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

Area of Science:

• Marine ecology
• Environmental science
• Ecosystem management

Background:

• Land-based pollution significantly drives coral reef degradation.
• Understanding the pathways from terrestrial activities to marine ecosystems is crucial for effective management.
• Previous methods struggled to resolve the complex links between land-based sources and marine ecological responses.

Purpose of the Study:

• To develop and test land-based pressure indices (LBPIs) for assessing pollution pathways affecting coral reefs.
• To evaluate LBPIs as proxies for nutrient enrichment and integrative measures of land-based pressure.
• To systematically analyze how different representations of land-based pollution influence predictions of ecological exposure and response.

Main Methods:

• Developed 78 LBPIs using alternative spatial assumptions for pollutant sources, catchments, and dispersion.
• Evaluated LBPIs against water-quality indicators (nutrient enrichment) and benthic condition (ecological response).
• Assessed LBPIs' ability to explain spatial variation in reef pollution signatures (macroalgal δ¹⁵N) and coral cover over time.

Main Results:

• LBPIs effectively captured spatial variation in macroalgal δ¹⁵N (R² = 0.78), indicating success in representing land-derived nutrient exposure.
• Coral cover was less explained by LBPIs alone (R² = 0.23), but improved with added environmental variables.
• Proxy performance varied over time, with localized metrics stronger in 1982 and broader/model-based metrics in 2015.

Conclusions:

• Alternative LBPIs significantly influence predictions of ecological exposure and response in coral reefs.
• The framework advances process-based modeling of pollutant transport across the land-sea continuum.
• Provides transferable methods for diagnosing and managing land-derived pressures on coral reef ecosystems.