What do Halpern et al. show about oceans?

• A. Oceans affected by a single pressure.
• B. There is uniform impact of humans across regions.
• C. Oceans affected by multiple, cumulative human pressures with spatial variation; global mapping reveals cumulative effects.
• D. Human impacts negligible.

Answer: (C)

Oceans are influenced by many human pressures that accumulate and vary across space, and a global map shows where these cumulative effects appear most strongly. Halpern and colleagues combined multiple stressors—things like fishing pressure, pollution, nutrient runoff, habitat destruction, warming, and acidification—into a single global assessment. By mapping these pressures together, they demonstrate that the impact on marine ecosystems isn’t about one threat in isolation but about how several pressures overlap in different regions. Near coastal areas and certain basins, multiple stressors overlap, producing higher cumulative impacts, while other regions experience fewer overlapping pressures. This global, spatially varying view reveals the cumulative nature of human impacts on the oceans, rather than a uniform or negligible effect.