Algae
Template:Short description Template:Hatgrp Template:Use dmy dates Template:Infobox
Algae (Template:IPAc-en Template:Respell, Template:IPAc-en Template:Respell;<ref>Template:Cite web</ref> Template:Singular: alga Template:IPAc-en Template:Respell) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, such as cyanobacteria,Template:Efn Chlorella, and diatoms, to multicellular macroalgae such as kelp or brown algae which may grow up to Template:Convert in length. Most algae are aquatic organisms and lack many of the distinct cell and tissue types, such as stomata, xylem, and phloem that are found in land plants. The largest and most complex marine algae are called seaweeds. In contrast, the most complex freshwater forms are the Charophyta, a division of green algae which includes, for example, Spirogyra and stoneworts. Algae that are carried passively by water are plankton, specifically phytoplankton.
Algae constitute a polyphyletic group<ref name="Nabors-2004" /> because they do not include a common ancestor, and although eukaryotic algae with chlorophyll-bearing plastids seem to have a single origin (from symbiogenesis with cyanobacteria),<ref name="Keeling-2004">Template:Cite journal</ref> they were acquired in different ways. Green algae are a prominent example of algae that have primary chloroplasts derived from endosymbiont cyanobacteria. Diatoms and brown algae are examples of algae with secondary chloroplasts derived from endosymbiotic red algae, which they acquired via phagocytosis.<ref>Template:Cite journal</ref> Algae exhibit a wide range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction via spores.<ref>Smithsonian National Museum of Natural History; Department of Botany. Template:Cite web</ref>
Algae lack the various structures that characterize plants (which evolved from freshwater green algae), such as the phyllids (leaf-like structures) and rhizoids of bryophytes (non-vascular plants), and the roots, leaves and other xylemic/phloemic organs found in tracheophytes (vascular plants). Most algae are autotrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy or phagotrophy. Some unicellular species of green algae, many golden algae, euglenids, dinoflagellates, and other algae have become heterotrophs (also called colorless or apochlorotic algae), sometimes parasitic, relying entirely on external energy sources and have limited or no photosynthetic apparatus.<ref>Pringsheim, E. G. 1963. Farblose Algen. Ein beitrag zur Evolutionsforschung. Gustav Fischer Verlag, Stuttgart. 471 pp., species:Algae#Pringsheim (1963).</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Some other heterotrophic organisms, such as the apicomplexans, are also derived from cells whose ancestors possessed chlorophyllic plastids, but are not traditionally considered as algae. Algae have photosynthetic machinery ultimately derived from cyanobacteria that produce oxygen as a byproduct of splitting water molecules, unlike other organisms that conduct anoxygenic photosynthesis such as purple and green sulfur bacteria. Fossilized filamentous algae from the Vindhya basin have been dated to 1.6 to 1.7 billion years ago.<ref>Template:Cite journal</ref>
Because of the wide range of types of algae, there is a correspondingly wide range of industrial and traditional applications in human society. Traditional seaweed farming practices have existed for thousands of years and have strong traditions in East Asian food cultures. More modern algaculture applications extend the food traditions for other applications, including cattle feed, using algae for bioremediation or pollution control, transforming sunlight into algae fuels or other chemicals used in industrial processes, and in medical and scientific applications. A 2020 review found that these applications of algae could play an important role in carbon sequestration to mitigate climate change while providing lucrative value-added products for global economies.<ref>Template:Cite book</ref>
Etymology and study
[edit]The singular Template:Lang is the Latin word for 'seaweed' and retains that meaning in English.<ref>Template:Cite book</ref> The etymology is obscure. Although some speculate that it is related to Latin Template:Lang, 'be cold',<ref>Template:Cite book</ref> no reason is known to associate seaweed with temperature. A more likely source is Template:Lang, 'binding, entwining'.<ref>Template:Cite book</ref>
The Ancient Greek word for 'seaweed' was Template:Lang (Template:Lang), which could mean either the seaweed (probably red algae) or a red dye derived from it. The Latinization, Template:Lang, meant primarily the cosmetic rouge. The etymology is uncertain, but a strong candidate has long been some word related to the Biblical Template:Lang (Template:Lang), 'paint' (if not that word itself), a cosmetic eye-shadow used by the ancient Egyptians and other inhabitants of the eastern Mediterranean. It could be any color: black, red, green, or blue.<ref>Template:Cite book</ref>
The study of algae is most commonly called phycology (Template:Etymology); the term algology is falling out of use.<ref>Template:Citation</ref>
Classifications
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One definition of algae is that they "have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells".<ref>Template:Cite book</ref> On the other hand, the colorless Prototheca under Chlorophyta are all devoid of any chlorophyll. Cyanobacteria are often referred to as "blue-green algae" and are included as algae by the International Code of Nomenclature for algae, fungi, and plants, although some authorities exclude all prokaryotes, including cyanobacteria, from the definition of algae.<ref name="Nabors-2004">Template:Cite book</ref><ref>Template:Cite dictionary</ref>
Eukaryotic algae contain chloroplasts that are similar in structure to cyanobacteria. Chloroplasts contain circular DNA like that in cyanobacteria and are interpreted as representing reduced endosymbiotic cyanobacteria. However, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events. The table below describes the composition of the three major groups of algae. Their lineage relationships are shown in the figure in the upper right. Many of these groups contain some members that are no longer photosynthetic. Some retain plastids, but not chloroplasts, while others have lost plastids entirely.<ref>Template:Cite journal</ref>
Phylogeny based on plastid<ref>Template:Cite journal</ref> not nucleocytoplasmic genealogy:
| Supergroup affiliation | Members | Endosymbiont | Summary |
|---|---|---|---|
| Primoplantae/ Archaeplastida |
Cyanobacteria | These algae have "primary" chloroplasts, i.e. the chloroplasts are surrounded by two membranes and probably developed through a single endosymbiotic event. The chloroplasts of red algae have chlorophylls a and c (often), and phycobilins, while those of green algae have chloroplasts with chlorophyll a and b without phycobilins. Land plants are pigmented similarly to green algae and probably developed from them, thus the Chlorophyta is a sister taxon to the plants; sometimes the Chlorophyta, the Charophyta, and land plants are grouped together as the Viridiplantae. | |
| Excavata and Rhizaria | Green algae |
These groups have green chloroplasts containing chlorophylls a and b.<ref>Template:Cite book</ref> Their chloroplasts are surrounded by four and three membranes, respectively, and were probably retained from ingested green algae. Chlorarachniophytes, which belong to the phylum Cercozoa, contain a small nucleomorph, which is a relict of the algae's nucleus. Euglenids, which belong to the phylum Euglenozoa, live primarily in fresh water and have chloroplasts with only three membranes. The endosymbiotic green algae may have been acquired through myzocytosis rather than phagocytosis.<ref>Template:Cite journal</ref> (Another group with green algae endosymbionts is the dinoflagellate genus Lepidodinium, which has replaced its original endosymbiont of red algal origin with one of green algal origin. A nucleomorph is present, and the host genome still have several red algal genes acquired through endosymbiotic gene transfer. Also, the euglenid and chlorarachniophyte genome contain genes of apparent red algal ancestry)<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> | |
| Halvaria and Hacrobia | Red algae |
These groups have chloroplasts containing chlorophylls a and c, and phycobilins. The shape can vary; they may be of discoid, plate-like, reticulate, cup-shaped, spiral, or ribbon shaped. They have one or more pyrenoids to preserve protein and starch. The latter chlorophyll type is not known from any prokaryotes or primary chloroplasts, but genetic similarities with red algae suggest a relationship there.<ref>Template:Cite journal</ref> In the first three of these groups, (Chromista), the chloroplast has four membranes, retaining a nucleomorph in cryptomonads, and they likely share a common pigmented ancestor, although other evidence casts doubt on whether the heterokonts, Haptophyta, and cryptomonads are in fact more closely related to each other than to other groups.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> The typical dinoflagellate chloroplast has three membranes, but considerable diversity exists in chloroplasts within the group, and a number of endosymbiotic events apparently occurred.<ref name="Keeling-2004" /> The Apicomplexa, a group of closely related parasites, also have plastids called apicoplasts, which are not photosynthetic.<ref name="Keeling-2004" /> The Chromerida are the closest relatives of apicomplexans, and some have retained their chloroplasts.<ref name="Moore 2008">Template:Cite journal</ref> The three alveolate groups evolved from a common myzozoan ancestor that obtained chloroplasts.<ref>Template:Cite journal</ref> |
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Linnaeus, in Species Plantarum (1753),<ref>Template:Cite book</ref> the starting point for modern botanical nomenclature, recognized 14 genera of algae, of which only four are currently considered among algae.<ref>Template:Cite book</ref> In Systema Naturae, Linnaeus described the genera Volvox and Corallina, and a species of Acetabularia (as Madrepora), among the animals.
In 1768, Samuel Gottlieb Gmelin (1744–1774) published the Historia Fucorum, the first work dedicated to marine algae and the first book on marine biology to use the then new binomial nomenclature of Linnaeus. It included elaborate illustrations of seaweed and marine algae on folded leaves.<ref>Template:Cite book</ref><ref>Template:Cite book</ref>
W. H. Harvey (1811–1866) and Lamouroux (1813)<ref name="Medlin-1997">Template:Cite journal</ref> were the first to divide macroscopic algae into four divisions based on their pigmentation. This is the first use of a biochemical criterion in plant systematics. Harvey's four divisions are: red algae (Rhodospermae), brown algae (Melanospermae), green algae (Chlorospermae), and Diatomaceae.<ref>Template:Cite book</ref><ref>Template:Cite book.</ref>
At this time, microscopic algae were discovered and reported by a different group of workers (e.g., O. F. Müller and Ehrenberg) studying the Infusoria (microscopic organisms). Unlike macroalgae, which were clearly viewed as plants, microalgae were frequently considered animals because they are often motile.<ref name="Medlin-1997" /> Even the nonmotile (coccoid) microalgae were sometimes merely seen as stages of the lifecycle of plants, macroalgae, or animals.<ref>Braun, A. Algarum unicellularium genera nova et minus cognita, praemissis observationibus de algis unicellularibus in genere (New and less known genera of unicellular algae, preceded by observations respecting unicellular algae in general) Template:Webarchive. Lipsiae, Apud W. Engelmann, 1855. Translation at: Lankester, E. & Busk, G. (eds.). Quarterly Journal of Microscopical Science, 1857, vol. 5, (17), 13–16 Template:Webarchive; (18), 90–96 Template:Webarchive; (19), 143–149 Template:Webarchive.</ref><ref>Siebold, C. Th. v. "Ueber einzellige Pflanzen und Thiere (On unicellular plants and animals) Template:Webarchive". In: Siebold, C. Th. v. & Kölliker, A. (1849). Zeitschrift für wissenschaftliche Zoologie, Bd. 1, p. 270. Translation at: Lankester, E. & Busk, G. (eds.). Quarterly Journal of Microscopical Science, 1853, vol. 1, (2), 111–121 Template:Webarchive; (3), 195–206 Template:Webarchive.</ref>
Although used as a taxonomic category in some pre-Darwinian classifications, e.g., Linnaeus (1753),<ref name="Ragan-2010">Template:Cite journal</ref> de Jussieu (1789),<ref name="de Jussieu-1789">Template:Cite book</ref> Lamouroux (1813), Harvey (1836), Horaninow (1843), Agassiz (1859), Wilson & Cassin (1864),<ref name="Ragan-2010" /> in further classifications, the "algae" are seen as an artificial, polyphyletic group.<ref name="Khan-2020b">Template:Cite journal</ref>
Throughout the 20th century, most classifications treated the following groups as divisions or classes of algae: cyanophytes, rhodophytes, chrysophytes, xanthophytes, bacillariophytes, phaeophytes, pyrrhophytes (cryptophytes and dinophytes), euglenophytes, and chlorophytes. Later, many new groups were discovered (e.g., Bolidophyceae), and others were splintered from older groups: charophytes and glaucophytes (from chlorophytes), many heterokontophytes (e.g., synurophytes from chrysophytes, or eustigmatophytes from xanthophytes), haptophytes (from chrysophytes), and chlorarachniophytes (from xanthophytes).<ref>Template:Cite journal</ref>
With the abandonment of plant-animal dichotomous classification, most groups of algae (sometimes all) were included in Protista, later also abandoned in favour of Eukaryota. However, as a legacy of the older plant life scheme, some groups that were also treated as protozoans in the past still have duplicated classifications (see ambiregnal protists).<ref>Template:Cite journal</ref>
Some parasitic algae (e.g., the green algae Prototheca and Helicosporidium, parasites of metazoans, or Cephaleuros, parasites of plants) were originally classified as fungi, sporozoans, or protistans of incertae sedis,<ref>Template:Cite book</ref> while others (e.g., the green algae Phyllosiphon and Rhodochytrium, parasites of plants, or the red algae Pterocladiophila and Gelidiocolax mammillatus, parasites of other red algae, or the dinoflagellates Oodinium, parasites of fish) had their relationship with algae conjectured early. In other cases, some groups were originally characterized as parasitic algae (e.g., Chlorochytrium), but later were seen as endophytic algae.<ref>Round (1981). pp. 398–400, Template:Cite book.</ref> Some filamentous bacteria (e.g., Beggiatoa) were originally seen as algae. Furthermore, groups like the apicomplexans are also parasites derived from ancestors that possessed plastids, but are not included in any group traditionally seen as algae.<ref>Template:Cite book</ref><ref>Template:Cite journal</ref>
Evolution
[edit]Prokaryotic algae
[edit]Prokaryotic algae, i.e., cyanobacteria, are the only group of organisms where oxygenic photosynthesis has evolved. The oldest undisputed fossil evidence of cyanobacteria is dated at 2100 million years ago,<ref name="Schirrmeister-2013">Template:Cite journal</ref> although stromatolites, associated with cyanobacterial biofilms, appear as early as 3500 million years ago in the fossil record.<ref name="Baumgartner-2019">Template:Cite journal</ref>
Eukaryotic algae
[edit]Eukaryotic algae are polyphyletic thus their origin cannot be traced back to single hypothetical common ancestor. It is thought that they came into existence when photosynthetic coccoid cyanobacteria got phagocytized by a unicellular heterotrophic eukaryote (a protist),<ref name="Reyes-Prieto-2007">Template:Cite journal</ref> giving rise to double-membranous primary plastids. Such symbiogenic events (primary symbiogenesis) are believed to have occurred more than 1.5 billion years ago during the Calymmian period, early in Boring Billion, but it is difficult to track the key events because of so much time gap.<ref name="Khan-2020a">Template:Cite journal</ref> Primary symbiogenesis gave rise to three divisions of archaeplastids, namely the Viridiplantae (green algae and later plants), Rhodophyta (red algae) and Glaucophyta ("grey algae"), whose plastids further spread into other protist lineages through eukaryote-eukaryote predation, engulfments and subsequent endosymbioses (secondary and tertiary symbiogenesis).<ref name="Khan-2020a"/> This process of serial cell "capture" and "enslavement" explains the diversity of photosynthetic eukaryotes.<ref name="Reyes-Prieto-2007"/> The oldest undisputed fossil evidence of eukaryotic algae is Bangiomorpha pubescens, a red alga found in rocks around 1047 million years old.<ref name="Butterfield-2000">Template:Cite journal</ref><ref name="Gibson-2018"> Template:Cite journal</ref>
Recent genomic and phylogenomic approaches have significantly clarified plastid genome evolution, the horizontal movement of endosymbiont genes to the "host" nuclear genome, and plastid spread throughout the eukaryotic tree of life.<ref name="Reyes-Prieto-2007"/> It is accepted that both euglenophytes and chlorarachniophytes obtained their chloroplasts from chlorophytes that became endosymbionts.<ref name="Keeling-2017">Template:Cite book</ref> In particular, euglenophyte chloroplasts share the most resemblance with the genus Pyramimonas.<ref name="Bicudo-2016">Template:Cite journal</ref>
However, there is still no clear order in which the secondary and tertiary endosymbioses ("serial" endosymbioses) occurred for the "chromist" lineages (ochrophytes, cryptophytes, haptophytes and myzozoans). Two main models have been proposed to explain the order, both of which agree that cryptophytes obtained their chloroplasts from red algae. One model, hypothesized in 2014 by John W. Stiller and coauthors,<ref name="Stiller-2014">Template:Cite journal</ref> suggests that a cryptophyte became the plastid of ochrophytes, which in turn became the plastid of myzozoans and haptophytes. The other model, suggested by Andrzej Bodył and coauthors in 2009,<ref name="Bodył-2009">Template:Cite journal</ref> describes that a cryptophyte became the plastid of both haptophytes and ochrophytes, and it is a haptophyte that became the plastid of myzozoans instead.<ref name="Strassert-2021">Template:Cite journal</ref>
The following cladogram is a summary of the occurrence of algae across the tree of life, and the evolutionary relationships of each ancestrally photosynthetic group (shown in bold).<ref name="Strassert-2021"/><ref name="Eliáš-2021">Template:Cite journal</ref>
Relationship to land plants
[edit]Fossils of isolated spores suggest land plants may have been around as long as 475 million years ago (mya) during the Late Cambrian/Early Ordovician period,<ref>Template:Cite news</ref><ref>Template:Cite journal</ref> from sessile shallow freshwater charophyte algae much like Chara,<ref name="Kenrick-1997">Template:Cite book</ref> which likely got stranded ashore when riverine/lacustrine water levels dropped during dry seasons.<ref name="Raven-2001">Template:Cite journal</ref> These charophyte algae probably already developed filamentous thalli and holdfasts that superficially resembled plant stems and roots, and probably had an isomorphic alternation of generations. They perhaps evolved some 850 mya<ref name="Knauth-2009">Template:Cite journal</ref> and might even be as early as 1 Gya during the late phase of the Boring Billion.<ref name="Strother-2011">Template:Cite journal</ref>
Morphology
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A range of algal morphologies is exhibited, and convergence of features in unrelated groups is common. The only groups to exhibit three-dimensional multicellular thalli are the reds and browns, and some chlorophytes.<ref name="Xiao-2004">Template:Cite journal</ref> Apical growth is constrained to subsets of these groups: the florideophyte reds, various browns, and the charophytes.<ref name="Xiao-2004" /> The form of charophytes is quite different from those of reds and browns, because they have distinct nodes, separated by internode 'stems'; whorls of branches reminiscent of the horsetails occur at the nodes.<ref name="Xiao-2004" /> Conceptacles are another polyphyletic trait; they appear in the coralline algae and the Hildenbrandiales, as well as the browns.<ref name="Xiao-2004" />
Most of the simpler algae are unicellular flagellates or amoeboids, but colonial and nonmotile forms have developed independently among several of the groups. Some of the more common organizational levels, more than one of which may occur in the lifecycle of a species, are
- Colonial: small, regular groups of motile cells
- Capsoid: individual non-motile cells embedded in mucilage
- Coccoid: individual non-motile cells with cell walls
- Palmelloid: nonmotile cells embedded in mucilage
- Filamentous: a string of connected nonmotile cells, sometimes branching
- Parenchymatous: cells forming a thallus with partial differentiation of tissues
In three lines, even higher levels of organization have been reached, with full tissue differentiation. These are the brown algae,<ref>Template:Cite web</ref>—some of which may reach 50 m in length (kelps)<ref>Template:Cite book</ref>—the red algae,<ref>Template:Cite web</ref> and the green algae.<ref>Template:Cite web</ref> The most complex forms are found among the charophyte algae (see Charales and Charophyta), in a lineage that eventually led to the higher land plants. The innovation that defines these nonalgal plants is the presence of female reproductive organs with protective cell layers that protect the zygote and developing embryo. Hence, the land plants are referred to as the Embryophytes.
Turfs
[edit]The term algal turf is commonly used but poorly defined. Algal turfs are thick, carpet-like beds of seaweed that retain sediment and compete with foundation species like corals and kelps, and they are usually less than 15 cm tall. Such a turf may consist of one or more species, and will generally cover an area in the order of a square metre or more. Some common characteristics are listed:<ref name="Connell-2014" >Template:Cite journal</ref>
- Algae that form aggregations that have been described as turfs include diatoms, cyanobacteria, chlorophytes, phaeophytes and rhodophytes. Turfs are often composed of numerous species at a wide range of spatial scales, but monospecific turfs are frequently reported.<ref name="Connell-2014" />
- Turfs can be morphologically highly variable over geographic scales and even within species on local scales and can be difficult to identify in terms of the constituent species.<ref name="Connell-2014" />
- Turfs have been defined as short algae, but this has been used to describe height ranges from less than 0.5 cm to more than 10 cm. In some regions, the descriptions approached heights which might be described as canopies (20 to 30 cm).<ref name="Connell-2014" />
Physiology
[edit]Many algae, particularly species of the Characeae,<ref>Template:Cite book</ref> have served as model experimental organisms to understand the mechanisms of the water permeability of membranes, osmoregulation, salt tolerance, cytoplasmic streaming, and the generation of action potentials. Plant hormones are found not only in higher plants, but in algae, too.<ref>Template:Cite journal</ref>
Symbiotic algae
[edit]Some species of algae form symbiotic relationships with other organisms. In these symbioses, the algae supply photosynthates (organic substances) to the host organism providing protection to the algal cells. The host organism derives some or all of its energy requirements from the algae. Examples are:
Lichens
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Lichens are defined by the International Association for Lichenology to be "an association of a fungus and a photosynthetic symbiont resulting in a stable vegetative body having a specific structure".<ref>Template:Cite book</ref> The fungi, or mycobionts, are mainly from the Ascomycota with a few from the Basidiomycota. In nature, they do not occur separate from lichens. It is unknown when they began to associate.<ref>Template:Cite book</ref> One or more<ref>Template:Cite journal</ref> mycobiont associates with the same phycobiont species, from the green algae, except that alternatively, the mycobiont may associate with a species of cyanobacteria (hence "photobiont" is the more accurate term). A photobiont may be associated with many different mycobionts or may live independently; accordingly, lichens are named and classified as fungal species.<ref>Brodo et al. (2001), p. 6: "A species of lichen collected anywhere in its range has the same lichen-forming fungus and, generally, the same photobiont. (A particular photobiont, though, may associate with scores of different lichen fungi)."</ref> The association is termed a morphogenesis because the lichen has a form and capabilities not possessed by the symbiont species alone (they can be experimentally isolated). The photobiont possibly triggers otherwise latent genes in the mycobiont.<ref>Brodo et al. (2001), p. 8.</ref>
Trentepohlia is an example of a common green alga genus worldwide that can grow on its own or be lichenised. Lichen thus share some of the habitat and often similar appearance with specialized species of algae (aerophytes) growing on exposed surfaces such as tree trunks and rocks and sometimes discoloring them.
Coral reefs
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Coral reefs are accumulated from the calcareous exoskeletons of marine invertebrates of the order Scleractinia (stony corals). These animals metabolize sugar and oxygen to obtain energy for their cell-building processes, including secretion of the exoskeleton, with water and carbon dioxide as byproducts. Dinoflagellates (algal protists) are often endosymbionts in the cells of the coral-forming marine invertebrates, where they accelerate host-cell metabolism by generating sugar and oxygen immediately available through photosynthesis using incident light and the carbon dioxide produced by the host. Reef-building stony corals (hermatypic corals) require endosymbiotic algae from the genus Symbiodinium to be in a healthy condition.<ref>Template:Cite book</ref> The loss of Symbiodinium from the host is known as coral bleaching, a condition which leads to the deterioration of a reef.
Sea sponges
[edit]Template:Main Endosymbiontic green algae live close to the surface of some sponges, for example, breadcrumb sponges (Halichondria panicea). The alga is thus protected from predators; the sponge is provided with oxygen and sugars which can account for 50 to 80% of sponge growth in some species.<ref>Template:Cite journal</ref>
Life cycle
[edit]Template:Details Rhodophyta, Chlorophyta, and Heterokontophyta, the three main algal divisions, have life cycles which show considerable variation and complexity. In general, an asexual phase exists where the seaweed's cells are diploid, a sexual phase where the cells are haploid, followed by fusion of the male and female gametes. Asexual reproduction permits efficient population increases, but less variation is possible. Commonly, in sexual reproduction of unicellular and colonial algae, two specialized, sexually compatible, haploid gametes make physical contact and fuse to form a zygote. To ensure a successful mating, the development and release of gametes is highly synchronized and regulated; pheromones may play a key role in these processes.<ref>Template:Cite journal</ref> Sexual reproduction allows for more variation and provides the benefit of efficient recombinational repair of DNA damages during meiosis, a key stage of the sexual cycle.<ref>Template:Cite journal</ref> However, sexual reproduction is more costly than asexual reproduction.<ref>Template:Cite journal</ref> Meiosis has been shown to occur in many different species of algae.<ref>Template:Cite journal</ref>
Numbers
[edit]
The Algal Collection of the US National Herbarium (located in the National Museum of Natural History) consists of approximately 320,500 dried specimens, which, although not exhaustive (no exhaustive collection exists), gives an idea of the order of magnitude of the number of algal species (that number remains unknown).<ref>Template:Cite web</ref> Estimates vary widely. For example, according to one standard textbook,<ref>John (2002), p. 1.</ref> in the British Isles, the UK Biodiversity Steering Group Report estimated there to be 20,000 algal species in the UK. Another checklist reports only about 5,000 species. Regarding the difference of about 15,000 species, the text concludes: "It will require many detailed field surveys before it is possible to provide a reliable estimate of the total number of species ..."
Regional and group estimates have been made, as well:
- 5,000–5,500 species of red algae worldwide
- "some 1,300 in Australian Seas"<ref>Huisman (2000), p. 25.</ref>
- 400 seaweed species for the western coastline of South Africa,<ref>Stegenga (1997).</ref> and 212 species from the coast of KwaZulu-Natal.<ref>Template:Cite book</ref> Some of these are duplicates, as the range extends across both coasts, and the total recorded is probably about 500 species. Most of these are listed in List of seaweeds of South Africa. These exclude phytoplankton and crustose corallines.
- 669 marine species from California (US)<ref>Abbott and Hollenberg (1976), p. 2.</ref>
- 642 in the check-list of Britain and Ireland<ref>Hardy and Guiry (2006).</ref>
and so on, but lacking any scientific basis or reliable sources, these numbers have no more credibility than the British ones mentioned above. Most estimates also omit microscopic algae, such as phytoplankton.
The most recent estimate (as of the beginning of 2024) suggests 50,589 recent and 10,556 fossil algal species, generally classified into 14 traditional phyla/divisions (other representatives such as incertae sedis, etc.):<ref name="Guiry-2024"/>
| phylum (division) | number of described genera | number of described species |
|---|---|---|
| "Charophyta" (Streptophyta without land plants) | 236 | 5 644 |
| Chlorophyta (s.s.) | 1 513 | 7 934 |
| Chromeridophyta (Chromerida) | 6 | 8 |
| Cryptophyta (Cryptista s.s.) | 44 | 245 |
| Cyanobacteriota (Cyanophyta) | 866 | 5 723 |
| Dinoflagellata (Dinophyta, Dinozoa) | 710 | 3 911 |
| Euglenophyta (Euglenozoa) | 164 | 2 057 |
| Glaucophyta | 8 | 25 |
| Haptophyta | 391 | 1 722 |
| Heterokontophyta (Ochrophyta) | 1 781 | 23 314 |
| Picophyta (Picozoa) | 1 | 1 |
| Prasinodermatophyta (Prasinodermophyta) | 5 | 10 |
| Rhodelphidophyta (Rhodelphidia) | 1 | 2 |
| Rhodophyta | 1094 | 7554 |
| Incertae sedis etc. | 887 | 2 995 |
| Total | 7 707 | 61 145 |
Distribution
[edit]The distribution of algal species has been fairly well studied since the founding of phytogeography in the mid-19th century.<ref name="Round-1981">Template:Cite book</ref> Algae spread mainly by the dispersal of spores analogously to the dispersal of cryptogamic plants by spores. Spores can be found in a variety of environments: fresh and marine waters, air, soil, and in or on other organisms.<ref name="Round-1981" /> Whether a spore is to grow into an adult organism depends on the species and the environmental conditions where the spore lands.
The spores of freshwater algae are dispersed mainly by running water and wind, as well as by living carriers.<ref name="Round-1981" /> However, not all bodies of water can carry all species of algae, as the chemical composition of certain water bodies limits the algae that can survive within them.<ref name="Round-1981" /> Marine spores are often spread by ocean currents. Ocean water presents many vastly different habitats based on temperature and nutrient availability, resulting in phytogeographic zones, regions, and provinces.<ref>Round (1981), p. 362.</ref>
To some degree, the distribution of algae is subject to floristic discontinuities caused by geographical features, such as Antarctica, long distances of ocean or general land masses. It is, therefore, possible to identify species occurring by locality, such as "Pacific algae" or "North Sea algae". When they occur out of their localities, hypothesizing a transport mechanism is usually possible, such as the hulls of ships. For example, Ulva reticulata and U. fasciata travelled from the mainland to Hawaii in this manner.
Mapping is possible for select species only: "there are many valid examples of confined distribution patterns."<ref>Round (1981), p. 357.</ref> For example, Clathromorphum is an arctic genus and is not mapped far south of there.Template:Where<ref>Round (1981), p. 371.</ref> However, scientists regard the overall data as insufficient due to the "difficulties of undertaking such studies."<ref>Round (1981), p. 366.</ref>
Ecology
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Algae are prominent in bodies of water, common in terrestrial environments, and are found in unusual environments, such as on snow and ice. Seaweeds grow mostly in shallow marine waters, under Template:Convert deep; however, some such as Navicula pennata have been recorded to a depth of Template:Convert.<ref>Round (1981), p. 176.</ref> A type of algae, Ancylonema nordenskioeldii, was found in Greenland in areas known as the 'Dark Zone', which caused an increase in the rate of melting ice sheet.<ref>Template:Cite web</ref> The same algae was found in the Italian Alps, after pink ice appeared on parts of the Presena glacier.<ref>Template:Cite web</ref>
The various sorts of algae play significant roles in aquatic ecology. Microscopic forms that live suspended in the water column (phytoplankton) provide the food base for most marine food chains. In very high densities (algal blooms), these algae may discolor the water and outcompete, poison, or asphyxiate other life forms.
Algae can be used as indicator organisms to monitor pollution in various aquatic systems.<ref name="Omar-2010">Template:Cite journal</ref> In many cases, algal metabolism is sensitive to various pollutants. Due to this, the species composition of algal populations may shift in the presence of chemical pollutants.<ref name="Omar-2010" /> To detect these changes, algae can be sampled from the environment and maintained in laboratories with relative ease.<ref name="Omar-2010" />
On the basis of their habitat, algae can be categorized as: aquatic (planktonic, benthic, marine, freshwater, lentic, lotic),<ref>Necchi Jr., O. (ed.) (2016). River Algae. Springer, Template:Cite book.</ref> terrestrial, aerial (subaerial),<ref>Template:Cite book</ref> lithophytic, halophytic (or euryhaline), psammon, thermophilic, cryophilic, epibiont (epiphytic, epizoic), endosymbiont (endophytic, endozoic), parasitic, calcifilic or lichenic (phycobiont).<ref>Sharma, O. P. (1986). pp. 2–6, [1].</ref>
Cultural associations
[edit]In classical Chinese, the word Template:Lang is used both for "algae" and (in the modest tradition of the imperial scholars) for "literary talent". The third island in Kunming Lake beside the Summer Palace in Beijing is known as the Zaojian Tang Dao (藻鑒堂島), which thus simultaneously means "Island of the Algae-Viewing Hall" and "Island of the Hall for Reflecting on Literary Talent".
Cultivation
[edit]Seaweed farming
[edit]Bioreactors
[edit]Uses
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Agar
[edit]Agar, a gelatinous substance derived from red algae, has a number of commercial uses.<ref>Template:Cite book</ref> It is a good medium on which to grow bacteria and fungi, as most microorganisms cannot digest agar.
Alginates
[edit]Alginic acid, or alginate, is extracted from brown algae. Its uses range from gelling agents in food, to medical dressings. Alginic acid also has been used in the field of biotechnology as a biocompatible medium for cell encapsulation and cell immobilization. Molecular cuisine is also a user of the substance for its gelling properties, by which it becomes a delivery vehicle for flavours.
Between 100,000 and 170,000 wet tons of Macrocystis are harvested annually in New Mexico for alginate extraction and abalone feed.<ref>Template:Cite web</ref><ref>Template:Cite web</ref>
Energy source
[edit]To be competitive and independent from fluctuating support from (local) policy on the long run, biofuels should equal or beat the cost level of fossil fuels. Here, algae-based fuels hold great promise,<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> directly related to the potential to produce more biomass per unit area in a year than any other form of biomass. The break-even point for algae-based biofuels is estimated to occur by 2025.<ref>Template:Cite journal</ref>
Fertilizer
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For centuries, seaweed has been used as a fertilizer; George Owen of Henllys writing in the 16th century referring to drift weed in South Wales:<ref>Template:Cite journal</ref> Template:Quote
Today, algae are used by humans in many ways; for example, as fertilizers, soil conditioners, and livestock feed.<ref>Template:Cite book</ref> Aquatic and microscopic species are cultured in clear tanks or ponds and are either harvested or used to treat effluents pumped through the ponds. Algaculture on a large scale is an important type of aquaculture in some places. Maerl is commonly used as a soil conditioner.
As food
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Algae are used as foods in many countries: China consumes more than 70 species, including fat choy, a cyanobacterium considered a vegetable; Japan, over 20 species such as nori and aonori;<ref>Template:Cite book</ref> Ireland, dulse; Chile, cochayuyo.<ref>Template:Cite web</ref> Laver is used to make laverbread in Wales, where it is known as Template:Lang. In Korea, green laver is used to make Template:Lang.<ref>Template:Cite web</ref>
Three forms of algae used as food:
- Chlorella: This form of alga is found in freshwater and contains photosynthetic pigments in its chloroplast.
- Klamath AFA: A subspecies of Aphanizomenon flos-aquae found wild in many bodies of water worldwide but harvested only from Upper Klamath Lake, Oregon.
- Spirulina: Known otherwise as a cyanobacterium (a prokaryote or a "blue-green alga")
The oils from some algae have high levels of unsaturated fatty acids. Some varieties of algae favored by vegetarianism and veganism contain the long-chain, essential omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA).<ref name=":0">Template:Cite web</ref> Fish oil contains the omega-3 fatty acids, but the original source is algae (microalgae in particular), which are eaten by marine life such as copepods and are passed up the food chain.<ref name=":0" />
Pollution control
[edit]- Sewage can be treated with algae,<ref>Template:Cite web</ref> reducing the use of large amounts of toxic chemicals that would otherwise be needed.
- Algae can be used to capture fertilizers in runoff from farms. When subsequently harvested, the enriched algae can be used as fertilizer.
- Aquaria and ponds can be filtered using algae, which absorb nutrients from the water in a device called an algae scrubber, also known as an algae turf scrubber.<ref>Template:Cite web</ref><ref>Template:Cite journal</ref>
Agricultural Research Service scientists found that 60–90% of nitrogen runoff and 70–100% of phosphorus runoff can be captured from manure effluents using a horizontal algae scrubber, also called an algal turf scrubber (ATS). Scientists developed the ATS, which consists of shallow, 100-foot raceways of nylon netting where algae colonies can form, and studied its efficacy for three years. They found that algae can readily be used to reduce the nutrient runoff from agricultural fields and increase the quality of water flowing into rivers, streams, and oceans. Researchers collected and dried the nutrient-rich algae from the ATS and studied its potential as an organic fertilizer. They found that cucumber and corn seedlings grew just as well using ATS organic fertilizer as they did with commercial fertilizers.<ref>Template:Cite web</ref> Algae scrubbers, using bubbling upflow or vertical waterfall versions, are now also being used to filter aquaria and ponds.
Polymers
[edit]Various polymers can be created from algae, which can be especially useful in the creation of bioplastics. These include hybrid plastics, cellulose-based plastics, poly-lactic acid, and bio-polyethylene.<ref>Template:Cite web</ref> Several companies have begun to produce algae polymers commercially, including for use in flip-flops<ref>Template:Cite news</ref> and in surf boards.<ref>Template:Cite web</ref> Even algae is also used to prepare various polymeric resins suitable for coating applications.<ref>Chandrashekhar K Patil, Harishchandra D Jirimali, Jayasinh S Paradeshi, Bhushan L Chaudhari, Prakash K Alagi, Sung Chul Hong, Vikas V Gite, Synthesis of biobased polyols using algae oil for multifunctional polyurethane coatings, Volume 6 Issue 4, December 2018, pp. 165-177, https://doi.org/10.1680/jgrma.18.00046</ref><ref>CK Patil, HD Jirimali, JS Paradeshi, BL Chaudhari, VV Gite, Functional antimicrobial and anticorrosive polyurethane composite coatings from algae oil and silver doped egg shell hydroxyapatite for sustainable development, Progress in Organic Coatings 128, 127-136, https://doi.org/10.1016/j.porgcoat.2018.11.002</ref><ref>Chandrashekhar K Patil, Harishchandra D Jirimali, Jayasinh S Paradeshi, Bhushan L Chaudhari, Prakash K Alagi, Pramod P Mahulikar, Sung Chul Hong, Vikas V Gite, Chemical transformation of renewable algae oil to polyetheramide polyols for polyurethane coatings, Progress in Organic Coatings 151, 106084, https://doi.org/10.1016/j.porgcoat.2020.106084</ref>
Bioremediation
[edit]The alga Stichococcus bacillaris has been seen to colonize silicone resins used at archaeological sites; biodegrading the synthetic substance.<ref>Template:Cite journal</ref>
Pigments
[edit]The natural pigments (carotenoids and chlorophylls) produced by algae can be used as alternatives to chemical dyes and coloring agents.<ref>Template:Cite book</ref> The presence of some individual algal pigments, together with specific pigment concentration ratios, are taxon-specific: analysis of their concentrations with various analytical methods, particularly high-performance liquid chromatography, can therefore offer deep insight into the taxonomic composition and relative abundance of natural algae populations in sea water samples.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>
Stabilizing substances
[edit]Template:Main Carrageenan, from the red alga Chondrus crispus, is used as a stabilizer in milk products.
Additional images
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Algae bladder
See also
[edit]- AlgaeBase
- AlgaePARC
- Eutrophication
- Iron fertilization
- Marimo algae
- Microbiofuels
- Microphyte
- Photobioreactor
- Phycotechnology
- Plants
- Toxoid – anatoxin
Notes
[edit]References
[edit]Bibliography
[edit]General
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Regional
[edit]Britain and Ireland
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Australia
[edit]New Zealand
[edit]Europe
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Arctic
[edit]Greenland
[edit]Faroe Islands
[edit]Canary Islands
[edit]Morocco
[edit]South Africa
[edit]North America
[edit]External links
[edit]Template:Commons category Template:Wikispecies
- Template:Cite web – a database of all algal names including images, nomenclature, taxonomy, distribution, bibliography, uses, extracts
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