Coral reefs in the Maldives are under severe stress after suffering mass bleaching this year as sea temperatures soared, a top conservationist body warned on Monday.

Around 60 per cent of Maldives’ coral colonies have been bleached, with the figure reaching 90 per cent in some areas, the International Union for Conservation of Nature (IUCN) said in a statement. It cited data from a survey it carried out with the Maldives Marine Research Centre (MRC) and the US Environmental Protection Agency (EPA).

“Preliminary findings of the extent of the bleaching are alarming, with initial coral mortality already observed,” said Ameer Abdulla, the research team leader and senior advisor to IUCN on marine biodiversity and conservation science. “We are expecting this mortality to increase if bleached corals are unable to recover.”

Bleaching occurs when abnormal conditions, such as warmer sea temperatures, cause corals to expel tiny photosynthetic algae and thus become drained of colour.

Bleached corals risk dying if conditions do not return to normal. Land and ocean surface temperatures rose to record highs in 2015 and at the beginning of this year, according to scientists. The surge has coincided with an exceptionally strong El Nino — a cyclical phenomenon that disrupts weather around the Pacific and is driven by sea temperature.

Warmer seas are a main culprit for the decline of coral reefs — considered among the most diverse and delicate ecosystems on the planet. “Bleaching events are becoming more frequent and more severe due to global climate change,” Abdulla said. Coral reef and bleaching experts from 11 countries and international institutions and universities helped conduct the survey at the height of the 2016 El Nino event, the statement said. The Maldives, a nation of 1,192 tiny coral islands, contain around three per cent of global coral reefs.