seaweed

Seaweed
Ascophyllum nodosum exposed to the sun in Nova Scotia, Canada.
Scientific classification
Domain: Eukarya
Included groups
Some members of: Rhodophyta Phycophyta Chlorophyta Charophyta

Dead Man's Fingers (Codium fragile) off Massachusetts coast in the United States.

The top of a kelp forest in Otago, New Zealand.

Seaweed is a loose colloquial term encompassing macroscopic, multicellular, benthic marine algae.^[1] 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.).

Taxonomy

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 paraphyletic group. In addition, some tuft-forming bluegreen algae (Cyanobacteria) are sometimes considered as seaweeds—"seaweed" is a colloquial term and lacks a formal definition.

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.
  • haptera: finger-like extensions of holdfast anchoring to benthic substrate

The stipe and blade are collectively known as the frond.

Ecology

The ecology of seaweeds is dominated by two specific environmental requirements. These are the presence of seawater (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 the tops of sea spray, the deepest living are those that are attached to the seabed under several meters 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 seaweeds are the various kelps. In addition to the familiar seashore 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 known examples of this type of seaweed.

A number of species have adapted to the specialised environment of tidal rock pools. In this niche seaweeds are able to withstand rapidly changing temperature and salinity and even occasional drying.^[2]

Uses

Small plots being used to farm seaweed in Indonesia, with each square belonging to a different family.

Seaweed has a variety of purposes, for which it is farmed,^[3] or foraged from the wild.^[4]

Food

See also Edible seaweed.

Packaged nori.

Seaweeds are extensively used as food by coastal people, particularly in East Asia, e.g. Japan, China, Korea, Taiwan, Thailand, and Vietnam, but also in Indonesia, Belize, Peru, the Canadian Maritimes, Scandinavia, Ireland, Wales, Philippines, and Scotland, among other places. Tiwi, Albay residents discovered a new pancit or noodles made from seaweed, which has health benefits. It is rich in calcium and magnesium and the seaweed noodles can be cooked into pancit canton, pancit luglug, spaghetti or carbonara.^[5]

In Asia, Zicai (紫菜) (in China), gim (in Korea) and nori (in Japan) 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 in Wales. Affectionately called "Dulce" in northern Belize, seaweeds are mixed uniquely with milk, nutmeg, cinnamon, and vanilla to be served as a common beverage throughout the country.

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.^[6] The food industry exploits the gelling, water-retention, emulsifying and other physical properties of these hydrocolloids. 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.

Medicine

Seaweed-covered rocks in the United Kingdom.

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]} Seaweed is also a known source of iodine,^[7] an element necessary for thyroid function with deficiencies leading to goitre. It has been asserted that seaweeds may have curative properties for tuberculosis, arthritis, colds and influenza, worm infestations and even tumors.[1]^{[dubious – discuss]} A number of research studies have been conducted to investigate these claims and other effects of seaweed on human health.^{[citation needed]}

Some studies have found that seaweed can promote weight loss^[8][9]. For this reason, seaweed extract is used in some diet pills.^[10] Other seaweed pills work similar to gastric banding, they will expand in the stomach to make the body feel more full. ^[11][12]

Other uses

Other seaweeds may be used as seaweed fertilizer.^{[citation needed]} Seaweed is currently being researched as a potential source of biofuel in the form of bioethanol.^[13][14] Seaweed is also an ingredient in some toothpaste, cosmetics and paints.^[3]

See also

• Algaculture
• Algal fuel
• Kelp
• Ogonori
• Sea lettuce
• Seaweed dermatitis
• Wakame

Seaweed genera

• Caulerpa
• Fucus
• Gracilaria
• Laminaria
• Macrocystis
• Monostroma
• Porphyra

References

External links

• The Seaweed Site, information on all aspects of 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.