Abstract
This report provides an assessment of the sensitivity of the benthic habitats and associated biological communities to offshore wind farms in Danish waters. A Marine Strategy Framework Directive (MSFD) based approach was adopted, with the aim of the MSFD is to achieve good environmental status, which, among other elements, is defined by maintaining “sea-floor integrity”. Sea-floor integrity in this framework is considered as maximum of 2% loss on broad habitat types defined for the purpose of the MSFD and a maximum of 25% adverse effects on these habitats. More targets for additional indicators are expected to be decided upon by EU in the future. The existing broad-scale habitat map was updated with new seabed sediment information. Soft bottom fauna baseline data for MSFD habitat mapping projects and planned offshore wind farms have been combined with data from the Danish monitoring program and linked to the new habitat map.
The sensitivity was estimated as the percentage of each broad habitat within the three subregions in Danish waters, the North Sea/Skagerrak, Kattegat and the Baltic Sea. A low percentage indicates higher sensitivity and a high percentage lower sensitivity. The purpose of the habitat sensitivity provided in this study is to be used in the overall sensitivity mapping of nature, environmental, wind and hydrodynamic conditions in relation to the planning of future wind farms. Additionally, we estimated how much the existing and planned offshore wind farms could impact each broad habitat type, based on the 2030 plan provided by the Energy Agency. The contribution of wind farms to the loss of benthic habitats is minor and linked to the construction of turbine foundations and scour protection surrounding it. It is in all cases far from reaching the threshold level of habitat loss of 2%. The expected effects on benthic communities in the vicinity of the scour protection (the reef effect) are also minor and far from the 25% target of adverse effect. However, the potential cumulative loss by all types of pressures generated by establishing windfarms can be relevant for the MSFD thresholds if new knowledge documents that there are overall negative park effects. In the Baltic Sea, three of the highly sensitive broad habitats are covered between 25 and 100 % by the existing and planned wind farm areas. It is important to keep in mind that other pressures like fishery and extraction of raw material also generate loss and pressure on the seafloor, but an assessment of the cumulative effect of all pressures was beyond the scope of this report.
Community analysis revealed distinct soft-bottom communities between the North Sea, Kattegat and Baltic Sea sub-regions. This agrees with the sensitivity analysis approach to treat each broad habitat as distinct between subregions. Furthermore, multivariate analysis revealed the key characterising species for each habitat type and provided the basis for description of community structure. While some of the impacts of Offshore Wind Farms (OWFs) have been investigated, other effects and their magnitude are currently unknown and require further studies. The assessment of sensitivity and potential impacts based on the best available knowledge, but with several simplifications and assumptions, as the state of knowledge of ecological effects of wind turbines and wind parks are still insufficient. Despite these knowledge gaps, the report illustrates in which areas and for which benthic habitat types the greatest areal challenges may arise with the future expansion of offshore wind farms.