A drop in seawater temperatures has caused corals to whiten off the coast of Tanabe, Wakayama Prefecture. (Video taken by Ryo Kato)

TANABE, Wakayama Prefecture--Abnormal conditions have led to a drop in seawater temperatures near here, causing 30 to 40 percent of corals to whiten and sensitive fish to die.

Since autumn 2017, cold air waves have repeatedly hit the area, while the warm Kuroshio current, which normally runs northeast in a straight line along the Pacific coast, has taken a meandering route that veers south from the Kii Peninsula.

This combination has led to chilly water temperatures that are whitening corals and killing such fish as moray eels.

According to Tomoki Ri, 45, a local diving guide, it is rare for the seawater temperature in the area to fall below 16 degrees.

But on Feb. 9, the water temperature was 14 degrees around Okinoshima island, located about 2.7 kilometers off the coast of Tanabe, Wakayama Prefecture, in the southern part of the peninsula.

In early February, the temperature of the sea area fell below 12 degrees.

In that area, part of “kushihadamidoriishi,” a coral that forms a table-shaped colony, has whitened. Phytoplankton, called zooxanthellae, that live together with the corals have fled due to stress from the low temperature, turning white the corals’ healthy colors of green or brown.

If the phytoplankton do not return to the corals, they will die.

A similar situation has been observed in sea areas off Shirahama, south of Tanabe, although on a smaller scale.

“Corals live in warm seas. They whiten and die in environments with temperatures lower than 14 degrees,” said Keiichi Nomura, 59, director of the aquarium at Kushimoto Marine Park in Kushimoto, Wakayama Prefecture.

“If the seawater temperature continues to be low, it will lead to a serious situation. If the seawater temperature rises, the corals could revive again,” he added.