STORY: Once vibrant and colorful, these corals in Thailand's Eastern Gulf coast have turned white.

It's a phenomenon known as coral bleaching, and is a sign of deteriorating health.

:: Coral bleaching

Scientists say it's due to the rising sea surface temperatures, which hit record highs this month amid a regional heatwave.

:: This Earth

The coral reefs act as both a food resource and habitat, which is why deteriorating reefs can have a significant impact on marine biodiversity.

Rising temperatures are not only impacting marine life, but also the livelihoods of local communities.

Sommay Singsura is a local fisherman:

:: Sommay Singsura, Fisherman

"The coral reef is my heart and soul. When it isn't bleached, healthy and abundant, and you go out fishing at night, you can easily catch squid and fish near the coral reef - earning a living was nice and easy. Each time when we set out at night and return in the morning, we would earn at least earn 2000 to 3000 baht ($55 - $83) from the catch. If all the corals died, we'd be in trouble."

Singsura's daily catch of seafood has dwindled in recent years - sometimes he comes back empty handed.

Marine biologist Lalita Putchim has just completed a dive in the area.

:: Lalita Putchim, Marine biologist, Thailand's Department of Marine and Coastal Resources

"I couldn't find a single healthy coral. Right now, most of it has turned pale in color. Around 20 to 30% is in the middle of bleaching, around 5% have already died due to the rising temperatures. The bleaching is quite fast-paced. There were reports of the coral bleaching in mid-April, and in 2 to 3 weeks, some of the corals had already died from the bleaching. Almost all of the species have bleached, there's very little that's not affected."

Her underwater reading shows the ocean reached more than 33 degrees Celsius - that's 90 degrees Fahrenheit - on the day of her dive.

She calls this "global boiling."

Lalita says if water temperatures do not cool, more coral will die.

"The corals have survived many hundreds of years so it is hoped that they can endure the climate. However, if the rate of the increase in sea temperature or global warming accelerates significantly, the ecosystem will be even more severely affected."

In April, the U.S. National Oceanic and Atmospheric Administration - NOAA - confirmed that the world's coral reefs were experiencing a fourth global bleaching event due to climate change.

An estimated 90% of live coral on reefs could decrease by 2050, without drastic action to limit global warming to 1.5°C, according to the UN.

Global scientists say the best chance for coral survival is for the world to cut greenhouse gas emissions.