Economic Importance
Because of their production of oxygen and their role in the food web, algae are normally beneficial to aquatic life. However, a bloom (a large and sudden growth in the population of phytoplankton) can cause the death of many fish. In most cases fish die because the decomposition of large amounts of algae depletes the oxygen in the water. Phytoplankton that produce blooms called red tides produce toxins that kill fish directly. These toxins are also poisonous to humans; persons who eat shellfish contaminated with the toxins can become seriously ill. Most blooms occur in bodies of water that have been polluted with sewage or with runoff containing organic substances such as fertilizers.
Large forms of algae, primarily kelp, are a popular food in the Far East. They are dried and compressed into flat cakes. In Wales, a species of red alga is used to make a flat bread called laver bread. Algae are rich in vitamin C, thiamine, and potassium. They are used extensively as food for livestock and as fertilizers.
Agar, or agar-agar, is a gelatinous substance derived from marine algae. Agar has many uses. It is used in laxatives, in materials on which dental impressions are made, in textile sizing, and in additives that thicken such foods as cheese, soup, and bakery products. Agar is also used as a gelling agent in cooking and, in laboratory work, as a medium in which bacteria are grown.
Carrageenin, a jellylike substance derived from a marine alga commonly known as Irish moss, is also important in industry. Its most frequent use is in chocolate milk, where it holds the cocoa particles in suspension. In addition, carrageenin is used in sauces, syrups, toothpastes, and cosmetics. Algin, derived from giant kelp, is also widely used in industry. The shells of dead diatoms make up diatomite, which has many commercial uses, including heat insulation and the filtration of liquids. Certain species of single-celled algae have been tested for possible use in spacecraft as a source of oxygen and food for astronauts.
