Kelp

Source: Wikipedia, the free encyclopedia.
For other uses, see Kelp (disambiguation).

Kelp
Temporal range: Lutetian–Present [1]
Scientific classification Edit this classification
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Clade: Stramenopiles
Phylum: Gyrista
Subphylum: Ochrophytina
Class: Phaeophyceae
Order: Laminariales
Migula, 1909[2]
Families

Agaraceae
Akkesiphycaceae
Alariaceae
Aureophycaceae

Chordaceae

Laminariaceae
Lessoniaceae
Pseudochordaceae

Kelps are large brown algae or seaweeds that make up the order Laminariales. There are about 30 different genera.[3] Despite its appearance, kelp is not a plant but a stramenopile, a group containing many protists.[4]

Kelp grows in "underwater forests" (kelp forests) in shallow oceans, and is thought to have appeared in the Miocene, 5 to 23 million years ago.[5] The organisms require nutrient-rich water with temperatures between 6 and 14 °C (43 and 57 °F). They are known for their high growth rate—the genera Macrocystis and Nereocystis can grow as fast as half a metre a day, ultimately reaching 30 to 80 metres (100 to 260 ft).[6]

Through the 19th century, the word "kelp" was closely associated with seaweeds that could be burned to obtain

soda ash (primarily sodium carbonate). The seaweeds used included species from both the orders Laminariales and Fucales. The word "kelp" was also used directly to refer to these processed ashes.[7]

Description

Alaskan beach kelp

In most kelp, the thallus (or body) consists of flat or leaf-like structures known as blades. Blades originate from elongated stem-like structures, the stipes. The holdfast, a root-like structure, anchors the kelp to the substrate of the ocean. Gas-filled bladders (pneumatocysts) form at the base of blades of American species, such as Nereocystis lueteana, (Mert. & Post & Rupr.)[6] to hold the kelp blades close to the surface.

Growth and reproduction

Growth occurs at the base of the

diploid sporophyte and haploid gametophyte stage. The haploid phase begins when the mature organism releases many spores, which then germinate to become male or female gametophytes. Sexual reproduction
then results in the beginning of the diploid sporophyte stage, which will develop into a mature individual.

The parenchymatous thalli are generally covered with a mucilage layer, rather than cuticle.[9]

Taxonomy

Phylogeny

Under evolution by

sporangia. With radiometric dating and the measure Ma “unequivocal minimum constraint for total group Pinaceae” vascular plants have been measured as having evolved around 419–454 Ma[12] while the ancestors of laminariales are much younger at 189 Ma.[13] Although these groups are distantly related as well as different in evolutionary age, there are still comparisons that can be made between the structures of terrestrial plants and kelp but in terms of evolutionary history, most of these similarities come from convergent evolution
.

Some kelp species including giant kelp, have evolved transport mechanisms for organic as well as

giant kelp (Macrocystis pyrifera) transport anatomy looked at 6 different laminariales species to see if they had typical vascular plant allometric relationships (if SEs had a correlation with the size of an organism). Researchers expected to find the kelp’s phloem to work similarly to a plant's xylem and therefore display similar allometric trends to minimize pressure gradient. The study found no universal allometric scaling between all tested structures of the laminariales species which implies that the transport network of brown algae is only just beginning to evolve to efficiently fit their current niches.[11]

Apart from undergoing convergent evolution with plants, species of kelp have undergone convergent evolution within their own phylogeny that has led to niche conservatism.[15] This niche conservatism means that some species of kelp have convergently evolved to share similar niches, as opposed to all species diverging into distinct niches through adaptive radiation. A 2020 study looked at functional traits (blade mass per area, stiffness, strength, etc.) of 14 species of kelp and found that many of these traits evolved convergently across kelp phylogeny. With different species of kelp filling slightly different environmental niches, specifically along a wave disturbance gradient, many of these convergently evolved traits for structural reinforcement also correlate with distribution along that gradient. The wave disturbance gradient that this study refers to is the environments that this kelp inhabit have a varied level of perturbation from the tide and waves that pull at the kelp. It can be assumed from these results that niche partitioning along wave disturbance gradients is a key driver of divergence between closely related kelp.[15]

Due to the often varied and turbulent habitat that kelp inhabit, plasticity of certain structural traits has been a key for the evolutionary history of the phyla. Plasticity helps with a very important aspect of kelp adaptations to ocean environments, and that is the unusually high levels of morphological homoplasy between lineages. This in fact has made classifying brown algae difficult.[16] Kelp often have similar morphological features to other species within its own area since the roughness of the wave disturbance regime, but can look fairly different from other members of its own species that are found in different wave disturbance regimes. Plasticity in kelps most often involves blade morphology such as the width, ruffle, and thickness of blades.[17] Just one example is the giant bull kelp Nereocystis luetkeana, which have evolved to change blade shape in order to increase drag in water and interception of light when exposed to certain environments. Bull kelp are not unique in this adaptation; many kelp species have evolved a genetic plasticity for blade shapes for different water flow habitats. So individuals of the same species will have differences to other individuals of the same species due to what habitat they grow in.[18] Many species have different morphologies for different wave disturbance regimes[17] but giant kelp Macrocystis integrifolia has been found to have plasticity allowing for 4 distinct types of blade morphology depending on habitat.[19] Where many species only have two or three different blade shapes for maximizing efficiency in only two or three habitats. These different blade shapes were found to decrease breakage and increase ability to photosynthesize. Blade adaptations like these are how kelp have evolved for efficiency in structure in a turbulent ocean environment, to the point where their stability can shape entire habitats. Apart from these structural adaptations, the evolution of dispersal methods relating to structure have been important for the success of kelp as well.

Kelp have had to adapt

Macrocystis pyrifera, adaptation of pneumatocysts and raft forming have made the species dispersal method so successful that the immense spread of coast in which the species can be found has been found to actually be very recently colonized. This can be observed by the low genetic diversity in the subantarctic region.[22] Dispersal by rafts from buoyant species also explains some evolutionary history for non-buoyant species of kelp. Since these rafts commonly have hitchhikers of other diverse species, they provide a mechanism for dispersal for species that lack buoyancy. This mechanism has been recently confirmed to be the cause of some dispersal and evolutionary history for kelp species in a study done with genomic analysis.[23] Studies of kelp structure evolution have helped in the understanding of the adaptations that have allowed for kelp to not only be extremely successful as a group of organisms but also successful as an ecosystem engineer of kelp forests
, some of the most diverse and dynamic ecosystems on earth.

Prominent species

Species of Laminaria in the British Isles;

Species of Laminaria worldwide, listing of species at AlgaeBase:[24]

Costaria costata, five-ribbed kelp

Other species in the

Laminariales
that may be considered as kelp:

Non-Laminariales species that may be considered as kelp:

A kelp forest
Anemone and seastar in kelp forest

Ecology

Kelp forests

Main article: Kelp forest

Kelp may develop dense forests with high production,

sessile animals (sponges, bryozoans and ascidians) are found on kelp stipes and mobile invertebrate fauna are found in high densities on epiphytic algae on the kelp stipes and on kelp holdfasts.[31] More than 100,000 mobile invertebrates per square meter are found on kelp stipes and holdfasts in well-developed kelp forests.[32] While larger invertebrates and in particular sea urchins (Strongylocentrotus droebachiensis) are important secondary consumers controlling large barren ground areas on the Norwegian coast, they are scarce inside dense kelp forests.[33]

Interactions

Some animals are named after the kelp, either because they inhabit the same

habitat
as kelp or because they feed on kelp. These include:

Conservation

Overfishing nearshore ecosystems leads to the degradation of kelp forests. Herbivores are released from their usual population regulation, leading to over-grazing of kelp and other algae. This can quickly result in barren landscapes where only a small number of species can thrive.[34][35] Other major factors which threaten kelp include marine pollution and the quality of water, climate changes and certain invasive species.[36]

Uses

Main article: Kelp farming
Seaweed, kelp, raw
Nutritional value per 100 g (3.5 oz)
Energy180 kJ (43 kcal)
9.57 g
Sugars0.6
Dietary fiber1.3 g
0.56 g
1.68 g
Niacin (B3)
3%
0.47 mg
Pantothenic acid (B5)
13%
0.642 mg
Folate (B9)
45%
180 μg
Vitamin C
3%
3 mg
Vitamin E
6%
0.87 mg
Vitamin K
55%
66 μg
MineralsQuantity
%DV†
Calcium
13%
168 mg
Iron
16%
2.85 mg
Magnesium
29%
121 mg
Manganese
9%
0.2 mg
Phosphorus
3%
42 mg
Potassium
3%
89 mg
Sodium
10%
233 mg
Zinc
11%
1.23 mg
Link to USDA Database entry
†Percentages estimated using US recommendations for adults,[37] except for potassium, which is estimated based on expert recommendation from the National Academies.[38]

Giant kelp can be harvested fairly easily because of its surface canopy and growth habit of staying in deeper water.

Kelp ash is rich in iodine and alkali. In great amount, kelp ash can be used in soap and glass production. Until the Leblanc process was commercialized in the early 19th century, burning of kelp in Scotland was one of the principal industrial sources of soda ash (predominantly sodium carbonate).[39] Around 23 tons of seaweed was required to produce 1 ton of kelp ash. The kelp ash would consist of around 5% sodium carbonate.[40]

Once the Leblanc Process became commercially viable in Britain during the 1820s, common salt replaced kelp ash as raw material for sodium carbonate. Though the price of kelp ash went into steep decline, seaweed remained the only commercial source of iodine. To supply the new industry in iodine synthesis, kelp ash production continued in some parts of West and North Scotland, North West Ireland and Guernsey. The species

lixiviation process.[41] As with sodium carbonate however, mineral sources eventually supplanted seaweed in iodine production.[42]

jelly, salad dressing, and toothpaste, as well as an ingredient in exotic dog food and in manufactured goods.[43][44][45] Alginate powder is also used frequently in general dentistry and orthodontics for making impressions of the upper and lower arches.[46] Kelp polysaccharides are used in skin care as gelling ingredients and because of the benefits provided by fucoidan.[citation needed
]

Kombu (昆布 in Japanese, and 海带 in Chinese, Saccharina japonica and others), several Pacific species of kelp, is a very important ingredient in Chinese, Japanese, and Korean cuisines. Kombu is used to flavor broths and stews (especially dashi), as a savory garnish (tororo konbu) for rice and other dishes, as a vegetable, and a primary ingredient in popular snacks (such as tsukudani). Transparent sheets of kelp (oboro konbu) are used as an edible decorative wrapping for rice and other foods.[47]

Kombu can be used to soften beans during cooking, and to help convert indigestible sugars and thus reduce flatulence.[48]

Saccharina latissima in canned salad form

In Russia, especially in the Russian Far East, and former Soviet Union countries several types of kelp are of commercial importance: Saccharina latissima, Laminaria digitata, Saccharina japonica. Known locally as "Sea Cabbage" (Морская капуста in Russian), it comes in retail trade in dried or frozen, as well as in canned form and used as filler in different types of salads, soups and pastries.[49]

Because of its high concentration of iodine, brown kelp (

thyrotoxicosis.[51]

In 2010, researchers found that

soluble fibre substance in sea kelp, was better at preventing fat absorption than most over-the-counter slimming treatments in laboratory trials. As a food additive, it may be used to reduce fat absorption and thus obesity.[52]
Kelp in its natural form has not yet been demonstrated to have such effects.

Kelp's rich iron content can help prevent iron deficiency.[53]

Commercial production

Commercial production of kelp harvested from its natural habitat has taken place in Japan for over a century. Many countries today produce and consume laminaria products; the largest producer is China.

Laminaria japonica, the important commercial seaweed, was first introduced into China in the late 1920s from Hokkaido, Japan. Yet mariculture
of this alga on a very large commercial scale was realized in China only in the 1950s. Between the 1950s and the 1980s, kelp production in China increased from about 60 to over 250,000 dry weight metric tons annually.

In culture

Scuba diver in kelp forest

Some of the earliest evidence for human use of marine resources, coming from Middle Stone Age sites in South Africa, includes the harvesting of foods such as abalone, limpets, and mussels associated with kelp forest habitats.

In 2007, Erlandson et al. suggested that kelp forests around the Pacific Rim may have facilitated the dispersal of anatomically modern humans following a coastal route from Northeast Asia to the Americas. This "kelp highway hypothesis" suggested that highly productive kelp forests supported rich and diverse marine food webs in nearshore waters, including many types of fish, shellfish, birds, marine mammals, and seaweeds that were similar from Japan to California, Erlandson and his colleagues also argued that coastal kelp forests reduced wave energy and provided a linear dispersal corridor entirely at sea level, with few obstacles to maritime peoples. Archaeological evidence from California's Channel Islands confirms that islanders were harvesting kelp forest shellfish and fish, beginning as much as 12,000 years ago.

During the Highland Clearances, many Scottish Highlanders were moved on to areas of estates known as crofts, and went to industries such as fishing and kelping (producing soda ash from the ashes of kelp). At least until the 1840s, when there were steep falls in the price of kelp, landlords wanted to create pools of cheap or virtually free labour, supplied by families subsisting in new crofting townships. Kelp collection and processing was a very profitable way of using this labour, and landlords petitioned successfully for legislation designed to stop emigration. The profitability of kelp harvesting meant that landlords began to subdivide their land for small tenant kelpers, who could now afford higher rent than their gentleman farmer counterparts.[54] But the economic collapse of the kelp industry in northern Scotland during the 1820s led to further emigration, especially to North America.[citation needed]

Natives of the

applied by outsiders rather than the natives themselves
.

In Chinese slang, "kelp" (simplified Chinese: 海带; traditional Chinese: 海帶; pinyin: hǎi dài), is used to describe an unemployed returnee.[clarification needed] It has negative overtones, implying the person is drifting aimlessly, and is also a homophonic expression (Chinese: 海待; pinyin: hǎidài, literally "sea waiting"). This expression is contrasted with the employed returnee, having a dynamic ability to travel across the ocean: the "sea turtle" (simplified Chinese: 海龟; traditional Chinese: 海龜; pinyin: hǎi gūi) and is also homophonic with another word (simplified Chinese: 海归; traditional Chinese: 海歸; pinyin: hǎi gūi, literally "sea return").

Gallery

See also

References

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Further reading

External links

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