Kelp, the common name for brown seaweeds. Kelp is especially plentiful off the coasts of temperate and colder regions, where it clings to submerged rocks by means of root-like holdfasts. Dense forests of giant kelp grow off the Pacific coast, from northern California northward. Kelp provides food and shelter for fish and other seadwellers.

Kelp is rich in iodine, potash, and other salts. Dried giant kelp, for example, which weighs 1/10 as much as wet kelp, consists of one-third minerals. Kelp is used chiefly for fertilizer. Large quantities are used also for food and livestock feed. Many species are used in eastern Asia for foods ranging from soups to desserts and candies.

Algin is a sticky substance obtained from kelp and used in a great variety of products in which its properties of thickening, emulsifying, stabilizing, and water-holding are useful. It is used in making ice cream, jelly, salad dressings, paint, printing inks, cosmetics, and numerous other products. It is also used to size paper and textiles, finish leather, and waterproof concrete.

Kelps are algae. They belong to the phylum Phaeophyta. The Pacific giant kelp is Macrocystis pyrifera. Atlantic kelps are Laminaria saccharina and L. digitata.