Potential marine benthic colonisers of offshore wind farms in the English channel: A functional trait-based approach

Offshore wind farms (OWFs) have gained attention as a promising alternative to conventional energy sources. However, their installation and operation may have multiple ecological impacts on the marine environment, including the "reef effect". The reef effect is the colonisation of wind turbines and other artificial substrates by benthic organisms, which has a major impact on marine biodiversity as it changes community assemblages and ecosystem functioning. We conducted a two-step study to predict the reef effect of a future OWF (Dunkirk, northern France). First, we explored similarities between colonisers of existing OWFs and those of other hard substrates (oil and gas platforms (O&GP) and hard substrates in the English Channel (HSEC)). We then analysed functional traits to determine a trait profile of potential colonisers of Dunkirk's OWF. Statistical analyses revealed that OWF and O&GP communities were more similar to each other than to that of HSEC. Comparing the three communities revealed that they shared 157 taxa, which could be potential colonisers of Dunkirk's future OWF. The functional profile revealed that OWF colonisers were species ranging from 10 to 100 mm in size, with gonochoric reproduction, pelagic and planktotrophic larvae, a life span of less than 2 years or 5-20 years, were sessile, and were carnivores or suspension feeders. Functional trait analysis revealed that during their intermediate stage of development, OWF benthic communities have a functional richness and diversity (0.68 and 0.53, respectively) similar to those of HSEC communities (0.54 and 0.50, respectively). However, based on using O&GP as a long-term view of the colonisation of OWFs, functional richness and diversity could decrease during the climax stage (0.07 and 0.42, respectively).