Algae Photos

The most extensively cultivated species of algae in the world belong to the genus Porphyra in the red algal division Rhodophyta. Porphyra includes many species of intertidal algae with broad, ruffled blades that are thin and membranous. The blades are collected as a popular Asian food known as "nori." In Japan, nori is typically cultivated in shallow muddy bays along the coast. At low tide during autumn, thousands of bamboo poles are driven into the mud, and miles of coarse-mesh netting are strung on the poles so they are exposed at low tide. Porphyra spores germinate on the netting and grow into harvestable plants in a few months. After harvesting, the nori is chopped into small fragments, spread over porous mats, and dried into thin sheets which are packaged for the market. According to E. Yale Dawson (Marine Botany, 1966), up to 2.5 billion dried sheets are produced in a single year from 133,000 tons of nori. Nori is used extensively in Asian countries as food. In fact, one of the most widespread and popular uses for nori is the dark outer wrapping of sushi.

Like other members of the algae, fungi and plant kingdoms, Porphyra has a separate haploid gametophyte and diploid sporophyte generation in its life cycle. This plant phenomenon known as the alternation of generations is taught in every introductory botany class. The gametophyte of Porphyra is the conspicuous alga harvested in Japan for nori, while the sporophyte is reduced to a minute filamentous form that appears like a small rosy patch inside sea shells. These small "plants" were formerly known under the genus name of Conchocelis. In 1950, Dr. Kathleen Drew worked out this unusual algal life history in her laboratory in Manchester, England. Until that time, no one knew where the spores came from that seeded the elaborate nets used by nori fishermen in Japan. The conchocelis stage of Porphyra is now grown commercially in oyster shells and used in "seeding" the nori plantations in shallow bays. To commemorate Dr. Drew's significant discovery, a monument was erected in her honor on the shores of Tokyo Bay overlooking the nori beds.

The mucilaginous red alga called "Irish moss" (Chondrus crispus) is the source of carrageenan (from the Irish "carrageen", meaning rock moss). Another important commercial source is the red alga Eucheuma from the Philippines. Most Irish moss is harvested from the North Atlantic coasts of the United States and Canada. It is especially abundant along beaches after hurricanes. According to E. Yale Dawson (Marine Botany, 1966), 10 million pounds of Irish moss are processed annually in Rockland, Maine. Carrageenans are hydrophilic (water-loving) polysaccharides closely related to gums. Like gums, they absorb water and are used as thickening agents, emulsifiers and to prevent the formation of ice crystals in frozen deserts. They are also referred to as phycocolloids because they come from algae (phyco) and they form jelly-like, colloidal suspensions in water. Carrageenan is especially valuable because it reverses its state when heated to a liquid and then cooled back to a gel. When added to hot milk and cooled, bonds are formed between the carrageenan and casein protein molecules in the milk, thus creating a thick, creamy texture. For this unique property carrageenans are used in many foods and pharmaceutical products, including chocolate toppings, jellies, frostings, milk puddings (blancmanges), yogurts, eggnog mixes, ice creams, sherbets, whipped cream, creamed soups, surgical jellies, salves, ointments, and toothpastes. It is also used as a sizing agent in the textile and leather industries, and as an emulsifier in oil-based printing inks.