|This article contains too many pictures, charts or diagrams for its overall length.|
Seaweed is a loose colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae. Seaweeds can also be classified by use (as food, medicine, fertilizer, industrial, etc.).
A seaweed may belong to one of several groups of multicellular algae: the red algae, green algae, and brown algae. As these three groups are not thought to have a common multicellular ancestor, the seaweeds are a polyphyletic group. In addition, some tuft-forming bluegreen algae (Cyanobacteria) are sometimes considered to be seaweeds — "seaweed" is a colloquial term and lacks a formal definition.
- thallus: the algal body
- lamina: a flattened structure that is somewhat leaf-like
- stipe: a stem-like structure, may be absent
- holdfast: specialized basal structure providing attachment to a surface, often a rock or another alga.
- haptera: finger-like extensions of holdfast anchoring to benthic substrate
The stipe and blade are collectively known as the frond.
Two specific environmental requirements dominate seaweed ecology. These are the presence of seawater (or at least brackish water) and the presence of light sufficient to drive photosynthesis. Another common requirement is a firm attachment point. As a result, seaweeds most commonly inhabit the littoral zone and within that zone more frequently on rocky shores than on sand or shingle. Seaweeds occupy a wide range of ecological niches. The highest elevation is only wetted by the tops of sea spray, the lowest is several meters deep. In some areas, littoral seaweeds can extend several miles out to sea. The limiting factor in such cases is sunlight availability. The deepest living seaweeds are some species of red algae.
Seaweeds are consumed by coastal people, particularly in East Asia, e.g., Brunei, Japan, China, Korea, Taiwan, Singapore, Thailand, Cambodia, and Vietnam, but also in South Africa, Indonesia, Malaysia, Belize, Peru, Chile, the Canadian Maritimes, Scandinavia, South West England, Ireland, Wales, California, Philippines, and Scotland.
In Asia, Nori (海苔, Japan), Zicai (紫菜, China), and Gim (김, Korea) are sheets of dried Porphyra used in soups or to wrap sushi. Chondrus crispus (commonly known as Irish Moss or carrageenan moss) is another red alga used in producing various food additives, along with Kappaphycus and various gigartinoid seaweeds. Porphyra is a red alga used in Wales to make laver. Laverbread, made from oats and the laver, is a popular dish there. In northern Belize, edible seaweeds are mixed with milk, nutmeg, cinnamon, and vanilla to make a common beverage affectionately called "Dulce" (or "sweet").
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 as food additives. The food industry exploits their gelling, water-retention, emulsifying and other physical properties. Agar is used in foods such as confectionery, meat and poultry products, desserts and beverages and moulded foods. Carrageenan is used in salad dressings and sauces, dietetic foods, and as a preservative in meat and fish products, dairy items and baked goods.
Alginates are commonly used in wound dressings, and production of dental moulds. In microbiology research, agar - a plant-based goo similar to gelatin and made from seaweed - 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.
Seaweed is a source of iodine, necessary for thyroid function and to prevent goitre. However, an excess of iodine is suspected in the heightened cancer risk in Japanese who consume a lot of the plant, and even bigger risks in post-menopausal women.
Seaweeds may have curative properties for tuberculosis, arthritis, colds and influenza, worm infestations and even tumors.[dubious ] In Japan, seaweed eaten as nori is known as a remedy for radiation poisoning.
Other uses 
Other seaweeds may be used as fertilizer, compost for landscaping, or a means of combating beach erosion through burial in beach dunes. Seaweed is currently under consideration as a potential source of bioethanol. Seaweed is an ingredient in toothpaste, cosmetics and paints.
Alginates enjoy many of the same uses as carrageenan, and are used in industrial products such as paper coatings, adhesives, dyes, gels, explosives and in processes such as paper sizing, textile printing, hydro-mulching and drilling.
Health risks 
|Fucus||Brown||In intertidal zones on rocky shores.|
|Gracilaria||Red||Cultivated for food|
|Laminaria||Brown||Also known as kelp, 8–30 m under water, cultivated for food.|
|Macrocystis||Brown||Giant kelp, forming floating canopies.|
|Porphyra||Red||Intertidal zones in temporate climate. Cultivated for food.|
See also 
- Algal fuel
- Aonori, Hijiki, Kombu, Mozuku, Nori, Ogonori, and Wakame - seaweed preparations used in Japan, and occasionally Korea and parts of Oceania
- Laver - seaweed prepared as food in Wales
- List of seaweeds of South Africa
- Sea lettuce
- Seaweed dermatitis
- Silas Seaweed (mystery book series)
- Smith, G.M. 1944. Marine Algae of the Monterey Peninsula, California. Stanford Univ., 2nd Edition.
- Lewis, J.R. 1964. The Ecology of Rocky Shores. The English Universities Press Ltd.
- "Seaweed farmers get better prices if united". Sun.Star. 2008-06-19. Retrieved 2008-07-16.
- "Springtime's foraging treats". Life and Health, Guardian.co.uk. The Guardian. 2007-01-06. Retrieved 2008-07-16.
- "RI aims to become world`s largest seaweed producer". Waspada.co.id. 2011-04-16. Retrieved 2012-06-28.
- "Devon Family Friendly - Tasty Seaweed Recipe - Honest!". BBC. 2005-05-25. Retrieved 2012-06-28.
- Round F.E. 1962 The Biology of the Algae. Edward Arnold Ltd.
- Iodine in Seaweed (dead link 2011-11-20)
- [dead link]
- "Michael GuiryÃs seaweed website". Seaweed.ie. 2010-09-19. Retrieved 2012-06-28.
- Maeda, H; Hosokawa, M; Sashima, T; Funayama, K; Miyashita, K (Jul 2005). "Fucoxanthin from edible seaweed, Undaria pinnatifida, shows antiobesity effect through UCP1 expression in white adipose tissues". Biochemical and Biophysical Research Communications 332 (2): 392–7. doi:10.1016/j.bbrc.2005.05.002. PMID 15896707.
- Rodriguez, Ihosvani (April 11, 2012). "Seaweed invading South Florida beaches in large numbers". South Florida Sun-Sentinel. Retrieved 2012-04-11.
- Ireland Taps New Energy Source : Discovery News : Discovery Channel
- Seaweed Biofuels: Production of Biogas and Bioethanol from Brown Macroalgae
- "Algues vertes: la famille du chauffeur décédé porte plainte contre X" AFP, retrieved 2010-04-22 (in French)
|Wikimedia Commons has media related to: Seaweed|
- Michael Guiry's Seaweed Site, information on all aspects of algae, seaweeds and marine algal biology
- AlgaeBase, a searchable taxonomic, image, and utilization database of freshwater, marine and terrestrial algae, including seaweed.
- SeaweedAfrica, information on seaweed utilisation for the African continent.
- Seaweed. A chemical industry in Brittany, in the past and today.