A team of international scientists has found that soil erosion, land degradation, and climate change pose a mounting threat to coastal reefs and their ecosystems in the western Indian Ocean.
The study examined sediment and freshwater discharge over recent decades in two catchments in Madagascar’s Antongil Bay and the island nation’s Great Barrier Reef of Tulear, and the climatic processes that drive them.
Deforestation is often linked with degradation of terrestrial ecosystems but until now no study has revealed its impact on adjacent coral reefs.
“Results from the study suggest that changes in land use - primarily the removal of forests - and Madagascar’s increased population density are the key drivers of long-term reef sedimentation trends but that these are slow processes,” said study co-leader Dr Jens Zinke, of UWA’s Oceans Institute.
Dr Zinke said those factors combined with climate changes - including hinterland rainfall, temperature and El Niño-Southern Oscillation - to influence the amount of sediment transported through river run-off, which is subsequently deposited in coastal waters and reflected in elevated geochemical indicators in corals.
“This is the first direct evidence that catchment activity in Madagascar through deforestation and land use practices affects near-shore reef ecosystems,” Dr Zinke said. “Just as importantly, these results reinforce the need to incorporate terrestrial land-use management in the design of coral reef protection networks in the region.”
“When water quality deteriorates, we see deterioration of important habitats, including coral reefs that are home to many species of reef fish, crustaceans and marine mammals.”
The study, Linking coral river runoff proxies with climate variability, hydrology and land-use in Madagascar catchments, is published in the Marine Pollution Bulletin.
