The epithallium or epithallus is the outer layer of a crustose coralline alga , which in some species is periodically shed to prevent organisms from attaching to and overgrowing the alga.
70-503: Coralline algae are red algae in the order Corallinales . They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls. The colors of these algae are most typically pink, or some other shade of red, but some species can be purple, yellow, blue, white, or gray-green. Coralline algae play an important role in the ecology of coral reefs . Sea urchins , parrot fish , and limpets and chitons (both mollusks) feed on coralline algae. In
140-469: A and d . Red algae are red due to phycoerythrin . They contain the sulfated polysaccharide carrageenan in the amorphous sections of their cell walls, although red algae from the genus Porphyra contain porphyran . They also produce a specific type of tannin called phlorotannins , but in a lower amount than brown algae do. As enlisted in realDB , 27 complete transcriptomes and 10 complete genomes sequences of red algae are available. Listed below are
210-399: A tetrasporophyte – this produces spore tetrads, which dissociate and germinate into gametophytes. The gametophyte is typically (but not always) identical to the tetrasporophyte. Carpospores may also germinate directly into thalloid gametophytes, or the carposporophytes may produce a tetraspore without going through a (free-living) tetrasporophyte phase. Tetrasporangia may be arranged in
280-407: A 150 ug/day requirement of iodine is obtained from a single gram of red algae. Red algae, like Gracilaria , Gelidium , Euchema , Porphyra , Acanthophora , and Palmaria are primarily known for their industrial use for phycocolloids (agar, algin, furcellaran and carrageenan) as thickening agent, textiles, food, anticoagulants, water-binding agents, etc. Dulse ( Palmaria palmata )
350-482: A carbon source have less negative δ C values than those that only use CO 2 . An additional difference of about 1.71‰ separates groups intertidal from those below the lowest tide line, which are never exposed to atmospheric carbon. The latter group uses the more C-negative CO 2 dissolved in sea water, whereas those with access to atmospheric carbon reflect the more positive signature of this reserve. Photosynthetic pigments of Rhodophyta are chlorophylls
420-592: A crustose stage; some later become frondose . As sessile encrusting organisms, the corallines are prone to overgrowth by other "fouling" algae. The group have many defences to such immuration, most of which depend on waves disturbing their thalli. However, the most relied-upon method involves waiting for herbivores to devour the potential encrusters. This places them in the unusual position of requiring herbivory, rather than benefiting from its avoidance. Many species periodically slough their surface epithallus – and anything attached to it. Some corallines slough off
490-436: A double membrane, lack grana and phycobilisomes on the stromal surface of the thylakoid membrane. The major photosynthetic products include floridoside (major product), D‐isofloridoside, digeneaside, mannitol, sorbitol, dulcitol etc. Floridean starch (similar to amylopectin in land plants), a long-term storage product, is deposited freely (scattered) in the cytoplasm. The concentration of photosynthetic products are altered by
560-514: A few species can reach lengths of 2 m. In the SCRP clade the class Compsopogonophyceae is multicellular, with forms varying from microscopic filaments to macroalgae. Stylonematophyceae have both unicellular and small simple filamentous species, while Rhodellophyceae and Porphyridiophyceae are exclusively unicellular. Most rhodophytes are marine with a worldwide distribution, and are often found at greater depths compared to other seaweeds. While this
630-449: A living organism was probably Corallina in the 1st century AD. In 1837, Rodolfo Amando Philippi recognized coralline algae were not animals, and he proposed the two generic names Lithophyllum and Lithothamnion as Lithothamnium . For many years, they were included in the order Cryptonemiales as the family Corallinaceae until, in 1986, they were raised to the order Corallinales. Many corallines produce chemicals which promote
700-541: A millimetre to several centimetres high. Some are free-living as rhodoliths (rounded, free-living specimens). The morphological complexity of rhodoliths enhances species diversity, and can be used as a non-taxonomic descriptor for monitoring. Thalli can be divided into three layers: the hypothallus , perithallus and epithallus . The epithallus is periodically shed, either in sheets or piecemeal. Corallines live in varying depths of water, ranging from periodically exposed intertidal settings to 270 m water depth (around
770-482: A parasitic lifestyle and may be found on closely or more distantly related red algal hosts. In the classification system of Adl et al. 2005, the red algae are classified in the Archaeplastida , along with the glaucophytes and the green algae plus land plants ( Viridiplantae or Chloroplastida). The authors use a hierarchical arrangement where the clade names do not signify rank; the class name Rhodophyceae
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#1732802517905840-415: A pit connection is formed, tubular membranes appear. A granular protein called the plug core then forms around the membranes. The tubular membranes eventually disappear. While some orders of red algae simply have a plug core, others have an associated membrane at each side of the protein mass, called cap membranes. The pit plug continues to exist between the cells until one of the cells dies. When this happens,
910-521: A representative coralline ( Clathromorphum ). The thickness is variable within species; in Lithothamnion , a single cell thickness is the norm, but three- or four-cell thick regions are also common. The epithallus sometimes overlies the roof of conceptacles , which are exposed only when the overlying epithallus is eventually shed. The epithallium is less strongly calcified than the underlying cells, facilitating its removal. The meristem itself
980-568: A row ( zonate ), in a cross (cruciate), or in a tetrad. The carposporophyte may be enclosed within the gametophyte, which may cover it with branches to form a cystocarp . The two following case studies may be helpful to understand some of the life histories algae may display: In a simple case, such as Rhodochorton investiens : A rather different example is Porphyra gardneri : The δ C values of red algae reflect their lifestyles. The largest difference results from their photosynthetic metabolic pathway : algae that use HCO 3 as
1050-419: A spike in coralline diversity, and the extinction of many delicately branched (and thus predation-prone) forms. The group's internal taxonomy is in a state of flux; molecular studies are proving more reliable than morphological methods in approximating relationships within the group. Recent advances in morphological classification based on skeletal ultrastructure, however, are promising. Crystal morphology within
1120-520: A surface layer of epithallial cells, which in a few cases may be an antifouling mechanism which serves the same function as enhancing herbivore recruitment. This also affects the community, as many algae recruit on the surface of a sloughing coralline, and are then lost with the surface layer of cells. This can also generate patchiness within the community. The common Indo-Pacific corallines, Neogoniolithon fosliei and Sporolithon ptychoides , slough epithallial cells in continuous sheets which often lie on
1190-681: A taxonomic grouping: Geniculate corallines are branching, tree-like organisms which are attached to the substratum by crustose or calcified, root-like holdfasts. The organisms are made flexible by having noncalcified sections (genicula) separating longer calcified sections (intergenicula). Nongeniculate corallines range from a few micrometres to several centimetres thick crusts. They are often very slow growing, and may occur on rock, coral skeletons, shells, other algae or seagrasses. Crusts may be thin and leafy to thick and strongly adherent. Some are parasitic or partly endophytic on other corallines. Many coralline crusts produce knobby protuberances ranging from
1260-405: A traditional part of European and Asian cuisines and are used to make products such as agar , carrageenans , and other food additives . Chloroplasts probably evolved following an endosymbiotic event between an ancestral, photosynthetic cyanobacterium and an early eukaryotic phagotroph . This event (termed primary endosymbiosis ) is at the origin of the red and green algae (including
1330-507: A worldwide distribution in various habitats; they generally prefer clean, high-flow streams with clear waters and rocky bottoms, but with some exceptions. A few freshwater species are found in black waters with sandy bottoms and even fewer are found in more lentic waters. Both marine and freshwater taxa are represented by free-living macroalgal forms and smaller endo/epiphytic/zoic forms, meaning they live in or on other algae, plants, and animals. In addition, some marine species have adopted
1400-455: Is energetically costly, does not affect seaweed recruitment when herbivores are removed. The surface of these plants is usually kept clean by herbivores, particularly the pear limpet, Patella cochlear . Sloughing in this case is probably a means of eliminating old reproductive structures and grazer-damaged surface cells, and reducing the likelihood of surface penetration by burrowing organisms. The corallines have an excellent fossil record from
1470-823: Is estimated that more than half of all known species of microbial eukaryotes harbor red-alga-derived plastids. Red algae are divided into the Cyanidiophyceae , a class of unicellular and thermoacidophilic extremophiles found in sulphuric hot springs and other acidic environments, an adaptation partly made possible by horizontal gene transfers from prokaryotes, with about 1% of their genome having this origin, and two sister clades called SCRP ( Stylonematophyceae , Compsopogonophyceae , Rhodellophyceae and Porphyridiophyceae ) and BF ( Bangiophyceae and Florideophyceae ), which are found in both marine and freshwater environments. The BF are macroalgae, seaweed that usually do not grow to more than about 50 cm in length, but
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#17328025179051540-452: Is incomplete. Typically, a small pore is left in the middle of the newly formed partition. The pit connection is formed where the daughter cells remain in contact. Shortly after the pit connection is formed, cytoplasmic continuity is blocked by the generation of a pit plug, which is deposited in the wall gap that connects the cells. Connections between cells having a common parent cell are called primary pit connections. Because apical growth
1610-726: Is one of the most consumed red algae and is a source of iodine, protein, magnesium and calcium. Red algae's nutritional value is used for the dietary supplement of algas calcareas . China, Japan, Republic of Korea are the top producers of seaweeds. In East and Southeast Asia, agar is most commonly produced from Gelidium amansii . These rhodophytes are easily grown and, for example, nori cultivation in Japan goes back more than three centuries. Researchers in Australia discovered that limu kohu ( Asparagopsis taxiformis ) can reduce methane emissions in cattle . In one Hawaii experiment,
1680-443: Is probably an important factor affecting the distribution and grazing effects of herbivores within marine communities. Nothing is known about the microhabitat role of Indo-Pacific corallines. However, the most common species in the region, Hydrolithon onkodes , often forms an intimate relationship with the chiton Cryptoplax larvaeformis . The chiton lives in burrows it makes in H. onkodes plants, and comes out at night to graze on
1750-528: Is supported by various structural and genetic similarities. Red algae have a long history of use as a source of nutritional, functional food ingredients and pharmaceutical substances. They are a source of antioxidants including polyphenols, and phycobiliproteins and contain proteins, minerals, trace elements, vitamins and essential fatty acids. Traditionally, red algae are eaten raw, in salads, soups, meal and condiments. Several species are food crops, in particular dulse ( Palmaria palmata ) and members of
1820-419: Is the isopod Idotea balthica. The trichogyne will continue to grow until it encounters a spermatium ; once it has been fertilized, the cell wall at its base progressively thickens, separating it from the rest of the carpogonium at its base. Upon their collision, the walls of the spermatium and carpogonium dissolve. The male nucleus divides and moves into the carpogonium; one half of the nucleus merges with
1890-416: Is the least calcified portion; sometimes there is no mineralization at all, which makes it a plane of weakness where breaking often occurs. Periodic sloughing of this surface is thought to reduce colonization of corallines by kelp (such as Laminaria ), epiphytes, and sessile invertebrates. Epithallial cells are covered (in patches) by a cuticle. The deterioration of the outer cells is accelerated in
1960-426: Is the norm in red algae, most cells have two primary pit connections, one to each adjacent cell. Connections that exist between cells not sharing a common parent cell are labelled secondary pit connections. These connections are formed when an unequal cell division produced a nucleated daughter cell that then fuses to an adjacent cell. Patterns of secondary pit connections can be seen in the order Ceramiales . After
2030-510: Is used for the red algae. No subdivisions are given; the authors say, "Traditional subgroups are artificial constructs, and no longer valid." Many subsequent studies provided evidence that is in agreement for monophyly in the Archaeplastida (including red algae). However, other studies have suggested Archaeplastida is paraphyletic . As of January 2011 , the situation appears unresolved. Below are other published taxonomies of
2100-510: The Ediacaran Period. Thallophytes resembling coralline red algae are known from the late Proterozoic Doushantuo formation . Chromista and Alveolata algae (e.g., chrysophytes, diatoms, phaeophytes, dinophytes) seem to have evolved from bikonts that have acquired red algae as endosymbionts . According to this theory, over time these endosymbiont red algae have evolved to become chloroplasts. This part of endosymbiotic theory
2170-586: The Solenoporaceae , a view that has been disputed. Their fossil record matches their molecular history, and is complete and continuous. The Sporolithaceae tend to be more diverse in periods of high ocean temperatures; the opposite is true for the Corallinaceae . The group's diversity has closely tracked the efficiency of grazing herbivores; for instance, the Eocene appearance of parrotfish marked
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2240-706: The 10 complete genomes of red algae. One of the oldest fossils identified as a red alga is also the oldest fossil eukaryote that belongs to a specific modern taxon . Bangiomorpha pubescens , a multicellular fossil from arctic Canada , strongly resembles the modern red alga Bangia and occurs in rocks dating to 1.05 billion years ago. Two kinds of fossils resembling red algae were found sometime between 2006 and 2011 in well-preserved sedimentary rocks in Chitrakoot, central India. The presumed red algae lie embedded in fossil mats of cyanobacteria, called stromatolites, in 1.6 billion-year-old Indian phosphorite – making them
2310-477: The 18th century. This is particularly significant in Britain and France , where more than 300,000 tonnes of Phymatolithon calcareum ( Pallas , Adey & McKinnin) and Lithothamnion corallioides are dredged annually. The earliest use of corallines in medicine involved the preparation of a vermifuge from ground geniculate corallines of the genera Corallina and Jania . This use stopped towards
2380-576: The Assembling the Tree of Life Program. Porphyridiales Bangiales Some sources (such as Lee) place all red algae into the class "Rhodophyceae". (Lee's organization is not a comprehensive classification, but a selection of orders considered common or important. ) A subphylum - Proteorhodophytina - has been proposed to encompass the existing classes Compsopogonophyceae , Porphyridiophyceae , Rhodellophyceae and Stylonematophyceae . This proposal
2450-543: The Early Cretaceous onwards, consistent with molecular clocks that show the divergence of the modern taxa beginning in this period. The fossil record of nonarticulated forms is better: the unmineralized genuiculae of articulated forms break down quickly, scattering the mineralized portions, which then decay more quickly. This said, non-mineralizing coralline algae are known from the Silurian of Gotland showing that
2520-508: The Mediterranean. Their ability to calcify in low light conditions makes them the some of deepest photosynthetic multicellular organisms in the ocean, having been found as deep as 268 metres (879 ft), and as such a critical base of mesophotic ecological systems. Since coralline algae contain calcium carbonate, they fossilize fairly well. They are particularly significant as stratigraphic markers in petroleum geology. Coralline rock
2590-468: The absence of chloroplast endoplasmic reticulum. The presence of the water-soluble pigments called phycobilins ( phycocyanobilin , phycoerythrobilin , phycourobilin and phycobiliviolin ), which are localized into phycobilisomes , gives red algae their distinctive color. Their chloroplasts contain evenly spaced and ungrouped thylakoids and contain the pigments chlorophyll a, α- and β-carotene, lutein and zeaxanthin. Their chloroplasts are enclosed in
2660-751: The asexual class Cyanidiophyceae , no terrestrial species exist, which may be due to an evolutionary bottleneck in which the last common ancestor lost about 25% of its core genes and much of its evolutionary plasticity. Red algae form a distinct group characterized by eukaryotic cells without flagella and centrioles , chloroplasts without external endoplasmic reticulum or unstacked (stroma) thylakoids , and use phycobiliproteins as accessory pigments , which give them their red color. Despite their name, red algae can vary in color from bright green, soft pink, resembling brown algae, to shades of red and purple, and may be almost black at greater depths. Unlike green algae, red algae store sugars as food reserves outside
2730-511: The calcified cell wall of coralline algae was found to have a high correspondence with molecular studies. These skeletal structures thus provide morphologic evidence for molecular relationships within the group. According to AlgaeBase : According to the World Register of Marine Species : According to ITIS : Fresh surfaces are generally colonized by thin crusts, which are replaced by thicker or branched forms during succession over
2800-404: The carpogonium's nucleus. The polyamine spermine is produced, which triggers carpospore production. Spermatangia may have long, delicate appendages, which increase their chances of "hooking up". They display alternation of generations . In addition to a gametophyte generation, many have two sporophyte generations, the carposporophyte -producing carpospores , which germinate into
2870-460: The cells above the intercalary meristem; these are not involved in photosynthesis. In Phymatolithon , the epithallium is usually one cell thick, whereas in other genera, such as Pseudolithophyllum , multiple cells exist, with the thickness determined by the difference between their rate of production at the intercalary meristem, and the rate of shedding at the surface; thicknesses of 16 cells or more, spanning 100 μm, have been measured in
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2940-541: The chloroplasts as floridean starch , a type of starch that consists of highly branched amylopectin without amylose . Most red algae are multicellular , macroscopic, and reproduce sexually . The life history of red algae is typically an alternation of generations that may have three generations rather than two. Coralline algae , which secrete calcium carbonate and play a major role in building coral reefs , belong there. Red algae such as Palmaria palmata (dulse) and Porphyra species ( laver / nori / gim ) are
3010-751: The community level; the presence of herbivores associated with corallines can generate patchiness in the survival of young stages of dominant seaweeds. This has been seen this in eastern Canada , and it is suspected the same phenomenon occurs on Indo-Pacific coral reefs , yet nothing is known about the herbivore enhancement role of Indo-Pacific corallines, or whether this phenomenon is important in coral reef communities. Some coralline algae develop into thick crusts which provide microhabitat for many invertebrates. For example, off eastern Canada , Morton found juvenile sea urchins , chitons , and limpets suffer nearly 100% mortality due to fish predation unless they are protected by knobby and undercut coralline algae. This
3080-500: The course of one (in the tropics) to ten (in the Arctic) years. However, the transition from crusts to branched form depends on environmental conditions. Crusts may also become detached and form calcareous nodules known as Rhodoliths . Their growth may be also disrupted by local environmental factors. While coralline algae are present in most hard substrate marine communities in photic depths, they are more common in higher latitudes and in
3150-520: The end of the 18th century. Medical science now uses corallines in the preparation of dental bone implants. The cell fusions provide the matrix for the regeneration of bone tissue. Maërl is also used as a food additive for cattle and pigs , as well as in the filtration of acidic drinking water. As a colorful component of live rock sold in the marine aquarium trade, and an important part of reef health, coralline algae are desired in home aquariums for their aesthetic qualities, and ostensible benefit to
3220-441: The environmental conditions like change in pH, the salinity of medium, change in light intensity, nutrient limitation etc. When the salinity of the medium increases the production of floridoside is increased in order to prevent water from leaving the algal cells. Pit connections and pit plugs are unique and distinctive features of red algae that form during the process of cytokinesis following mitosis . In red algae, cytokinesis
3290-438: The genus Porphyra , variously known as nori (Japan), gim (Korea), zicai 紫菜 (China), and laver (British Isles). Red algal species such as Gracilaria and Laurencia are rich in polyunsaturated fatty acids (eicopentaenoic acid, docohexaenoic acid, arachidonic acid ) and have protein content up to 47% of total biomass. Where a big portion of world population is getting insufficient daily iodine intake,
3360-515: The land plants or Embryophytes which emerged within them) and the glaucophytes , which together make up the oldest evolutionary lineages of photosynthetic eukaryotes, the Archaeplastida . A secondary endosymbiosis event involving an ancestral red alga and a heterotrophic eukaryote resulted in the evolution and diversification of several other photosynthetic lineages such as Cryptophyta , Haptophyta , Stramenopiles (or Heterokontophyta) , and Alveolata . In addition to multicellular brown algae, it
3430-692: The lineage has a much longer history than molecular clocks would indicate. The earliest known coralline deposits date from the Ordovician , although modern forms radiated in the Cretaceous . True corallines are found in rocks of Jurassic age onwards. Stem group corallines are reported from the Ediacaran Doushantuo formation ; later stem-group forms include Arenigiphyllum , Petrophyton , Graticula , and Archaeolithophyllum . The corallines were thought to have evolved from within
3500-454: The living cell produces a layer of wall material that seals off the plug. The pit connections have been suggested to function as structural reinforcement, or as avenues for cell-to-cell communication and transport in red algae, however little data supports this hypothesis. The reproductive cycle of red algae may be triggered by factors such as day length. Red algae reproduce sexually as well as asexually. Asexual reproduction can occur through
3570-518: The main reef structures that prevent oceanic waves from striking adjacent coastlines , helping to prevent coastal erosion . Because of their calcified structure, coralline algae have a number of economic uses. Some harvesting of maërl beds that span several thousand kilometres off the coast of Brazil takes place. These beds contain as-yet undetermined species belonging to the genera Lithothamnion and Lithophyllum . The collection of unattached corallines (maërl) for use as soil conditioners dates to
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#17328025179053640-473: The maximum penetration of light). Some species can tolerate brackish or hypersaline waters, and only one strictly freshwater coralline species exists. (Some species of the morphologically similar, but non-calcifying, Hildenbrandia , however, can survive in freshwater.) A wide range of turbidities and nutrient concentrations can be tolerated. Corallines, especially encrusting forms, are slow growers, and expand by 0.1–80 mm annually. All corallines begin with
3710-472: The oldest plant-like fossils ever found by about 400 million years. Red algae are important builders of limestone reefs. The earliest such coralline algae, the solenopores , are known from the Cambrian period. Other algae of different origins filled a similar role in the late Paleozoic , and in more recent reefs. Calcite crusts that have been interpreted as the remains of coralline red algae, date to
3780-530: The polysaccharides agarose and agaropectin that can be extracted from the cell walls as agar by boiling. The internal walls are mostly cellulose. They also have the most gene-rich plastid genomes known. Red algae do not have flagella and centrioles during their entire life cycle. The distinguishing characters of red algal cell structure include the presence of normal spindle fibres, microtubules, un-stacked photosynthetic membranes, phycobilin pigment granules, pit connection between cells, filamentous genera, and
3850-435: The presence of bacteria. A similar mechanism is found in geniculate reds. Epidermal tissue is also shed by unrelated algae: the fleshy reds and browns, (e.g. Chondrus , Ascophyllum ; Halidrys , Himanthalia ) and the calcaerous greens. Some sea grasses also periodically shed their external cell walls to avoid epiphyte cover. In the browns, this is accomplished by shedding cell wall material, without damaging
3920-419: The production of spores and by vegetative means (fragmentation, cell division or propagules production). Red algae lack motile sperm . Hence, they rely on water currents to transport their gametes to the female organs – although their sperm are capable of "gliding" to a carpogonium 's trichogyne . Animals also help with the dispersal and fertilization of the gametes. The first species discovered to do so
3990-585: The red algae using molecular and traditional alpha taxonomic data; however, the taxonomy of the red algae is still in a state of flux (with classification above the level of order having received little scientific attention for most of the 20th century). A major research initiative to reconstruct the Red Algal Tree of Life (RedToL) using phylogenetic and genomic approach is funded by the National Science Foundation as part of
4060-402: The reduction reached 77%. The World Bank predicted the industry could be worth ~$ 1.1 billion by 2030. As of 2024, preparation included three stages of cultivation and drying. Australia's first commercial harvest was in 2022. Agriculture accounts for 37% of the world’s anthropogenic methane emissions. One cow produces between 154 to 264 pounds of methane/yr. Epithallus It is defined as
4130-534: The reef materials into a sturdy structure. Corallines are particularly important in constructing the algal ridge's reef framework for surf-pounded reefs in both the Atlantic and Indo-Pacific regions. Algal ridges are carbonate frameworks constructed mainly by nongeniculate coralline algae (after Adey, 1978). They require high and persistent wave action to form, so develop best on windward reefs with little or no seasonal change in wind direction. Algal ridges are one of
4200-441: The rock surfaces. These patches of pink "paint" are actually living crustose coralline red algae. The red algae belong to the division Rhodophyta , within which the coralline algae form the order Corallinales . There are over 1600 described species of nongeniculate coralline algae. The corallines are presently grouped into two families on the basis of their reproductive structures. Coralline algae are widespread in all of
4270-458: The settlement of the larvae of certain herbivorous invertebrates , particularly abalone . Larval settlement is adaptive for the corallines because the herbivores remove epiphytes which might otherwise smother the crusts and preempt available light. Settlement is also important for abalone aquaculture ; corallines appear to enhance larval metamorphosis and the survival of larvae through the critical settlement period. It also has significance at
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#17328025179054340-402: The structure of the reef, help cement the reef together, and are important sources of primary production. Coralline algae are especially important in reef construction, as they lay down calcium carbonate as calcite. Although they contribute considerable bulk to the calcium carbonate structure of coral reefs, their more important role in most areas of the reef, is in acting as the cement which binds
4410-433: The surface of the coralline. This combination of grazing and burrowing results in a peculiar growth form (called "castles") in H. onkodes , in which the coralline produces nearly vertical, irregularly curved lamellae. Coralline algae are part of the diet of shingle urchins ( Colobocentrotus atratus ). Nongeniculate corallines are of particular significance in the ecology of coral reefs, where they add calcareous material to
4480-496: The surface of the plants. Not all sloughing serves an antifouling function. Epithallial shedding in most corallines is probably simply a means of getting rid of damaged cells whose metabolic function has become impaired. Morton and his students studied sloughing in the South African intertidal coralline alga, Spongites yendoi , a species which sloughs up to 50% of its thickness twice a year. This deep-layer sloughing, which
4550-859: The tank ecosystem. Red algae Red algae , or Rhodophyta ( / r oʊ ˈ d ɒ f ɪ t ə / , / ˌ r oʊ d ə ˈ f aɪ t ə / ; from Ancient Greek ῥόδον ( rhódon ) 'rose' and φυτόν ( phutón ) 'plant'), make up one of the oldest groups of eukaryotic algae . The Rhodophyta comprises one of the largest phyla of algae , containing over 7,000 recognized species within over 900 genera amidst ongoing taxonomic revisions. The majority of species (6,793) are Florideophyceae , and mostly consist of multicellular , marine algae, including many notable seaweeds . Red algae are abundant in marine habitats. Approximately 5% of red algae species occur in freshwater environments, with greater concentrations in warmer areas. Except for two coastal cave dwelling species in
4620-586: The temperate Mediterranean Sea , coralline algae are the main builders of a typical algal reef, the Coralligène ("coralligenous"). Many are typically encrusting and rock-like, found in marine waters all over the world. Only one species lives in freshwater. Unattached specimens ( maerl , rhodoliths ) may form relatively smooth compact balls to warty or fruticose thalli. A close look at almost any intertidal rocky shore or coral reef will reveal an abundance of pink to pinkish-grey patches, distributed throughout
4690-520: The world's oceans, where they often cover close to 100% of rocky substrata . Only one species, Pneophyllum cetinaensis , is found in freshwater. Its ancestor lived in brackish water, and was already adapted to osmotic stress and rapid changes in water salinity and temperature. Many are epiphytic (grow on other algae or marine angiosperms), or epizoic (grow on animals), and some are even parasitic on other corallines. Corallines have been divided into two groups, although this division does not constitute
4760-525: Was formerly attributed to the presence of pigments (such as phycoerythrin ) that would permit red algae to inhabit greater depths than other macroalgae by chromatic adaption, recent evidence calls this into question (e.g. the discovery of green algae at great depth in the Bahamas). Some marine species are found on sandy shores, while most others can be found attached to rocky substrata. Freshwater species account for 5% of red algal diversity, but they also have
4830-534: Was made on the basis of the analysis of the plastid genomes. Over 7,000 species are currently described for the red algae, but the taxonomy is in constant flux with new species described each year. The vast majority of these are marine with about 200 that live only in fresh water . Some examples of species and genera of red algae are: Red algal morphology is diverse ranging from unicellular forms to complex parenchymatous and non- parenchymatous thallus. Red algae have double cell walls . The outer layers contain
4900-528: Was used as building stone since the ancient Greek culture. The calcite crystals composing the cell wall are elongated perpendicular to the cell wall. The calcite normally contains magnesium (Mg) , with the magnesium content varying as a function of species and water temperature. If the proportion of magnesium is high, the deposited mineral is more soluble in ocean water, particularly in colder waters, making some coralline algae deposits more vulnerable to ocean acidification . The first coralline alga recognized as
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