Probably the most widely used ingredient from the sea in Japan is seaweed. It is an essential part of the Japanese diet, providing plenty of protein, dietary fibre, and a range of beneficial vitamins and minerals. Seaweed is used in various forms of cooking—as a seasoning, in soup stock, as part of a salad, or as a wrapping for other foods.
There are about seven major varieties of seaweed eaten in Japan, but the three most commonly used are nori, kombu, and wakame.
Nori (海苔)
Nori is one of the most widely consumed seaweeds in Japan. It is typically processed into thin, paper-like sheets and is commonly used to wrap sushi or shredded as a garnish for soups and broths.
Nori is made from red algae, which is first dried and shredded before being made into a fine paste. This paste is then spread out into sheets and left to dry in a process similar to traditional paper-making.
Much of the red algae used for nori is cultivated on nets suspended on the sea surface. Farmers harvest the plants from boats about six weeks after planting. An estimated 600 square kilometres of Japanese coastal waters are used for nori production, yielding around 350,000 tons annually.
While nori sheets are generally inexpensive, high-quality nori, which is more delicate and flavourful, comes from the first harvest of the season—especially from the waters off Kyushu. Premium nori can fetch up to 100 yen per 20-centimetre square sheet.
Kombu (昆布)
Kombu is a thick, kelp-like seaweed with a strong, salty flavour. Most kombu is harvested from the waters around Hokkaido, but it is also popular in other parts of Asia.
Kombu is the key ingredient in dashi (出汁), Japan’s fundamental soup stock. This stock is made by combining kombu with katsuobushi (fermented bonito fish shavings) and is used in many Japanese recipes. Kombu is typically sold dried, known as dashi kombu, though it is sometimes pickled in vinegar.
Rich in glutamic acid, kombu plays a role in the production of monosodium glutamate (MSG), a common flavour enhancer in Asian cuisine.
Additionally, research is underway to explore kombu as a biofuel, with the potential to support the marine industry in the future.
Wakame (わかめ)
Wakame is a soft, lettuce-like seaweed commonly used in salads and soups, including miso soup. It has a mildly sweet flavour and a slippery texture.
Wakame grows rapidly and is considered an invasive species in some areas outside Japan. It is usually sold dried and needs to be rehydrated in warm water before use. A fresh variety is also available but is less common.
Studies suggest that wakame contains fucoxanthin, a compound believed to help burn fatty tissue. It has also been used in traditional medicine for improving blood circulation, strengthening hair and intestines, and supporting reproductive health. In Korea, many women consume wakame soup after pregnancy to aid postpartum recovery.
