Land meets sea: How upland clearing threatens coral reef health in Ambon Bay, Maluku Province, Indonesia

Land–sea interactions play a crucial role in determining coral reef health. However, comprehensive evaluations connecting terrestrial disturbances, climatic influences, and reef health conditions are limited in small island systems, such as Ambon Island, Indonesia. This study examined the effects of upland clearing (UC) on coral reef deterioration by conducting a multi-temporal analysis that integrated land cover changes with normalized difference vegetation index (NDVI) data, rainfall variations, and field surveys using the line intercept transect (LIT) method and coral reef health index (RHI). The findings revealed a rapid increase in bare soil in upland regions, from 31 ha to 2900 ha, whereas dense vegetation decreased from 12,389 ha to 8655 ha. This alteration in the landscape heightened the erosion risk and sediment transport to coastal waters, with sedimentation rates reaching 0.40 g/cm 2 /day during intense rainfall events, exceeding the coral tolerance threshold (0.015 g/cm 2 /day). The RHI indicated a significant decline in reef health over the study period. These results support a mechanism in which upland clearing driven by growth increases sediment availability, while rainfall variability intensifies transport, contributing to sediment-associated stress on coral reef ecosystems. This interaction underscores nonlinear land–sea connections. This study advances land–sea connectivity by integrating terrestrial and marine data in a ridge-to-reef framework, showing that bare soil expansion was negatively correlated with reef fish biomass (ρ = −0.90) and the reef health index (ρ = −0.80). Ridge-to-reef management considering upstream land-use practices is critical to protect coral reefs during increasing climate variability.