Mobile demersal megafauna abundances at wind farm alpha ventus foundations (German Bight) – two years after construction
Several thousand planned wind turbine foundations will substantially increase the amount of habitat available for hard bottom associated mobile demersal megafauna (MDM) in the German Bight (North Sea). To assess the effect of the large scale habitat creation on MDM-stocks, the foundations of the wind farm alpha ventus were systematically scrutinized by diving. Two years after construction, hard bottom species already reached 100fold higher abundances at the foundations than at autochthonous soft sediments. Large concentrations of pouting (Trisopterus luscus) and the Atlantic horse mackerel (Trachurus trachurus) were detected. The brown crab (Cancer pagurus) reached abundances of 2,300 at single foundations, whereas it was only 29 individuals at the reference areas of comparable sizes. The uppermost parts of the foundations were densely colonised exclusively by young C. pagurus– potentially functioning as a nursery ground. The adjacent sea floor was inhabited by adults. The stocks of predatory hard bottom species could multiply with the establishment of numerous foundations in the North Sea. Calculative, 5,000 tripods provide habitat for up to 275 % more C. pagurus in the German Bight. The settlement of MDM at the foundations of wind farms should be considered when assessing offshore wind power reef effects and environmental impacts.