Seaweed

Seaweed-covered rocks in the UK

Biologists, specifically phycologists, consider seaweed to be any of a large number of marine benthic algae that are multicellular, macrothallic, and thus differentiated from most algae that tend to be microscopic in size Smith, G.M. 1944. Marine Algae of the Monterey Peninsula, California. Stanford Univ., 2nd Edition.. Many phycologists prefer the term "marine macroalgae" over "seaweeds". Seaweeds are classified into brown (Phaeophyta), red (Rhodophyta) and green algae (Chlorophyta) based on their pigment composition. There are a few species of cyanobacteria however, that may also be categorized as seaweeds. Seaweeds are to be confused neither with things like seagrasses (which are vascular plants), nor actual weeds in the sense of nuisance blooms or accumulations of unwanted species — certainly, seaweeds are natural components of pristine marine ecosystems.

Contents

1 Structure
2 Uses
3 References
4 External links

Structure

The top of a kelp forest in Otago, New Zealand

Seaweeds may have an appearance that 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 (in between lamina and stipe)
* stipe: a stem-like structure, may be absent
* holdfast: specialized basal structure providing attachment to the bottom

The stipe and blade are collectively known as frond.

Uses

Seaweeds are extensively used as food by coastal peoples, particularly in Japan and Korea, but also in China, Vietnam, 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) is another red alga used in producing various food additives.

Seaweeds are also harvested or cultivated for the extraction of Alginate, Agar and Carrageenan, collectively known as hydrocolloids or phycocolloids. Hydrocolloids have attained commercial significance because they are used in various industries, the most common being food productionRound F.E. 1962 The Biology of the Algae. Edward Arnold Ltd.. Agar is found in foods such as confectionary, 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. Alginate enjoy many of the same uses as carrageenan, but is 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. 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 less-know macroalgal polysaccharides, also have several important biological activities or applications in biomedicine. For instance, it has been demonstrated in laboratory studies that seaweeds may have curative properties for tuberculosis, arthritis, colds and influenza, and worm infestations. [link]

A number of research studies have been conducted to investigate claims of seaweed's effects on human health. [link]

Other seaweeds may be used as seaweed fertiliser.

Knotted wrack, a type of seaweed, on an exposed tidal shore-line

References

External links

[The Seaweed Site], information on all aspects of seaweeds and marine algal biology
[AlgaeBase], a taxonomic database of algae
[SeaweedAfrica], information on seaweed utilisation
[NCBI PubMed Search], allows for search on health research studies, including seaweed

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