Seaweed or macroalgae refers to several species of macroscopic,
multicellular, marine algae.
The term includes some types of red, brown, and green macroalgae.
Seaweed offer excellent opportunities for its industrial exploitation
as they could be a source of multiple compounds (i.e. polysaccharides,
proteins and phenols) with applications as food  and animal
feed, pharmaceuticals  or fertilizers
4.4 Other uses
4.4.1 Photo essay showing women in Zanzibar, Tanzania farming seaweed
and making seaweed soap
5 Health risks
7 See also
9 Further reading
10 External links
"Seaweed" is a colloquial term and lacks a formal definition. A
seaweed may belong to one of several groups of multicellular algae:
the red algae, green algae, and brown algae. As these three groups do
not have a common multicellular ancestor, the seaweed are in a
polyphyletic group. In addition, some tuft-forming bluegreen algae
(Cyanobacteria) are sometimes considered to be seaweed.
Seaweed's appearance somewhat resembles non-arboreal terrestrial
thallus: the algal body
lamina or blade: a flattened structure that is somewhat leaf-like
sorus: a spore cluster
on Fucus, air bladder: a flotation-assisting organ on the blade
on kelp, float: a flotation-assisting organ between the lamina and
stipe: a stem-like structure, may be absent
holdfast: a specialized basal structure providing attachment to a
surface, often a rock or another alga
haptera: a finger-like extension of the holdfast anchoring to a
The stipe and blade are collectively known as the frond.
Seaweed cover this rocky seabed on the east coast of Australia
Two specific environmental requirements dominate seaweed ecology.
These are the presence of seawater (or at least brackish water) and
the presence of light sufficient to drive photosynthesis. Another
common requirement is a firm attachment point, although some genera
Gracilaria have species that float freely. As a
result, seaweed most commonly inhabit the part of a sea that is close
to the shore (the littoral zone) and within that zone more frequently
on rocky shores than on sand or shingle.
Seaweed occupy a wide range
of ecological niches. The highest elevation is only wetted by the tops
of sea spray, the lowest is several meters deep. In some areas,
littoral seaweed can extend several miles out to sea. The limiting
factor in such cases is sunlight availability. 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
even occasional drying.
Onigiri and wakame miso soup, Japan
Laver and toast
Small plots being used to farm seaweed in Indonesia, with each
rectangle belonging to a different family
Seaweed has a variety of purposes, for which it is farmed or
foraged from the wild.
At the beginning of 2011,
Indonesia produced 3 million tonnes of
seaweed and surpassed the
Philippines as the world's largest seaweed
producer. By 2011, the production was estimated to have reached 10
Main article: Edible seaweed
Seaweed is consumed by coastal people, particularly in East Asia, e.g.
Japan, China, Korea, Taiwan, and Southeast Asia, e.g. Brunei,
Singapore, Thailand, Burma, Cambodia, Vietnam, Indonesia, Philippines,
and Malaysia, and also in South Africa, Belize, Peru, Chile, the
Canadian Maritimes, Scandinavia, South West England, Ireland,
Wales, California, and Scotland.
In Asia, Gim (Korean food) (김, Korea), nori (海苔, Japan), zicai
(紫菜, China) are sheets of dried
Porphyra used in soups, sushi wrap
or onigiri (rice balls).
Chondrus crispus (commonly known as 'Irish
moss' or carrageenan moss) is another red alga used in producing food
additives, along with
Kappaphycus and gigartinoid seaweed.
a red alga used in
Wales to make laver. Laverbread, made from oats and
the laver, is a popular dish there. In northern Belize, edible seaweed
are mixed with milk, nutmeg, cinnamon, and vanilla to make a common
beverage affectionately called "dulce" (or "sweet").
Seaweed 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 as food additives. The food industry
exploits their gelling, water-retention, emulsifying and other
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 products, dairy items and baked
The development of seaweed as an alternative and sustainable source of
food and animal feed ingredients depends on the sustainability of the
natural resource of raw biomass and on moving the process of feed
development from laboratory to industrial scale.
See also: Fucoidan
Seaweed-covered rocks in the United Kingdom
Seaweed on rocks in Long Island
Alginates are commonly used in wound dressings (see alginate
dressing), and production of dental moulds. In microbiology research,
agar — a plant-based goo similar to gelatin and made from seaweed
— is extensively used as culture medium. Carrageenans, alginates and
agaroses (the latter are prepared from agar by purification), with
other lesser-known macroalgal polysaccharides, have several important
biological activities or applications in biomedicine.
Seaweed extract is used in some diet pills. Other seaweed pills
exploit the same effect as gastric banding, expanding in the stomach
to make the body feel more full.
The strong photosynthesis of algae creates a large affinity for
nutrients; this allows the seaweed to be used purposely to remove
undesired nutrients from water. Nutrients such as ammonia, ammonium
nitrate, nitrite, phosphate, iron, copper, as well as CO2 are rapidly
consumed by growing seaweed. Reefs and lakes are naturally filtered
this way (the seaweed being consumed by fish and invertebrates), and
this filtering process is duplicated in artificial seaweed filters
such as algae scrubbers.
Modern floating algae scrubber/cultivator on a reef pond
Seaweed (macroalgae), as opposed to phytoplankton (microalgae), is
used almost universally for filtration purposes because of the need to
be able to easily remove (harvest) the algae from the water, which
then removes the nutrients. Microalgae require more processing to
separate it from the water than macroalgae does; macroalgae is simply
When used for filtration, saltwater algae commonly grows species of
Ulva (sea lettuce), and Chaetomorpha. Freshwater
filtration applications are useful, too, and will commonly grow
species such as Spirogyra.
Seaweed fertiliser and
Other seaweed may be used as fertilizer, compost for landscaping, or a
means of combating beach erosion through burial in beach dunes.
Seaweed is under consideration as a potential source of
Seaweed is lifted out of top of algae scrubber/cultivator, to be
discarded or used as food, fertilizer, or skin care
Seaweed is an ingredient in toothpaste, cosmetics and paints.
Alginates enjoy many of the same uses as carrageenan and 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. Research suggests that the Australian
seaweed Delisea pulchra may interfere with bacterial colonization.
Sulfated saccharides from both red and green algae have been known to
inhibit some DNA and RNA enveloped viruses.
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
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 purpose: food,
cosmetics, fabric, etc.
Seaweed is sometimes used to build roofs on houses on
Seaweeds are also used as animal feeds. They have long been grazed by
sheep, horses and cattle in Northern Europe. They are currently
particularly valuable for fish production. Adding seaweed to
livestock feed can substantially reduce methane emissions from
Photo essay showing women in Zanzibar, Tanzania farming seaweed and
making seaweed soap
Zanzibar's seaweed growers face a changing climate. Here, a farmer
tends to her farm in Paje, on the southeast coast of the island.
Mwanaisha Makame and Mashavu Rum, who have been farming seaweed on
beautiful Zanzibar island for 20 years, wade through the low tide to
The seaweed grows underwater for 45 days. When it reaches one
kilogram, the women pick it and dry it, then pack it in bags to be
exported to countries like China,
Korea and Vietnam. There, it's used
in medicines and shampoos.
The farmers have a lot of problems due to climate change. Two decades
ago, 450 seaweed farmers roamed Paje. Now, only about 150 farmers
Mwanaisha holds up a healthy clump of seaweed. Then she holds up
seaweed the farmers won't be able to use. A hard white substance grows
on it - ice-ice disease, caused by higher ocean temperatures and
The seaweed farmers learned how to make soap from their seaweed at the
Seaweed Center, a business that started as an NGO in 2009. At
their homes, they mix water, ground seaweed powder, coconut oil,
caustic soda and essential oils in a large plastic tub.
Later in the week, the seaweed farmers will sell their finished soaps
in Zanzibar town or to regular local customers. As seaweed levels
decline, they have found a way to increase the value of their work.
The finished product - a bar of seaweed soap.
Rotting seaweed is a potent source of hydrogen sulfide, a highly toxic
gas, and has been implicated in some incidents of apparent
hydrogen-sulphide poisoning. It can cause vomiting and diarrhea.
The following table lists a very few example genera of seaweed.
In intertidal zones on rocky shores.
Cultivated for food
Also known as kelp, 8–30 m under water, cultivated for food.
Giant kelp, forming floating canopies.
Intertidal zones in temperate climate. Cultivated for food.
Claudea elegans tetrasporangia
Aonori, Hijiki, Kombu, Mozuku, Nori, Ogonori, and
Wakame - seaweed
preparations used in Japan, and occasionally
Korea and parts of
Cochayuyo, a form of kelp used as a vegetable in Chile
^ Smith, G.M. 1944. Marine
Algae of the Monterey Peninsula,
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^ Garcia-Vaquero, M; Rajauria, G; O'Doherty, JV; Sweeney, T (2017).
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low-degree-polymerisation sulfated saccharides from
Gracilaria sp. and
Monostroma nitidum". Food Chem. 133 (3): 866–74.
^ Lewis, J.R. 1964. The
Ecology of Rocky Shores. The English
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^ Round F.E. 1962 The Biology of the Algae. Edward Arnold Ltd.
^ Hayato Maeda, Masashi Hosokawa, Tokutake Sashima, Katsura Funayama
& Kazuo Miyashita (2005). "Fucoxanthin from edible seaweed,
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Seaweed Pill Works Like Gastric Banding". Fox News.
^ Elena Gorgan (6 January 2009). "Appesat, the
Seaweed Diet Pill that
Expands in the Stomach". softpedia.
^ Rodriguez, Ihosvani (April 11, 2012). "
Seaweed invading South
Florida beaches in large numbers". South Florida Sun-Sentinel.
Seaweed Biofuels: Production of Biogas and
Bioethanol from Brown
^ Francesca Cappitelli & Claudia Sorlini (2008). "Microorganisms
attack synthetic polymers in items representing our cultural
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^ Heuzé V., Tran G., Giger-Reverdin S., Lessire M., Lebas F., 2017.
Seaweeds (marine macroalgae). Feedipedia, a programme by INRA, CIRAD,
AFZ and FAO. https://www.feedipedia.org/node/78 Last updated on May
29, 2017, 16:46
Seaweed shown to reduce 99% methane from cattle - The Irish Times
^ "Algues vertes: la famille du chauffeur décédé porte plainte
contre X" AFP, retrieved 2010-04-22 (in French)
Christian Wiencke, Kai Bischof [editors]:
Seaweed Biology: Novel
Insights into Ecophysiology,
Ecology & Utilization. Springer,
2012. ISBN 978-3-642-28450-2 (print); ISBN 978-3-642-28451-9
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