Researchers from the Amami Marine Life Research Association have reported that warmer ocean temperatures are responsible for a significant coral bleaching event off Amami-Oshima island. The survey, which spanned 63 different locations surrounding the island, found that the event—a recurrence on par with the devastating 1998 mass bleaching—resulted in the death of 61.2 percent of the corals. The study revealed that the average ocean temperature during this summer was notably higher, with August temperatures recorded at 30.4 degrees Celsius, which was 2.1 degrees higher than the same period in 2023.
Field surveys were carried out by association members who snorkeled through the area between October and November, documenting coral mortality across various seabed regions. They found that bleaching was consistent at all surveyed points, with particularly high mortality rates in areas such as Kasari Bay in Amami and Ongachi Bay in Yamato, while regions like the Oshima Straits in Setouchi and the outer reefs remained relatively unscathed. The results indicate that high ocean temperatures, aided by fewer typhoons, likely intensified the bleaching effect.
The report also highlighted that many colonies, particularly table-shaped and branch-shaped Acropora corals, suffered extensive damage. Local experts note that while the area experienced a catastrophic bleaching event in 1998 and additional stresses such as an outbreak of crown-of-thorns starfish that further impacted coral health, the current signs are promising, as corals growing in deeper waters and the absence of recent starfish outbreaks suggest potential for a quicker recovery.