Abstract
Since 2005, ILVO performs beam trawl monitoring surveys to evaluate the potential effects of offshore wind farms (OWFs) on soft sediment epibenthos and demersal-benthopelagic fish. The study effort has been concentrated on the C-Power and Belwind OWFs. The time series has been investigated in detail in a previous report, therefore this chapter focuses on the results of 2017, which is resp. 6 (C-Power) and 7 (Belwind) years after construction.
No direct wind farm (‘reef’) effect, nor indirect fisheries exclusion effect, was yet observed for the soft-bottom epibenthos and demersal-benthopelagic fish assemblage in 2017. Species composition, species number, density and biomass (for epibenthos only) of the soft-bottom assemblage inside the OWFs were very similar compared to the assemblage in reference locations outside the OWFs. The species, originally inhabiting the soft sediments of both OWFs, remain to be dominant.
Remarkable was that two epifaunal animals, i.e., Mytilus edulis and Anthozoa sp., known to be fouling on the foundations, were quite abundant in the C-Power OWF soft sediment samples, and totally absent or only present in much lower densities in the reference locations outside the OWF. This could indicate that the ‘reef’ effect is starting to expand beyond the direct vicinity of the turbines. However, detailed follow-up is needed to validate whether this is a one-off observation or a real wind farm effect reflected with time after construction possibly because of increasing epifaunal biomass on the foundations.