Zebra, or kikumeishimodoki coral, found off Tsuruoka in Yamagata Prefecture (The Asahi Shimbun)

Photo/Illutration Kikumeishimodoki is seen attached to a rock on the sea floor at a depth of about 4 meters off Tsuruoka, Yamagata Prefecture, on Nov. 14. (Wataru Sekita)

TSURUOKA, Yamagata Prefecture--A species of coral previously not found this far north in Japanese waters has been found to be thriving, a possible sign of global warming, according to an expert.

The kikumeishimodoki, or zebra coral, lies about 20 meters off the coast of the Kamo district of Tsuruoka in Yamagata Prefecture, which faces the Sea of Japan.

The northern limit of the reef-building coral habitat was previously believed to be just off Sado Island in Niigata Prefecture. The newly found coral lies about 80 kilometers north of Sado.

The reef-building coral has a hard shell and creates coral reef landforms. Its scientific name is oulastrea crispate.

Its existence was first spotted by a staff member of local diving store Urban Sports in April 2023 who posted photos on social media.

Hiroya Yamano, a professor at the University of Tokyo's Graduate School of Science, learned of the development last month and surveyed the seafloor at the site.

He confirmed that the coral was distributed in nine locations.

Yamano, 54, noted that kikumeishimodoki is known for thriving in a murky environment where the water temperature is low.

Until now, it was believed that kikumeishimodoki could survive in low average monthly water temperatures of up to 10 degrees.

But the average monthly temperature of the waters where the coral was recently found drops to about 8 degrees.

Based on the size of the coral bed, Yamano estimated it has been growing for several years.

Yamano said the fact the coral was able to grow at even lower-than-expected water temperatures “could be due to global warming.”

He also said changes in ocean currents could be responsible or simply that kikumeishimodoki is a species that can live at even lower water temperatures than previously considered.

However, he said, “The distribution map of reef-building coral will probably change to the north more than before.”

Yamano said he plans to present his findings in a research paper in December.

Yoshifumi Aihoshi, 63, who heads the diving store, said, “It is so sweet to think that the coral quietly and slowly migrated northward and settled in the cold sea.”

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