Bleaching hits over 90% of Japan’s largest coral reef

Courtesy of the Environment Ministry
Bleached coral in the Sekisei Lagoon in Okinawa Prefecture in September

More than 90% of coral in the Sekisei Lagoon, located between Iriomote and Ishigaki islands in Okinawa Prefecture, has bleached, the Environment Ministry has announced.

The low number of typhoons and warm sea temperatures over the year have likely contributed to the bleaching which hit 92.8% of the area, home to the largest coral reef in Japan. More than half of the reef has died. This is the worst since 2016, when 97% of coral breached and more than half died.

Bleaching occurs when overly warm water causes corals to expel algae, turning them white. If bleaching continues for an extended period, the coral cannot get enough nutrients and subsequently dies.

The Yomiuri Shimbun

The ministry has conducted annual surveys of the lagoon since 2005. This year, the ministry examined 31 locations between Sept. 24 and 29 for signs of bleaching. The survey found that 17.7% of the coral colonies had completely bleached and died, up 15.7 percentage points from last year, and 32.3% had completely bleached but not died, an increase of 29.3 percentage points. When partially bleached colonies were included, a total of 92.8% of coral in the lagoon was confirmed to have suffered bleaching. Only 7.2% of coral – a drop of 12.3 percentage points – showed no signs of bleaching.

“Given this widespread bleaching, implementing countermeasures such as cultivating coral will be necessary,” an official of the ministry’s Biodiversity Policy Division said.

The ministry plans to conduct another survey to check the status of the coral around December.