•Rising temperatures have caused Singapore's underwater gardens to lose their colours earlier this year.

Preliminary assessments by scientists in Singapore have shown that coral bleaching this year is more severe than two other major bleaching events in 1998 and 2010, The Straits Times reported last month.

Corals depend on symbiotic algae, called zooxanthellae, for food. Bleaching occurs when abnormally high sea temperatures cause corals to expel the zooxanthellae living in them, turning them white.

In 2010, the bleaching event started in June and ended in September, said Dr Karenne Tun, director of the coastal and marine division at the National Parks Board's (NParks) National Biodiversity Centre. In 1998, it lasted from June to August, said coral expert Chou Loke Ming, an adjunct research professor at the National University of Singapore's Tropical Marine Science Institute.

This year, water temperatures began exceeding the bleaching threshold of 31.14 deg C from end-April.

The good news, however, is that some corals are starting to recover from what is the longest bleaching incident to hit Singapore so far.

Scientists observed last month that recovery from bleaching is still ongoing. They are hopeful that the remaining bleached corals will recover within one to two months, if the sea surface temperatures continue on their downward trend.

A bleaching event is considered to have ended when sea surface temperatures go back to normal.