The small town of Futtsu, close to the mouth of Tokyo Bay, has been farming nori — the thin sheets of seaweed used in Japanese cuisine to wrap rice balls and make sushi rolls — for centuries. Five years ago, the seaweed began to disappear.
What were once long and luxuriant strands come out of the water thin, straggly and sometimes discoloured. “The conditions are really tough,” said Satoshi Koizumi, head of the local fishing co-operative. “People are giving up.”
In 2015, the co-operative had more than 100 members farming seaweed in the bay; last year there were only 73.
The troubles in Futtsu are part of a nationwide decline in nori production, which last year fell to its lowest level since 1972, pushing up prices and threatening a cherished staple of the Japanese diet. The disruption offers an early hint of how environmental change will affect food production, forcing longstanding industries to adapt.
The problems are two-fold: warming seas and not enough pollution. Climate change has led to a significant rise in water temperatures around Japan in recent decades. “We don’t know the causes for sure but I think the biggest factor here is global warming,” said Mr Koizumi.
At the same time, however, regulations to clean up Japan’s rivers have led to a decline in the run-off of agricultural wastes and fertilisers into the ocean — stripping the waters of nutrients that used to help the seaweed grow.
Nori is particularly sensitive to climate change because it grows in the winter, said Kyosuke Niwa, a biologist at the Tokyo University of Marine Science. The most widely cultivated species originated in the north of Japan and its growing season does not start until the water temperature drops to 23°C.
“Recently, the sea temperature has been rising because of global warming, and there are fewer episodes when the water temperature drops,” he said. “Either the timing of a drop to 23 degrees is later or there isn’t an episode when it drops that low. That makes it hard to cultivate nori.”
Rising temperatures delay the start of the growing season from early October to late October or even November. But even when the crop starts off well, some farmers are suffering at the other end of the season. Their maturing seaweed is often pale and brown, meaning it will be tasteless and lacking in nutrients.
“Episodes of discolouration have been becoming more frequent and if it’s discoloured, we can’t sell it,” said Hiroaki Ebisumoto of the Akashiura fishing co-operative, which grows nori in Japan’s inland sea, the waters between the islands of Honshu and Shikoku.
“It became tougher about 20 years ago. The regulations on phosphorus and nitrogen came in at pretty much the same time,” he said. Clean water standards have reduced blooms of algae, which used to kill fish, but unless there is winter rain to wash nutrients into the ocean, then the nori loses its colour.
Nori farmers are demanding a change in the rules to stabilise the level of phosphorus and nitrogen in the ocean, instead of minimising it. Mr Ebisumoto and his fishermen even volunteer to muck out dams and ponds in the mountains, to wash more nutrients out to sea.
Mr Ebisumoto acknowledged that climate change is playing a role but said fishermen cannot do much about it. “We can’t change the water temperature by raising our voices. The one thing we may be able to change is how the country handles its sewerage,” he said.
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Shifting production to colder, more northerly waters is not a practical option, said Mr Niwa. For one thing, only shallow, sheltered bays are suitable for growing nori in the stormy winter months, and there are few of those north of Tokyo.
It also takes large capital investment to farm nori. The Akashiura co-operative has several multimillion-dollar drying lines, bought by small groups of members banding together, which turn the strands of seaweed into compact sheets. They stand idle for most of the year and then work frantic 24-hour days during the harvest in spring.
The best hope, said Mr Niwa, is selective breeding. “There are different species of seaweed that are well adapted to warmer water. Those species normally don’t grow very long but we’re working to breed them for cultivation,” he said.
For Japan’s food-obsessed public, the alternatives are unappealing. There has been a surge in imports of nori from Korea. That, for now, has helped to fend off the ultimate convenience store indignity: the nori-less rice ball, wrapped only in plastic.