From land to deep sea: A continuum of cumulative human impacts on marine habitats in Atlantic Canada

Effective management and mitigation of multiple human impacts on marine ecosystems require accurate knowledge of the spatial patterns of human activities and their overlap with vulnerable habitats. Cumulative impact (CI) mapping combines spatial information and the intensity of human activities with the spatial extent of habitats and their vulnerabilities to those stressors into an intuitive relative CI score that can inform marine spatial planning processes and ecosystem-based management. Here, we mapped potential CIs of 45 human activities from five sectors (climate change, land-based, marine-based, coastal, commercial fishing) on 21 habitats in Atlantic Canada's Scotian Shelf bioregion. We applied an uncertainty and sensitivity analysis to assess the robustness of results and identify hot and cold spots of CIs. Nearly the entire Scotian Shelf bioregion experiences the CIs of human activities, and high CIs were frequently associated with multiple stressors. CIs varied widely across habitats: CI scores in habitats >30 m deep were dominated by climate change and commercial fishing, while nearshore habitats were influenced by a much wider range of activities across all five sectors. When standardized by area, coastal habitats had among the highest CI scores, highlighting the intensity of multiple stressors in these habitats despite their relatively small spatial extent and emphasizing the importance of a multisector approach when managing coastal ecosystems. Robust hot spots of CIs (i.e., areas with high CI scores that were insensitive to alternative modeling assumptions and simulated data quality issues) occurred mostly in coastal areas where multiple high-intensity activities overlapped with highly vulnerable biogenic habitats. In contrast, robust cold spots of CI mostly occurred offshore. Overall, our results emphasize the need to consider CIs in management and protection and demonstrates that, in many areas, targeting only one activity will be insufficient to reduce overall human impact. The CI map will be useful to highlight areas in need of protection from multiple human impacts, provide information for ecological indicator development, and establish a baseline of the current state of human use in the bioregion.