Seaweed
Seaweeds are any of a large number of marine benthic algae. They are macroscopic, multicellular, and macrothallic, in contrast with most other algae [1].
Taxonomy
Template:Stub-section Seaweeds are classified into brown (Phaeophyta), red (Rhodophyta) and green algae (Chlorophyta) based on their pigment composition.
Kelp are large seaweeds (algae), belonging to the brown algae and classified in the order Laminariales. Despite their appearance they are not grouped with the normal aquatic or land plants (kingdom Plantae), but instead are included in either kingdom Protista or Chromista. There are about 30 different genera. Kelp grows in underwater forests (kelp forests) in clear, shallow, oceans, requiring nutrient rich water below about 20 °C, it offers a protection to some sea creatures, or food for others. It is known for its high growth rate - the genus Macrocystis grows up to 30 cm per day, to a total length of over 60 meters.
Through the 19th Century, the word "kelp" was closely associated with seaweeds that could be burned to obtain soda ash (primarily sodium carbonate). The seaweeds used included species from both the orders Laminariales and Fucales. The word "kelp" was also used directly to refer to these processed ashes.[2]
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]
Brown algae
Kingdom: Protista Division: Heterokontophyta Class: Phaeophyceae
The Phaeophyta or the brown algae are a large group of multicellular, mostly marine, algae, including many seaweeds of colder Northern Hemisphere waters. They play an important role in marine environments both as food, and for the habitats they can form. For instance Macrocystis, a member of the Laminariales or kelps, may reach 60 meters in length, and forms prominent underwater forests. Another example is Sargassum, which creates unique habitats in the tropical waters of the Sargasso Sea. This is one of the few areas where a large biomass of brown algae may be found in tropical waters. Many brown algae such as members of the order Fucales (the rockweeds) are commonly found along rocky seashores. Some members of the division are used as food for humans.
Red algae
domain = Eukaryota phylum = Rhodophyta
The red algae (Rhodophyta, IPA: [ˌrəʊdə(ʊ)ˈfʌɪtə], from Greek: ῥόδον (rhodon) = rose + φυτόν (phyton) = plant, thus red plant) are a large group of mostly multicellular, marine algae, including many notable seaweeds. Most of the coralline algae, which secrete calcium carbonate and play a major role in building coral reefs, belong here. Red algae such as dulse and nori are a traditional part of European and Asian cuisine and are used to make other products like agar, carrageenans and other food additives.
Green algae
divisio = Chlorophyta
Classes
subdivision =
Chlorophyceae
Ulvophyceae
Trebouxiophyceae
Prasinophyceae
The Chlorophyta, or green algae, include about 8000 species[3] of mostly aquatic photosynthetic eukaryotic organisms. Like the land plants (Bryophyta and Tracheophyta), green algae contain chlorophylls a and b, and store food as starch in their plastids. They are related to the Charophyta and Embryophyta (land plants), together making up the Viridiplantae.
They contain both unicellular and multicellular species. While most species live in freshwater habitats and a large number in marine habitats, other species are adapted to a wide range of environments. Watermelon snow, or Chlamydomonas nivalis, of the class Chlorophyceae, lives on summer alpine snowfields. Others live attached to rocks or woody parts of trees. Some lichens are symbiotic relationships with fungi and a green alga. Members of the Chlorophyta also form symbiotic relationships with protozoa, sponges and coelenterates.
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!" [3]
Structure
Seaweeds' appearance somewhat resembles non-arboreal terrestrial plants.
- 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.
The stipe and blade are collectively known as fronds.
Ecology
Template:Stub-section
ReferencesISBN links support NWE through referral fees
Lewis, J.R. 1964. The Ecology of Rocky Shores. The English Universities Press Ltd.
Uses
Food
Seaweeds are extensively used as food by coastal peoples, particularly in Japan and Korea, but also in China, Vietnam, Indonesia, Peru, Taiwan, 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 [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[5]. It has been asserted that seaweeds may have curative properties for tuberculosis, arthritis, colds and influenza, worm infestations and even tumors[6].[dubious — see talk page]
Other uses
Other seaweeds may be used as seaweed fertiliser.
References
- ↑ Smith, G.M. 1944. Marine Algae of the Monterey Peninsula, California. Stanford Univ., 2nd Edition.
- ↑ "Kelp," in Oxford English Dictionary (Second Edition), (Oxford University Press, 1989). Definition retrieved December 1, 2006 from online edition.
- ↑ Landsborough, D. 1857. A Popular History of British Seaweeds
- ↑ Round F.E. 1962 The Biology of the Algae. Edward Arnold Ltd.
- ↑ [1]
- ↑ [2]
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 seaweeds. The database is searched 10,000 times a day.
- SeaweedAfrica, information on seaweed utilisation for the African continent.
- NCBI PubMed Search, allows for search on health research studies, including seaweed
- Seaweed Research Links, Many useful seaweed research links
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