, 7 m, 15 m and 25 m) from the scour protection layer (SPL) around a monopile and a gravity-based foundation in two Belgian OWFs, 10–13 years post-installation. Results show a localized AR footprint for both turbine foundations, with enriched benthic communities within 15 m of the SPL. In comparison to communities 25 m distanced away from the SPL, a higher average species richness (+100 %), abundance (+117 %), functional richness (+438 %), and bioturbation potential (+86 %) was prevalent, whereas the magnitude of enriched structural and functional diversity in the footprint varied respectively between 16 and 80 % and 15–110 % depending on the OWF. Beyond the AR footprint, communities resembled those at reference sites (240–570 m), with less surface dwellers, suspension feeders and a prevalence of burrowing biodiffusors that contribute little to bioturbation. While the AR effect's magnitude depends on local conditions and foundation design, our trait-based analysis indicates that sediment fining, biofouling drop-offs and organic enrichment are consistent drivers shaping the AR footprint.