The use of seaweed as food has been traced back to the fourth century in Japan and the sixth century in China. Today those two countries and the Republic of Korea are the largest consumers of seaweed as food and their requirements provide the basis of an industry that worldwide harvests 6 000 000 tonnes of wet seaweed per annum with a value of around US$ five billion.

Increasing demand over the last fifty years outstripped the ability to supply requirements from natural (wild) stocks. Research into the life cycles of these algae has led to the development of cultivation industries that now produce more than 90 percent of the marketís demand.

China is the largest producer of edible seaweeds, about five million tonnes and the greater part of this is for kombu, produced from hundreds of hectares of Laminaria japonica that is grown on suspended ropes in the ocean. The Republic of Korea grows about 800 000 tonnes of three different species and about 50 percent of this is for wakame, produced from Undaria pinnatifida grown in a similar fashion to Laminaria in China. Japanese production is around 600 000 tonnes and 75 percent of this is for nori, produced from Porphyra species; this is a high value product, about US$ 16 000 per tonne, compared to kombu at US$ 2 800 per tonne and wakame at US$ 6 900.

Alginate, agar and carrageenan are thickening and gelling agents extracted from seaweeds and these three form the main basis of the industrial uses of seaweeds. Seaweeds as a source of these hydrocolloids dates back to 1658 when the gelling properties of agar, extracted with hot water from a red seaweed, were first discovered in Japan. Extracts of Irish Moss, another red seaweed, contain carrageenan and were popular as thickening agents in the nineteenth century but it was not until the 1930s that extracts of brown seaweeds, containing alginate, were produced commercially and sold as thickening and gelling agents. Industrial uses of seaweed extracts expanded rapidly after World War II but were sometimes limited by the availability of raw materials.

Today approximately 1 000 000 tonnes of wet seaweed are harvested and extracted to produce the above three hydrocolloids. 55 000 tonnes of hydrocolloids are produced with a total value of US$ 585 000 000.

Alginate production (US$ 213 million) is by extraction from brown seaweeds, all of which are harvested from the wild; cultivation of brown seaweeds is too expensive to provide raw material for industrial uses.

Agar production (US$ 132 million) is principally from two types of red seaweed, one of which has been cultivated since the 1960-70s, but on a much larger scale since 1990, and this has allowed the expansion of the agar industry.

Carrageenan production (US$ 240 million) was originally dependent on wild seaweeds, especially Irish Moss, a small alga growing in cold waters with a limited resource base. However since the early 1970s the industry has expanded rapidly because of the availability of other carrageenan-containing seaweeds that have been successfully cultivated in warm-water countries with low labour costs. Today most of the seaweed used for carrageenan production comes from cultivation although there is still a small demand for Irish Moss and some other wild species from South America.

In the 1960s, Norway pioneered the production of seaweed meal, made from a dried and powdered brown seaweed, used as an additive to animal feed. Drying is usually by oil-fired furnaces so costs are affected by crude oil prices. Approximately 50 000 tonnes of wet seaweed are harvested annually to yield 10 000 tonnes of seaweed meal, which is sold for US$ five million.

The total value of the industrial products from seaweeds is US$ 590 million.

The total value of all products from the seaweed industry is estimated at US$ 5.6 billion.