The sea off Wagu, a port in the city of Shima, Mie Prefecture, used to be rich in abalone, but the seaweed they fed on has disappeared. And changes to the marine environment are hurting the pearl business.

“Lots of abalone used to be taken. But now we can take only ear shells,” said Kazu Yamamoto, 74, who has been diving for 60 years, as she set off for another catch.

Female divers 40 years ago used to compete with one other to catch abalone, pushing their way through the dense forests of seaweed the abalone used to feed on.

But about 10 years ago the seaweed disappeared, leaving only a rocky bottom.

“The natural environment is terrible. Without algae, abalone cannot survive,” Yamamoto said.

The changes in the sea have also dealt a heavy blow to the pearl industry.

In 1992, a red tide caused by a type of algae toxic to marine life appeared in Ago Bay, also in Mie Prefecture, causing losses to the local pearl industry estimated at 3 billion yen.

Kiyohito Nagai, 48, head of Pearl Research Institute in Shima, an affiliate of Tokyo-based K. Mikimoto & Co., the well-known pearl company, observed unusual increases in the opening and closing of the shells a few days before the outbreak of the red tide.

In 2004, Nagai and Kyushu University developed sensors and a data transmission system for the institute. The sensors are attached to the oysters to monitor the opening and closing of the shells.

The sensors can detect subtle movements of the shells, invisible to the human eye, and transmit data 24 hours a day. The monitoring system allows the institute to keep track of the oysters’ depth and location, and the oysters can be moved before a red tide hits.

“Humans cannot control the sea but can respond to a change in the sea if what the shells are saying is heard,” Nagai said.

Nagai hopes to encourage the use of the system, which he has dubbed “Shell Lingual,” around the world.

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