A survey by a French institute shows that up to 70 percent of coral reefs in Japan's southwestern prefecture of Okinawa are dead due to warm temperatures.
The French National Center for Science's research vessel began the survey of how climate change affects the environment and coral reefs in the Pacific Ocean in May of last year. The survey will continue through October of next year.
The ship has traveled about 50,000 kilometers and collected 15,000 pieces of coral.
The survey says up to 90 percent of coral had died from bleaching in Samoa. It adds that coral reefs in Tuvalu and Kiribati have been damaged irreversibly.
A scientist warns that coral bleaching occurs more frequently than before.
Researchers in Australia issued a report last year that says coral bleaching has taken place at more than 90 percent of the Great Barrier Reef off northeastern Australia.