Algae

The most important economic products obtained from algae are associated with brown and red seaweeds, which can be utilized as food for people, and as resources for the manufacturing of industrial products. These seaweeds are mostly harvested from the wild, although increasing attention is being paid to the cultivation of large algae.

Some species of algae can be directly eaten by humans, and in eastern Asia they can be especially popular, with various species used as foods. An especially common food is the red alga known as nori in Japan and as laver in western Europe (Porphyra spp.), which has long been eaten by coastal peoples of China and Japan. This alga is often used as a wrapper for other foods, such as rice or plums, or it may be cooked into a clear soup. Nori has been cultivated for centuries in eastern Asia. Another alga known as dulse or sea kale (Rhodymenia palmata) is consumed dried or cooked into various stews or soups. Other commonly eaten seaweeds include the sea lettuce (Ulva lactuca), and murlins or edible kelp (Alaria esculenta).

Potentially, seaweeds are quite nutritious foods, because about 50% of their weight occurs as carbohydrates, with smaller concentrations of proteins and fats, and diverse micronutrients, including iodine. In practice, however, seaweeds are not very nutritious foods for humans, because we do not have the enzymes necessary to metabolize the most abundant of the complex, algal carbohydrates.

In some places, coastal livestock such as sheep and cattle, and wild ungulates such as deer, will graze algal biomass from the intertidal zone at low tide. These animals can take better advantage of the algal carbohydrates than can humans, largely because of the digestive abilities of the symbiotic microorganisms in their rumens and guts. Sometimes, algal biomass is harvested by humans and added to the fodder of livestock as a source of micronutrients.

The major economic importance of brown seaweeds, however, is as a natural resource for the manufacturing of a class of industrial chemicals known as alginates. These chemicals are extracted from algal biomass, and are used as thickening agents and as stabilizers for emulsions in the industrial preparation of foods and pharmaceuticals, and for other purposes.

Agar is another seaweed product, prepared from the mucilaginous components of the cell walls of certain red algae. Agar is used in the manufacturing of pharmaceuticals and cosmetics, as a culture medium for laboratory microorganisms, and for other purposes, including the preparation of jellied desserts and soups. Carrageenin is another, agar-like compound obtained from red algae that is widely used to stabilize emulsions in paints, pharmaceuticals, ice cream, and other products. Irish moss (Chondrus crispus) is a purplish alga that is a major source of carrageenin.

Researchers are investigating methods for the economic cultivation of red and brown seaweeds for the production of alginates, agar, and carrageenin. In California, use has been made of rafts anchored to float about 13 yd (12 m) below the surface, in shallow, less than 328-ft (100-m) deep water, to grow the highly productive, giant kelp Macrocystis as an industrial feedstock. Seaweeds are also cultivated on floating devices in coastal China, and research is investigating whether growth rates in dense plantings can be economically increased by enriching the seawater with nitrogen-containing fertilizers.

In some places, large quantities of the biomass of brown and red algae wash ashore, especially after severe storms that detach these algae from their substrates. This material, known as wrack, is an excellent substrate for composting into an organic-rich material that can greatly improve soil qualities in terms of aeration and water- and nutrient-holding capacity.

Over extremely long periods of time, the frustules of diatoms can accumulate in large quantities. This material is known as diatomaceous earth, and its small reserves are mined for use as a fine polishing substrate, as a fine filtering material, and for other industrial purposes.