Cumulative impact assessment of human and environmental stressors on subtidal benthic habitats in Bohai Bay using a spatially explicit framework

Bohai Bay, a semi-enclosed and ecologically vital bay in northern China, is increasingly threatened by multiple anthropogenic stressors and nutrient enrichment and pollution, particularly excessive nutrient enrichment (cultural eutrophication) from land-based sources (e.g., aquaculture wastewater, riverine input). This study presents a spatially explicit, pressure–sensitivity-based framework to quantify the cumulative impacts of physical loss, physical damage, and eutrophication on subtidal benthic habitats. By integrating spatial data on human uses, eutrophication indices (E), and habitat-specific sensitivity scores, we identified significant spatial heterogeneity in ecological risks, with benthic communities in high-impact zones showing distinct shifts toward pollution-tolerant taxa and degraded ecological quality (e.g., 75% dominance of pollution-tolerant polychaetes). The infralittoral mud habitat, covering ~60% of the bay, was most affected by environmental pressure (31.96% of its area), primarily driven by eutrophication (E>9 in nearshore areas), followed by physical damage (4.72%) and physical loss (0.17%). Although physical loss had a limited spatial extent, its irreversible nature poses high ecological risks. The circalittoral zone, in contrast, faced minimal physical disturbance but remained vulnerable to eutrophication. Our findings highlight the need for differentiated, spatially explicit marine management strategies, particularly for muddy infralittoral habitats where long-term pollution control (e.g., C DIN < 0.5 mg/L) and habitat restoration should be prioritized. This study provides a scientific foundation for conservation planning and ecological risk mitigation in Bohai Bay and similar nutrient-enriched coastal ecosystems globally.