Because of the wide range of types of algae, there is a correspondingly wide range of industrial and traditional applications in human society. Traditionalseaweed farming practices have existed for thousands of years and have strong traditions inEast Asian food cultures. More modernalgaculture applications extend thefood traditions for other applications, including cattle feed, using algae forbioremediation or pollution control, transforming sunlight intoalgae 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 incarbon sequestration tomitigate climate change while providing lucrative value-added products for global economies.[12]
The singularalga is the Latin word for 'seaweed' and retains that meaning in English.[13] Theetymology is obscure. Although some speculate that it is related to Latinalgēre, 'be cold',[14] no reason is known to associate seaweed with temperature. A more likely source isalliga, 'binding, entwining'.[15]
TheAncient Greek word for 'seaweed' wasφῦκος (phŷkos), which could mean either the seaweed (probably red algae) or a red dye derived from it. The Latinization,fūcus, meant primarily the cosmetic rouge. The etymology is uncertain, but a strong candidate has long been some word related to theBiblicalפוך (pūk), 'paint' (if not that word itself), acosmetic eye-shadow used by theancient Egyptians and other inhabitants of the eastern Mediterranean. It could be any color: black, red, green, or blue.[16]
The study of algae is most commonly calledphycology (from Greek phykos'seaweed'); the termalgology is falling out of use.[17]
The algae are a heterogeneous group of mostly photosynthetic organisms that produce oxygen and lack the reproductive features and structural complexity of land plants. This concept includes the cyanobacteria, which are prokaryotes, and all photosyntheticprotists, which are eukaryotes. They containchlorophylla as their primaryphotosynthetic pigment, and generally inhabit aquatic environments.[18][19]
However, there are many exceptions to this definition. Many non-photosynthetic protists are included in the study of algae, such as the heterotrophic relatives ofeuglenophytes[19] or the numerous species of colorless algae that have lost their chlorophyll during evolution (e.g.,Prototheca). Some exceptional species of algae tolerate dry terrestrial habitats, such as soil, rocks, or caves hidden from light sources, although they still need enough moisture to become active.[19]
Thekelp forest exhibit at the Monterey Bay Aquarium: A three-dimensional, multicellular thallus
A range of algalmorphologies is exhibited, andconvergence of features in unrelated groups is common. The only groups to exhibit three-dimensional multicellularthalli are thereds andbrowns, and somechlorophytes.[20] Apical growth is constrained to subsets of these groups: theflorideophyte reds, various browns, and the charophytes.[20] 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 thehorsetails occur at the nodes.[20]Conceptacles are anotherpolyphyletic trait; they appear in thecoralline algae and theHildenbrandiales, as well as the browns.[20]
Most of the simpler algae are unicellularflagellates oramoeboids, 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 thelifecycle of a species, are
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,[21]—some of which may reach 50 m in length (kelps)[22]—the red algae,[23] and the green algae.[24] The most complex forms are found among the charophyte algae (seeCharales andCharophyta), 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 theEmbryophytes.
The term algal turf is commonly used but poorly defined. Algal turfs are thick, carpet-like beds of seaweed that retainsediment and compete with foundation species likecorals andkelps, 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:[25]
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.[25]
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.[25]
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).[25]
Rhodophyta,Chlorophyta, andHeterokontophyta, 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 arediploid, a sexual phase where the cells arehaploid, followed by fusion of the male and femalegametes. 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 azygote. 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.[28] Sexual reproduction allows for more variation and provides the benefit of efficient recombinational repair of DNA damages duringmeiosis, a key stage of the sexual cycle.[29] However, sexual reproduction is more costly than asexual reproduction.[30] Meiosis has been shown to occur in many different species of algae.[31]
The most recent estimate (as of January 2024) documents 50,605 living and 10,556 fossil algal species, according to the online databaseAlgaeBase.[b] They are classified into 15phyla ordivisions. Some phyla are not photosynthetic, namelyPicozoa andRhodelphidia, but they are included in the database due to their close relationship withred algae.[1][35]
The various algal phyla can be differentiated according to several biological traits. They have distinct morphologies, photosynthetic pigmentation, storage products, cell wall composition,[19] and mechanisms of carbon concentration.[36] Some phyla have unique cellular structures.[19]
Macro- and microscopic photographs ofNostoc, the most common genus of cyanobacteria.[37]
Among prokaryotes, five major groups of bacteria have evolved the ability to photosynthesize, includingheliobacteria,green sulfur andnonsulfur bacteria andproteobacteria.[38] However, the only lineage whereoxygenic photosynthesis has evolved is in thecyanobacteria,[39] named for their blue-green (cyan) coloration and often known as blue-green algae.[40] They areclassified as thephylum Cyanobacteriota or Cyanophyta. However, this phylum also includes twoclasses of non-photosynthetic bacteria:Melainabacteria[41] (also called Vampirovibrionia[42] or Vampirovibrionophyceae)[43] and Sericytochromatia[44] (also known as Blackallbacteria).[45] A third class contains the photosynthetic ones, known asCyanophyceae[43] (also called Cyanobacteriia[42] or Oxyphotobacteria).[44]
As bacteria, their cells lack membrane-bound organelles, with the exception ofthylakoids. Like other algae, cyanobacteria have chlorophylla as their primary photosynthetic pigment. Their accessory pigments includephycobilins (phycoerythrobilin and phycocyanobilin),carotenoids and, in some cases,b,d, orf chlorophylls, generally distributed inphycobilisomes found in the surface of thylakoids. They display a variety of body forms, such as single cells, colonies, and unbranched or branched filaments. Their cells are commonly covered in a sheath ofmucilage, and they also have a typicalgram-negative bacterial cell wall composed largely ofpeptidoglycan. They have various storage particles, includingcyanophycin as aminoacid and nitrogen reserves, "cyanophycean starch" (similar to plantamylose) for carbohydrates, andlipid droplets. TheirRubisco enzymes are concentrated incarboxysomes. They occupy a diverse array of aquatic and terrestrial habitats, including extreme environments from hot springs to polar glaciers. Some are subterranean, living via hydrogen-basedlithoautotrophy instead of photosynthesis.[40]
Three lineages of cyanobacteria,Prochloraceae,Prochlorothrix andProchlorococcus, independently evolved to have chlorophyllsa andb instead of phycobilisomes. Due to their different pigmentation, they were historically grouped in a separate division,Prochlorophyta, as this is the typical pigmentation seen in green algae (e.g., chlorophytes). Eventually, this classification became obsolete, as it is apolyphyletic grouping.[46][47]
Eukaryotic algae containchloroplasts that are similar in structure to cyanobacteria. Chloroplasts contain circularDNA like that in cyanobacteria and are interpreted as representing reduced endosymbioticcyanobacteria. However, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events. Many groups contain some members that are no longer photosynthetic. Some retain plastids, but not chloroplasts, while others have lost plastids entirely.[50]
These algae, grouped in thecladeArchaeplastida (meaning 'ancient plastid'), have "primarychloroplasts", i.e. the chloroplasts are surrounded by two membranes and probably developed through a single endosymbiotic event with a cyanobacterium. The chloroplasts of red algae havechlorophyllsa andc (often), andphycobilins, while those of green algae have chloroplasts with chlorophylla andb without phycobilins. Land plants are pigmented similarly to green algae and probably developed from them, thus theChlorophyta is a sister taxon to the plants; sometimes the Chlorophyta, theCharophyta, and land plants are grouped together as theViridiplantae.[citation needed]
There is also a minor group of algae with primary plastids of different origin than the chloroplasts of the archaeplastid algae. The photosynthetic plastid of three species of the genusPaulinella (Rhizaria –Cercozoa –Euglyphida), often referred to as a 'cyanelle', was originated in the endosymbiosis of a α-cyanobacterium (probably an ancestral member ofChroococcales).[51][52]
These algae appeared independently in various distantly related lineages after acquiring a chloroplast derived from another eukaryotic alga. Two lineages of secondary algae,chlorarachniophytes andeuglenophytes have "green" chloroplasts containing chlorophyllsa andb.[53] Their chloroplasts are surrounded by four and three membranes, respectively, and were probably retained from ingested green algae.[54][55][56]
Euglenophytes, which belong to the phylumEuglenozoa, live primarily in fresh water and have chloroplasts with only three membranes. The endosymbiotic green algae may have been acquired throughmyzocytosis rather thanphagocytosis.[58]
Another group with green algae endosymbionts is the dinoflagellate genusLepidodinium, 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.[59][60][61]
Other groups have "red" chloroplasts containing chlorophyllsa andc, 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.[62] In some of these groups, the chloroplast has four membranes, retaining anucleomorph incryptomonads, and they likely share a common pigmented ancestor, although other evidence casts doubt on whether theheterokonts,Haptophyta, andcryptomonads are in fact more closely related to each other than to other groups.[63][64]
The typical dinoflagellate chloroplast has three membranes, but considerable diversity exists in chloroplasts within the group, and a number of endosymbiotic events apparently occurred.[5] TheApicomplexa, a group of closely related parasites, also have plastids calledapicoplasts, which are not photosynthetic.[5] TheChromerida are the closest relatives of apicomplexans, and some have retained their chloroplasts.[65] The threealveolate groups evolved from a commonmyzozoan ancestor that obtained chloroplasts.[66]
In 1768,Samuel Gottlieb Gmelin (1744–1774) published theHistoria Fucorum, the first work dedicated to marine algae and the first book onmarine biology to use the then new binomial nomenclature of Linnaeus. It included elaborate illustrations of seaweed and marine algae on folded leaves.[69][70]
W. H. Harvey (1811–1866) andLamouroux (1813)[71] 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.[72][73]
At this time, microscopic algae were discovered and reported by a different group of workers (e.g.,O. F. Müller andEhrenberg) studying theInfusoria (microscopic organisms). Unlikemacroalgae, which were clearly viewed as plants,microalgae were frequently considered animals because they are often motile.[71] Even the nonmotile (coccoid) microalgae were sometimes merely seen as stages of the lifecycle of plants, macroalgae, or animals.[74][75]
Although used as a taxonomic category in some pre-Darwinian classifications, e.g., Linnaeus (1753),[76] de Jussieu (1789),[77] Lamouroux (1813), Harvey (1836), Horaninow (1843), Agassiz (1859), Wilson & Cassin (1864),[76] in further classifications, the "algae" are seen as an artificial, polyphyletic group.[78]
With the abandonment of plant-animal dichotomous classification, most groups of algae (sometimes all) were included inProtista, later also abandoned in favour ofEukaryota. However, as a legacy of the older plant life scheme, some groups that were also treated asprotozoans in the past still have duplicated classifications (seeambiregnal protists).[80]
Some parasitic algae (e.g., the green algaePrototheca andHelicosporidium, parasites of metazoans, orCephaleuros, parasites of plants) were originally classified asfungi,sporozoans, orprotistans ofincertae sedis,[81] while others (e.g., the green algaePhyllosiphon andRhodochytrium, parasites of plants, or the red algaePterocladiophila andGelidiocolax mammillatus, parasites of other red algae, or the dinoflagellatesOodinium, 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 asendophytic algae.[82] Some filamentous bacteria (e.g.,Beggiatoa) were originally seen as algae. Furthermore, groups like theapicomplexans are also parasites derived from ancestors that possessed plastids, but are not included in any group traditionally seen as algae.[83][84]
Prokaryotic algae, i.e.,cyanobacteria, are the only group of organisms whereoxygenic photosynthesis has evolved. The oldest undisputed fossil evidence of cyanobacteria is dated at 2100 million years ago,[85] althoughstromatolites, associated with cyanobacterialbiofilms, appear as early as 3500 million years ago in the fossil record.[86]
Eukaryotic algae arepolyphyletic thus their origin cannot be traced back to single hypotheticalcommon ancestor. It is thought that they came into existence when photosyntheticcoccoidcyanobacteria gotphagocytized by aunicellularheterotrophic eukaryote (aprotist),[87] giving rise to double-membranous primaryplastids. Suchsymbiogenic events (primary symbiogenesis) are believed to have occurred more than 1.5 billion years ago during theCalymmianperiod, early inBoring Billion, but it is difficult to track the key events because of so much time gap.[88] Primary symbiogenesis gave rise to three divisions ofarchaeplastids, namely theViridiplantae (green algae and laterplants),Rhodophyta (red algae) andGlaucophyta ("grey algae"), whose plastids further spread into other protist lineages through eukaryote-eukaryotepredation, engulfments and subsequent endosymbioses (secondary and tertiary symbiogenesis).[88] This process of serial cell "capture" and "enslavement" explains the diversity of photosynthetic eukaryotes.[87] The oldest undisputed fossil evidence of eukaryotic algae isBangiomorpha pubescens, a red alga found in rocks around 1047 million years old.[89][90]
Plastid acquisitions across eukaryotes, shown in discontinuous arrows: blue for the primary plastids derived directly from a cyanobacterium, and red and green for the secondary plastids derived from red algae and green algae, respectively. Red arrows are placed according to the 2024 hypothesis;[91] disagreements with previous hypotheses are marked '?'.[92]
However, there is still no clear order in which the secondary and tertiary endosymbioses occurred for the "chromist" lineages (ochrophytes,cryptophytes,haptophytes andmyzozoans).[94] Two main models have been proposed to explain the order, both of which agree that cryptophytes obtained their chloroplasts fromred algae. One model, hypothesized in 2014 by John W. Stiller and coauthors,[95] 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,[96] describes that a cryptophyte became the plastid of both haptophytes and ochrophytes, and it is a haptophyte that became the plastid of myzozoans instead.[92]In 2024, a third model by Filip Pietluch and coauthors proposed that there were two independent endosymbioses with red algae: one that originated the cryptophyte plastids (as in the previous models), and subsequently the haptophyte plastids; and another that originated the ochrophyte plastids, where the myzozoans obtained theirs.[91]
The distribution of algal species has been fairly well studied since the founding ofphytogeography in the mid-19th century.[103] Algae spread mainly by the dispersal ofspores analogously to the dispersal ofcryptogamicplants byspores. Spores can be found in a variety of environments: fresh and marine waters, air, soil, and in or on other organisms.[103] 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.[103] 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.[103] 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.[104]
To some degree, the distribution of algae is subject to floristic discontinuities caused by geographical features, such asAntarctica, 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 andU. fasciata travelled from the mainland toHawaii in this manner.
Mapping is possible for select species only: "there are many valid examples of confined distribution patterns."[105] For example,Clathromorphum is an arctic genus and is not mapped far south of there.[where?][106] However, scientists regard the overall data as insufficient due to the "difficulties of undertaking such studies."[107]
TheAlgal Collection of the US National Herbarium (located in theNational 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).[108] Estimates vary widely. For example, according to one standard textbook,[109] in theBritish Isles, theUK 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:
400 seaweed species for the western coastline of South Africa,[111] and 212 species from the coast of KwaZulu-Natal.[112] 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 inList of seaweeds of South Africa. These excludephytoplankton and crustose corallines.
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.[citation needed]
Algae are prominent in bodies of water, common in terrestrial environments, and are found in unusual environments, such as onsnow andice. Seaweeds grow mostly in shallow marine waters, less than100 m (330 ft) deep; however, some such asNavicula pennata have been recorded to a depth of 360 m (1,180 ft).[115] A type of algae,Ancylonema nordenskioeldii, was found inGreenland in areas known as the 'Dark Zone', which caused an increase in the rate of melting ice sheet.[116] The same algae was found in theItalian Alps, after pink ice appeared on parts of the Presena glacier.[117]
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 marinefood chains. In very high densities (algal blooms), these algae may discolor the water and outcompete, poison, orasphyxiate other life forms.[118]
Algae can be used asindicator organisms to monitor pollution in various aquatic systems.[119] 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.[119] To detect these changes, algae can be sampled from the environment and maintained in laboratories with relative ease.[119]
Some species of algae formsymbiotic 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.[citation needed] Examples are:
Lichens are defined by theInternational Association for Lichenology to be "an association of a fungus and a photosyntheticsymbiont resulting in a stable vegetative body having a specific structure".[123] The fungi, or mycobionts, are mainly from theAscomycota with a few from theBasidiomycota. In nature, they do not occur separate from lichens. It is unknown when they began to associate.[124] One or more[125] 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.[126] 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.[127]
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.[citation needed]
Coral reefs are accumulated from thecalcareous exoskeletons ofmarine invertebrates of the orderScleractinia (stonycorals). These animalsmetabolize sugar and oxygen to obtain energy for their cell-building processes, includingsecretion of the exoskeleton, with water andcarbon dioxide as byproducts. Dinoflagellates (algal protists) are oftenendosymbionts 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 genusSymbiodinium to be in a healthy condition.[128] The loss ofSymbiodinium from the host is known ascoral bleaching, a condition which leads to the deterioration of a reef.
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.[129]
Inclassical Chinese, the word藻 is used both for "algae" and (in the modest tradition of theimperial scholars) for "literary talent". The third island inKunming Lake beside theSummer 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".[citation needed]
The majority of algae that are intentionally cultivated fall into the category ofmicroalgae (also referred to asphytoplankton,microphytes, orplanktonic algae).Macroalgae, commonly known asseaweed, also have many commercial and industrial uses, but due to their size and the specific requirements of the environment in which they need to grow, they do not lend themselves as readily to cultivation (this may change, however, with the advent of newer seaweed cultivators, which are basicallyalgae scrubbers using upflowing air bubbles in small containers, known as tumble culture).[131]
Global production of farmed aquatic plants, overwhelmingly dominated by seaweeds, grew in output volume from 13.5 million tonnes in 1995, to just over 30 million tonnes in 2016 and 37.8 million tonnes in 2022.[137][138] This increase was the result of production expansions led by China, followed by Malaysia, the Philippines, the United Republic of Tanzania, and the Russian Federation.[137]
Cultured microalgae already contribute to a wide range of sectors in the emergingbioeconomy.[139] Research suggests there are large potentials and benefits of algaculture for the development of a futurehealthy andsustainable food system.[140][136]
The largest seaweed-producing countries as of 2022 areChina (58.62%) andIndonesia (28.6%); followed bySouth Korea (5.09%) and thePhilippines (4.19%). Other notable producers includeNorth Korea (1.6%),Japan (1.15%),Malaysia (0.53%),Zanzibar (Tanzania, 0.5%), andChile (0.3%).[143][144] Seaweed farming has frequently been developed to improve economic conditions and to reduce fishing pressure.[145]
TheFood 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 marineaquaculture.[146] In 2023, the global seaweed extract market was valued at $16.5 billion, with strong projected growth.[147]
A close up of microalgae –Pavlova sp.Analgae bioreactor is used for cultivatingmicro ormacroalgae. Algae may be cultivated for the purposes ofbiomass production (as in aseaweed cultivator),wastewater treatment,CO2 fixation, or aquarium/pond filtration in the form of analgae scrubber.[151] Algae bioreactors vary widely in design, falling broadly into two categories: open reactors and enclosed reactors. Open reactors are exposed to the atmosphere while enclosed reactors, also commonly calledphotobioreactors, are isolated to varying extents from the atmosphere. Specifically, algae bioreactors can be used to produce fuels such asbiodiesel andbioethanol, to generate animal feed, or to reduce pollutants such asNOx andCO2 in flue gases of power plants. Fundamentally, this kind of bioreactor is based on thephotosynthetic reaction, which is performed by thechlorophyll-containing algae itself using dissolved carbon dioxide and sunlight. The carbon dioxide is dispersed into the reactor fluid to make it accessible to the algae. The bioreactor has to be made out of transparent material.
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,[152][153] 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.[154]
This kind of ore they often gather and lay on great heapes, where it heteth and rotteth, and will have a strong and loathsome smell; when being so rotten they cast on the land, as they do their muck, and thereof springeth good corn, especially barley ... After spring-tydes or great rigs of the sea, they fetch it in sacks on horse backes, and carie the same three, four, or five miles, and cast it on the lande, which doth very much better the ground for corn and grass.
Today, algae are used by humans in many ways; for example, asfertilizers,soil conditioners, and livestock feed.[156] 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 ofaquaculture in some places.Maerl is commonly used as a soil conditioner.[157]
Klamath AFA: A subspecies of Aphanizomenon flos-aquae found wild in many bodies of water worldwide but harvested only fromUpper Klamath Lake, Oregon.[162]
The naturalpigments (carotenoids andchlorophylls) produced by algae can be used as alternatives to chemicaldyes and coloring agents.[165]The presence of some individual algal pigments, together with specific pigment concentration ratios, are taxon-specific: analysis of their concentrations with various analytical methods, particularlyhigh-performance liquid chromatography, can therefore offer deep insight into the taxonomic composition and relative abundance of natural algae populations in sea water samples.[166][167]
Carrageenan, from the red algaChondrus crispus, is used as a stabilizer in milk products.[citation needed]
Agar, agelatinous substance derived from red algae, has a number of commercial uses.[168] It is a good medium on which to grow bacteria and fungi, as most microorganisms cannot digest agar.[169]
Alginic acid, or alginate, is extracted frombrown algae. Its uses range from gelling agents in food, to medical dressings. Alginic acid also has been used in the field ofbiotechnology as abiocompatible 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.[170]
Sewage can be treated with algae,[173] 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.[174]
Aquaria and ponds can be filtered using algae, which absorb nutrients from the water in a device called analgae scrubber, also known as an algae turf scrubber.[175][176]
Agricultural Research Service scientists found that 60–90% of nitrogen runoff and 70–100% of phosphorus runoff can be captured frommanure effluents using a horizontal algae scrubber, also called analgal 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.[177] Algae scrubbers, using bubbling upflow or vertical waterfall versions, are now also being used to filter aquaria and ponds.[citation needed]
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.[179] Several companies have begun to produce algae polymers commercially, including for use in flip-flops[180] and in surf boards.[181] Even algae is also used to prepare various polymeric resins suitable forcoating applications.[182][183][184]
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