Seaweed

Seaweed, ormacroalgae, refers to thousands of species ofmacroscopic,multicellular,marinealgae. The term includes some types ofRhodophyta(red),Phaeophyta(brown) andChlorophyta(green) macroalgae. Seaweed species such askelpsprovide essential nursery habitat for fisheries and other marine species and thus protect food sources; other species, such asplanktonicalgae, play a vital role incapturing carbonand producing at least 50% of Earth's oxygen.
Natural seaweed ecosystems are sometimes under threat from human activity. For example, mechanicaldredgingof kelp destroys the resource and dependent fisheries. Other forces also threaten some seaweed ecosystems; for example, awasting diseasein predators ofpurple urchinshas led to an urchin population surge which has destroyed largekelp forestregions off the coast of California.
Humans have a long history of cultivating seaweeds for their uses. In recent years,seaweed farminghas become a global agricultural practice, providing food, source material for various chemical uses (such ascarrageenan), cattle feeds and fertilizers. Due to their importance in marine ecologies and for absorbing carbon dioxide, recent attention has been on cultivating seaweeds as a potentialclimate change mitigationstrategy forbiosequestration of carbon dioxide, alongside other benefits likenutrient pollutionreduction, increased habitat for coastal aquatic species, and reducing localocean acidification.TheIPCCSpecial Report on the Ocean and Cryosphere in a Changing Climaterecommends "further research attention" as a mitigation tactic.
"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, likeeelgrass, as well as larger marine algae. Generally, it is one of several groups of multicellularalgae;red,greenandbrown.They lack one common multicellular ancestor, forming apolyphyleticgroup.  In addition, blue-green algae (Cyanobacteria) are occasionally considered in seaweed literature.
The number of seaweed species is still a topic of discussion among scientists, but it is most likely that there are several thousand species of seaweed.
The following table lists a very few example genera of seaweed.
Seaweed's appearance resembles non-woodyterrestrialplants. Its anatomy includes:
The stipe and blade are collectively known as thefrond.
Two environmental requirements dominate seaweedecology. These are seawater (or at leastbrackish water) and light sufficient to supportphotosynthesis. Another common requirement is an attachment point, and therefore seaweed most commonly inhabits thelittoral zone(nearshore waters) and within that zone, on rocky shores more than on sand or shingle. In addition, there are fewgenera(e.g.,SargassumandGracilaria) 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.The deepest living seaweed are some species ofred algae. Others have adapted to live intidal rock pools. In this habitat, seaweed must withstand rapidly changing temperature andsalinityand occasional drying.
Macroalgae and macroalgal detritus have also been shown to be an important food source for benthic organisms, because macroalgae shed oldfronds.These macroalgal fronds tend to be utilized bybenthosin theintertidal zoneclose to the shore.Alternatively,pneumatocysts(gas filled "bubbles") can keep the macroalgaethallusafloat; fronds are transported by wind and currents from the coast into the deep ocean.It has been shown thatbenthic organismsalso at several 100 m tend to utilize these macroalgae remnants.
As macroalgae takes upcarbon dioxideand releasesoxygenin thephotosynthesis, macroalgae fronds can also contribute tocarbon sequestrationin the ocean, when the macroalgal fronds drift offshore into the deepocean basinsand sink to the sea floor without being remineralized by organisms.The importance of this process forblue carbonstorage is currently a topic of discussion among scientists.
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.
As of 2019, 35,818,961 tonnes were produced, of which 97.38% were produced in Asian countries.
Seaweed has a variety of uses, for which it isfarmedor foraged.
Seaweed is consumed across the world, particularly inEast Asia, e.g.,Japan,China,Korea,TaiwanandSoutheast Asia, e.g.Brunei,Singapore,Thailand,Burma,Cambodia,Vietnam,Indonesia, thePhilippines, andMalaysia,as well as inSouth Africa,Belize,Peru,Chile, theCanadian Maritimes,Scandinavia,South West England,Ireland,Wales,HawaiiandCalifornia, andScotland.
Gim(김, Korea),nori(海苔, Japan) andzicai(紫菜, China) are sheets of driedPorphyraused in soups,sushioronigiri(rice balls).Gametin the Philippines, from driedPyropia, is also used as a flavoring ingredient for soups, salads andomelettes.Chondrus crispus('Irish moss' orcarrageenanmoss) is used in food additives, along withKappaphycusandGigartinoidseaweed.Porphyrais used inWalesto makelaverbread(sometimes withoatflour). In northernBelize, seaweed is mixed withmilk,nutmeg,cinnamonandvanillato make "dulce" ("sweet").
Alginate,agarandcarrageenanare gelatinous seaweed products collectively known ashydrocolloidsorphycocolloids. Hydrocolloids are 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, dairy items and baked goods.
Seaweeds are used as animal feeds. They have long been grazed by sheep, horses and cattle in Northern Europe, even though their nutritional benefits are questionable. Their protein content is low and their heavy metal content is high, especially for arsenic and iodine, which are respectively toxic and nutritious.
They are valued for fish production.Adding seaweed to livestock feed can substantially reducemethane emissionsfrom cattle,but only from their feedlot emissions. As of 2021, feedlot emissions account for 11% of overall emissions from cattle.
Alginates are used in wound dressings (seealginate dressing), and dental moulds. Inmicrobiology,agaris used as a culture medium. Carrageenans, alginates and agaroses, with other macroalgal polysaccharides, havebiomedicineapplications.Delisea pulchramay interfere with bacterial colonization.Sulfated saccharides from red and green algae inhibit someDNAandRNA-envelopedviruses.
Seaweed extract is used in some diet pills.Other seaweed pills exploit the same effect asgastric banding, expanding in the stomach to make the stomach feel more full.
Other seaweed may be used asfertilizer,compostfor landscaping, or to combatbeach erosionthrough burial in beach dunes.
Seaweed is under consideration as a potential source ofbioethanol.
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).
Several of these resources can be obtained from seaweed throughbiorefining.
Seaweed collectingis 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.
Seaweed is sometimes used to build roofs on houses onLæsøinDenmark.
Rotting seaweed is a potent source ofhydrogen sulfide, a highly toxic gas, and has been implicated in some incidents of apparent hydrogen sulfide poisoning.It can cause vomiting and diarrhea.
The so-called "stinging seaweed"Microcoleus lyngbyaceusis a filamentouscyanobacteriawhich contains toxins includinglyngbyatoxin-aanddebromoaplysiatoxin. Direct skin contact can causeseaweed dermatitischaracterized by painful, burning lesions that last for days.
Bacterial diseaseice-iceinfectsKappaphycus(red seaweed), turning its branches white. The disease caused heavy crop losses in the Philippines, Tanzania and Mozambique.
Seaurchin barrenshave replaced kelp forests in multiple areas. They are "almost immune to starvation". Lifespans can exceed 50 years. When stressed by hunger, their jaws and teeth enlarge, and they form "fronts" and hunt for food collectively.