Foundations of Wind Turbines as Stepping Stones for Non-Indigenous Species in the Southern North Sea

Since 2008, offshore wind farms have been constructed in the shallow waters (<50m) of the Southern North Sea. At present, hundreds of turbines are operational and many more are planned. A new habitat for benthos has been created, with vertical hard structures in the offshore environment, extending from the sandy seabed to the sea surface. Monitoring in Belgian waters focussed on the succession of the fouling community in the sub- and intertidal zone, with special attention to non-indigenous species (NIS). A Metridium senile-Jassa herdmani dominated community developed in the subtidal, and only few NIS were present (3 out of a total of 90 species observed). Their presence was however most striking in the intertidal zone, where we identified 17 obligate intertidal species with about half of them being non-indigenous. This study confirmed the hypothesis that the introduced hard substrata within offshore wind farms play an important role in the establishment and the expansion of the population of both indigenous and non-indigenous species. Foundations of wind turbines strengthen the strategic position of NIS in the southern North Sea. An ongoing study on the population genetics of a fouling species (Patella vulgata) will, in combination with dispersal modelling, elucidate the dispersal pattern and connectivity with neighbouring areas, and the role of the foundations as stepping stones.