TOKYO >> The vast majority of coral reefs examined off Wakayama Prefecture — the world’s northernmost coral reef zone — are bleached and facing extinction, a recent survey by the Environment Ministry has found.

Coral bleaching, which leads to coral extinction, was observed at all six points the ministry surveyed. At five of the points, 85 percent to 95 percent of coral was found to be dead.

Lower sea temperatures are believed to be behind the bleaching. The falling temperatures are caused by the “great meandering” of the Kuroshio current that occurred for the first time in 12 years last autumn, as well as a cold wave this winter.

The ministry’s Tanabe Ranger Office conducted the survey in February and March in and around Tanabe Bay.

Coral bleaching occurs when coral is stressed by fluctuating sea temperatures and the plankton that live symbiotically with coral leave. The phenomenon was observed in more than 90 percent of the coral surveyed at all six points.

Bleaching likely accelerated over the winter, as the phenomenon was observed on less than 5 percent of the coral at two examination points in December.

The ranger office plans to continue fixed-point observations and monitor developments.

The average sea temperature in Tanabe Bay was 58 degrees in January and 56 degrees in February, about 5.5 degrees colder than the previous year, according to Kyoto University’s Shirahama Oceanographic Observatory.