Coral Bleaching Event Devastates Amami-Oshima Island

A recent survey by the Amami Marine Life Research Association revealed a devastating coral bleaching event off the coast of Amami-Oshima island. The survey, conducted in 63 locations around the island, found that 61.2% of the corals had died due to bleaching.

This event is comparable in scale to the mass bleaching of 1998, which also saw a significant portion of the area's corals perish. The association attributes the latest bleaching to unusually high ocean temperatures, which were up to 2 degrees Celsius higher than in 2023 during the summer months.

The survey team, led by Katsuki Oki, conducted visual checks on the seafloor between October and November. They confirmed coral mortality at all surveyed points, with higher rates in bays and reefs like Kasari Bay in Amami and Ongachi Bay in Yamato. The Oshima Straits in Setouchi and outer reefs were less affected.

Table-shaped and branch-shaped Acropora corals were particularly impacted, with many colonies succumbing to the bleaching. The high temperatures, averaging 30.2 degrees Celsius in July and 30.4 degrees Celsius in August, are believed to be the primary cause. Notably, the August temperature was 2.1 degrees Celsius higher than the same period in 2023. The lack of typhoons approaching Japan contributed to the sustained high temperatures.

Amami's corals have faced numerous challenges in recent decades. The 1998 bleaching event and subsequent outbreaks of crown-of-thorns starfish, which prey on corals, caused significant damage. While bleaching events have occurred periodically since then, the corals were showing signs of recovery.

"I was shocked because the corals had been recovering since 1998," said Oki. However, he remains optimistic about the future. "Because corals growing in deeper waters have had little impact and because there are no signs of an outbreak of crown-of-thorns starfish, I expect that the corals will recover quickly.