The algae are simple photosynthetic plants that live in water. Most species are small to very tiny; many can only be seen with a microscope and often float or swim as plankton in the water column. But some algae--what we often call pond scum or seaweed--are conspicuous plants that can form dense mats of vegetation. The largest of these, the kelp, can be hundreds of feet in length and form impressive underwater forests. Macroscopic algae are frequently washed up on our beaches.
Algae have found their way into our lives as food, hidden ingredients in commercial products, and pests in our waters.
Food. Algae have been collected for more than 4000 years in China and Japan for use as human food. Today Japan is the principal user of edible algae, and the Japanese have developed methods for culturing and harvesting "leafy" algae. Large-scale farming practices are used to grow the red alga Porphyra, which is commonly called nori. Porphyra spores are sprinkled on oyster shells, which are placed into shallow tanks. The spores germinate and form tiny filaments on the shells. These filaments then make their own spores. Strings are dipped into the tank to catch the spores, and then the strings are placed into shallow bays. Within two month the Porphyra plants are full grown on the strings, and they are stripped from the strings and dried in the sun. Resultant sheets of Porphyra are eaten as is, added to soups, or used to wrap rice, e.g., California rolls at your favorite sushi bar.
Special commercial products of algae. Profitable products can be extracted from algae. There are four major algal products, and all four are extracted from the cell walls of the organism.
Killer algae.Certain single-celled organisms called dinoflagellates can produce deadly toxins. Dinoflagellates are the organisms responsible for creating marine "red tides." When dinoflagellates multiply rapidly, they actually can give the ocean a reddish tint.
A red tide may be pretty, but two disastrous results may occur. First, massive fish kills occur when toxins are present in the water. Humans swimming in a red tide can also experience eye and skin irritations. Giant fish kills have been reported in California, the Gulf of Mexico, Peru, Japan, Australia, and Africa. The other effect of red tide is shellfish poisoning. Shellfish, such as clams, scallops, and mussels, are filter feeders; they consume plankton (dinoflagellates are plankton) and filter the cells out of the water. When the shellfish eat toxic dinoflagellates, they can sequester the toxin in a special organ and not be harmed themselves. However, the problem comes when humans eat the poisoned shellfish. Within an hour the poison affects the nervous system, and the victim experiences a numbing of the lips, tongue, and fingertips. Eventually respiratory failure occurs. If kept alive by artificial respiration, the victim can be treated. Unfortunately, the symptoms of shellfish poisoning resemble drunkenness, and are usually not diagnosed and treated until it is too late!
Algal "pollution" is also a serious problem in water purification and preserving good water quality. Most of the noxious freshwater contaminants are the so-called blue-green algae, which are actually photosynthetic bacteria, the cyanobacteria.