Environment

Cold water devastates Japan’s coral reefs

Unusually cold water has devastated some of the world’s most northerly coral reefs, which lie off the coast of western Japan, an environment ministry official said on Wednesday.

The ministry surveyed the reefs in recent months and found widespread bleaching, with between 90% an 100% of each of the six spots surveyed being affected.

In four of the surveyed areas, researchers reported between 85% and 95% of the bleached areas were now dead, said Yuto Takahashi, a ranger at the regional ministry office that conducted the survey.

The devastation is thought to be the result of unusually cold water temperatures in the area this year, partly produced by the meandering of the Kuroshio current.

Very strong cold fronts of the winter contributed to the low water temperature. The meandering of the Kuroshio current is also known to have lowered water temperatures off Wakayama and other areas along the Pacific coast.

The Kuroshio is a warm current in the north-western Pacific Ocean, and its unusual movement away from the area brought up cold water from the depths. Little is known about exactly why the Kuroshio current changes its flows, but scientists have observed the meandering phenomenon six times since 1965, most recently last summer.

Coral bleaching and death is irreversible, but differs from similar events seen in other more southerly reefs.

Whereas coral bleaching in the Great Barrier Reef or Okinawa is caused by unusual warming of water temperatures, cold water also makes the corals very vulnerable.