Under pressure: accounting for multiple human pressures outside and inside marine protected areas in the Skagerrak

The combined effects of multiple pressures pose critical threats to marine ecosystems. As an initial spatial assessment of cumulative pressures in the Skagerrak, we mapped where multiple pressures coincided with sensitive habitats and species, combining recent spatial data sets on 20 pressures and 39 habitats and species. The spatial data were linked with sensitivity weights obtained with a novel partly data-driven method. We found major spatial variation in the risk of cumulative impacts, identifying areas with high human impact, termed hot spots (such as shallow areas in southern and eastern Skagerrak), and areas with low human impact, termed cold spots (such as the deeper parts of the Norwegian Trench). The dominating human pressures were 1) fishing activities, 2) climate change, 3) underwater noise, 4) input of contaminants, 5) light pollution and 6) input of nutrients. Analyses of human pressures within and outside 20 Marine Protected Areas (MPAs) indicated significantly reduced levels in nine MPAs; however, these reductions were limited (less than 15%). One MPA (Skagens Gren og Skagerrak, DK) had significantly higher total human pressure inside the protected area, while ten MPAs did not yield significant results. We therefore recommend that the conservation measures in MPAs in the region be critically addressed and human pressures mitigated, to reduce the potential negative impact of human activities.