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 the temperate Mediterranean Sea, coralline algae are the main builders of a typical algal reef, the Coralligène ("coralligenous").[5] Many are typically encrusting and rock-like, found in marine waters all over the world. Only one species lives in freshwater.[6] Unattached specimens (maerl, rhodoliths) may form relatively smooth compact balls to warty or fruticose thalli.
A close look at almost any intertidalrocky shore or coral reef will reveal an abundance of pink to pinkish-grey patches, distributed throughout 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 1600described species of nongeniculate coralline algae.[7]
The corallines are presently grouped into two families on the basis of their reproductive structures.[8]
Distribution
Coralline algae are widespread in all of 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.[6][9] Many are epiphytic (grow on other algae or marine angiosperms), or epizoic (grow on animals), and some are even parasitic on other corallines.
Forms
Corallines have been divided into two groups, although this division does not constitute 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 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.[10]
Thalli can be divided into three layers: the hypothallus, perithallus and epithallus.[11] The epithallus is periodically shed, either in sheets or piecemeal.[12]
Corallines live in varying depths of water, ranging from periodically exposed intertidal settings to 270m water depth (around the maximum penetration of light).[13] Some species can tolerate brackish[13] or hypersaline[14] waters, and only one strictly freshwater coralline species exists.[6] (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.[13]
Growth
Corallines, especially encrusting forms, are slow growers, and expand by 0.1–80mm annually.[13] All corallines begin with a crustose stage; some later become frondose.[15]
Avoidance of fouling
Coralline algae about 20 meter deep at the lower limit of kelp forest
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.[17] This places them in the unusual position of requiring herbivory, rather than benefiting from its avoidance.[18] Many species periodically slough their surface epithallus– and anything attached to it.[17]
Some corallines slough off 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 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 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.
Evolutionary history
The corallines have an excellent fossil record from the Early Cretaceous onwards, consistent with molecular clocks that show the divergence of the modern taxa beginning in this period.[1] 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.[1] This said, non-mineralizing coralline algae are known from the Silurian of Gotland[19] showing that the lineage has a much longer history than molecular clocks would indicate.
The Sporolithaceae tend to be more diverse in periods of high ocean temperatures; the opposite is true for the Corallinaceae.[13] The group's diversity has closely tracked the efficiency of grazing herbivores; for instance, the Eocene appearance of parrotfish marked a spike in coralline diversity, and the extinction of many delicately branched (and thus predation-prone) forms.[17]
Taxonomy
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.[23] Recent advances in morphological classification based on skeletal ultrastructure, however, are promising. Crystal morphology within 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.[24]
Fresh surfaces are generally colonized by thin crusts, which are replaced by thicker or branched forms during succession over the course of one (in the tropics) to ten (in the Arctic) years.[17] However, the transition from crusts to branched form depends on environmental conditions. Crusts may also become detached and form calcareous nodules known as Rhodoliths.[27] Their growth may be also disrupted by local environmental factors.[28] While coralline algae are present in most hard substrate marine communities in photic depths, they are more common in higher latitudes and in the Mediterranean.[29] Their ability to calcify in low light conditions makes them the some of deepest photosynthetic multicellular organisms in the ocean,[30] having been found as deep as 268 meters,[31] and as such a critical base of mesophotic ecological systems.[32][33]
Mineralogy
Since coralline algae contain calcium carbonate, they fossilize fairly well. They are particularly significant as stratigraphic markers in petroleum geology. Coralline rock was used as building stone since the ancient Greek culture.[34]
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.[35] 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.[36]
History
The first coralline alga recognized as a living organism was probably Corallina in the 1st century AD.[37] In 1837, Rodolfo Amando Philippi recognized coralline algae were not animals, and he proposed the two generic names Lithophyllum and Lithothamnion as Lithothamnium.[37] For many years, they were included in the order Cryptonemiales as the family Corallinaceae until, in 1986, they were raised to the order Corallinales.
Corallines in community ecology
Branched coralline algae washed ashore on the beach of the county park refuge at Moss Beach, California
Many corallines produce chemicals which promote the settlement of the larvae of certain herbivorousinvertebrates, 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 abaloneaquaculture; corallines appear to enhance larval metamorphosis and the survival of larvae through the critical settlement period. It also has significance at 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-Pacificcoral reefs, yet nothing is known about the herbivore enhancement role of Indo-Pacific corallines, or whether this phenomenon is important in coral reef communities.[citation needed]
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 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 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 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 the reef materials into a sturdy structure.[38]
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 the main reef structures that prevent oceanic waves from striking adjacent coastlines, helping to prevent coastal erosion.[citation needed]
Economic importance
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.
Soil conditioning
The collection of unattached corallines (maërl) for use as soil conditioners dates to the 18thcentury. This is particularly significant in Britain and France, where more than 300,000tonnes of Phymatolithon calcareum (Pallas, Adey & McKinnin) and Lithothamnion corallioides are dredged annually.
Medicine and food
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 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.
Aquaria
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 the tank ecosystem.[citation needed]
See also
Coralline for other organisms that resemble coral, or contribute materially to reef creation
A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic (non-living) processes such as deposition of sand or wave erosion planing down rock outcrops. However, reefs such as the coral reefs of tropical waters are formed by biotic (living) processes, dominated by corals and coralline algae. Artificial reefs such as shipwrecks and other man-made underwater structures may occur intentionally or as the result of an accident, and are sometimes designed to increase the physical complexity of featureless sand bottoms to attract a more diverse range of organisms. Reefs are often quite near to the surface, but not all definitions require this.
Halimeda is a genus of green macroalgae. The algal body (thallus) is composed of calcified green segments. Calcium carbonate is deposited in its tissues, making it inedible to most herbivores. However one species, Halimeda tuna, was described as pleasant to eat with oil, vinegar, and salt.
Crustose is a habit of some types of algae and lichens in which the organism grows tightly appressed to a substrate, forming a biological layer. Crustose adheres very closely to the substrates at all points. Crustose is found on rocks and tree bark. Some species of marine algae of the Rhodophyta, in particular members of the order Corallinales, family Corallinaceae, subfamily Melobesioideae with cell walls containing calcium carbonate grow to great depths in the intertidal zone, forming crusts on various substrates. The substrate can be rocks throughout the intertidal zone, or, as in the case of the Corallinales, reef-building corals, and other living organisms including plants, such as mangroves and animals such as shelled molluscs. The coralline red algae are major members of coral reef communities, cementing the corals together with their crusts. Among the brown algae, the order Ralfsiales comprises two families of crustose algae.
Maerl is a collective name for non-geniculate coralline red algae with a certain growth habit. Maerl grows at a rate of c. 1 mm per year. It accumulates as unattached particles and forms extensive beds in suitable sublittoral sites. The term maerl originally refers to the branched growth form of Lemoine (1910) and rhodolith is a sedimentological or genetic term for both the nodular and branched growth forms.
Rhodoliths are colorful, unattached calcareous nodules, composed of crustose, benthic marine red algae that resemble coral. Rhodolith beds create biogenic habitat for diverse benthic communities. The rhodolithic growth habit has been attained by a number of unrelated coralline red algae, organisms that deposit calcium carbonate within their cell walls to form hard structures or nodules that resemble beds of coral.
Wataru Ishijima was a paleontologist and geologist. Ishijima was one of the most prolific researchers of fossil calcareous algae. After graduating from the Imperial Fisheries Institute in 1927, Ishijima joined the Institute of Geology and Paleontology, Faculty of Science, Tohoku Imperial University (Sendai) from 1927–1931. He then worked at the Institute of Geology, Taihoku Imperial University (Taipei) during 1942–1945 and then at the Rikkyo University (Tokyo) from 1945–1980. His doctoral dissertation was submitted to Tohoku University and was privately published by Yūhodō. He described a total of 139 taxa of fossil calcareous algae including at least 114 species of Corallinales, and he produced more than 45 publications on coralline algal taxonomy.
Phymatolithon is a genus of non geniculate coralline red algae, known from the UK, and Australia. It is encrusting, flat, and unbranched; it has tetrasporangia and bisporangia borne in multiporate conceptacles. Some of its cells bear small holes in the middle; this distinctive thallus texture is termed a "Leptophytum-type" thallus surface, and has been posited as a taxonomically informative character. It periodically sloughs off its epithallus, reducing its overgrowth by algae by as much as 50% compared to bare rock.
The Rhodogorgonales are an order of red algae, a sister group to the corallines. They are always thalloid and calcified; their calcification is very different from the corallines, as individual calcite crystals are deposited in the cell wall of specialised cells; this suggests that the evolution of calcification may have been independent from the corallines. They have no fossil record.
Trichocyte in algae are cells which grow on the outside of the thallus, from which hairs grow. In algae, trichocytes grow principally over the summer; their growth is mediated by water temperature and day length.
Calliarthron is a genus containing two species of thalloid intertidal alga. Specimens can reach around 30 cm in size. The thalli take a crustose form. The organisms lack secondary pit connections. Calliarthron reproduces by means of conceptacles; it produces tetraspores, dispores and carpospores. The genus has lignin and contains secondary cell walls, traits which are normally associated with the vascular plants. It is similar to the genus Bossiella.
Red algae, or Rhodophyta, are one of the oldest groups of eukaryotic algae. The Rhodophyta comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority of species (6,793) are found in the Florideophyceae (class), and mostly consist of multicellular, marine algae, including many notable seaweeds. Red algae are abundant in marine habitats but relatively rare in freshwaters. Approximately 5% of red algae species occur in freshwater environments, with greater concentrations found in warmer areas. Except for two coastal cave dwelling species in the asexual class Cyanidiophyceae, there are no terrestrial species, 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.
The Sporolithaceae is the only known family of algae in the Sporolithales order.
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.
Jania is a genus of red macroalgae with hard, calcareous, branching skeletons in the family Corallinaceae.
Spongites yendoi is a species of crustose red seaweed with a hard, calcareous skeleton in the family Corallinaceae. It is found on the lower shore as part of a diverse community in the southeastern Atlantic Ocean and the Indo-Pacific Ocean.
Marine biogenic calcification refers to the production of calcium carbonate by organisms in the global ocean.
Sporolithon ptychoides is a species of crustose red seaweed with a hard, calcareous skeleton in the family Corallinaceae. It has a widespread distribution, being present in the Pacific and Indian Oceans, the Mediterranean Sea and the southwestern Atlantic Ocean.
Lithophyllum orbiculatum is a species of thalloid coralline algae, which are a red algae whose cell walls contain calcareous deposits.
Crustaphytum is a genus of red alga first discovered in Taoyuan algal reefs by Taiwanese scientists. The epithet “crusta” refers to crustose thallus and “phytum” refers to plant. Belonging to the family Hapalidiaceae in the order Hapalidiales, Crustaphytum is one kind of crustose coralline algae.
Peyssonneliales is a monotypic order of red algae belonging to the class Florideophyceae and the subclass Rhodymeniophycidae. It contains only 1 known family, PeyssonneliaceaeDenizot, M., 1968.
References
1 2 3 4 Aguirre, J.; Perfectti, F.; Braga, J.C. (2010). "Integrating phylogeny, molecular clocks, and the fossil record in the evolution of coralline algae (Corallinales and Sporolithales, Rhodophyta)". Paleobiology. 36 (4): 519. Bibcode:2010Pbio...36..519A. doi:10.1666/09041.1. S2CID85227395.
↑ Silva, P.; Johansen, H. W. (1986). "A reappraisal of the order Corallinales (Rhodophyceae)". European Journal of Phycology. 21 (3): 245–254. doi:10.1080/00071618600650281.
↑ Ballesteros E., 2006 Mediterranean coralligenous assemblages: A synthesis of present knowledge. Oceanography and Marine Biology - an Annual Review 44: 123–130
↑ Woelkerling, Wm.J. (1988). The coralline red algae: An analysis of the genera and subfamilies of non-geniculate Corallinaceae. Natural History. London, UK: British Museum. ISBN978-0-19-854249-0.
↑ Blackwell, W.H.; Marak, J.H.; Powell, M.J. (1982). "The identity and reproductive structures of a misplaced Solenopora (Rhodophycophyta) from the Ordovician of southwestern Ohio and eastern Indiana". Journal of Phycology. 18 (4): 477. doi:10.1111/j.0022-3646.1982.00477.x.
↑ Keats, D.W.; Knight, M.A.; Pueschel, C.M. (1997). "Antifouling effects of epithallial shedding in three crustose coralline algae (Rhodophyta, Coralinales) on a coral reef". Journal of Experimental Marine Biology and Ecology. 213 (2): 281. doi:10.1016/S0022-0981(96)02771-2.
↑ Thornton, Scott E.; Orrin, H. Pil (1978). "A lagoonal crustose coralline algal micro-ridge: Bahiret el Bibane, Tunisia". SEPM Journal of Sedimentary Research. 48. doi:10.1306/212F7554-2B24-11D7-8648000102C1865D.
↑ Küpper, F.C. and Kamenos, N.A. (2018) "The future of marine biodiversity and marine ecosystem functioning in UK coastal and territorial waters (including UK Overseas Territories)–with an emphasis on marine macrophyte communities". Botanica Marina, 61(6): 521-535. doi:10.1515/bot-2018-0076.
↑ Smith, M.R. and Butterfield, N.J. 2013: A new view on Nematothallus: coralline red algae from the Silurian of Gotland. Palaeontology 56, 345–359. 10.1111/j.1475-4983.2012.01203.x
↑ Dulin, Tuvia; Avnaim-Katav, Simona; Sisma-Ventura, Guy; Bialik, Or M.; Angel, Dror L. (January 2020). "Rhodolith beds along the southeastern Mediterranean inner shelf: Implications for past depositional environments". Journal of Marine Systems. 201: 103241. Bibcode:2020JMS...20103241D. doi:10.1016/j.jmarsys.2019.103241. S2CID210297206.
↑ Btracchi, Valentina; Savini, Alessandra; Marchese, Fabio; Palamara, Serena; Basso, Daniela; Corselli, Cesare (February 2015). "Coralligenous habitat in the Mediterranean Sea: a geomorphological description from remote". Italian Journal of Geosciences. 134 (1): 32–40. doi:10.3301/IJG.2014.16.
↑ Coletti; etal. (2017). "Economic Importance of Coralline Carbonates". In Riosmena-Rodríguez; etal. (eds.). Rhodolith/Maërl Beds: A Global Perspective. Coastal Research Library. Vol.15. pp.87–101. doi:10.1007/978-3-319-29315-8_4. ISBN978-3-319-29313-4.
↑ Baas-Becking, L. G.; Galliher, E. W. (1931). "Wall structure and mineralization in coralline algae". Journal of Physical Chemistry. 35 (2): 467–479. doi:10.1021/j150320a006.
1 2 Irvine, Linda M.; Chamberlain, Yvonne M. (1994). Corallinales, Hildenbrandiales. London, UK: Her Majesty's Stationery Office. ISBN978-0-11-310016-3.
↑ Caragnano et al., 2009. 3-D distribution of nongeniculate corallinales: A case study from a reef crest of South Sinai (Red Sea, Egypt). Coral Reefs 28: 881-891
Further reading
Morton, O.; Chamberlain, Y.M. (1985). "Records of some epiphytic coralline algae in the north-east of Ireland". Ireland Naturalists' Journal. 21: 436–440.
Morton, O.; Chamberlain, Y.M. (1989). "Further records of encrusting coralline algae on the north-east coast of Ireland". Irish Naturalists' Journal. 23: 102–106.
Suneson, S (1943). "The structure, life-history, and taxonomy of the Swedish Corallinaceae". Acta Universitatis Lundensis. N.F. Avd. 2. 39 (9): 1–66.
Woelkerling, W. J. (1993). "Type collections of Corallinales (Rhodophyta) in the Foslie Herbarium (TRH)". Gunneria. 67: 1–289.
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