Beneath the blades: Marine wind farms support parts of local biodiversity - a systematic review.

Offshore wind energy developments in European waters are rapidly expanding to meet the increasing global demand for renewable energy. These developments provide new substrates for species colonisation, but also introduce changes in electromagnetic fields, noise levels, and hydrological conditions. Understanding how these man-made structures affect marine biodiversity across various species groups is crucial, yet our knowledge in this field remains incomplete. In this synthesis paper, based on 14 case studies conducted in northeastern Atlantic (North, Irish and Baltic seas), we aggregated species-level data on abundance, biomass, and other quantity proxies spanning the entire food chain from invertebrates to mammals, and compared these variables between wind farms and nearby control sites. Overall, our analysis revealed that in wind farm areas, species tend to occur at higher quantities than in control areas. Additionally, we noticed a slight trend where the positive effect of wind farms was more pronounced in newly established ones, gradually diminishing as wind farms aged. None of the tested covariates (depth, distance from coastline, years in commission) nor species' characteristics (habitat and spawning types, trophic level) showed statistical significance. When examining species groups individually, there was a tendency for wind farm areas to harbour higher quantities of polychaetes, echinoderms and demersal fishes. These findings suggest that wind farms contribute to the so-called reef-effect, providing shelter and food supplies to their inhabitants and acting as no-take-zones. Our results support the idea that wind farms could serve as zones of increased local biodiversity, potentially facilitating spillover effects to nearby areas for certain species groups. Further studies are necessary to gain a more comprehensive understanding of the adverse effects of wind farms on associated biodiversity, while also exploring avenues to amplify their positive impacts.