Seaweed

[박대선]

Seaweed

50 languages

• Article
• Talk

• Read
• Edit
• View history

From Wikipedia, the free encyclopedia

This article is about the aquatic plant-like algae. For its culinary uses, see Edible seaweed. For the similarly-named plant, see Seagrass. For other uses, see Seaweed (disambiguation).

SeaweedInformal group of macroscopic marine algaeScientific classification

Seaweeds can be found in the following groups

Fucus serratus
Domain:	Eukaryota
Chlorophyta (green algae) Phaeophyceae (brown algae) Phaeothamniophyceae Chrysophyceae (gold algae) Cyanobacteria[1][2] Rhodophyta (red algae)

Ascophyllum nodosum exposed to the sun in Nova Scotia, Canada

Dead man's fingers (Codium fragile) off the Massachusetts coast in the United States

The top of a kelp forest in Otago, New Zealand

Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of Rhodophyta (red), Phaeophyta (brown) and Chlorophyta (green) macroalgae. Seaweed species such as kelps provide essential nursery habitat for fisheries and other marine species and thus protect food sources; other species, such as planktonic algae, play a vital role in capturing carbon, producing at least 50% of Earth's oxygen.[3]

Natural seaweed ecosystems are sometimes under threat from human activity. For example, mechanical dredging of kelp destroys the resource and dependent fisheries. Other forces also threaten some seaweed ecosystems; a wasting disease in predators of purple urchins has led to a urchin population surge which destroyed large kelp forest regions off the coast of California.[4]

Humans have a long history of cultivating seaweeds for their uses. In recent years, seaweed farming has become a global agricultural practice, providing food, source material for various chemical uses (such as carrageenan), cattle feeds and fertilizers. Because of their importance in marine ecologies and for absorbing carbon dioxide, recent attention has been on cultivating seaweeds as a potential climate change mitigation strategy for biosequestration of carbon dioxide, alongside other benefits like nutrient pollution reduction, increased habitat for coastal aquatic species, and reducing local ocean acidification.[5] The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate recommends "further research attention" as a mitigation tactic.[6]

Taxonomy[edit]

"Seaweed" lacks a formal definition, but seaweed generally lives in the ocean and is visible to the naked eye. The term refers to both flowering plants submerged in the ocean, like eelgrass, as well as larger marine algae. Generally it is one of several groups of multicellular algae: red, green and brown. They lack one common multicellular ancestor, forming a polyphyletic group. In addition, bluegreen algae (Cyanobacteria) are occasionally considered in seaweed literature.[7]

The number of seaweed species is still discussed among scientists, but most likely there are several thousand species of seaweed.[8]

Genera[edit]

Claudea elegans tetrasporangia

The following table lists a very few example genera of seaweed.

GenusAlgaePhylumRemarks

Caulerpa		Green	Submerged
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
Monostroma		Green
Porphyra		Red	Intertidal zones in temperate climate Cultivated for food
Sargassum		Brown	Pelagic especially in the Sargasso Sea

Anatomy[edit]

Seaweed's appearance resembles non-woody terrestrial plants. Its anatomy includes:[9][10]

• Thallus: algal body
  • Lamina or blade: flattened structure that is somewhat leaf-like
    • Sorus: spore cluster
    • pneumatocyst, air bladder: a flotation-assisting organ on the blade
    • Kelp, float: a flotation-assisting organ between the lamina and stipe
  • Stipe: stem-like structure, may be absent
  • Holdfast: basal structure providing attachment to a substrate
    • Haptera: finger-like extension of the holdfast that anchors to a benthic substrate

The stipe and blade are collectively known as the frond.

Ecology[edit]

Seaweed covers this rocky seabed on the east coast of Australia

Two environmental requirements dominate seaweed ecology. These are seawater (or at least brackish water) and light sufficient to support photosynthesis. Another common requirement is an attachment point, and therefore seaweed most commonly inhabits the littoral zone (nearshore waters) and within that zone, on rocky shores more than on sand or shingle. In addition, there are few genera (e.g., Sargassum and Gracilaria) which do not live attached to the sea floor, but float freely.

Seaweed occupies various ecological niches. At the surface, they are only wetted by the tops of sea spray, while some species may attach to a substrate several meters deep. In some areas, littoral seaweed colonies can extend miles out to sea.[citation needed] The deepest living seaweed are some species of red algae. Others have adapted to live in tidal rock pools. In this habitat, seaweed must withstand rapidly changing temperature and salinity and occasional drying.[11]

Macroalgae and macroalgal detritus have also been shown to be an important food source for benthic organisms, because macroalgae shed old fronds.[12] These macroalgal fronds tend to be utilized by benthos in the intertidal zone close to the shore.[13][14] Alternatively, pneumatocysts (gas filled “bubbles”) can keep the macroalgae thallus afloat fronds are transported by wind and currents from the coast into the deep ocean.[12] It has been shown that benthic organisms also at several 100 m tend to utilize these macroalgae remnants.[14]

As macroalgae takes up carbon dioxide and release oxygen in the photosynthesis, macroalgae fronds can also contribute to carbon sequestration in the ocean, when the macroalgal fronds drift offshore into the deep ocean basins and sink to the sea floor without being remineralized by organisms.[12] The importance of this process for the Blue Carbon storage is currently discussed among scientists.[15][16][17]

Biogeographic expansion[edit]

Nowadays a number of vectors - e.g., transport on ship hulls, exchanges among shellfish farmers, global warming, opening of trans-oceanic canals - all combine to enhance the transfer of exotic seaweeds to new environments. Since the piercing of the Suez Canal,the situation is particularly acute in the Mediterranean Sea, a 'marine biodiversity hotspot' that now registers over 120 newly introduced seaweed species -the largest number in the world.[18]

Production[edit]

As of 2018, the top 10 countries produced 96% of the global total of 2,165,675 metric tons.[19]

Seaweed productionCountrymetric tonsper year ('000),cultured+wild

China	699
France	617
United Kingdom	205
Japan	123
Chile	109
Philippines	96
North Korea	71
South Korea	67
Indonesia	47
Norway	41

Farming[edit]

This section is an excerpt from Seaweed farming.[edit]

Seaweed farming or kelp farming is the practice of cultivating and harvesting seaweed. In its simplest form, it consists of the management of naturally found batches. In its most advanced form, it consists of fully controlling the life cycle of the algae. The top seven most cultivated seaweed taxa are Eucheuma spp., Kappaphycus alvarezii, Gracilaria spp., Saccharina japonica, Undaria pinnatifida, Pyropia spp., and Sargassum fusiforme. Eucheuma and K. alvarezii are farmed for carrageenan (a gelling agent); Gracilaria is farmed for agar; while the rest are farmed for food.[20] The largest seaweed-producing countries are China, Indonesia, and the Philippines. Other notable producers include South Korea, North Korea, Japan, Malaysia, and Zanzibar (Tanzania).[21] Seaweed farming has frequently been developed as an alternative to improve economic conditions and to reduce fishing pressure and overexploited fisheries.[22]

Global production of farmed aquatic plants, overwhelmingly dominated by seaweeds, grew in output volume from 13.5×106 t (13,300,000 long tons; 14,900,000 short tons) in 1995 to just over 30×106 t (30,000,000 long tons; 33,000,000 short tons) in 2016.[23] As of 2014, seaweed was 27% of all marine aquaculture.[24]

Seaweed farming is a carbon negative crop, with a high potential for climate change mitigation.[25][24] The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate recommends "further research attention" as a mitigation tactic.[26]

Uses[edit]

Further information: Seaweed farming § Uses

Seaweed has a variety of uses, for which it is farmed[27] or foraged.[28]

Food[edit]

Main article: Edible seaweed

Seaweed is consumed across the world, particularly in East Asia, e.g. Japan, China, Korea, Taiwan and Southeast Asia, e.g. Brunei, Singapore, Thailand, Burma, Cambodia, Vietnam, Indonesia, the Philippines, and Malaysia,[29] as well as in South Africa, Belize, Peru, Chile, the Canadian Maritimes, Scandinavia, South West England,[30] Ireland, Wales, Hawaii and California, and Scotland.

Gim (김, Korea), nori (海苔, Japan) and zicai (紫菜, China) are sheets of dried Porphyra used in soups, sushi or onigiri (rice balls). Chondrus crispus ('Irish moss' or carrageenan moss) is used in food additives, along with Kappaphycus and Gigartinoid seaweed. Porphyra is used in Wales to make laverbread (sometimes with oat flour). In northern Belize, seaweed is mixed with milk, nutmeg, cinnamon and vanilla to make "dulce" ("sweet").

Alginate, agar and carrageenan are gelatinous seaweed products collectively known as hydrocolloids or phycocolloids. Hydrocolloids are food additives.[31] 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, dairy items and baked goods.

Medicine and herbs[edit]

See also: Fucoidan

Seaweed-covered rocks in the United Kingdom

Seaweed on rocks on Long Island

Alginates are used in wound dressings (see alginate dressing), and dental moulds. In microbiology, agar is used as a culture medium. Carrageenans, alginates and agaroses, with other macroalgal polysaccharides, have biomedicine applications. Delisea pulchra may interfere with bacterial colonization.[32] Sulfated saccharides from red and green algae inhibit some DNA and RNA-enveloped viruses.[33]

Seaweed extract is used in some diet pills.[34] Other seaweed pills exploit the same effect as gastric banding, expanding in the stomach to make the stomach feel more full.[35][36]

Climate change mitigation[edit]

Further information: Carbon sequestration and blue carbon

This section is an excerpt from Seaweed farming § Climate change mitigation.[edit]

There has been considerable attention to how large-scale seaweed cultivation in the open ocean can act as a form of carbon sequestration to mitigate climate change.[37][38] A number of academic studies have demonstrated that nearshore seaweed forests constitute a source of blue carbon, as seaweed detritus is carried by wave currents into the middle and deep ocean thereby sequestering carbon.[26][24][39][40][41] Moreover, nothing on earth sequesters carbon faster than Macrocystis pyrifera (also known as giant kelp) which can grow up to 60 m in length and as rapidly as 50 cm a day in ideal conditions.[42] It has therefore been suggested that growing seaweeds at scale can have a significant impact on climate change. According to one study, covering 9% of the world’s oceans with kelp forests “could produce sufficient biomethane to replace all of today’s needs in fossil fuel energy, while removing 53 billion tons of CO2 per year from the atmosphere, restoring pre-industrial levels”.[43]

Other uses[edit]

See also: Seaweed fertilizer and Seaweed fuel

Other seaweed may be used as fertilizer, compost for landscaping, or to combat beach erosion through burial in beach dunes.[44]

Seaweed is under consideration as a potential source of bioethanol.[45][46]

Seaweed is lifted out of the top of algae scrubber/cultivator, to be discarded or used as food, fertilizer, or skin care

Alginates 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. Seaweed is an ingredient in toothpaste, cosmetics and paints. Seaweed is used for the production of bio yarn (a textile).[47]

Several of these resources can be obtained from seaweed through biorefining.

Seaweed collecting is the process of collecting, drying and pressing seaweed. It was a popular pastime in the Victorian era and remains a hobby today. In some emerging countries, Seaweed is harvested daily to support communities.

Women in Tanzania grow "Mwani" (seaweed in Swahili). The farms are made up of little sticks in neat rows in the warm, shallow water. Once they harvest the seaweed, it is used for many purposes: food, cosmetics, fabric, etc.

Seaweed is sometimes used to build roofs on houses on Læsø in Denmark[48]

Seaweeds are used as animal feeds. They have long been grazed by sheep, horses and cattle in Northern Europe. They are valued for fish production.[49] Adding seaweed to livestock feed can substantially reduce

[박대선]

https://en.wikipedia.org/wiki/Seaweed