Equivocal effects of offshore wind farms in Belgium on soft substrate epibenthos and fish assemblages

With the construction of wind farms, new hard substrates are introduced in the marine environment. Between the turbine rows and around the wind farms, however, the soft sediments remain. The inhabiting fauna of these sandy sediments may be influenced by the presence of the turbines and the absence of fisheries in the wind farms. These effects were investigated for epibenthos, demersal fish, and benthopelagic fish in the Thorntonbank and Bligh Bank wind farms in the Belgian part of the North Sea. Inside the wind farms, several local and temporal effects were detected, including both temporary construction effects (e.g., decreased densities of dab, ophiuroids and dragonets) as refugium effects (e.g., the presence of relatively large plaice). At the wind farm edges, only few temporary effects were noted, but real edge effects due to changes in fisheries intensity or 'spillover' from the wind farms could not be shown. The observed effects were not consistent between both wind farms, which is not surprising, given the differences in epibenthos and fish communities, sandbank topography, fishing pressure, development stage of the wind farms, and the used foundation types. This inconsistency stresses the importance to replicate monitoring activities across wind farms and along the identified gradients.