SINGAPORE – While corals in Singapore live in murky waters, future coastal development and climate change could send more harmful mud to the coral reefs, threatening their long-term survival.

Scientists from Nanyang Technological University (NTU) found that it is mud from land – be it from reclamation or intense rainfall – that could smother corals and later impede their recovery from bleaching events.

The study, which was published in scientific journal Marine Pollution Bulletin in March, looked into six reefs in the Southern Islands. The results shed light on the possible dangers that healthy reefs in the region could face as coastal development ramps up in South-east Asia.

“As coastal development in the region increases, greater amounts of mud are being washed into the sea during rainfall events. Our study finds that even corals which have adapted to living in murky waters will struggle to grow when there is too much sediment,” said Assistant Professor Kyle Morgan from the NTU Asian School of the Environment and the Earth Observatory of Singapore, who led the research.

The research also found that reefs with more mud settled on them exhibited slower recovery after coral bleaching events.

Bleaching is caused by marine heatwaves, where higher sea temperatures stress coral reefs, forcing them to expel the algae that give them their vibrant colours. This causes corals to turn an ashen white.

“For the very muddy reefs, there would be no or very little bounce-back after bleaching. The mud covers the soil surfaces. No new corals can settle... The corals that are bleached, they’re fighting additional stressors from the mud,” said PhD student Marlena Joppien from the same NTU institutes, who is the study’s first author.

Singapore’s corals, which were gripped by a mass bleaching event between May and October 2024, have mostly recovered, with an estimated 5 per cent of them left dead.

Since climate change is expected to lead to more bleaching events, coastal developments near reefs should pause during a marine heatwave, said Prof Morgan.

The waters of Singapore and the surrounding region are known to be murky, causing poor visibility for divers. But corals here have survived in such turbid conditions for several thousand years.

Beyond run-off from rainfall, rivers in Sumatra pump sediment towards Singapore.

And over the years, human activities have further discharged sediment into Singapore’s waters. Lan...