Coral reefs are visible off the coast of Nha Trang, Vietnam, on Oct 24. YANNICK PETERHANS/AP

The gentle waves off the coast of central Vietnam's Nha Trang obscure an open secret: The life-giving coral reefs below are dying. The waters are eerily devoid of fish. The bounty of the ocean is coming to an end.

This is why Binh Van — who has fished in these waters for more than two decades — now charters his boat to Vietnamese tourists wanting to experience the thrill of fishing in the deep waters.

However, there is only squid, which is flourishing in oceans warmed by climate change, to catch.

It was not always like this. There was a time when he would catch 70 kilograms of fish in one night. He cannot make money on squid.

Southeast Asia's coral reefs make up more than one-third of the world's coral reefs. But most of these are now at risk of being destroyed. Only 1 percent of Vietnam's reefs are still healthy, and that is because of their remoteness, according to the World Resources Institute.

The coral reefs of Nha Trang have also had to contend with local pressures as Vietnam's economy boomed and coastal towns grew.

This has affected not only the local fishing industry but also Vietnam's tourism industry, especially among divers from all over the world who flock to the country because of its long coastline.

Tourism and reefs can go hand in hand if they are well-managed, said Emma Camp, a coral expert at the University of Technology Sydney in Australia. There are instances of tourism supporting marine conservation and programs to help reefs recover, she said.

Konstantin Tkachenko, a professor of marine ecology at Russia's Samara University who has been studying Vietnam's reefs for years, said the country could do more to protect them.

It could create more marine parks where protections are actually enforced, obligate the tourism industry to restore vegetation on the coasts to reduce sediment pouring into the ocean, and regulate fisheries.