Increasing reforestation efforts in coastal regions could substantially reducethe amount of sediment run-off reaching coral reefs and improve theirresilience, a University of Queensland-led study has found.

The study analysed more than 5,500 coastal areas from around the world andfound that nearly 85 per cent of them leached sediment to coral reefs, thesecond most serious threat facing the world’s reefs behind climate change.

Dr Andrés Suárez-Castro from UQ’s Centre for Biodiversity and ConservationScience said it was important to address the issue of sediment runoff ifefforts to reduce the human impact on reefs were to be successful.

“Increased sedimentation can cause aquatic ecosystems to be more sensitive toheat stress, which decreases the resilience of corals to pressures caused byclimate change,” Dr Suárez-Castro said.

“If the link between the land and sea is not recognised and managedseparately, any future efforts to conserve marine habitats and species arelikely to be ineffective.”

Excess sediment runoff from land clearing and agrichemical pollution alongcoastlines can increase sediment transport to coastal waters.

Dr Suárez-Castro said one of the impacts of sediment runoff on coral reefs isa massive reduction in light levels that were key for coral and sea grassgrowth and reproduction.

One solution proposed by Dr Suárez-Castro and his team is for countries tocommit to land and forest restoration in coastal regions, which will helpreduce the amount of sediment runoff.

“Reforestation is hugely important as it maintains the stability of soils thatare vital in limiting erosion risk – it also helps to trap more sediments andprevent them from reaching aquatic systems,” he said.

“Building coral resilience through reducing sediment and pollution is also keyto improving a coral reef’s potential for recovery.

“If land management to reduce sediment runoff does not become a globalpriority, it will become increasingly challenging, if not impossible, toprotect marine ecosystems in the face of climate change.”

The researchers said that while the benefits of land restoration activitieswere clear, it would be a challenge to get countries and governments to committo restoration activities.

“It’s encouraging to see many countries with high coral diversity committinglarge areas to land restoration, however the cost of reforestation, as well aspolitical and social barriers may make it difficult to achieve these ambitiousgoals,” Dr Suárez-Castro said.

“If an average of 1000 hectares of forest was restored per coastal basin,land-based sediments reaching coral reefs could be cut by an average of 8.5per cent among 63,000 square kilometres of reefs.”

Dr Suárez-Castro and his team hope that local authorities can use theirresults to identify areas where reforestation can have the highest benefit oncoral reefs.

“Our approach can be adapted with local data to identify optimal actions forpreserving ‘win-wins’ for multiple ecosystems spanning the land and sea,” DrSuárez-Castro said.

“Several global initiatives such as the Paris Climate Agreement are bringingforest restoration to the forefront of global conservation discussions and ourhope is that our study can facilitate more informed and educated conversationsaround the importance of a more integrated land-sea approach.”

The research has been published in Global Change Biology (DOI:10.1111/gcb.15811).

Captions: (1) Managing coral reef stressors such as poor water quality canimprove reef health and mitigate the effects of global climate change. Imagecredit: Diego Correa Gomez. (2) Sediment runoff from disturbed coastalcatchments is a major threat to marine ecosystems. Understanding wheresediments are produced and where they are delivered enables managers to designmore effective strategies for protecting coral reefs. Image credit: Ove Hoegh-Guldberg.

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