Seaweed prices surge in Japan due to poor harvests amid rising sea temperatures

TOKYO – Poor seaweed harvests due to rising sea temperatures and damage from fish have led to a drastic fall in nori – or seaweed – production. Sales prices have also soared, leaving industry officials at their wits’ end.

“Purchasing costs have doubled in the last four or five years,” said an official in charge at Yamamotoyama, a Tokyo-based company that sells domestic nori meant as gifts. “Such price increases have never been seen before.”

The company raised its prices for roasted nori and nori-based processed products by about 20 per cent in March.

“We can’t lower the quality of our products, so there is nothing we can do about it,” he said.

Long-established Tokyo-based nori manufacturer Shirako also raised the prices of its nori products by 20 per cent to 36 per cent in June 2025.

Another major nori seller reportedly changed its labels, which previously read, “Grown in Ariake, Saga prefecture”, to “Domestically produced”, as the company has had to use nori from various areas in order to secure a sufficient amount.

The poor harvests have been primarily the result of rising sea temperatures, according to the Fisheries Agency and other such entities.

Nori cultivation generally begins around October, when the sea temperature falls. However, in recent years, seaweed farmers have been starting around one month later, thus shortening the growing period.

The rising sea temperatures have also led to black sea bream and other fish becoming more active, resulting in them eating the seaweed.

Seeking government support

According to the National Federation of Fisheries Cooperative Associations’ nori business promotion council, the domestic production of nori for fiscal 2024 – between November 2024 and October 2025 – was 5.94 billion sheets, about half the fiscal 2001 figure of 10.68 billion sheets.

One sheet is 21cm long and 19cm wide.

The average business-to-business wholesale price reached a record high of 24.1 yen (20 Singapore cents) per sheet in fiscal 2024, more than double the fiscal 2020 figure.

“Prices are unlikely to fall in the days ahead,” said Mr Hiroshi Shiraha, president of Koasa, a trading company based in Nagoya that specialises in nori.

He added that it has become difficult even for industry officials to predict what will happen to nori production.

“The future is full of uncertainty,” Mr Shiraha added. “We want government support, such as help in securing new production sites.”

The Fisheries Agency is working on developing different varieties of nori that are more resistant to high water temperatures, but it is expected to take time before they can become commercially available.

“Since it is due to environmental changes, it is difficult to drastically improve the harvest,” said Professor Masahiko Ariji of Kindai University, an expert on aquaculture.

“But currently available measures should be implemented, such as setting up barriers to prevent damage from fish.”

Onigiri prices surge

The surge in nori prices is causing the price of onigiri rice balls sold at convenience stores to increase.

Seven-Eleven Japan has successively raised the prices of 13 types of onigiri by 11 yen to 43 yen since Feb 10. Soaring costs for rice, distribution and packaging have led to the price increases.

The company also raised the prices of onigiri in April 2025, citing the surge in nori prices as the primary reason.

FamilyMart and Lawson have also announced successive price hikes for onigiri since the spring of 2025.

To keep customers purchasing onigiri, Seven-Eleven has started selling soba-meshi omusubi, which are onigiri made with rice and noodles, while FamilyMart and Lawson have increased their onigiri varieties that do not use nori.

Omusubi Gonbei, a chain store that specialises in selling onigiri, also raised the prices of its Kishu Nankoume – onigiri with umeboshi pickled plum– and its Japanese-style tuna from 160 yen to 200 yen in 2024 and 2025.

Omusubi Gonbei uses only domestic nori for its onigiri due to its colour, flavour and crispy texture.

“Costs for ingredients have been gradually rising over the past few years,” said an official of Iwai, a Tokyo-based company that operates the chain.

“We worry about consumers drifting away from onigiri.” THE JAPAN NEWS/ASIA NEWS NETWORK