Seaweed

Source: 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).
Seaweed
Informal group of macroscopic marine algae
"Fucus serratus"
Fucus serratus
Scientific classificationEdit this classification
Domain: Eukaryota
Seaweeds can be found in the following groups
Ascophyllum nodosum exposed to the sun in Nova Scotia, Canada
Photo of detached seaweed frond lying on sand
Dead man's fingers (Codium fragile) off the Massachusetts coast in the United States
Photo of seaweed with the tip floating at the surface
The top of a kelp forest in Otago, New Zealand

Seaweed, or macroalgae, refers to thousands of species 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 and producing at least 50% of Earth's oxygen.[3]

Natural seaweed ecosystems are sometimes under threat from human activity. For example, mechanical

wasting disease in predators of purple urchins has led to an urchin population surge which has 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,

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

"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.[7] They lack one common multicellular ancestor, forming a polyphyletic group. In addition, blue-green algae (Cyanobacteria) are occasionally considered in seaweed literature.[8]

The number of seaweed species is still a topic of discussed among scientists, but it is most likely that there are several thousand species of seaweed.[9]

Genera

Claudea elegans tetrasporangia

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

Genus Algae
Phylum		 Remarks
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 and
cultivated for food.
Macrocystis Brown Giant kelp
forming floating canopies.
Monostroma Green
Porphyra Red Intertidal zones in temperate climate and
cultivated for food.
Sargassum Brown Pelagic especially in the Sargasso Sea.

Anatomy

Seaweed's appearance resembles non-woody terrestrial plants. Its anatomy includes:[10][11]

  • 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

Seaweed covers this rocky seabed on the east coast of Australia

Two environmental requirements dominate seaweed

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.[12] 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.[13]

Macroalgae and macroalgal detritus have also been shown to be an important food source for benthic organisms, because macroalgae shed old

fronds.[14]
These macroalgal fronds tend to be utilized by benthos in the intertidal zone close to the shore.[15][16] Alternatively,
benthic organisms also at several 100 m tend to utilize these macroalgae remnants.[16]

As macroalgae takes up

Blue Carbon storage is currently a topic of discussion among scientists.[17][18][19]

Biogeographic expansion

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.[20]

Production

As of 2019, 35,818,961 tonnes were produced, of which 97.38% were produced in Asian countries.[21]

Seaweed production
Country tonns
per year,
cultured and wild
China 20,351,442
Indonesia 9,962,900
South Korea 1,821,475
Philippines 1,500,326
North Korea 603,000
Chile 427,508
Japan 412,300
Malaysia 188,110
Norway 163,197
United Republic of Tanzania 106,069

Farming

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 farmers gather from natural beds, while at the other extreme farmers fully control the crop's life cycle.

The seven most cultivated

seagrasses, as they are photosynthetic algal organisms[23] and are non-flowering.[22]

The largest seaweed-producing countries as of 2022 are China (58.62%) and Indonesia (28.6%); followed by South Korea (5.09%) and the Philippines (4.19%). Other notable producers include North Korea (1.6%), Japan (1.15%), Malaysia (0.53%), Zanzibar (Tanzania, 0.5%), and Chile (0.3%).[24][25] Seaweed farming has frequently been developed to improve economic conditions and to reduce fishing pressure.[26]

The Food and Agriculture Organization (FAO), reported that world production in 2019 was over 35 million tonnes. North America produced some 23,000 tonnes of wet seaweed. Alaska, Maine, France, and Norway each more than doubled their seaweed production since 2018. As of 2019, seaweed represented 30% of marine aquaculture.[27]

Seaweed farming is a
World Wildlife Fund, Oceans 2050, and The Nature Conservancy publicly support expanded seaweed cultivation.[27]

Uses

Further information: Seaweed farming § Uses

Seaweed has a variety of uses, for which it is farmed[31] or foraged.[32]

Food

Main article: Edible seaweed

Seaweed is consumed across the world, particularly in

Canadian Maritimes, Scandinavia, South West England,[34] Ireland, Wales, Hawaii and California, and Scotland
.

zicai (紫菜, China) are sheets of dried Porphyra used in soups, sushi or onigiri (rice balls). Gamet in the Philippines, from dried Pyropia, is also used as a flavoring ingredient for soups, salads and omelettes.[35] 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").

hydrocolloids or phycocolloids. Hydrocolloids are food additives.[36]
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.[37][38]

They are valued for fish production.[39] Adding seaweed to livestock feed can substantially reduce methane emissions from cattle,[40] but only from their feedlot emissions. As of 2021, feedlot emissions account for 11% of overall emissions from cattle. [41]

Medicine and herbs

See also: Fucoidan
Photo of rocks covered by dried plant matter
Seaweed-covered rocks in the United Kingdom
Photo of a rock jetty covered with seaweed
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.[42] Sulfated saccharides from red and green algae inhibit some DNA and RNA-enveloped viruses.[43]

Seaweed extract is used in some diet pills.

gastric banding, expanding in the stomach to make the stomach feel more full.[45][46]

Climate change mitigation

Further information: Carbon sequestration and blue carbon
This section is an excerpt from Seaweed farming § Climate change mitigation.[edit]
Seaweed cultivation in the open ocean can act as a form of carbon sequestration to mitigate climate change.
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”.[53][54]

Other uses

See also:
Seaweed fuel

Other seaweed may be used as

fertilizer, compost for landscaping, or to combat beach erosion through burial in beach dunes.[55]

Seaweed is under consideration as a potential source of

bioethanol.[56][57]

Seaweed is lifted out of the top of an 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).[58]

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[59]

Health risks

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.[60] It can cause vomiting and diarrhea.[61]

The so-called "stinging seaweed"

seaweed dermatitis characterized by painful, burning lesions that last for days.[1][62]

Threats

Bacterial disease ice-ice infects Kappaphycus (red seaweed), turning its branches white. The disease caused heavy crop losses in the Philippines, Tanzania and Mozambique.[63]

Sea urchin barrens have 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.[63]

See also

References

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Further reading

  • Iselin, Josie. An Ocean Garden: The Secret Life of Seaweed (Oregon State University Press, 2023) online book review
  • Wiencke, Christian, Kai Bischof (ed.) Seaweed Biology: Novel Insights into Ecophysiology, Ecology & Utilization. Springer (2012).
    ISBN 978-3-642-28451-9
    (eBook).

External links

Wikimedia Commons has media related to Marine algae.
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