Coral reefs and islands.
In their formation, the main role is played by solid polypnyaks. coral polyps(see) and products of their destruction. Although coral polyps are common in the seas of all zones and are found at all kinds of depths, from the lower limit of low tides to the enormous ocean depths, however, their mass development is limited to relatively narrow horizontal and vertical limits. This applies especially to those K. polyps that form colonies, equipped with a dense calcareous skeleton, which develop in huge masses and islands. These animals find conditions favorable for their development in relatively shallow layers: from the low tide line to 20-30 fathoms; below this depth, living K. polyps, which take part in the construction of K. reefs, are found only as an exception (to a depth of about 90 m ); In general, below 20-30 fathoms we find only dead masses of K. polypnyaks. The most abundant growth of corals is limited to even tighter limits - from the low tide line to 10-15 fathoms. In the horizontal direction, the distribution area of reef-building corals is limited to a narrow strip on both sides of the equator; Only near the Bermuda Islands are there significant coral formations at 32° N. w. Within the specified zone of K., reefs and islands are not widespread; Research by the American zoologist Dan showed that K. reefs and islands are found only where the temperature sea water does not fall below 20° C (however, there is a known case of reef corals being found at several lowest temperature, about 18° C). Therefore, we do not find significant K. formations off the western coasts of America, Africa and Australia; due to the existence of cold currents here, the line connecting the points where the temperature does not fall below 20° C (“20° isocrime”) approaches the equator here and only at the west. On the coast of America there are poorly developed coral reefs between California and Guayaquil. Meanwhile, the eastern coasts of all these continents are surrounded by numerous and extensive K. buildings.
Fig. 1. General form coastal and barrier reef.
Corals of the Great Barrier Reef, Australia
The most developed K. buildings are in Great Ocean where they are found in all typical forms (coastal reefs, barrier reefs and K. islands - see below). The central and southern parts are dominated by atolls (Lowland, Alice, Gilbert, Marshall, and Caroline islands); coastal reefs fringe Elizabeth Island, Navigators Islands, Friendship Islands, New Hebrides, Solomon Islands, Sandwich Islands, Mariana Islands and some islands China Sea; in the Australian seas there are barrier reefs and partly atolls (the most important are the reefs off the eastern coast of Australia, off the western coast of New Caledonia and the reefs of the Fiji islands). Of the East Asian islands, coral formations (especially coastal reefs) are found in the Philippine Islands, Borneo, Java, Celebes, Timor, etc. Indian Ocean South coast Asia, in general, is poor in coral formations; Significant coastal reefs border individual points in the southwest. and southeast the coast of Ceylon; in the islands of the Maldives, Lakedives and Chagos there are extensive K. formations in the form of atolls; in the western part Indian Ocean the islands are fringed mainly by coastal reefs (Seychelles, Mauritius, partly Bourbon); part of the coast of Madagascar is fringed by coastal reefs, the Comoros coastline is lined with barrier reefs, and the eastern coast of Africa has extensive coastal reefs. K. reefs abound in the Red Sea, where a little interrupted coastal reef stretches along the African coast from Suez to Bab el-Mandeb; in addition, there are formations similar to barrier reefs, and according to Walter, atolls. K. reefs are also common in the Persian Gulf. IN Atlantic Ocean significant K. buildings are located in the east. the coast of America, here significant reefs are found off the coast of Brazil, along the coasts of Yucatan and Florida, Cuba, Jamaica, Haiti, in the Bahamas and Bermuda Islands; There are coastal and barrier reefs here, and in the Bermuda Islands there are atolls.
A section of the Great Barrier Reef as seen from space. The Great Barrier Reef is not a single formation; it consists of thousands of interconnected segments, the most massive and oldest of which are located at its northern tip
Fig. 2. General view of the atoll.
Barrier Reef Islands.
The main role in the formation of K. structures is played by polypnyas of a number of forms from the group of 6-rayed or multi-tentacled polyps (Hexactinia s. Polyactinia), especially the families Astraeidae (Astraea, Meandrina, Diploria, Astrangia, Cladocora, etc.), Madreporidae (Madrepora, etc. ), Poritidae (Pontes, Goniopora, Montipora, etc.), partly Oculinidae (Orbicella, Stylaster, Poecillopora, etc.) and most of the representatives of Fungidae (Fungia, etc.). In addition, some 8-rayed polyps with a calcareous skeleton (for example, Heliopora, Tubipora), as well as horny polyps of gorgonids, take part in the formation of K. islands and reefs. In addition to the coral polyps themselves, important In the formation of reefs and islands there are also representatives of one group of hydromedusae, distinguished by calcareous deposits - Hydrocorallinae (Millepora, etc.). Finally, significant component The masses of reefs and islands consist of masses of calcareous algae, nullipores and partly coralline. Finally, the composition of coral structures includes shells of mollusks, calcareous skeletons of bryozoans (Bryozoa), shells of rhizopoda (Rhizopoda) and radiolarians (Radiolaria), and other solid parts of animals; these foreign elements can sometimes form a very significant part of the mass of coral structures. The composition of reefs and islands in different seas shows significant differences; Thus, in the Red Sea, the polypnyas Porites, Madrepora and Stylophora predominate and make up the bulk, in the reefs of the island of Mauritius - Porites and Montipora, in Ceylon - Madrepora and Poecilopora, in Singapore - Madrepora, on the Sandwich Islands - Poecillopora, in the west. the coast of America - Porites and Poecillopora, off Florida - Porites, Madrepora and Meandrina, etc.
Porite coral
For the most part, the base of a reef or island is solid rocks - seamounts or the coasts of continents and islands. Loose soil, especially silt, is unfavorable for the development of corals. However, latest research Sluiter off the coast of Java showed that coral reefs can also arise on the bottom covered with silt, if on its surface there are shells, stones or pieces of pumice to which young corals can attach. As the latter grow and the weight of a colony of polyps sitting on a piece of pumice, etc., increases, its base is pressed deeper and deeper into the silt, while on upper parts polypnyak coral polyps continue to successfully reproduce and grow upward. Reaching denser soil with its base, the young reef receives a dense foundation, relying on which it can successfully grow further. Some polyps, according to other studies, can grow successfully on gravel soil if it is held together by algae (such as Psammocora, Montipora, Lophoseris off the eastern coast of Africa). Most coral polyps find the most favorable conditions in the upper layers, where there is strong water movement, and only a few, more fragile forms seek protection from the surf. At the same time, most of them strive for light (represents positive heliotropism - see). Therefore, polypnyaks continuously grow upward, while the parts lying below die off. Thus, living colonies of polyps form, so to speak, a living crust on the dead mass of the reef, containing various cavities and voids. Thick masses of coral structures are compacted due to the fact that the empty spaces between individual polypnyaks and their branches are gradually filled with coral fragments and other calcareous deposits. The strong surf to which the polypnyaks are exposed breaks off significant masses of them and the movement of water wears the fragments into smaller material. The process of destruction and change of the reef under the mechanical action of waves is greatly facilitated by various marine animals drilling into coral structures; such are boring sponges, some mollusks (for example, Lithodomus) and partly crustaceans. Some fish that feed on corals gnaw branches and, crushing them, give rise to the formation of thin calcareous silt, which also cements the fragments of polypnyaks. Some role in the formation of this thin silt is also played by sea cucumbers, which are found in abundance on the K. reefs, from where hundreds of centners of some species are annually taken to China under the name sea cucumber. The growth of K. polypnyaks occurs at different speeds. Branched tree-like forms grow fastest; so in one case, on the remains of a broken ship at 64 years old, Madrepora grew up to 1 6 ft. in height; Madrepora alcicornis in Haiti formed branches 7-12 cm long at 3 months; Usually, branched polyp forests lengthen by a smaller amount per year. The growth of massive polypnyaks, such as Astraea, Meandrina, etc., occurs much more slowly; Thus, there is a known case when Meandrina grew 6 inches at the age of 12, but usually the polyp grows thicker by about a year. most inches. K. polyps can live only below the low tide line, and for the most part, even a short stay out of water entails the death of animals (only some forms, like Porites, Goniastraea, Coeloria, Tubipora, can remain alive out of water for whole hours). The polyps themselves can, therefore, build their buildings only to the lower low tide line, and any elevation of reefs and islands above this level can only be determined by the action of other factors. Pieces of polypnyaks, broken off by the surf, are thrown out by the sea onto the surface of the reefs and, gradually piling up, give rise to the above-water parts of K. buildings. And here the gaps are filled with smaller fragments, sand and other dense remains of animals, and the individual pieces are finally cemented, merging into solid rock, thanks to the release of lime from the solution in water. Another reason that can cause a strong increase in the altitude of buildings above the sea is a negative fluctuation in sea level, due to which the altitude of buildings can rise to 80 or more m above sea level. seas. The dissolution of part of the dead polypnyaks in water containing carbon dioxide occurs as at eq. sea, and on the surface of the surface parts of K. buildings. The accumulation of K. sand on the surface of K. islands can reach such a size that real dunes are formed, which, under the influence of prevailing winds, gradually move inland, filling up plantations and farms; this was the case, for example, at Paget Parish in the Bermuda Islands, where the movement of the “sand glacier,” as they called the moving dune that covered the farms, was stopped only by planting trees. The surface of islands and reefs, being covered with a layer of humus, provides soil on which very luxurious tropical vegetation often develops. Coastal structures are found in a wide variety of forms, which can be reduced to three main types: 1) coastal reefs, 2) barrier reefs, and 3) individual coastal islands and shoals. Coastal reefs are formed in cases where coastal structures are directly adjacent to the shores of islands or continents and border them, interrupted in those places where streams and rivers flow in (since polyps for the most part cannot live in muddy and especially desalinated water). or where their development is hampered by the quality or structure of the bottom (for example, a steep cliff). Coastal reefs can either remain under water or, for the above reasons, become above water. Sluiter's research on the formation of K. reefs off the coast of Krakatoa Island, after the famous eruption of this volcano, proved that reefs can arise at some distance from the coast and gradually grow towards it. A study of the bottom surrounding the coastal reef shows that it gradually decreases towards open sea. Barrier reefs (also underwater or surface) stretch along the shores of an island or mainland, remaining separated from them by a relatively shallow channel of varying widths (10-15 and up to 50 nautical miles). The depth of the channel can be very different, but is always relatively small. Sometimes its bottom dries up at low tide, but usually its depth is several fathoms and can even reach 40-50 fathoms. Meanwhile, outside the reef, the depths are relatively great and can reach several hundred fathoms, and the outer edge of the reef falls very steeply into the depths. In some places the barrier reefs are interrupted. Sometimes they surround the island on all sides. In some cases, barrier reefs reach enormous sizes; so at the east. coast of Australia from Cape Kar Sunday (24 about 40" S) to the southern coast of New Guinea stretches the "Great Australian Reef" about km long, separated from the coast by a channel 25-160 km wide; its main passage with a lighthouse lies under 11°35" S. w. (Raines Inlet), the depth of the channel is 10-60 fathoms, and in places outside the reef it is more than 300 fathoms. The islands (and individual shoals) represent a very diverse form; the predominant forms are round, oblong, ring-shaped (“atolls”) and semi-lunar. Most characteristic appearance have atolls; This is a ring-shaped strip of land, usually no more than 100-200 m wide, surrounding a central basin ("lagoon"), which is usually connected to the surrounding sea by several passages lying on the side opposite to that from which the wind blows. prevailing winds. Rarely (eg Whitsunday Island) atolls form a continuous continuous ring. The sizes of the lagoons are very different and their diameter can reach 75 km. or more (and a diameter of 30-45 km is not uncommon). The depth of the lagoon is generally insignificant, usually several fathoms, but can reach up to 50 fathoms; meanwhile, on the outer side of the atoll we find, as with barrier reefs, for the most part very significant depths. The bottom of the lagoon is covered (like the barrier reef channel) with sand and calcareous silt and contains relatively few living corals, the advantage of more delicate forms. Sometimes there may be small islands in the lagoon. The height of the atolls above sea level is mostly insignificant, no more than 3-4 m; Sometimes surf waves crash through the atoll into the lagoon. The windward side of the atoll is generally higher. Relatively rarely, the Caucasian islands reach a significant height above sea level (which is explained by negative fluctuations in sea level: the resulting reefs move out of the sea). So at Vanikoro, according to Darwin, the wall of the K. reef reaches 100 m in height, according to Dana in Metia, in the Low Islands, rocks from K. limestone are 80 m high. Sometimes there are underwater atolls, such, for example, big reef in the Chagos Islands, lying at a depth of 5-10 fathoms. below sea level. Other forms of islands and shoals are also very common, and sometimes also reach significant sizes; Thus, the reef lying to the west of the two main islands of the Fiji group represents a surface of about 3000 square meters. English miles; The coastline of the Saya de Malha bank, NE of Madagascar, extends from 60°20"E to 62°10" (GMT) and from 8°18"S to 11°30", and then to South lies the Nazarethbank, about 400 km long. Seas overflowing with coastal reefs generally pose significant dangers to navigation, especially since coastal islands and reefs often rise steeply from considerable depths and there is nothing to indicate the proximity of the reefs, except for breakers in case of waves. On the other hand, barrier reefs in some cases allow ships to safely pass along the coast while the open sea is in severe weather. Fencing the shores with reefs prevents the eroding effect of waves on the shores. In addition, thanks to reefs, in some cases, erosion products brought from land are deposited off the coast and cause a significant increase in land mass; Thus, Tahiti is surrounded by a strip of land with a width of 0.5 to 3 English. miles, which occurred this way and was covered with rich vegetation.
mushroom coral
Black corals
Along with the process of formation of the K. islands (for example, near Florida), we encounter phenomena of their destruction in other places (for example, on the Bermuda Islands); in these cases, the formation of caves (sometimes stalactites and stalagmites), arches, etc. is observed; at the same time, on the surface of the island there is a special red soil, in which they see a residue from the erosion and dissolution of the lime of the reef. The peculiar structure of K. reefs and islands, their importance and enormous distribution have long aroused interest in these formations, especially in atolls; to explain the shape of the latter, some resorted (with Steffens, in) to the hypothesis that atolls are crowned with underwater craters; others believed that K. polyps, due to a special instinct, erect their buildings in the shape of a ring in order to enjoy protection from the surf. The theory of K. formations given by Darwin explained mysterious fact existence of K. buildings on great depths, where corals that build reefs cannot live, explained the reason for the significant thickness of K. sediments (which, by the way, was confirmed by the latest drilling experiments on K. reefs), as well as the shape of K. buildings and the connection between them. Despite a number of recent objections, Darwin's theory remains dominant. Darwin's theory is the name. the theory of immersion (Senkungstheorie), the essence of which is as follows. If coastal structures arise near the shore of an island or mainland, where the water level remains more or less constant (the bottom does not sink), then, as they grow, they should give rise to a coastal reef. If the bottom goes down, the reef will continue to grow upward and should take on the character of a barrier reef, separated from the land by a channel. This will be facilitated by the fact that K. polyps will be found Better conditions for life on the outer side of the reef, which will therefore grow stronger. If, finally, with further diving island, surrounded by a ring-shaped reef, will completely disappear under the surface of the sea, leaving in its place an atoll (underwater or surface, depending on the speed of the dive). This explanation of the origin of K. buildings and the connections between them explains many of their features and is based on a number of diverse facts. However, extensive K. formations, in the form of barrier reefs, are also observed in places where, on the contrary, a rise in the bottom obviously occurs, and atolls are also observed in such areas. In general, we must admit that various shapes The formation of buildings can also occur in another way, in addition to any lowering of the bottom, for example, on underwater banks and mountains, and the shape of islands (including atolls) is sometimes determined by the direction of sea currents or by the fact that the corals of a given reef grow more successfully on its edges than in the middle, the middle ones die off and are subject to the destructive action of currents and water containing carbon dioxide, which leads to the formation of a lagoon. Be that as it may, the latest objections to Darwin's theory represent rather additions and amendments to it than a new explanation that could completely replace that given by Darwin. Extensive K. formations existed in previous times geological periods and in many deposits we find distinct traces of reefs. In the most ancient periods of Cyprus, reefs occupied a relatively large area. Paleozoic reef corals are found in Scandinavia and Russia well beyond 60° N. w. and some genera even on Spitsbergen, Novaya Zemlya and the Barents Islands; Lithost r otion was found during the Nares expedition to the north of 81° N. w. In the Silurian and Devonian periods, corals abounded in the seas over a wide range. Canada and Scandinavia. In later geological periods, we see that the K. reefs are retreating more and more towards the equator, which was, in all likelihood, due to a decrease in sea temperature at high latitudes. IN Triassic period reefs were abundant in central and southern Europe; V Jurassic period the vast K. Sea occupied a significant part of the western and central Europe, and traces of reefs remained in England, France, summaries of the most important data in Keller, “Leben des Meeres” (unfinished edition), Marschell in Bram’s “Thierleben” (Bd. X; new edition, ending in Russian), as well as Kingsley, "The Riverside Zoology" (Vol. I); Heilprin, "The Distribution of Animals" (1887) and Nicholson's article in the Encyclopedia Britannica.
There are large islands in the ocean, the builders of which are small creatures whose size does not exceed the head of a pin. These are coral polyps - translucent columns with tentacles at the end. The body of the polyp is very delicate, so for its protection it builds a small limestone cell called a calyx. The calyx is glued to the calyx, and as a result, Coral reefs, which resemble a fairy tale kingdom. 2 water world
IN dense thickets Numerous mollusks, fish and many other animals find shelter and food in corals. Some of them hide inside the colony all their lives. Sometimes the reef is overgrown by such an animal on all sides, and it ends up forever walled up in the thickness of the corals, receiving food through small holes. Other aquatic inhabitants take refuge in the thickets only when there is danger, while others constantly crawl along the surface of the colony or stay close. 3 water world
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If you swim up to the reef, you will see a completely extraordinary underwater forest. There are colonies of reefs, similar in shape to Christmas trees, dense thorny bushes, mushrooms, giant funnels, vases, bowls, trees. Bright colors predominate: lemon yellow, emerald green, light brown, crimson. water world 6
For a coral reef to grow and thrive, it needs to have favorable conditions. Sea water should have normal ocean salinity. Therefore, during heavy rains when salinity in the coastal parts of the sea decreases, a large number of corals are dying. This has bad consequences for various sea creatures, as the decaying coral tissue poisons the water and causes death to marine animals. water world 7
The second condition for coral life is high and constant water temperature. In this regard, most reefs are found in tropical parts Quiet, Indian and Atlantic Oceans. Following important condition normal functioning of corals - cleanliness and transparency of sea water. Clear water passes better Sun rays. And most importantly, corals need food; they feed on microscopic animals from plankton. water world 8
A large expanse of tropical oceans is suitable for corals to thrive. The area of their structures amounts to more than 27 million square meters. km. The area of the islands and reefs alone, which are exposed at low tide, is 8 million square meters. km., this more area Australia (7.7 million sq. km). The largest coral reef is located off the coast of Australia - the Great Barrier Reef, which stretches for many thousands of kilometers. water world 9
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The entire space occupied by the coral reef is a huge natural lime factory. Year after year, small polyps extract lime from sea water and deposit it in their bodies. Since corals settle near the surface of the sea (along the shores of islands, or form an island themselves), lime is easily accessible, and its reserves are almost unlimited. water world 11
Corals are widely used in agriculture. In coastal tropical countries they are used as construction material for houses, street paving. Corals are used for polishing and grinding wooden and metal products, for making medicines, and also as a decoration for artificial rocks in gardens, parks and aquariums water world 12
The ancient Greeks considered coral a symbol of immortality and happiness. In the Middle Ages it was believed that it bestows wisdom and youth. Due to its wonderful properties, coral helps relieve high emotional tension and reduce negative qualities souls - hatred, anger, envy. Coral cures sadness. water world 13
14 The presentation uses data taken from open sources:
I will never forget my holiday in Egypt! He was amazing! Most of all I remember the sea; I have never seen such a sea anywhere else! In Egypt, it is simply teeming with colorful, eye-catching inhabitants. I consider corals to be one of the most beautiful inhabitants of the Red Sea.
Corals: animals or plants
When I returned from Egypt and showed my friends the photographs, for some reason almost everyone was worried about this question. So, corals are living microorganisms that live in colonies.
By the way, we found this out not so long ago. It was only in 1982 in France that they proved that corals are not plants. They are based on invertebrate polyps. These organisms originated back in the days when mammoths lived on Earth. They have a single cavity - the intestine, which is responsible for digesting food.
The size of polyps is not always small. More often they range from a millimeter to a couple of centimeters, but sometimes there are also huge ones up to half a meter.
Formation of coral reefs
Polyps have a very delicate body. To protect yourself from predatory fish, they have to build a protective cell of limestone. This cell is called a calyx. Polyps mainly lead a colonial lifestyle. They glue their cups together, thereby forming coral reefs of fantastic beauty.
Do you know how corals reproduce? In fact, they do this in several ways:
- Sexual method. When corals live together, the male is with the female. As a result, small larvae are formed that swim in the sea. This is not observed in all subtypes of polyps.
- Budding. The appearance of a baby followed by its separation from the parental polyp. In this case, a shoot is formed at the base of the coral, which over time detaches and takes root as an independent individual on the bottom.
- Division. This method of reproduction is characteristic of some solitary soft individuals.
Amazing, right? The sexual reproduction of corals is actually a very beautiful sight.
This usually occurs under the cover of darkness at the end of spring and coincides with the full moon. Many tourists come to see it.
There are three types of islands: continental, volcanic and coral. The formation of islands occurred not only many thousands of years ago, but also now new island territories are emerging.
How were mainland islands formed?
Continental islands were formed due to the movement of tectonic plates earth's crust. The islands were once part of larger continents. Vertical movements of tectonic plates, together with rising sea levels, formed faults in the continents. Nature mainland islands and the nature of the continent closest to them are almost identical. Mainland or continental islands are located within a single shelf, or are separated from the mainland by a deep fault. Continental islands include Greenland, New land, Madagascar, British Isles, etc.
How are volcanic islands formed?
There is constant volcanic activity in the oceans. Erupting volcano releases great amount lava, which solidifies upon contact with water and air, forms new volcanic islands. Such islands experience great water erosion and gradually go under water. Volcanic islands are often significantly removed from the continents and form a unique ecological system. An example of volcanic islands is the Hawaiian Island chain.
How are they formed coral islands?
Such islands can form only in equatorial and tropical latitudes. The shallows are populated by corals and polyps, which cling to the seabed with their roots. Over time, the underside of the coral hardens, forming a solid base for the island. Such a foundation begins to retain the sand that the ocean carries with its current. Coral reefs are formed, which are populated by the most outlandish animals of the ocean. An excellent example of such islands is the Great Barrier Reef off the coast of Australia.
How are coral islands formed?
Representatives of the coelenterates - corals - are the direct creators of underwater mountain ranges and islands. The relief-forming role of these animals is unique phenomenon nature. Coral reefs are formed as a result of the vital activity of corals and calcareous algae. Corals are the largest group of coelenterates: there are over six thousand species. An individual coral polyp resembles a small, usually transparent gut - a sac with a rim of tentacles near the mouth. In size it is often less than 1 cm in length. It all starts with the fact that the polyp takes care of personal protection: it builds a lime tube around its body - a house. He can hide there in case of danger. The composition of the “house” is similar to chalk, only more durable. When a coral reproduces, a bud - a tubercle - grows on its body. A mouth breaks out on the bud and becomes overgrown with tentacles. This is already a new polyp. But it may not separate from the parent coral. They remain connected by a thin tube through which they exchange food, and their “houses” grow together. Millions of polyps with fused “houses” form limestone stones. Old corals die off, but their “houses” remain, new ones grow on top of them, and the stones gradually increase in size, taking on the most bizarre shapes. The corals themselves, including reef-forming ones, are quite widespread, penetrating far beyond the tropics. For example, they are found in rather cold waters off the coast of Australia, where temperatures can drop to +9 °C. However, reefs, as a rule, form only within the zone limited by the +18 °C isotherms of the coldest month of the year. In some places, for example in the Gulf of Oman, reefs are formed under conditions of regular decrease in water temperature to +15... +16 oC, but this is an exception - usually sudden drops in temperature below +16 oC lead to mass death coralsAnother important factor The factors that determine the possibility of reef formation are water salinity and light. Reef-forming corals do not grow deeper than 30-40 m, and their most massive and intense growth is observed at depths of no more than 10-20 m. Such an important role of light in the life of corals is due to the fact that the symbiotic algae zooxanthellae play the main role in their nutrition. Zooxanthellae live in the tissues of coral polyps, and they secrete organic matter in organic-poor tropical waters they provide 90% nutrition for these coelenterates. It was the symbiosis of corals and zooxanthellae that led to the possibility of the emergence of reefs - the rate of release of skeletal calcium carbonate by corals in the presence of these algae increases by an order of magnitude.
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But corals are not the only reef builders, along with them vital role calcareous algae play a role in building the reef, such as Porolithon, Lithophyllum, Basiella, Goniolithon, etc. By mass, they make up the majority of modern reefs, and their rate of calcium carbonate release is higher than that of corals. However, the largest structures, reaching hundreds of meters, are formed by corals and algae together. Here algae not only construct the framework of the reef, but also cement the clastic material. Outside the distribution of corals, calcareous algae do not form such powerful structures and those created by them are no more than a few meters in size.
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