Seaweed is a macroscopic, multicellular, benthic marine algae.
The term includes some members of the red, brown and green algae.
Seaweeds can also be classified by use.
Taxonomy A seaweed may belong to one of several groups
of multicellular algae: the red algae, green algae, and brown algae.
As these three groups are not thought to have a common multicellular ancestor, the seaweeds
are a polyphyletic group.
In addition, some tuft-forming bluegreen algae are sometimes considered to be seaweeds — "seaweed"
is a colloquial term and lacks a formal definition.
Structure Seaweeds' appearance somewhat resembles non-arboreal
terrestrial plants.
thallus: the algal body lamina or blade: a flattened structure that
is somewhat leaf-like sorus: a spore cluster
on Fucus, air bladder: a floatation-assisting organ on the blade
on kelp, float: a floatation-assisting organ between the lamina and stipe
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 benthic substrate
The stipe and blade are collectively known as the frond.
Ecology
Two specific environmental requirements dominate seaweed ecology.
These are the presence of seawater and the presence of light sufficient to drive photosynthesis.
Another common requirement is a firm attachment point.
As a result, seaweeds most commonly inhabit the littoral zone and within that zone more
frequently on rocky shores than on sand or shingle.
Seaweeds 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 seaweeds can extend several miles out to sea.
The limiting factor in such cases is sunlight availability.
The deepest living seaweeds are some species of red algae.
A number of species such as Sargassum have adapted to a fully planktonic niche and are
free-floating, depending on gas-filled sacs to maintain an acceptable depth.
Others have adapted to live in tidal rock pools.
In this habitat seaweeds must withstand rapidly changing temperature and salinity and even
occasional drying.
Uses
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 to have hit 10 million tonnes.
Food
Seaweeds are consumed by coastal people, particularly in East Asia, e.g., Brunei, Japan, China,
Korea, Taiwan, Singapore, Thailand, Burma, Cambodia, and Vietnam, and also in South Africa,
Indonesia, Malaysia, Belize, Peru, Chile, the Canadian Maritimes, Scandinavia, South
West England, Ireland, Wales, California, Philippines, and Scotland.
In Asia, nori, zicai, and gim are sheets of dried Porphyra used in soups or to wrap sushi.
Chondrus crispus is another red alga used in producing food additives, along with Kappaphycus
and gigartinoid seaweeds.
Porphyra is 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 seaweeds are mixed with milk, nutmeg, cinnamon, and vanilla to
make a common beverage affectionately called "dulce".
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 as 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 products, dairy items and baked goods.
Herbalism
Alginates are commonly used in wound dressings, 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, with other lesser-known macroalgal polysaccharides,
have several important biological activities or applications in biomedicine.
Seaweed is a source of iodine, necessary for thyroid function and to prevent goitre.
However, an excess of iodine is suspected in the heightened cancer risk in Japanese
who consume a lot of the plant and even bigger risks in post-menopausal women.
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.
Filtration 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, and this filtering process is duplicated
in man-made seaweed filters such as algae scrubbers.
Seaweed, as opposed to microalgae, is used almost universally for filtration purposes
because of the need to be able to easily remove 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 pulled out.
When used for filtration, saltwater algae commonly grows species of Cladophora, Ulva,
and Chaetomorpha.
Freshwater filtration applications are useful, too, and will commonly grow species such as
Spirogyra.
Other uses
Other seaweeds 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 bioethanol.
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.
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.
It can cause vomiting and diarrhoea.
Genera See also
Algaculture Algal fuel
Aonori, Hijiki, Kombu, Mozuku, Nori, Ogonori, and Wakame - seaweed preparations used in
Japan, and occasionally Korea and parts of Oceania
Kelp Laver - seaweed prepared as food in Wales
List of seaweeds of South Africa Sea lettuce
Seaweed dermatitis Silas Seaweed
References
External links Michael Guiry's Seaweed Site, information
on all aspects of algae, seaweeds and marine algal biology
AlgaeBase, a searchable taxonomic, image, and utilization database of freshwater, marine
and terrestrial algae, including seaweed.
SeaweedAfrica, information on seaweed utilisation for the African continent.
Seaweed.
A chemical industry in Brittany, in the past and today.
Sea Greens.
An ingenious new business provides Maine’s lobster crews with a self-kelp manual for
their downtime in winter.
Portland Magazine, October 2013