Linking land-based pollution pathways to coral reef exposure and ecological response

Land-based pollution is a major driver of coral reef degradation, yet the pathways linking terrestrial activities to marine exposure and ecological response remain difficult to resolve. Using Curaçao as a case study, we developed and tested 78 land-based pressure indices (LBPIs) that represent alternative spatial assumptions about pollutant sources, contributing catchments, and coastal dispersion. These indices were evaluated both as proxies for nutrient enrichment, using water-quality indicators, and as integrative measures of land-based pressure, using benthic condition. The framework spans simple land-use metrics (e.g., built-up area) to process-based nutrient export and hydrodynamic connectivity models, allowing systematic evaluation of land-based pollution pathways and their ecological consequences. We assessed how these indices explain spatial variation in reef pollution signatures (macroalgal δ¹⁵N, a tracer of wastewater-derived nitrogen) and ecological condition. Coral cover was evaluated across two survey years (1982 and 2015), while δ¹⁵N and benthic community composition were assessed for 2015. Results show that LBPIs capture most of the spatial variation in δ¹⁵N (R² = 0.78), demonstrating their effectiveness in representing land-derived nutrient exposure. By contrast, coral cover was more weakly explained by LBPIs alone (R² = 0.23), but model fits improved markedly when environmental variables such as wave exposure and geomorphology were included. Proxy performance also shifted over time: localized dispersion and land-use intensity metrics performed best in 1982, while broader source metrics combined with model-based connectivity were strongest in 2015, suggesting changes in pollution regimes or reef sensitivity. These findings demonstrate how alternative representations of land-based pollution pathways influence predictions of ecological exposure and response. The approach advances process-based modeling of pollutant transport across the land-sea continuum, providing transferable methods for diagnosing and managing land-derived pressures on coral reef ecosystems.