Summary
We report the first ever ranking of the relative importance of human stressors along land-sea gradients based on a cumulative impact assessment sensu the methodology developed and published by Halpern et al. in 2008 and 2015. The study is based on a comprehensive Danish data set, originating from a broad range of projects and activities and a subsequent mapping of potential cumulative impacts of multiple human stressors in the Danish marine environment. The study is based on 35 data layers representing human stressors and 47 data layers representing ecosystem components. Our results document that the Danish marine waters, which are impaired, are prone to a wide range of human stressors. When combining individual stressors into groups, the top 5 groups are: (1) nutrients, (2) climate anomalies, (3) non-indigenous species (NIS), 4) contaminants and (5) fisheries. Gradient studies have focused on 16 case studies (where estuarine/fjord systems are linked to coastal and open waters) and we document land-sea gradients for key groups of stressors and how the relative importance of these vary, in some cases substantially (e.g. for the stressors Nutrients, Contaminants, Fishing, Non-indigenous species, Noise and Shipping).