Brown algae also produce a number of other useful substances. Many seaweeds, but particularly kelps, build up concentrations of iodine to as much as 20,000 times that of the surrounding seawater. Although it is cheaper to obtain iodine from other sources in North America, dried kelp has been used in the treatment of goiter, which results from iodine deficiency, in other parts of the world. Kelps are relatively high in nitrogen and potassium and have been used as fertilizer for many years. Before such use, the seaweeds need to be rinsed to rid them of salt. They also have been used as livestock feed in northern Europe and elsewhere. In the Orient, many marine algae are used for food—in soups, confections, meat dishes, vegetable dishes, and beverages. In Japan, acetic acid is produced through fermentation of seaweeds.
During the Irish famine of 1845-1846, dulse, a red seaweed, became an important substitute for the potato crop that had been destroyed by blight. Dulse also occurs along both the Atlantic and Pacific coasts of North America. In Maine and eastern Canada, where it is a popular snack food, dulse is referred to as "Nova Scotia Popcorn." Another red seaweed, purple laver ("nori"), occurs in both American and Asian waters and is used extensively for food, particularly in the Orient. In Japan, it is cultured on nets or bamboo stakes set out in shallow marine bays (Fig. 18.28). It is harvested when the thin, crinkly, gelatinous blades are several centimeters (2 to 3 inches) in diameter and is used in meat and macaroni dishes; soups; and dry, spiced delicacies.
Irish moss is another important edible red alga. It is also used in bulking laxatives, cosmetics, and pharmaceutical preparations. Blancmange is a dessert made from Irish moss and milk. Carrageenan is a mucilaginous substance extracted from Irish moss and used as a thickening agent in chocolate milk and other dairy products. Funori, obtained from yet another red alga, is used as a laundry starch, as an adhesive in hair dressings, and in some water-based paints.
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