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| Bombetoka Bay is located on the north-western coast of Madagascar near the city of Mahajanga, where the Betsiboka River flows into the Mozambique Channel. Numerous islands and sandbars have formed in the estuary due to sediment carried by the Betsiboka River as well as the push and pull of tides. The past few decades have witnessed a dramatic increase in the amount of sediment moved by the river and deposited in the estuary and offshore delta lobes, affecting agriculture, fisheries, and transportation in Mahajanga, one of Madagascar's busiest seaports. In this Terra image from 2000, dense vegetation is deep green and water is sapphire and tinged with pink where sediment is particularly thick [Credit: NASA] |
The study authors write that preventing soil erosion and sediment pollution arising from human activities such as deforestation are crucial to reef survival.
The study -- 'Human deforestation outweighs future climate change impacts of sedimentation on coral reefs' -- looked at the effects of future climate change on the hydroclimate of Madagascar's reefs and different deforestation scenarios.
"The findings are very relevant for Australia since intense land use and past deforestation have transformed the river catchments tremendously and are seen as a major threat to coral reefs in the Great Barrier Reef and elsewhere," said Dr Jens Zinke, of UWA's Oceans Institute.
"Managing hinterland land use is the major action needed to buy time for corals growing near rivers."
Dr Zinke said the study looked at four watersheds near coral reef ecosystems in Madagascar, which has different climate zones that mimic most of the world's coral reef climate and a range of different land uses.
"With Madagascar, we wanted to understand how soil erosion and sediment discharges into coral reefs adjacent to river catchments are going to change with these two factors," he said.
"Curbing sediment pollution to coral reefs is one of the major recommendations to buy time for corals to survive ocean warming and bleaching events in the future.
"Our results clearly show that land use management is the most important policy action needed to prevent further damage and preserve the reef ecosystem.
"The major question is: how do we manage the sedimentation through reforestation efforts and proper coastal management?
"Our study clearly shows that we need to have specific reforestation goals/targets for specific regions and make sure that the amount of land allocated for reforestation is enough to reduce sediments significantly.
"Until we precisely understand these relationships, reforestation as a tool for coral reef conservation might not meet its objective of sediment and pollution reduction."
The study was the result of a collaboration between the UWA Oceans Institute, the Australian Institute of Marine Science, Macquarie University, the Institute for Environmental Studies at the VU University Amsterdam (Netherlands) and the Wildlife Conservation Society in the US.
The lead author is Joseph Maina from Macquarie University.
The study was funded through the Marine Science for Management program of the Western Indian Ocean Marine Science Association.
Source: University of Western Australia [June 05, 2013]