Seaweed

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Seaweeds are any of a large number of marine benthic algae. They are macroscopic, multicellular, and macrothallic, in contrast with most other algae. ^[1] Seaweed is often found in the seashore biome.

Contents 1 Taxonomy 2 History 3 Structure 4 Ecology 5 Uses 5.1 Food 5.2 Medicine 5.3 Other uses 6 References 7 External links

Taxonomy

Seaweeds are algae and classified into brown (Phaeophyta), red (Rhodophyta) and green algae (Chlorophyta) based on their pigment composition. Seaweeds are often confused with other photosynthetic organisms. Seaweeds are popularly described as plants, but biologists typically do not consider them true Plantae.^{[citation needed]} They should not be confused either with plants, such as seagrasses (which are vascular plants). In addition, a few species of cyanobacteria bear a resemblance to seaweed algae.^{[citation needed]} Many phycologists prefer the term "marine macroalgae" over "seaweeds".^{[citation needed]}

History

In the early 19th century seaweeds were treated with disdain by some:

There was a time when a student who, having collected some beautiful algae on the shore, showed the contents of his vasculum to the Professor of Botany, expressing a wish to get some information respecting them. The Professor looked at them, and putting on his spectacles, again looked at them, when, pushing them from him, he exclaimed: "Pooh! a parcel of Seaweeds, Sir; a parcel of Seaweeds!" ^[2]

Structure

Seaweeds' appearance somewhat resembles non-arboreal terrestrial plants.

• thallus: the algal body
  • lamina: a flattened structure that is somewhat leaf-like
    • sorus: spore cluster
    • on Fucus, air bladders: float-assist organ (on blade)
    • on kelp, floats: float-assist organ (between lamina and stipe)
  • stipe: a stem-like structure, may be absent
  • holdfast: specialized basal structure providing attachment to a surface, often a rock or another alga.

The stipe and blade are collectively known as fronds.

Ecology

The ecology of seaweeds is dominated by two specific environmental requirements. These are the presence of sea-water (or at least brackish water) and the presence of light sufficient to drive photosynthesis. A very common requirement is also to have a firm point of attachment. As a result, seaweeds are most commonly found in the littoral zone and within that zone more frequently on rocky shores than on sand or shingle. The ecological niches utilised by seaweeds are wide ranging. At the highest level are those that inhabit the zone that is only wetted by sea spray through top the deepest living that are attached to the sea-bed under several metres of water. In some parts of the world, the area colonized by littoral seaweeds can extend for several miles away from the shore. The limiting factor in such cases is the availability of sufficient sun-light to support photosynthesis. The deepest living sea-weeds are the various kelps.

In addition to the familiar sea-shore seaweeds, a number of species have adapted to a fully planktonic niche and are free-floating, often with the assistance of gas filled sacs. Sargassum is one of the better know examples of this type of seaweed.

A number of species have adapted to the specilised environment of tidal rock pools. In this niche seaweeds are able to withstand rapidly changing temperature and salinity and even occasional drying. ^[3]

Uses

Food

Seaweeds are extensively used as food by coastal peoples, particularly in East Asia, e.g. China, Japan, Korea, Taiwan, and Vietnam, but also in Indonesia, Peru, the Canadian Maritimes, Scandinavia, Ireland, Wales, Philippines, and Scotland, among other places. For example, Porphyra is a red alga used in Wales to make laverbread, and in Japan dried, formed into sheets called nori which is widely used in soups, and for wrapping sushi, boiled rice stuffed with bits of raw fish, sea urchin roe, or other ingredients. Chondrus crispus (commonly known as Irish moss or carrageen moss) is another red alga used in producing various food additives, along with Kappaphycus and various gigartinoid seaweeds.

Seaweeds are also harvested or cultivated for the extraction of alginate, agar and carrageenan, gelatinous substances collectively known as hydrocolloids or phycocolloids. Hydrocolloids have attained commercial significance, especially in food production as food additives. ^[4] Agar is used in foods such as confectionery, meats and poultry products, desserts and beverages and moulded foods. Carrageenan is used in preparation of salad dressings and sauces, dietetic foods, and as a preservative in meat and fish products, dairy items and baked goods. Alginates enjoy many of the same uses as carrageenan, but are also used in production of industrial products such as paper coatings, adhesives, dyes, gels, explosives and in processes such as paper sizing, textile printing, hydro-mulching and drilling. The food industry exploits the gelling, water-retention, emulsifying and other physical properties of these hydrocolloids.

Medicine

In the biomedicine and pharmaceutical industries, alginates are used in wound dressings, and production of dental moulds and have a host of other applications. In microbiology research, agar is extensively used as culture medium. Carrageenans, alginates and agaroses (the latter are prepared from agar by purification), together with other lesser-known macroalgal polysaccharides, also have several important biological activities or applications in biomedicine.^{[citation needed]}

A number of research studies have been conducted to investigate claims of seaweed's effects on human health [1]. It has been asserted that seaweeds may have curative properties for tuberculosis, arthritis, colds and influenza, worm infestations and even tumors [2].^{[dubious — see talk page]}

Other uses

Other seaweeds may be used as seaweed fertiliser.

References

Wikipedia information about Seaweed This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Seaweed". It may not have been reviewed by professional editors (see full disclaimer). Help contribute to Americola and edit this article.