MUMM-RBINS: Monitoring of the effects of windmills at sea: report 2012
With the installation of already 91 windmills, the first two offshore wind farms on the Thorntonbank (C-Power project) and the Blighbank (Belwind project) are nearing completion. Since such major constructions are known to affect the marine environment, a mandatory monitoring programme keeps a close eye on possible major impacts. This year’s integrated report, written by the Management Unit of the Mathematical Model of the North Sea (of the Royal Belgian Institute for Natural Sciences), in cooperation with the Marine Biology Research Group (UGent), INBO and ILVO, confirms wind farms to be hotspots for biodiversity and to be affecting seabirds and marine mammals.
|Keywords||marine ecosystems, biodiversity,|
Although most effects might seem ecologically positive at first sight, an appropriate evaluation is needed. Concepts such as ecological pit falls, i.e. species being attracted to suboptimal habitat, are yet to be evaluated.
Wind farms as hotspots of marine biodiversity
Although the fauna growing on different windmill foundation types at different distances from the coast showed remarkable similarities, also clear differences were detected. No less than 50% of all 78 species detected was shared between the concrete foundations at the Thorntonbank and the steel foundations at the Blighbank. Both foundation types were also dominated by the same amphipod Jassa herdmani, attaining densities of up to 90.000 individuals per square meter, and the common starfish Asterias rubens. The concrete foundations at the Thorntonbank however had a significantly higher species richness and exclusively hosted some coastal water bivalves. As maturity of the communities has not been reached yet, we expect the hard substrate fauna to continue evolving at least within the next decade.
Drop off of organic matter from the foundations, together with altered currents and sediment composition are believed to be the reasons for an enriched bottom fauna from the natural sandy sediments surrounding the windmills. We demonstrated this effect to spatially expand on a yearly basis and to currently extend to more than 50 m away from the artificial hard structures at the Thorntonbank. Again, common starfish dominate the enriched area with up to 55.000 individuals per square meter. The bottom community close to the windmills is hence gently moving away from a natural rather poor offshore community to a much richer coastal community. As the minimal distance between the windmills in the C-Power wind farm for example is only about 350 m, a spread to full coverage of this enrichment throughout the wind farm should not be considered impossible.
The increased densities of the common starfish within the wind farm were also detected at greater distance from the windmills, whereas the lesser weaver Echiichthys vipera seems to avoid the wind farm. However, it remains difficult to detect unequivocally consistent long term trends in diversity and densities in this larger bottom fauna, including several species of fish. Wind farms also tend to host larger individuals of several species, some which are commercially important. Next to brown shrimps Crangon crangon, we also detected plaice Pleuronectes platessa and turbot Psetta maxima to be larger within the wind farm. The exclusion of fisheries from and the altered food webs within the wind farms are believed to be at the basis of this finding. The effect on densities, but more particularly on the size of for example fish is expected to become more pronounced as their populations continue developing in the unique environmental conditions of offshore wind farms.
Offshore wind farms, seabirds and marine mammals
Visual seabird counts showed little gull Hydrocoloeus minutus, common tern Sterna hirundo, and sandwich tern Sterna sandvicensis to be attracted to the C-Power wind farm, while the Belwind wind farm showed both attraction (common gull Larus canus and herring gull Larus argentatus) and avoidance (common guillemot Uria aalge and northern gannet Sula bassana). Gulls are probably attracted from a purely physical perspective, with the wind farm functioning as a stepping stone, a resting place or a reference feature in the wide open sea. Major changes in densities as high as 50 % might however become detectable only after 10 years of monitoring. The investigation of seabirds is hence complemented by radar observations, providing detailed information on the flight patterns, as well as on bird behaviour also when weather conditions do not allow for visual observations or during night time. The radar is now installed on the C-Power offshore high voltage station and is fully operational from the upcoming autumn migration period onwards.
With up to about 8500 individuals, the harbour porpoise is the most abundant marine mammal in Belgian waters. Given their sensitivity to excessive underwater noise, piling activities are a major environmental concern. The C-Power pinpiling activities in 2011 indeed produced sound pressure levels as high as 172-189 dB re 1 µPa at a distance of 750 m from the piling location. As 140 dB is the discomfort noise level for porpoises, dedicated aerial surveys were indeed able to demonstrate a disturbance up to about 22 km, as such affecting 2000 to 3800 porpoises. The impact range when piling much larger monopiles, as used within the Belwind wind farm and producing 194 dB at 750 m, is however predicted to be about 1.5 times larger. When the construction activities are halted, the harbour porpoise repopulated the abandoned area, with an impact radius of 13 km one day after cessation of piling.
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