Difference between revisions of "Seaweed" - New World Encyclopedia

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[[Image:Laurencia.jpg|240px|thumb|right|A seaweed (''Laurencia'') up close. The "branches" are multicellular and only about 1 millimeter thick. Much smaller algae are seen attached to the structure extending upwards in the lower right quarter.]]
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{{Copyedited}}{{Paid}}{{Approved}}{{Images OK}}{{Submitted}}
  
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'''Seaweeds''' are any of a large number of macroscopic, multicellular, [[ocean|marine]] [[algae]]. They are generally benthic, being anchored to the bottom of the ocean or to solid, structures.  
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[[Image:Laurencia.jpg|250px|thumb|right|A seaweed (''Laurencia'') up close. The "branches" are multicellular and only about one millimeter thick. Much smaller algae are seen attached to the structure extending upwards in the lower right quarter.]]
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'''Seaweeds''' are macroscopic, multicellular, [[ocean|marine]] [[algae]]. They are generally benthic, being anchored to the bottom of the ocean or to solid structures.  
  
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'''Algae''' (singular ''alga''), a name derived from the Latin word for seaweed, are a large and diverse group of photosynthetic, eukaryotic, plant-like organisms that use chlorophyll in capturing light energy, but lack characteristic plant structures such as [[leaf|leaves]], [[root]]s, [[flower]]s, vascular tissue, and seeds. Although they have historically been regarded as simple [[plant]]s, they are generally classified in the kingdom [[protist|Protista]], rather than [[Plant|Plantae]].  
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'''[[Algae]]''' (singular ''alga''), a name derived from the [[Latin]] word for seaweed, are a large and diverse group of [[photosynthesis|photosynthetic]], [[eukaryote|eukaryotic]], plant-like organisms that use [[chlorophyll]] in capturing light energy, but lack characteristic plant structures such as [[leaf|leaves]], [[root]]s, [[flower]]s, vascular tissue, and seeds. Although they have historically been regarded as simple [[plant]]s, they are generally classified in the kingdom [[protist|Protista]], rather than [[Plant|Plantae]].  
  
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Algae range from single-celled organisms to multicellular organisms, some with fairly complex differentiated form. If they are multicellular and are marine, they are generally called seaweeds. Single celled or few celled organisms are not usually called seaweeds. Seaweeds themselves have many forms, including those that appear as if terrestrial plants with leaves and stems, looking like moss, mushrooms, leaf lettuce, or even a palm tree. The multicellular giant kelp reaches 60 meters in length.
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Although algae range from single-[[Cell (biology)|celled]] organisms to multicellular organisms, if they are both multicellular and marine, and are easily seen by the naked eye, they are generally called seaweeds. Single-celled or few-celled organisms are not usually called seaweeds. Seaweeds themselves have many forms, including those that appear as if they are terrestrial [[plant]]s with leaves and stems, looking like moss, [[mushroom]]s, leaf [[lettuce]], or even a [[palm tree]]. Some are quite large: the multicellular giant kelp reaches 60 meters in length.
  
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Rather than a specific [[taxonomy|taxa]], seaweed can be brown algae, red algae, or green algae. Most of the seaweeds of the warm oceans are red algae. They absorb the deep penetrating blue light, allowing them to exist deeper than other algae. The brown algae include the major seaweeds found on the shores in the temperate zones and the large, offshore beds of kelps. There are few green algae that are seaweeds, but one is the sea lettuce.
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Various seaweeds serve as a habitat and food for other sea creatures. For humans, seaweed also can be used as [[food]] and as fertilizer. Red algae are a source of agar, a gelatinous [[carbohydrate#Polysaccharides|polysaccharide]] that is used as a culture medium for microbiological work, as well as vegetarian gelatin substitute, a thickener for [[soup]]s, in jellies, [[ice cream]], and so forth.
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{{toc}}
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Seaweed can be used as food, as fertilizer, and to produce agar (from the red alga GElidium).  
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Rather than a specific [[taxonomy|taxa]], seaweed can be one of several types of algae: brown algae, red algae, or green algae. Most of the seaweeds of the warm oceans are red algae. They absorb the deep penetrating blue light, allowing them to exist deeper than other algae. The brown algae include the major seaweeds found on the shores in the temperate zones and the large, offshore beds of kelps. There are few green algae that are seaweeds, but one is the sea lettuce.
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[[Image:codiumfragile.jpg|thumb|Dead Man's Fingers (''Codium fragile'') off [[Massachusetts]] coast]]
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== Types of seaweed ==
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Seaweeds are classified into brown algae (Phaeophyta), red algae (Rhodophyta), and green algae (Chlorophyta). Note that in reality the term algae is mainly used for convenience, rather than taxonomic purposes, as there appears little relationship between the various phyla.
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== Taxonomy ==
 
  
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In reality, the term algae is mainly used for convenience, rather than taxonomic purposes, as there appears little relationship between the various phyla. The designation algae includes such as diatoms (golden algae), green algae, euglenoids (flagellates), brown algae, and red algae, and range from single-celled organisms to giant seaweeds.
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Seaweeds are often confused with other photosynthetic organisms. Seaweeds are popularly described as plants, but biologists typically do not consider them true [[plant|Plantae]]. They also should not be confused with seagrasses, which are [[vascular plant]]s. In addition, a few species of [[cyanobacteria]] bear a resemblance to seaweed algae.
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Seaweeds are classified into [[brown alga|brown]] ([[Phaeophyta]]), [[red alga|red]] ([[Rhodophyta]]) and [[green alga|green]] [[algae]] ([[Chlorophyta]]) based on their pigment composition.
 
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'''Kelp''' are large [[seaweed]]s ([[algae]]), belonging to the [[brown alga]]e and classified in the order [[Laminariales]]. Despite their appearance they are not grouped with the normal aquatic or land plants ([[kingdom (biology)|kingdom]] [[Plantae]]), but instead are included in either kingdom [[Protista]] or [[Chromista]]. There are about 30 different [[genus|genera]]. Kelp grows in underwater [[forest]]s ([[kelp forest]]s) 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 [[1 E1 m|60 meters]].
 
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Kelp is a common seaweed, and is the largest seaweed.
 
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Through the 19<sup>th</sup> 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.<ref>
 
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"Kelp," in ''Oxford English Dictionary (Second Edition),'' (Oxford University Press, 1989). Definition retrieved December 1, 2006 from [http://www.oed.com online edition].</ref>
 
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Seaweeds are often confused with other photosynthetic organisms. Seaweeds are popularly described as plants, but biologists typically do not consider them true [[Plantae]].{{cn}} They should not be confused either with plants, such as [[seagrass|seagrasses]] (which are [[vascular plant]]s). In addition, a few species of [[cyanobacteria]] bear a resemblance to seaweed algae.{{cn}}
 
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Many phycologists prefer the term "[[Marine (ocean)|marine]] macroalgae" over "seaweeds". {{cn}}
 
  
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Some biologists prefer the term "marine macroalgae" over "seaweeds."
  
 
===Brown algae===
 
===Brown algae===
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Kingdom: Protista
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[[Image:Kelp_forest_Otago_1s.JPG|right|250px|thumb|The top of a kelp forest in Otago, [[New Zealand]]]]
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Division: Heterokontophyta
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The Phaeophyta, or '''brown algae''' (Class Phaeophyceae, Division Heterokontophyta or Phaeophyta, Kingdom Protista or Plantae or Chromalveolata), are a large group of multicellular, mostly marine algae, and include many seaweeds of colder Northern Hemisphere waters.
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Class: Phaeophyceae
 
  
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The Phaeophyta or the '''brown algae''' are a large group of multicellular, mostly marine, [[algae]], including many [[seaweed|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 [[kelp forest|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 [[Tropics|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.
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One example of brown algae seaweed 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.  
  
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sargassum is another brown algae. Gas in the fronds can hlep the fronds to be bouyant and at the survface.  
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'''Kelp''' are large seaweeds belonging to the brown algae and are classified in the order Laminariales. There are about 30 different genera. Kelp grows in underwater [[forest]]s (kelp forests) in clear, shallow [[ocean]]s. They require nutrient rich water below about 20 °C. Kelp is known for its high growth rate and is the largest seaweed. ''Macrocystis'', a member of the Laminariales, may reach 60 meters in length and grows up to 30 centimeters per day.
  
 
===Red algae===
 
===Red algae===
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domain = [[Eukaryota]]
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The '''red algae''' (Phylum ''Rhodophyta'', from Greek ''rhodon'' = rose + ''phyton'' = plant, thus red plant) are a large group of mostly multicellular, [[ocean|marine]] [[algae]], including many notable seaweeds. Red algae are a traditional part of [[Europe]]an and [[Asia]]n cuisine and are used to make other products like agar, carrageenans, and other food additives.
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phylum = '''Rhodophyta'''
 
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The '''red algae''' (''Rhodophyta'', {{IPA2|ˌrəʊdə(ʊ)ˈfʌɪtə}}, from [[Greek language|Greek]]: ''{{polytonic|ῥόδον}} (rhodon)'' = rose + ''{{polytonic|φυτόν}} (phyton)'' = plant, thus red plant) are a large group of mostly [[multicellular]], [[ocean|marine]] [[algae]], including many notable [[seaweed]]s. Most of the coralline algae, which secrete [[calcium carbonate]] and play a major role in building [[coral reef]]s, belong here.  Red algae such as [[dulse]] and [[nori]] are a traditional part of [[Europe]]an and [[Asia]]n cuisine and are used to make other products like [[agar]], [[carrageenan]]s and other [[food additives]].
 
  
 
===Green algae===
 
===Green algae===
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divisio = '''Chlorophyta'''
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The '''Chlorophyta''', or green algae (Division Chlorophyta), include about eight thousand species of mostly aquatic organisms. Like the land plants (Bryophyta and Tracheophyta), green algae contain [[chlorophyll]]s ''a'' and ''b'', and store food as [[starch]] in their plastids. 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. Few are actually seaweeds, however, either because they are freshwater or microscopic. The sea lettuces (genus genus) are a notable exception.
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Classes
 
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subdivision =
 
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[[Chlorophyceae]] <br>
 
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[[Ulvophyceae]] <br>
 
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[[Trebouxiophyceae]] <br>
 
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Prasinophyceae
 
  
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The '''Chlorophyta''', or [[green algae]], include about 8000 species[http://encarta.msn.com/media_461543986/Major_Algae_Phyla.html] of mostly [[Aquatic ecosystem|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]].
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== Structure ==
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[[Image:codiumfragile.jpg|thumb|250px|Dead Man's Fingers (''Codium fragile'') off [[Massachusetts]] coast]]
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They contain both unicellular and multicellular species. While most species live in [[freshwater biology|freshwater habitats]] and a large number in [[marine biology|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]].
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Seaweeds' appearance often resembles non-arboreal, terrestrial [[plant]]s. For example, they have root-like structures (holdfast) that anchor them to the substrate. However, in function they are unlike terrestrial plants, since they do not absorb nutrients, but solely serve to hold the seaweed in place. Examples of similar structures on the algal body (thallus) include:
  
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==History==
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* thallus: the algal body
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In the early 19th century seaweeds were treated with disdain by some:  
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** stipe: a stem-like structure (may be absent)
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: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!" <ref>Landsborough, D. 1857. ''A Popular History of British Seaweeds''</ref>
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** holdfast: specialized basal structure providing attachment to a surface, often a rock or another alga.
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** lamina: a flattened structure that is somewhat [[leaf]]-like
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*** sorus: [[spore]] cluster
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*** on ''Fucus'', air bladders: float-assist organ (on blade)
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*** on ''kelp'', floats: float-assist organ (between lamina and stipe)
  
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== Structure ==
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The stipe and blade are collectively known as fronds. Some seaweeds have gas in the fronds that help them to be buoyant and float at or near the surface.
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[[Image:Kelp_forest_Otago_1s.JPG|right|thumb|The top of a [[kelp forest]] in [[Otago]], [[New Zealand]] ]]
 
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Seaweeds' appearance somewhat resembles non-[[arboreal]] terrestrial [[plant]]s.
 
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* [[Thallus (tissue)|thallus]]: the algal body
 
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** [[lamina (algae)|lamina]]: a flattened structure that is somewhat leaf-like
 
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*** [[sorus]]: [[spore]] cluster
 
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*** on ''[[Fucus]]'', air bladders: [[float]]-assist organ (on blade)
 
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*** on ''[[kelp]]'', [[float]]s: float-assist organ (between lamina and stipe)
 
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** [[stipe]]: a stem-like structure, may be absent
 
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** [[holdfast]]: specialized basal structure providing attachment to a surface, often a rock or another alga.
 
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The [[stipe]] and blade are collectively known as [[frond]]s.
 
  
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== Uses ==
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Seaweed serves a number of ecological, commercial, and medical uses. For example, seaweed offers protection to some sea creatures and food for others. Some seaweeds are used as fertilizer.
  
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Have roots like structures that anchor them (not like roots of plants in terms of other function).  
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Through the nineteenth century, the word "kelp" was closely associated with seaweeds that could be burned to obtain soda ash (primarily [[sodium carbonate]]). Soda ash is used in the manufacture of [[glass]], [[pulp]] and [[paper]], [[detergent]]s, and some chemicals. It is used as an [[alkaline]] agent in many chemical industries, and used as a water softener for laundry, among other uses. The seaweeds used in obtaining soda ash included species from both the orders Laminariales and Fucales. The word "kelp" was also used directly to refer to these processed ashes (OED 1989).  
  
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Gas in the fronds can hlep the fronds to be bouyant and at the survface.
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=== Food and other commercial uses===
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== Uses ==
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[[Image:TaoKaeNoi Seaweed.JPG|thumb|250px|Packaged seaweed]]
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=== Food ===
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Seaweeds are extensively used as food by coastal peoples, particularly in [[Japan]] and [[Korea]], but also in [[China]], [[Vietnam]], [[Indonesia]], [[Peru]], [[Taiwan]], the [[Canada|Canadian Maritimes]], [[Scandinavia]], [[Ireland]], [[Wales]], [[Philippines]], and [[Scotland]], among other places.  
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[[Image:TaoKaeNoi Seaweed.JPG|thumb|Packaged seaweed]]
 
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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.
 
  
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Seaweeds are also harvested or cultivated for the extraction of [[alginate]], [[agar]] and [[carrageenan]], gelatinous substances collectively known as [[hydrocolloid]]s or phycocolloids. Hydrocolloids have attained commercial significance, especially in food production <ref>Round F.E. 1962 ''The Biology of the Algae''. Edward Arnold Ltd.</ref>. 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.
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For example, ''Porphyra'' is a red alga used in Wales to make laverbread. In Japan, dried seaweed, formed into sheets called ''nori'', is widely used in [[soup]]s, 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.
  
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=== Medicine ===
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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, with the food industry utilizing the gelling, water-retention, emulsifying, and other physical properties of these hydrocolloids.
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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.{{cn}}
 
  
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A number of research studies have been conducted to investigate claims of seaweed's effects on human health<ref>[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?CMD=search&DB=pubmed]</ref>. It has been asserted that seaweeds may have curative properties for [[tuberculosis]], [[arthritis]], colds and [[influenza]], worm infestations and even [[tumors]]<ref>[http://www.seaweed.ie/uses_general/MedicinalUses.html]</ref>.{{dubious}}
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[[Agar]] is used in foods such as confectionery, [[meat]] and poultry products, [[dessert]]s and [[beverage]]s, and molded 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.
  
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=== Other uses ===
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Alginates enjoy many of the same uses as carrageenan, but are also used in production of industrial products such as paper coatings, [[adhesive]]s, [[dye]]s, [[gel]]s, [[explosive]]s, and in processes such as paper sizing, [[textile]] printing, hydro-mulching, and drilling.
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Other seaweeds may be used as [[seaweed fertiliser]].
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=== Medicine and science===
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In the biomedicine and pharmaceutical industries, alginates are used in wound dressings and production of dental molds, and have a host of other applications. In [[microbiology]] research, [[agar]] is extensively used as culture medium for [[bacteria]]. Carrageenans, alginates, and agaroses (the latter are prepared from agar by purification), together with other lesser-known macroalgal [[carbohydrates#polysaccharides|polysaccharides]], also have several biological activities or applications in biomedicine.
  
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[[Image:Ascophylum nodosum.jpg|right|thumb|[[Knotted wrack]], a type of seaweed, on an exposed tidal shore-line]]
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A number of research studies have been conducted to investigate claims of seaweed's effects on human [[health]]. It has been asserted that seaweeds may have curative properties for a number of aliments. However, Guiry (2006) notes that many of the reported medicinal effects have not been substantiated. He does recognize, however, that Corallina is being used in bone-replacement therapy, some kelps have polysaccharides that apparently correlate with reduction in the occurrence of breast cancer, and some seaweeds, such as Sargassum, are used in Chinese medicine, including for treatment of [[cancer]].
  
 
==References==
 
==References==
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<references/>
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* Guiry, M. 2006. [http://www.seaweed.ie/uses_general/MedicinalUses.html Seaweed: Medicinal Uses.] Retrieved August 27, 2007.
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Lewis, J.R. 1964. ''The Ecology of Rocky Shores.'' The English Universities Press Ltd.
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* Lewis, J. R. 1964. ''The Ecology of Rocky Shores.'' The English Universities Press Ltd.
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Smith, G.M. 1944. ''Marine Algae of the Monterey Peninsula, California''. Stanford Univ., 2nd Edition.</ref>.
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* Oxford English Dictionary (OED). 2006. [http://www.oed.com “Kelp,”] In ''Oxford English Dictionary'', 2nd online edition. Oxford University Press.
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* Round F. E. 1962. ''The Biology of the Algae''. Edward Arnold Ltd.
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* Smith, G. M. 1944. ''Marine Algae of the Monterey Peninsula, California'', 2nd edition. Stanford Univ.  
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==External links==
 
==External links==
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* [http://www.seaweed.ie/ The Seaweed Site], information on all aspects of seaweeds and marine algal biology
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All links retrieved January 25, 2023.
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* [http://www.algaebase.org/ 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.
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* [http://www.seaweedafrica.org/ SeaweedAfrica], information on seaweed utilisation for the African continent.
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* [http://www.seaweed.ie/ The Seaweed Site] by Michael Guiry
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* [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?CMD=search&DB=pubmed NCBI PubMed Search], allows for search on health research studies, including seaweed 
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* [http://www.algaebase.org/ AlgaeBase] &ndash; Aearchable taxonomic, image, and utilization database of freshwater, marine and terrestrial algae, including seaweeds
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* [http://www.seavitaminsandmarinenutrition.com/sea-vegetation-research.php Seaweed Research Links], Many useful seaweed research links
 
  
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{{credit5|Seaweed|95950780|Brown_algae|95931788|Red_algae|96034590|Chlorophyta|95976158|Kelp|94695142}}
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{{credit7|Seaweed|95950780|Brown_algae|95931788|Red_algae|96034590|Chlorophyta|95976158|Kelp|94695142|Agar|94766990|Sodium_carbonate|96155753}}
 
[[Category:Life sciences]]
 
[[Category:Life sciences]]
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[[Category:Protists]]

Latest revision as of 17:38, 25 January 2023


A seaweed (Laurencia) up close. The "branches" are multicellular and only about one millimeter thick. Much smaller algae are seen attached to the structure extending upwards in the lower right quarter.

Seaweeds are macroscopic, multicellular, marine algae. They are generally benthic, being anchored to the bottom of the ocean or to solid structures.

Algae (singular alga), a name derived from the Latin word for seaweed, are a large and diverse group of photosynthetic, eukaryotic, plant-like organisms that use chlorophyll in capturing light energy, but lack characteristic plant structures such as leaves, roots, flowers, vascular tissue, and seeds. Although they have historically been regarded as simple plants, they are generally classified in the kingdom Protista, rather than Plantae.

Although algae range from single-celled organisms to multicellular organisms, if they are both multicellular and marine, and are easily seen by the naked eye, they are generally called seaweeds. Single-celled or few-celled organisms are not usually called seaweeds. Seaweeds themselves have many forms, including those that appear as if they are terrestrial plants with leaves and stems, looking like moss, mushrooms, leaf lettuce, or even a palm tree. Some are quite large: the multicellular giant kelp reaches 60 meters in length.

Various seaweeds serve as a habitat and food for other sea creatures. For humans, seaweed also can be used as food and as fertilizer. Red algae are a source of agar, a gelatinous polysaccharide that is used as a culture medium for microbiological work, as well as vegetarian gelatin substitute, a thickener for soups, in jellies, ice cream, and so forth.

Rather than a specific taxa, seaweed can be one of several types of algae: brown algae, red algae, or green algae. Most of the seaweeds of the warm oceans are red algae. They absorb the deep penetrating blue light, allowing them to exist deeper than other algae. The brown algae include the major seaweeds found on the shores in the temperate zones and the large, offshore beds of kelps. There are few green algae that are seaweeds, but one is the sea lettuce.

Types of seaweed

Seaweeds are classified into brown algae (Phaeophyta), red algae (Rhodophyta), and green algae (Chlorophyta). Note that in reality the term algae is mainly used for convenience, rather than taxonomic purposes, as there appears little relationship between the various phyla.

Seaweeds are often confused with other photosynthetic organisms. Seaweeds are popularly described as plants, but biologists typically do not consider them true Plantae. They also should not be confused with seagrasses, which are vascular plants. In addition, a few species of cyanobacteria bear a resemblance to seaweed algae.

Some biologists prefer the term "marine macroalgae" over "seaweeds."

Brown algae

The top of a kelp forest in Otago, New Zealand

The Phaeophyta, or brown algae (Class Phaeophyceae, Division Heterokontophyta or Phaeophyta, Kingdom Protista or Plantae or Chromalveolata), are a large group of multicellular, mostly marine algae, and include many seaweeds of colder Northern Hemisphere waters.

One example of brown algae seaweed 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.

Kelp are large seaweeds belonging to the brown algae and are classified in the order Laminariales. There are about 30 different genera. Kelp grows in underwater forests (kelp forests) in clear, shallow oceans. They require nutrient rich water below about 20 °C. Kelp is known for its high growth rate and is the largest seaweed. Macrocystis, a member of the Laminariales, may reach 60 meters in length and grows up to 30 centimeters per day.

Red algae

The red algae (Phylum Rhodophyta, from Greek rhodon = rose + phyton = plant, thus red plant) are a large group of mostly multicellular, marine algae, including many notable seaweeds. Red algae 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

The Chlorophyta, or green algae (Division Chlorophyta), include about eight thousand species of mostly aquatic organisms. Like the land plants (Bryophyta and Tracheophyta), green algae contain chlorophylls a and b, and store food as starch in their plastids. 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. Few are actually seaweeds, however, either because they are freshwater or microscopic. The sea lettuces (genus genus) are a notable exception.

Structure

Dead Man's Fingers (Codium fragile) off Massachusetts coast

Seaweeds' appearance often resembles non-arboreal, terrestrial plants. For example, they have root-like structures (holdfast) that anchor them to the substrate. However, in function they are unlike terrestrial plants, since they do not absorb nutrients, but solely serve to hold the seaweed in place. Examples of similar structures on the algal body (thallus) include:

  • thallus: the algal body
    • stipe: a stem-like structure (may be absent)
    • holdfast: specialized basal structure providing attachment to a surface, often a rock or another alga.
    • 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)

The stipe and blade are collectively known as fronds. Some seaweeds have gas in the fronds that help them to be buoyant and float at or near the surface.

Uses

Seaweed serves a number of ecological, commercial, and medical uses. For example, seaweed offers protection to some sea creatures and food for others. Some seaweeds are used as fertilizer.

Through the nineteenth century, the word "kelp" was closely associated with seaweeds that could be burned to obtain soda ash (primarily sodium carbonate). Soda ash is used in the manufacture of glass, pulp and paper, detergents, and some chemicals. It is used as an alkaline agent in many chemical industries, and used as a water softener for laundry, among other uses. The seaweeds used in obtaining soda ash included species from both the orders Laminariales and Fucales. The word "kelp" was also used directly to refer to these processed ashes (OED 1989).

Food and other commercial uses

Packaged seaweed

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. In Japan, dried seaweed, formed into sheets called nori, 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, with the food industry utilizing the gelling, water-retention, emulsifying, and other physical properties of these hydrocolloids.

Agar is used in foods such as confectionery, meat and poultry products, desserts and beverages, and molded 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 and science

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

A number of research studies have been conducted to investigate claims of seaweed's effects on human health. It has been asserted that seaweeds may have curative properties for a number of aliments. However, Guiry (2006) notes that many of the reported medicinal effects have not been substantiated. He does recognize, however, that Corallina is being used in bone-replacement therapy, some kelps have polysaccharides that apparently correlate with reduction in the occurrence of breast cancer, and some seaweeds, such as Sargassum, are used in Chinese medicine, including for treatment of cancer.

References
ISBN links support NWE through referral fees

  • Guiry, M. 2006. Seaweed: Medicinal Uses. Retrieved August 27, 2007.
  • Lewis, J. R. 1964. The Ecology of Rocky Shores. The English Universities Press Ltd.
  • Oxford English Dictionary (OED). 2006. “Kelp,” In Oxford English Dictionary, 2nd online edition. Oxford University Press.
  • Round F. E. 1962. The Biology of the Algae. Edward Arnold Ltd.
  • Smith, G. M. 1944. Marine Algae of the Monterey Peninsula, California, 2nd edition. Stanford Univ.

External links

All links retrieved January 25, 2023.

  • The Seaweed Site by Michael Guiry
  • AlgaeBase – Aearchable taxonomic, image, and utilization database of freshwater, marine and terrestrial algae, including seaweeds

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