Global priority areas for incorporating land–sea connections in marine conservation

Coastal marine ecosystems rank among the most productive ecosystems on earth but are also highly threatened by the exposure to both ocean- and land-based human activities. Spatially explicit information on the distributions of land-based impacts is critical for managers to identify where the effects of land-based activities on ecosystem condition are greatest and, therefore, where they should prioritize mitigation of land-based impacts. Here, we quantify the global cumulative impact of four of the most pervasive land-based impacts on coastal ecosystems—nutrient input, organic and inorganic pollution, and the direct impact of coastal populations (e.g., coastal engineering and trampling)—and identify hotspots of land-based impact using a variety of metrics. These threat hotspots were primarily in Europe and Asia, with the top three adjacent to the Mississippi, Ganges, and Mekong rivers. We found that 95% of coastal and shelf areas (<200 m depth) and 40% of the global coastline experience little to no impact from land-based human activities, suggesting that marine conservation and resource management in these areas can focus on managing current ocean activities and preventing future spread of land-based stressors. These results provide guidance on where coordination between marine and terrestrial management is most critical and where a focus on ocean-based impacts is instead needed.