Offshore Wind Power Reef Effects and Reef Fauna Roles

Abstract

The German Bight is dominated by sandy and muddy sediments whilst rocky terrain is rare. The only rocky intertidal is present on the island of Helgoland. However, thousands of ship wrecks are distributed in the German Bight. Such wrecks have only recently become part of investigations into species settlement and the underwater ecosystem. During the next 30 years 5000 wind power foundations are planned to be built in the German Bight as part of the German renewable energy program. Twelve foundations are completed and 197 in progress. The knowledge of the impact such constructions have on the German Bight underwater ecosystem is poor. Prognoses are the only form of estimation. The present study was conducted at the research platform FINO 1 and different ship wrecks which are located in the German Bight. Consistent with FINO1 it is expected that 4,300 kg biofouling will inhabit the wind power foundations. This means that the foundations can be interpreted as hotspots with 35 times more macrozoobenthos biomass than there was prior to the construction. The 5,000 wind power foundations mean an increased biomass of 0.8% for the entire German Bight. In addition, at least half of this biomasses will be produced at the foundations and leave the foundations on a yearly basis. What impact the increased production and high biomass concentration will have on the energy flow in the North Sea remains unknown. Other scenarios are more obvious. Changes include the increased food supply for species, such as crabs, fish and seals as well as the proliferation of the mussel Mytilus edulis. The number of Mytilus edulis inhabiting all wind power foundations will be the same as half of the amount of mussels currently living in German Wadden Sea. The mussel shell litter fall may lead to changing sediments and additional reefs. The mussels will also add to the significant increase of the filtration of sea water with the possible result of clearer waters. The mussels are seen as the main contributor to changes taking place in the German Bight following the introduction of wind power foundations. The increased number of mussels as well as the effects such increasing numbers of Mytilus edulis on the ecosystem will be titled Mytilusation. The introduction of wind power foundations into the German Bight will also mean an increase in rocky shallow waters and intertidal zones in the German Bight. The result will be a proliferation and the development of exotic species, such as the pacific oyster (Crassostrea gigas) which relies on low water depths. Whilst wind power foundations will be colonized by a similar range of species, they will be inhabited by a smaller number than ship wrecks. 2.0 Million brown crabs (Cancer pagurus) which will inhabit the wind power foundations will be added to the already existing number of 2.3 Million living at the 1,300 ship wrecks. Ship wrecks also provide an ideal environment for the endangered European lobster (Homarus gammarus). No lobsters were sighted at the already existing wind power foundations and it is yet to be seen whether the foundations will add to the spread of this species. Behaviour observations of the striped bristletooth surgeonfish (Ctenochaetus striatus) in the Indo-Pacific Coral Reefs revealed that he swept 18% of the sediment. Reef Sweeping as well as the bioerosion entail two major ecological functions of that fish. Ctenochaetus striatus therefore plays a major role in the preservation of coral reefs. Ongoing studies will show how certain species, such as the edible crab, which inhabit the new wind power foundations, influence the faunal community and surrounding areas. As with the striped bristletooth surgeonfish it is recommended to use behavioural investigations as fauna quantifications and community analyses do not provide satisfying results regarding the relationship between the various species and their environment. As part of the present study, techniques and materials were developed to activate or minimise certain functions of the wind power foundations, i.e., to increase or decrease the development of species at such foundations. Individual techniques are described in detail. Whether to activate wind power foundations or to make them passive, whether the reef effects are positive, negative or neither depends on the interpretation of the individual. The qualitative data reveals that the thousands of future wind power foundations will indeed transform the German North Sea ecosystem. The on-going scientific research is necessary to analyse the extent of such changes and to lead the pathway of renewable energy into the right direction.