Decadal trends in macrobenthic communities in offshore wind farms: Disentangling turbine and climate effects

We present results of a study covering 13 years of data (2008–2020), investigating for the first time the combined impacts of offshore windfarm (OWF) turbine-related and climate-related variables on soft-sediment macrobenthic communities in the Southern North Sea, focusing on two Belgian OWFs, Belwind and C-Power. We hypothesized that both turbine presence alongside climate change would affect macrobenthos in the long-term. Our analysis revealed that climate variables, particularly sea surface temperature (SST) influenced macrobenthos abundance, species richness and diversity. Species richness was additionally affected by the North Atlantic Oscillation (NAO). While most community indices increased with rising SST, diversity declined with higher temperatures. Our analysis supported that the already known short-term (max. 3 years) turbine-related impacts are consistent through time (13 years). Sediments near turbines and in deeper waters were richer in organic matter, characterized by finer sand, and supported more enriched soft-sediment communities compared to locations further away. A transition from the originally prevailing Nephtys cirrosa community towards a more diverse macrobenthic community was observed near the turbines. Our study emphasizes the need for long-term studies and the importance of distinguishing turbine presence from climate change effects when assessing the impacts of OWFs on marine ecosystems. • Turbine impacts on macrobenthos remained evident over 13 years. • Finer sediment and higher organic matter content in the vicinity of the turbine. • Higher macrobenthic richness and abundance close to the turbines. • Climate variables significantly influenced macrobenthic communities. • Different turbine-types have different effects on macrobenthic communities.