Seaweed (written as 若布, 和布, 稚海藻, or 裙蔕菜 in kanji; scientific name: Undaria pinnatifida) is a marine alga of the class Phaeophyceae, order Laminariales and family Alariaceae.
It grows south of Hokkaido on the Sea of Japan side, southwest of Hokkaido to Kyushu along the Pacific coastline, and around and below the low-tide line. The root-shaped part adheres to rocks while the phylloid part extends into the water, and its length reaches two meters. There is a main axis in the center of the phylloid part, and the foliage extends widely to the right and left with the main axis in the center, and then splits broadly in a pinnate manner. In the basal portion of the extended foliage, there is a part that resembles a thickened, shrunken and folded phylloid part. This part, called the mekabu, and where the germ cells are gathered.
Seaweed undergoes the alternation of generations. The commonly known seaweed is sporophyte (diploid generation), and the gametophyte germinated from zoospore, produced in the mekabu, is very small.
Seaweed has been familiar to Japanese through the ages as well as laver, and in fact nearly 100 poems in "Manyoshu" (Collection of Ten Thousand Leaves) contain the word 'nigime' (Japanese marine alga). It was mainly for edible use, such as vinegared food and ingredients in soup dishes, but it was also used for Shinto rituals such as in praying for a good harvest.
In the marine area around the 'Minatomirai district,' the project for ecological education called 'Yume wakame workshop' (dream seaweed workshop) is held, and a total of 300 local elementary students farm seaweed in the port of Yokohama. Seaweed grows while ingesting phosphorus and nitrogen undersea, with the expected benefit of cleaning the seawater.
Among taxi drivers, it's used as the meaning of 'Kaiso' (not in service) (with the same pronunciation for Kaiso (marine alga)) or drunken customer (since her/she sways like seaweed) as jargon. It is sometimes used as jargon for pubic hair (wakame-zake (pouring sake in the inner thighs) (adult)).
It is commoditized after its preservative quality is improved, mainly through salting or drying. When the seaweed is to be used, it should first be rinsed of its salt or reconstituted by soaking in water. Commercial seaweed is green, but live seaweed is brown and then turns green when it's blanched.
It is often used as an ingredient in soup dishes, such as miso soup. Other than that, it's widely used in vinegared food, fried dishes, salads and tempura in some regions. It contains many flavor components and is low in calories, so it's suitable for diet products.
The nutritive components in seaweed are dietary fiber, algin acid and fucoidan, and it's said that they serve to lower blood-cholesterol levels and prevent cardiac infarction and arterial sclerosis.
The custom of serving seaweed as an edible materials existed in Japan and the Korean Peninsula, but people in China did not eat seaweed even though they had the custom of eating marine alga, as in Japan and the Korean Peninsula. However, with the introduction of aquaculture technology from Japan, cultured seaweed for export to Japan appeared on the market in China, so people started to eat it.
However, seaweed is more widely consumed in the Korean Peninsula than in Japan, and the mean annual seaweed consumption per capita in Korea is three times higher than that of Japan. Unlike in Japan, there is an unbridgeable brand gap between natural seaweed and cultured seaweed, and natural seaweed is regarded as very precious and traded at a high price. The rocky shores and marine areas where natural seaweed can be caught are treated as property, like farms and rice fields; such areas are strictly controlled and have been subject to family succession for generations. Additionally, in Korea there is a custom of having seaweed soup on one's birthday.
Hypertension and seaweed
The algin acid contained in marine algae such as seaweed is, when combined with sodium in the diet, partially changed to alginate sodium in the gastrointestinal tract. The alginate sodium cannot be dissolved by digestive enzyme in the human intestine, so it's expelled in the feces. As a result, the amount of sodium absorbed into the body is limited.
Invasive foreign species
Seaweed is one of the selected species of the 100 worst invasive foreign species (IUCN, 2000).
The zoospores from seaweed are mixed in the ballast tank water on commercial ships from Japan and carried to the littoral regions of New Zealand, Australia and European counties. It is released with the water and grows there, so it's becoming a problem as an alien species. There is no dietary habit of eating marine alga in those countries, so it's treated as a nuisance.