1 Department of Bioscience - Applied Marine Ecology and Modelling, Department of Bioscience, Science and Technology, Aarhus University2 unknown3 Department of Bioscience - Applied Marine Ecology and Modelling, Department of Bioscience, Science and Technology, Aarhus University
Marine ecosystems are influenced by multiple anthropogenic stressors such as fishing, pollution and non-native species. The EU Marine Strategy Framework Directive (MSFD) explicitly requires an assessment of the cumulative effects of such stressors. Methods for mapping cumulative human impacts on marine ecosystems have only recently been developed. The aims of our study were: 1) to develop a map of cumulative human impacts for the Danish, Swedish, Norwegian and German parts of the Greater North Sea; 2) to adjust the existing methods for mapping cumulative human impacts to fit the requirements of the MSFD; and 3) to deepen the understanding of how errors in expert judgment affect the resulting cumulative human impact maps by means of Monte Carlo simulations. We combined existing data sets on the spatial distribution of 33 anthropogenic stressors (linked to the MSFD pressures) and 28 key habitats and marine species (linked to the MSFD environmental characteristics). The relationships between these data were established based on an online expert survey. The resulting cumulative human impact index predicted the highest impacts in the German Bight, along the Danish west coast and in the Kattegat. In contrast, the predicted impacts for much of the Norwegian EEZ and areas far offshore were lower. The Monte Carlo simulations confirmed earlier findings that mapping cumulative impacts is generally "robust", but also showed that specific combinations of errors can seriously change local and regional patterns. We finally present ways to manage such uncertainties, including a new software tool for cumulative impact mapping.