Seaweed Most people know two general categories of seaweeds: wracks (members of the brown algal order Fucales such as Fucus) and kelps (members of the brown algal order Laminariales such as Laminaria), and many have heard of Carrageen or Irish Moss (usually a red alga, Chondrus crispus) and Dulse or Dillisk (also a red alga, Palmaria palmata). Seaweeds make up the Sargasso Sea, a large ocean gyre in the western Atlantic where drift plants of several species of the genus Sargassum accumulate. Seaweeds are particularly important ecologically: they dominate the rocky intertidal in most oceans, and in temperate and polar regions cover rock surfaces in the shallow subtidal. Although only penetrating to 8-40 m in most oceans, some are found to depths of 250 m in particularly clear waters (Mediterranean, Caribbean, Brazil). The Giant Kelp (Macrocystis) is one of the largest plants in the world, which in western North America forms an important association with the newly rescued Sea Otter.
Yummy Seaweed Seaweeds are found throughout the world’s oceans and seas and none is known to be poisonous. Many are actually nice to eat and even considered a great delicacy in many Asian countries. Some recent, healthy recipes can be found here. Seaweeds are used in many maritime regions for industrial applications and as a fertiliser. The major direct use of these plants as food is in Japan, China and Korea, and in the Indian Ocean where seaweed cultivation has become a major coastal industry. The main food species grown by aquaculture in these countries are Nori or Zicai (Porphyra, a red alga), Kombu, Kunbu or Haidai (Laminaria or Saccharina: brown algae) and Wakame (Undaria, also a brown alga). In Japan alone, the total annual production value of nori amounts to more than US$2 billion, one of the most valuable crops produced by aquaculture in the world. In most western countries, seaweed consumption is relatively restricted and there has not been any great pressure to develop mass cultivation techniques. On this site, seaweed aquaculture, particularly nori, a Japanese red seaweed, is described in detail.
Uses of Seaweed Industrial utilisation of seaweed is mostly centred on the extraction of phycocolloids (marine hydrocolloids), and, to a much lesser extent, certain fine biochemicals. Fermentation and pyrolysis and the use of seaweed as biofuels are not an option on an industrial scale at present, but are possible options for the future, particularly as conventional fossil fuels run out. Seaweeds are being used in cosmetics, and as organic fertilisers. They have the potential to be much more widely used as a source of long- and short-chained biochemicals with medicinal and industrial uses. Marine algae may also be used as energy-collectors and potentially useful substances may be extracted by fermentation and pyrolysis. Seaweed extracts appear in the oddest of places; you almost certainly have eaten some sort of seaweed extract in the last 24 hours as many processed foods such as chocolate milk, yoghurts, health drinks, and even the highest-quality German beers contain seaweed polysaccharides such as agars, carrageenans and alginates! Seaweed baths have been popular in Ireland and Britain since Edwardian times, and seaweed wraps and treatments have become more poular in the last few years. A recent innovation is the apparent incorporation of seaweed into a fibre, although some commentators have cast doubt on the presence of any seaweed in fabrics advertised as such.
seaweed name commonly used for the multicellular marine algae . Simpler forms, consisting of one cell (e.g., the diatom ) or of a few cells, are not generally called seaweeds; these tiny plants help to make up plankton. The more highly developed types of seaweed usually have a basal disk, called a holdfast, and a frond of varying length and shape, which often resembles a plant in having stemlike and leaflike parts.
Types of Seaweed The simplest of the seaweeds are among the cyanobacteria , formerly called the blue-green algae, and green algae (division Chlorophyta ), found nearest the shore in shallow waters and usually growing as threadlike filaments, irregular sheets, or branching fronds. The brown algae (division Phaeophyta ), in which brown pigment masks the green of the chlorophyll, are the most numerous of the seaweeds of temperate and polar regions. They grow at depths of 50 to 75 ft (15-23 m). The red seaweeds (division Rhodophyta ), many of them delicate and fernlike, are found at the greatest depths (up to 879 ft/268 m); their red pigment enables them to absorb the blue and violet light present at those depths.
Reproduction in Seaweeds Seaweeds reproduce in a variety of ways. Lower types reproduce asexually. More advanced kinds produce motile zoospores that swim off, anchor themselves, and grow into new individuals, or they reproduce sexually by forming sex cells (gametes) that, after fusing, follow the same pattern. Sometimes pieces of a seaweed break off and form new plants; in a few species there is a cycle of asexual and sexual reproduction foreshadowing the alternation of generations characteristic of plants.
Common Species and Their Uses
The largest of the green algae, Ulva (sea lettuce), grows to a ribbon or sheet 3 ft (91 cm) long. It provides food for many sea creatures, and its broad surface releases a large amount of oxygen. Fucus, called rockweed or bladderwrack, is a tough, leathery brown alga (though it often looks olive-green) that clings to rocks and has flattened, branched fronds buoyed by air bladders at the tips.
Seaweeds, especially species of the red algae Porphyra (nori) and Chondrus, form an important part of the diet and are farmed for food in China and Japan; other species (often called laver) are eaten in the British Isles and Iceland. Commercial agar (vegetable gelatin) is obtained from species of red algae and is the most valuable seaweed product. Irish moss or carrageen ( Chondrus crispus ), a red alga, is one of the few seaweeds used commercially in the United States. After being bleached in the sun the fronds contain a high proportion of gelatin, which is used for cooking, textile sizing, making cosmetics, and other purposes. In Japan it is made into a shampoo to impart gloss to the hair.
The kelps generally include the many large brown seaweeds and are among the most familiar forms found on North American coasts. Some have fronds up to 200 ft (61 m) long, e.g., the Pacific coast Nereocystis and Macrocystis, found also off the Cape of Good Hope. Common Atlantic species include Laminaria and Agarum (devil’s apron). The kelps are a source of salts of iodine and potassium and, to a lesser extent, other minerals. When the seaweed is burned, the soluble mineral compounds are removed from the ashes (also called kelp) by washing. They are used chiefly as chemical reagents and for dietary deficiencies in people and in livestock. Kelp is also a commercial source of potash, fertilizer, and medicines made from its vitamin and mineral content. Kelps are especially abundant in Japan, and various foods known as kombu are made from them.
The brown algae of the genus Sargassum are called gulfweed. They inhabit warm ocean regions and are commonly found floating in large patches in the Sargasso Sea and in the Gulf Stream. Gulfweed was observed by Columbus. Although it was formerly thought to cover the whole Sargasso Sea, making navigation impossible, it has since been found to occur only in drifts. Numerous berrylike air sacs keep the branching plant afloat. The thick masses of gulfweed provide the environment for a distinctive and specialized group of marine forms, many of which are not found elsewhere.