Quantifying and mapping the human footprint across Earth's coastal areas

Coastal regions are home to hundreds of millions of people around the planet and the majority of the world's countries include coastal areas. Connecting diverse marine and terrestrial environments, coastal ecosystems support rich biodiversity and provide a wide range of ecosystem services. Systematic mapping and quantification of coastal stressors globally can assist in directing conservation efforts in coastal areas, and help better understand the spatial correspondence between the distribution of marine and land-based stressors across coasts globally. To advance this goal, we quantified and mapped the presence and extent of 10 major terrestrial stressors and 10 marine stressors to develop a cumulative coastal footprint score. We found that the vast majority (97%) of all coastal grid cells globally (1 km pixels of the global coastline) had at least one major stressor present. Human population density was a strong predictor of coastal human footprint scores around the globe, and sandy beaches, which attract the public, had higher coastal footprint scores than non-sandy beaches. Overall, changes in sea surface temperature presented the stressor with greatest presence across all coastal areas, and with the highest average scores. At the country-sea scale, the coasts of Belgium, Monaco and Singapore had the highest overall coastal footprint globally, whereas Antarctica and the Arctic had the lowest coastal footprint scores. Beyond the polar coastal areas, we identified 160 areas of low human pressure (defined as areas >25 km² composed of coastal grid cells in the lowest footprint decile), of which 38 (24%) were encompassed within protected areas, while 63 (39%) were unprotected, and the remainder were partially protected. We highlight the need to create platforms targeting both marine and land-based threats to coastal environments to further address the gaps in coastal area conservation and management.