There is a shortage of seaweed in Japan this year, including the red seaweed Gelidium amansii, (called “tengusa” in Japanese). It is rinsed, dried and boiled to extract a gelling substance that is usually translated as “agar” (or “agar agar”). In Japan, this is called “kanten.” Kanten made from tengusa has a firm texture, not wobbly or very soft like gelatin or typical agar.
What the Japanese would consider “agar” is made from the red seaweed commonly called “ogonori” (Gracilaria verrucosa). Some less expensive kanten includes a mixture of the two. Extraction of Gelidium species gives a higher quality agar than Gracilaria (as measured by the gel strength: the strength of a jelly formed by a 1.5 percent solution). Kanten is used in traditional Japanese sweets like “yokan,” a firm red bean jelly, and “anmitsu,” cubes of translucent jelly.
Demand for seaweed-based gelling agents to replace animal-derived gelatin is rising worldwide, as vegetarian diets gain popularity, but supply of tengusa is shrinking. Tengusa harvesting takes place from May through early summer. Last year, the harvest was low and prices rose from a normal range of around JPY 2,750 to JPY 3,750 (USD 25.41 to 34.64, EUR 22.60 to 30.82) per kilogram. The rise was due to sharply lower harvests around the Izu Peninsula in Shizuoka Prefecture, considered the source of the best quality seaweed. The amount was less than 100 metric tons (MT), down sharply from 1,000 MT the previous year. This year, divers have assessed the amount of seaweed in the area as low, indicating that high prices will continue.
A possible cause of the poor seaweed growth is that the nutrient supply was insufficient due to the influence of the Kuroshio large meander. In this phenomenon, the powerful Kuroshio Current that flows along Japan's southern coast deviates from its usual course. This meander started in September of 2017, for the first time in 12 years, and is continuing this year.
The nori seaweed commonly seen as wrappers for rice balls and rolled sushi, is also in short supply. The sheets are usually made from Pyropia yezoensis or P. tenerathe. Nori seaweed, farmed mainly in Hyogo and Saga prefectures, has hit its highest price since 1980, as warm water temperatures and light rains created poor growing conditions. The warm winter also encouraged the feeding of fish on the seaweed. Sales in the period from November to May 15 fell 20 percent from the previous year, to 6.3 billion sheets (sized 21 by 19 centimeters) and prices were 10 percent higher.
“Mozuku” seaweed (a salad or soup ingredient) from Okinawa, kelp (for “konbu” used for hotpot flavoring) from Hokkaido, and “wakame” (used in miso soup or on salads) from the Sanriku area are all in poor shape, due to the unfavorably warm winter.
