Coral Habitat Range in Japan Further North than Expected; Colonies Discovered off Yamagata Prefecture

The Yomiuri Shimbun

15:31 JST, November 21, 2024

A team of researchers led by a professor at the University of Tokyo said they confirmed in October coral inhabiting the sea off Tsuruoka, Yamagata Prefecture, far beyond their previously believed northernmost limit in Japan.

The team led by Prof. Hiroya Yamano confirmed the existence of coral in the sea area. Before the finding, the northernmost habitable zone for coral in Japan was believed to be areas off Sado Island in Niigata Prefecture.

The newly found coral is located about 80 kilometers further north in terms of latitude. The discovery indicates coral can inhabit areas where the water temperature had been thought to be too low for them.

Their habitable zone is believed to have expanded northward as water temperature rises due to global warming.

The coral species found is zebra coral (Oulastrea crispata) which is found in a wide area in the Pacific Ocean and the Indian Ocean.

It is a species which creates coral reef. Nine colonies of the coral were discovered, each of which was one to four centimeters in diameter, on rock beds at a depth of about five meters.

Yamano said that this species of coral’s habitable water temperature lower limit is about 10 C.

According to the Japan Meteorological Agency and other sources, the surface water temperature in the central part of the Sea of Japan, including the area off Yamagata Prefecture, had risen 1.9 C in 100 years through 2023.

In the area around the rock beds where the coral were found, the temperature is between 5 C and 8 C at the coldest time of year.

Yamano said, “It indicates that coral can live at lower temperature than previously thought. It affects predictions of coral habitat ranges.”

Yoshifumi Aihoshi, 63, president of Urban Sports, a local diving center in the prefecture, said, “I was surprised to find the coral last year. Because fish species which inhabit warm sea areas are swimming in the sea off Yamagata Prefecture, I can feel a change in the maritime environment.”

In some conventional coral habitats, bleaching has become a problem seemingly caused by record-high water temperatures.

The northernmost limit of coral’s habitable zone on the Pacific Ocean side is believed to be the sea areas off Chiba and Kanagawa prefectures.