Seventy-seven per cent of the total of 238.4 square kilometers of coral reefs in all of Thailand's waters has been devastated, according to Thon Thamrongnawasawat, deputy dean of the Faculty of Fisheries at Kasetsart University in Bangkok. That figure shows an alarming increase from 30 per cent a decade ago, the prominent marine ecologist said.

Thon named polluted water from beach-front hotels as the biggest cause of coral damage. Other factors include plastic rubbish dumped in the sea and physical damage from boat anchors.

Noticeable coral bleaching and damage in recent years have led to annual closures of some popular islands to allow marine life to recover.

Maya Bay, the picturesque main filming location of "The Beach," a Hollywood blockbuster released in 2000, will also be closed for the first time between June and September this year ahead of the high season, national park officials said.

"Temporary closures can help to a certain extent. But an ideal solution is a permanent closure, which is not possible due to our reliance on tourism revenue," Thon said.

Tourism revenue accounts for more than 20 per cent of Thailand's gross domestic product.

But the booming industry - which is seeing a constant rise in tourist numbers, from 32 million visitors in 2016 to 35 million in 2017, with an estimated 38 million this year - has raised concerns over environmental damage and the sustainability of the industry.

fm/ms (dpa)