Mr Somdee said the Department of National Parks (DNP) ordered the closure at Koh Ngam Noi, Koh Maprao, Koh Kula and Koh Rad, which are popular dive and snorkelling spots.
The decision followed a survey of coral reefs at marine national parks in the Gulf of Thailand that discovered large areas of coral bleaching.
The four islands are part of Mu Koh Chumphon National Park, which covers 317 square kilometres with a sea area of 165,969 rai.
Bleaching, or the whitening of coral as it loses its natural pigment, is caused by a rise in sea temperature, which has been linked to global climate change.
The four sites will be closed until further notice to prevent further damage from human activities and enable the corals to fully recover, Mr Somdee said.
Rakpong Boonyoi, head of Mu Koh Chumphon marine park, said all fishing and tourism activities will be banned at the islands, where bleaching of staghorn corals is widespread. The closure may affect tourism in the area, but visitors can still visit other popular dive and snorkelling sites in the park, such as Koh Ngam Yai and Hin Pa.
Staghorn corals are especially sensitive to bleaching and are among the corals most vulnerable to anthropogenic stressors, he said.
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