Green algae grow in both warm and cold seas. The greatest variety is found in shallow tropical waters. Most of these seaweeds are small. The name seaweed incorrectly implies that these organisms have little value. Actually, many seaweeds are rich in vitamins and minerals and are eaten in various parts of the world.
Seaweeds also have many industrial uses.
Brown algae yield a gummy substance called algin and red algae produce jellylike substances called agar and carrageenin. Manufacturers add these substances to various foods and drugs to give them a smooth texture and help them retain moisture. Manufacturers also use algins in lipsticks, soaps, photographic film, paint, varnish, and buttons. Agar serves as a culture medium, a base on which bacteria are grown in scientific laboratories. See Bacteriology .