Coral reefs and islands.
In education, the main role is played by solid polypnyaks of coral polyps (see) and the products of their destruction. Although coral polyps are distributed in the seas of all belts and are found on all sorts of depths, from the lower boundary of the tumps to huge ocean depths, however, their mass development is limited to a relatively narrow horizontal and vertical limits. This applies especially to those from K. polyps forming a colony equipped with a dense lime skeleton, which, developing in huge masses and islands. These animals find conditions favorable for their development, in layers are relatively shameless: from the line of low tide up to 20-30 seedlings, below this depth of living K. Polyps participating in the construction of K. Reefs are found only as an exception (to a depth of about 90 m ); In general, below 20-30 seeds we find only the dead masses of K. polypnyakov. The most powerful growth of corals is limited to even closer limits - from the line of low tide to 10-15. In the horizontal direction, the propagation area of \u200b\u200bcorals, reefs, is limited to a narrow strip on both sides of the equator; Only from the Bermuda islands there are significant coral formations at 32 ° C. sh. Within the specified belt K. Reef and O-Wa are not common; The studies of the American zoologist Dana showed that K. Reefs and O-BA are found only there, where the sea water temperature does not fall below 20 ° C, (known, however, the case of finding reef corals with a slightly low temperature, about 18 ° C). Therefore, we do not find significant K. formations at the Western shores of America, Africa and Australia; Due to the existence of cold flows here - a line connecting points where the temperature does not fall below 20 ° C ("isocrum 20 °"), approaching the equator and only at the Zap. The shores of America are weakly developed by K. Reefs between California and Gvestville. Meanwhile, the eastern shores of all these continents are obscured by numerous and extensive K. buildings.
FIG. 1. General view of the coastal and barrier reef.
Corals of Big Barrier Reef, Australia
The most developed K. Buildings in Great Ocean, where they are found in all typical forms (coastal reefs, barrier reefs and K. O-Great - see below). In the central and southern part, the atolls predominate (the islands of lowland, Alice, Gilbert, Marshal, as well as Caroline); Coastal reefs are fought by O-in Elizabeth, the on-line of marigors, friendship, new hebritis, Solomon, Sandwich, Mariana and some of the Chinese Sea; In the Australian seas there are barrier reefs and part of the atoll (the most important reefs at the eastern shore of Australia, the Western New Caledonia and the reef of Fiji Islands) are found. From the East Asian Islands, coral education (especially coastal reefs) are located in the Philippine O-Wah, Borneo, Java, Kependals, Timor, and others. In Indian Ocean South Coast of Asia, in general, poor coral formations; Significant coastal reefs are used by individual items of South-Zap. and south-east. the shores of Ceylon; In the O-Wax of Maldives, Lacdiiv and Chagos (Chagos) are extensive K. Education in the form of atolls; In the western part of the Indian Ocean, the O-VA is bordered mainly by coastal reefs (Seychelles, Mauritius, partly Bourbon); Part of Madagascar bordered by coastal reefs, Comoros - Barrier, East Coast Africa represents extensive coastal reefs. K. Reefs are replete in the Red Sea, where there is a little interrupted coastal reef from Suez to the Bab El Mandeb along the African coast; In addition, there are formations similar to barrier reefs, and on the Walter - and the atoll. K. Reefs are also common in the Persian Gulf. IN Atlantic Ocean Significant K. Buildings are in the East. The shores of America, here significant reefs are found at the shores of Brazil, on the shores of Yucatan and Florida, Cuba, Jamaica, Haiti, in the Bahamas and Bermuda O-Wah; There are coastal and barrier reefs, and in Bermuda O-Wah and Atoll.
A plot of a large barrier reef is a view from space. Big barrier reef is not a holistic education, it consists of thousands of interconnected segments, the most massive and old of which are on its northern tip
FIG. 2. General view of the atoll.
Islands of barrier reef.
The main role in the formation of K. construction is played by polypnias of a number of forms from a group of 6-beam or multigructure polyps (Hexactinia s. PolyActinia), especially the Astraeidae families (Astrangia, Meandrina, Diploria, Astrangia, Cladocora, and others), 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-ray polyps with a limestone (for example, Heliopora, Tubipora) take part in the formation of K. O-Gossi and reefs (eg Heliopora, Tubipora), as well as horn polypnias of the Gorgonide. In addition to the actual coral polyps, representatives of one group of hydraulices, characterized by lime deposits - Hydrocorallinae (MillePora, etc.) have important importance in the formation of reefs and OGs. Finally, a significant component of the mass of reefs and octs make up the masses of limestone algae, NalliP and partly Coraline. Finally, the composition of coral buildings includes mollusc shells, lime skeletons of Mshanok (Bryozoa), Cinelene's sinks (Rhizopoda) and radiolarium (Radiolaria) and others. Solids of animals; These extraneous elements can sometimes make a very significant part of the mass of coral buildings. The composition of the reefs and octorals in different seas represents significant differences; So, in the Red Sea predominant and constitute the main mass of polypnia Porites, Madrepora and Stylophora, in the reefs of Mauritius Island - Porites and MontiPora, on Ceylon - Madrepora and Poecilopora, in Singapore - Madrepora, on Sandwich O-Wah - Poecillopora, Zap. The shores of America - Porites and Poecillopora, Florida - Porites, Madrepora and Meandrina, etc.
Porody coral
For the most part, the base of K. Reef or Islands serve solid rocks - underwater mountains or coastries of continents and islands. Grinding ground, especially Ilova, adverse for the development of corals. However, the newest studies of the Slyuer at the shores of Java showed that K. Reefs may occur both at the bottom covered with sludge if there are sinks, stones or pieces of pembol, to which young corals can be attached. As the last and increase in the severity of the colony of polyps sitting on a piece of pembol, etc., the base is deeper and deeper and deeper into il, meanwhile, coral polyps continue to multiply successfully and grow up. Reaching its foundation of a more dense soil, the young reef gets a dense foundation, relying on which, he can successfully increase further. Some polyps, according to other studies, can successfully grow on a ground of gravel if it is fastened with algae (as follows: Psammocora, MontiPora, Lophoseris in the eastern shore of Africa). Most coral polyps find the most favorable conditions in the upper layers, where there is a strong movement of water, and only some, more fragile forms are looking for protection from the surf. At the same time, most of them tend to light (represents positive heliotropism - see). Therefore, polypnias are continuously growing upwards, meanwhile as part below the lying die. Thus, the living colonies of polyps form, so to speak, live boring on the dead mass of reef containing various cavities, emptiness. Powerful masses of coral buildings are compacted due to the fact that the empty gaps between individual polypnomas and their branches are gradually filled with coral chips and other lime deposits. A strong surf, the action of which polypnias is exposed, blends the significant masses of them and the movement of water fragments are abrained into a smaller material. The process of destruction and changes in reef under mechanical action of waves strongly contributes to various marine animals, ruling coral buildings; These are the drilling sponges, some mollusks (eg lithodomus) and partly crustaceans. Some fish feeding on with corals bristle branches and, shredy them, give rise to the formation of a thin lime alley, which also cements polypnyakov fragments. Some role in the formation of this subtle il is also played by the doctures, in many cars on K. Reiffes, from where hundreds of centners of some species are born annually into China called Trepenga. The growth of K. polypnyakov is performed with different speeds. Branchy tree shapes are most rapidly growing; So in one case, on the remnants of a broken vessel in 64, Madrepora rose up to 1 6 ft rose.; Madrepora Alcicornis in Haiti for 3 months formed a branch of 7-12 cm long; Usually, branchy polypnias are lengthened to a smaller value. Much more slowly, the increase in massive polypnias, what are the Astraea, Meandrina, etc.; So, the case is known when Meandrina increased by 6 inches in 12 years, usually the polypnyak thickens per year on a small part of the inches. K. Polyps can live only below the low-end features, and for the most part even a short stay outside the water entails the death of animals (only some forms, like Porites, Goniastraea, Coeloria, Tubipora, can remain alive outside the water. The polyps themselves can, therefore, to build their buildings only to the bottom line of the mist and any elevation of reefs and the islands above this level can only be caused by the action of other factors. Slices of polypnias, broken down, are thrown by sea to the surface of the reefs and, gradually sticking out, give rise to the surface parts of K. buildings. And here, the gaps are performed smaller fragments, k. sand and other dense remnants of animals and individual pieces are finally cemented, merging into a solid rock, due to the release of lime from the solution in water. Another reason that can cause a strong increase in K. Buildings over the sea is a negative oscillation of the sea level, thanks to which K. Buildings can rise to 80 or more over the UR. seas. The dissolution of the part of dead polypnias in water containing carbon dioxide occurs as under the UR. sea \u200b\u200band on the surface of the surface parts of K. Buildings. The accumulation of K. Sand on the surface K. O-GWI can reach such sizes that real dunes are formed, which, under the influence of dominant winds, are gradually moving inside the country, falling asleep plantations and farms; So it was, for example, at Paget Parish in Bermuda O-Wah, where the movement of the "sandy glacier", as the moving dune was called, covered farm, managed to stop only the planting of trees. The surface of K. O-GOB and reefs, covering a layer of humus, gives the soil on which often very luxurious tropical vegetation develops. K. Buildings are found in a wide variety of forms that can be reduced to the three main types: 1) coastal reefs, 2) barrier reefs and 3) separate K. O-Wa and Mel. Coastal reefs are formed in cases when K. The buildings are directly adjacent to the shores of the islands or the mainland and focus them, interrupting in those places where the streams and rivers flow (as the polyps for the most part cannot live in muddy and especially in desalinated water) or where the development of them is hampered or the structure of the bottom ( For example, a cool break). Coastal reefs may or remain under water, or, due to the indicated reasons, becomes supervised. Ruiter's research over the formation of K. Reefs off the coast of O-Vi Krakataau, after the famous eruption of this volcano, proved that reefs may arise at some distance from the coast and gradually grow towards it. The study of the bottom surrounding the coastal reef shows that it gradually decreases towards the open sea. Barrier reefs (also underwater or surface) stretch along the shores of O-Wa or the mainland, remaining separated from them a relatively shallow canal of various widths (10-15 and 50 nautical miles). Channel depth can be very different, but always relatively small. Sometimes the bottom dries on the bottom when the depth of it is somewhat large and even can reach 40-50 soot. Meanwhile, outside the reef of depth is relatively high and can reach several hundreds of seeds, and the outer edge of the reef falls into depth. In places, barrier reefs are interrupted. Sometimes they surround from all sides o-in. In some cases, barrier reefs achieve huge sizes; So in the East. the banks of Australia from Cape Car Sunday (24 o 40 "Yu. Sh.) to South. New Guinea shores the" Big Australian Reef "length about km, separated from the shore by the channel in 25-160 km; the main passage with the lighthouse lies under 11 ° 35 "Yu. sh. (Raines Inlet), channel depth 10-60 soot., And outside the reef, there are more than 300 soot. A very diverse form represents K. O-VA (and individual mels); Molds are dominated by rounded, oblong, ring-shaped ("Atolls") and semi-lunk. The most distinctive appearance have the atoll; This is a ring-shaped sushi band, a width is usually not more than 100-200 m, the surrounding central pool ("lagoon"), which is usually connected to the surrounding sea by several aisles lying on the side opposite to the opposite of the dominant winds. Rarely (eg whitsunday island) Atolls represent a solid continuous ring. The size of the lagoon is very different and the diameter of them can reach 75 km. And more (and the diameter is 30-45 km. It is often found). The depth of the lagoon is generally insignificant, usually somewhat large, but can reach the coarse up to 50; Meanwhile, from the outside of the atoll, we find, as at barrier reefs, mostly very significant depths. The bottom of the lagoon is covered (as well as the channel of barrier reefs) K. Sand and limestone and represents relatively few living corals, an advantage of more gentle forms. Sometimes small o-was can be in the lagoon. The height of the ataolls above sea level is mostly insignificant, not more than 3-4 m; Sometimes, through the atoll, the waves of the surf beyond the lagoon. The atoll side is generally above. Comparatively rare K. O-Wa reaches a significant height above sea level (which is explained by the negative fluctuation of the sea level: the reefs formed are extended from the sea). So at the Vikanoro, according to Darwin, the wall K. Reef reaches 100 m of the embroidered, according to the methium, in low-lying O-Wah, rocks from K. Limestone embroidered in 80 m. Sometimes the submarine atol, such, for example, a big reef In O-Wah, Chagos, lying at a depth of 5-10 soot. Under the sea level. Extremely ordinary and other forms of octoral and shames, which sometimes also achieve significant sizes; So reef lying to the two main islands of the Fiji Group, represents the surface of about 3000 square meters. English miles; K. Bank of Saya de Malha, to St. Madagascar, stretches from 60 ° 20 "c. D. Up to 62 ° 10" (according to Greenwich) and from 8 ° 18 "Yu. Sh. Up to 11 ° 30", and then Yu lies Nazareth Bank (NazarethBank) about 400 km long. The sea, crowded by K. Rifami, represent generally significant hazards for navigation, especially since K. O-Wa and reefs are often cool raised from a significant depth and nothing indicates the proximity of the reefs, except Burunov in case of excitement. On the other hand, the barrier reefs allow in some cases the ships to safely pass along the coast while in the open sea is a strong bad weather. The fence of shores reefs prevents the blurring action of waves on the shore. In addition, thanks to the reefs, in some cases, the erosion products brought from sushi are deposited from the coast and determine the significant increase in sushi; So, Tahiti surrounds the sushi band wide from 0.5 to 3 eng. The miles that occurred this path and covered with rich vegetation.
Mushroom coral
Black corals
Along with the process of education K. O-GOB (for example, Florida), in other places (for example, on Bermuda O-WAH) we meet the phenomenon of their destruction; In these cases, the formation of caves (sometimes stalactite and stalagmite), arches, etc.; At the same time, a special red soil is observed on the surface of the O-WA, in which the residue from the erosion is seen, dissolving the lime of reef. The peculiar structure of K. Reefs and O-Great Patriotic War, important and tremendous distribution were initiated by their interest in these formations, especially the atales; To explain the form of the last one, they resorted (from Steffens, in the city) to the hypothesis that the atolls crowned underwater crater; Others believed that K. Polyps, by virtue of a special instinct, build their arrangements in the form of a ring to use the protection against the surf. The theory of K. Education, given by Darwin, explained the mysterious fact of the existence of K. Buildings at large depths, where corals building reefs cannot live, explained the reason for the considerable thickness of K. sediments (which was confirmed by the way, and the newest drilling experiments on K. Rifa), as well as the form of K. Buildings and the relationship between them. Despite a number of new objections, Darwin's theory remains dominant. The theory of Darwin is so called. Immersion theory (Senkungstheorie), the essence of which is as follows. If K. buildings arise from the shore of the O-Wa or the mainland, where the water level remains more or less permanent (the bottom does not ignore), then it should give rise to the coastal reef. If the bottom is descended, the reef will continue to grow up and should take the character of the barrier reef separated from the sushi channel. This will be facilitated by the fact that K. Polyps will find better conditions for life on the outside of reef, which will therefore grow stronger. If finally, with further immersion of O-in, surrounded by an annular reef, it will completely disappear under the surface of the sea, on the spot it will remain atoll (underwater or surface, depending on the speed of immersion). Such an explanation of the origin of the K. Buildings and the relationship between them explains the many of their features and relies on a number of various facts. However, the extensive K. Education, in the form of barrier reefs, is observed in such places where it is obviously happening, on the contrary, the atoll is also observed in such locations. In general, it is necessary to recognize that various forms of K. builds can occur in and otherwise, in addition to the bottom of the bottom, for example, on underwater banks and mountains, and the form of O-GBIs (including the atolls) is sometimes determined by the direction of marine currents or those that the corals of this reef grow more successfully at the edges of it than in the middle, the average dying and subjected to the destructive action of flows and water containing carbon dioxide, which leads to the formation of the lagoon. Be that as it may, the latest objections against Darwin's theory are represented by addresses and amendments to it than a new explanation that could completely replace this Darwin. Extensive K. Education existed in former geological periods and in many sediments we find explicit traces of reefs. In the most ancient periods, K. Reef occupied, relatively, very extensive area. Paleozoic reef corals found in Scandinavia and Russia far in 60 ° C. sh. And some kind of childbirth even on Spitsbergen, new land and Barents O-Wah; Lithost R Otion was during the nonsense expedition (Nares) found from from 81 ° C. sh. In the Silurian and Devonian period, the corals were overcome in the seas on Shir. Canada and Scandinavia. In later geological periods, we see that K. Reefs are increasingly retreating to the equator, which stood, in all likelihood, due to the decrease in the sea temperature under high latitudes. In the Triassic period, the reefs were abundant in Central and Southern Europe; In the Jurassic period, the extensive K. Sea occupied a significant part of Western and Central Europe, and traces of reef remained in England, France, reports of the most important data from Keller, "Leben des Meeres" (Edition unfinished), Marschell in Thierleben Bram (BD. X ; a new edition, ends in Russian), as well as Kingsley, "The Riverside ZOOLOGY" (T. I); Heilprin, "The Di S Tribution of Animals" (1887) and Nicholson article in "Encyclopedia Britannica".
In the morphology of many coast tropical belts, lime buildings of rhyme-forming corals play a major role. Such coasts according to their originality can be allocated in a special type called Coral Coast. In addition, the construction of corals form many small low islands, scattered on huge spaces in the oceans and the seas of a tropical belt. It is convenient to consider them in the same section, since in its genesis they represent essentially coastal forms of the ocean levels of island hills.
The rhyme-forming corals represent colonial organisms forming a lime skeleton. This skeleton remaining after dying individuals, and is laying a lot of reef. Corals are divided into six and eight-beam. Reefs form predominantly six-bearing corals, the eight-beam play a subordinate role.
Coral buildings represent a kind of living environment in which very favorable conditions for asylum and abundance of food are many other organisms, both leading attached lifestyle and fluently moving. These are numerous mollusks with thick-walled sinks, marine hedgehogs, crustaceans, msanka, lime sponges, lime algae, dying fish, etc. As can be seen from the list of lists, many of these organisms also postpone the lime and, therefore, can contribute to the growing reef. A particularly important role from plant organisms play multicellular algae belonging to red (crimson) algae. The cells of these algae are distinguished as if the calcite and magnesite cover, which, however, does not destroy the flexibility and mobility of the branches of algae, which allows them without breaking, to withstand strong movements of water in the surf zone. Usually these carbonate peels are painted in red or pink color. Being less pleasant than corals, lithotaminium grow well in those places where corals can no longer develop. They are magnificently developing in the upper part of the reef in an adorption-taming area, where they can remain alive at low tide, wetted only by splashes of the surf. The best lithotamine feels in small transparent waters, at depths that do not exceed 10 m. In the lagunis of reefs, the multicellular, which highlights the lime of green algae - Khalimeda, forming lime, sintoid-cerebred branches. Khalmeda multiply and grow so quickly that they literally soaring their branches of the base of coral colonies.
The rhyme-forming corals are found only in the waters of the seas, the temperature of which is never falling below 20 ° (optimally 25-30 °). Such temperature conditions also determine the horizontal distribution of corals, limiting it only by the seas of the tropical belt. At the same time, coral buildings are stronger and further from the equator developed on the eastern shores of the continents, washed by warm currents, and almost absent from the Western shores, along which cold flows pass. In the northern hemisphere, the border of coral reef passes through the Bermuda Islands (about 30 ° C. sh.), The northern part of the Red Sea (26-27 ° C. sh.) And the Hawaiian Islands (20 ° C. sh.). In the southern hemisphere, this border passes through Hutmen (28 0 30 "Yu. Sh.) At the West Bank of Australia, Lord-How Island under 31 ° 30" Yu. sh. between Australia and New Zealand.
Most of the reefood corals can live at depths not exceeding 40 m, and only a few were at depths of 60-70 m. Coral polyps do not stand any long stay outside the water, so the living parts of the reef begin only on the water level when they are low. Next, corals love pure and transparent, although the water lively with a strong movement. Where water becomes muddy, for example, before the mouths of rivers carrying a lot of suspended nanos, coral buildings are usually interrupted. Corals need and in light, as the polyps are in symbiosis with one of the types of single-cell algae , for which the light is necessary. Waterly lively by wave motion and flows, water contributes to an abundant supply of coral food in the form of plankton and oxygen and therefore favors the enhanced growth of the colonies. It is usually believed that for the initial settlement of the coral colony, a solid rocky soil is required. This is true where the waves and surf are strong enough to destroy the coral building in the early stage of its development. But in the tranquil waters of the Lagoon of the Red Sea, it is often possible to meet small coral colonies, the substrate for which is sand, so that they can be easily shifted with their place. According to O. K. Leontiev's observations, there are colonial corals that settle not only on sandy and or etched soils, but sometimes even on a vegetable substrate. Thus, the southern shores of Cuba have forms of corals that are on the stems of seaweed (talascia).
Coral reef is composed of colonies of very many types of corals having a form of more or less compact mass, spherical or lepthekoid , or highly branching like bush , complete and merging with each other. There are often different cavities and channels, filled with water and giving the shelter and protect against the attacks of enemies with many other animals of organisms often between the colonies and their branches. Thus, the reef has in general loose addition.
As already mentioned, corals can build their buildings only to the sea level at low water. Having reached the latter, the reef can only grow to the sides, the average part of it, to which the access of fresh water and food is difficult, begin to die and collapse. Due to the growing, on the parties, individual shockers of coral buildings are often acquired by a mold-shaped form, starting at the bottom of a relatively "narrow barrel and expanding to the side at the top. Such coral formations are found, for example, off the shores of Brazil. The latter sometimes merge among themselves the upper parts into large reef arrays. , resting at the bottom, on the seabed, only on separate columns, between which cave-like underwater corridors are stretched.
Reef rising from the bottom of the sea at the very shore or at some distance from it, has an inner side facing land, and external to the open sea. On the outside of the reef, there is a particularly strong surf, and here the reef is subject to strong destruction. The dead parts of it are chopped up and in the form of a lime crushed stone and sand are pounced on a splash to the surface of the reef; They fill the emptiness and depressions with a loose mass, which, however, is quickly cemented by water penetrating into it. Reef, who had initially cavernous and spongy structure, turns into a dense and compact limestone.
Simultaneously with this process, the rope increases and raising it with free of sea levels. Detritus material thrifted on the surface of the reef surface forms gradually on its outer side, the shaft rises above the water. This shaft often serves as a source of coral sand, from which the wind forms behind the dune shaft, which, however, is rapidly cemented and secured. At the resulting surface in this way, in places not covered with water, even during high tides, the soil cover can be formed and vegetation can be formed due to the seeds of seeds and fruits (coconut palm tree, etc.).
By location, the plan distinguishes three main types of coast coral structures, due to the depth of the coastal part and the steepness of the underwater slope: 1) the focusing reefs; 2) barrier reefs and 3) Correspondent reefs.
Furifying reef It is formed if the underwater slope is cool and depths on which corals can develop, are located only at the coast itself. Reef then as far as it struck the coastal slope, adjacent to the root shore closely and forming its outer edge to the coastline. Two varieties of the binding reef can be distinguished: 1) reefs facing its outer edge to the open sea and not protected from its effects by any other barrier, and 2) reefs protected by barrier reef. Without experiencing the actions of a strong surf, such an ending reef has no rope formed by lime alga, although its outer edge is often almost drowned. The surface of the protected boundary reef is similar to the reef plateau described below the atolls, has an uneven surface, and often when low water is occupied by a series of small lakes or puddles. In some cases, the boundary reef is not completely close to the indigenous coast, and it is separated from it very shallow (0.3-1.5 m) channel with a bottom, covered with sand or gravel; This is the so-called "boat canal". Often, such a phenomenon is associated with the abundance of nanos of the shore, creating unfavorable conditions for the growth of corals. Channels of such origin are developed, for example, on the eastern shore of the Red Sea to the north of Jeddah and in the north-western coast of Madagascar.
Barrier Reef. It is a shaft, rising from the bottom of the sea and walking in parallel to the shore, separating from it a channel or a lagoon greater or less width. In a large barrier reef, stretching almost 2000 km along the east coast of Australia, the width of the lagoon is an average of 30-50 km. In places it is narrowed up to 7 km, the places are expanding to 100 and even 180 km. The depth of the reef channel usually does not exceed 50 m. Australian barrier reef does not stretch continuously: it is composed of a huge number of separate reef arrays, located the chain on the border with an open ocean, and, in addition, the mass of certain small reefs scattered among the lagoon. Some of these buildings represent submarine rocks, the surface of which is located at depths of 10-15 m. Such submarine rocks, very imperative swimming vessels in the areas of their development, represent early reef development stages. It is characterized by almost complete absence in their formation of the participation of limestone algae. In the process of further growth of corals, the reef rocks reach the water level when they are discontinued, which stops their further rise in height due to the livelihoods of corals. The surface of the building is now in other conditions than its slopes.
The strong movement of water in the zone of the surf causes the cropping of the lime breed of reef, the debris is shared and crushed,. Turning into coral sand, thrown into the surface of the reef.
Miniature sandy islands or coral shallows of several dozen or hundreds of square meters are scattered in large quantities in the lagoon of the Big Barrier Reef Australia. Sometimes these lagural reefs represent a miniature atoll, having a ring-shaped shape with a lagoon inside in the form of a small lake in just a few decimeters or meters deep. Such lagural reefs are very common in Indonesia's epicontinental seas, in the South China Sea, in the area of \u200b\u200bAntill,. In places in the Red Sea, along the north-west coast of Madagascar, in the reef canal of the coast of Queensland. Usually these atoll-shaped reefs are higher from the windward side.
Apparently, to the same category of shallow, lagural forms should also include those forms that are known in the literature - under the name of the cortical reefs.
Despite the intensive destruction of dead parts of the reef on the outside of the action of the surf, the reef expands specially vigorously from this side. This is explained by the fact that the strong movement of water brings food in the form of plankton. Thanks to this, the outer edge of the reef is usually very cool, often even hanging, and in barrier and boring reefs often breaks up to quite considerable depths.
With changing conditions of depth along the same coast, various types of reefs can move one to another. So, the barrier reef, bordering the new Caledonia, under. 21 ° sh. It is adjacent directly to the West Bank of the island and for 100 km stretches in the form of a border reef. Similarly, a large barrier reef, framing in the north of the island of Viti-Lev and Vanua Lev (Fiji), is adjacent to both islands directly. Sometimes the bounding reef separates the bay from the sea, being in the form of a barrier reef, as is observed, for example, on one of the bays about. OAU (in the Hawaiian Islands). In the Red Sea are developed nearby, barrier and cortical reefs. The last dominates in Suez Bay; Along the shore of Hijaz, the barrier reef stretches, separated from the bank of the channel in 70 m deep, and at the opposite African reef reef has the nature of the bordering.
The indigenous shore, bordered by the reefs of one or another, can be both low (for example, the Florida Peninsula) and the High (Eastern Coast of Australia, New Caledonia and. The shores of many other islands of the Pacific Ocean).
In some cases, it is observed that the coastal slope of the coast, accompanied by coral buildings, is also covered with the latter, arranged, however, at a significant height above sea level. It will be ancient, already dead coral reefs, formed with a different position of the sea level and experienced raising since then. Sometimes these raised coral reefs form as it were for several floors or terraces lying one over the other, respectively, several, quite a long-term stable position of the coastline. Raised coral reefs are known almost exclusively on the banks of the islands: on large and small Antille Islands (Cuba, Jamaica, Barbados, leeward), on the southern shore of Java, etc. Often in these coral limestones, karst phenomena are observed: small rivers, reaching the coastal strip of coral raised Reefs disappear from the surface and reach the sea underground paths. The outer edge of the ancient reefs, in some places, as far as it is lifted and roaming off dry depressions, having a drain through caves and canals in limestone. These depressions represent, apparently, nothing else, as the reef channels and lagows have drained when picked up.
On the other hand, many reefs with their morphological features often indicate a complete certainty of the existed and can still continue to lower the bottom. Many, on which corals were originally settled. Already noted that not only depth immediately before the outer edge of the barrier reef, but often the depths of the channel separating the reef from the root shore, significantly exceed those depths on which corals can develop. It is clear that this could only occur as a result of slow down the seabed lowering, and the lower parts of the reef died and turned into a coral limestone, while the upper part of the reef, consisting of still colonies, as the reef is constantly increasing to the sea level. The lowering tests in such cases and a significant width of the channel separating the reef from the coast, as well as the very young character of the indigenous shore, often almost deprived of apparent formations and rich in ingression bays, etc. (Australia's shores, New Caledonia).
Atoll. Types of coral structures considered so far only complicated the structure of coasts of continents and islands, isolated from non-nuclear origin. But in so-called atolls, coral reefs are already playing an independent role. The atoll marks the presence of a shallow underwater underwater, most often underwater volcanic cone, steeply climbing around the edges to considerable depths. The coral buildings are planned for this elevation, which are only issued from water in the form of a ring of low coral islands or in the form of a solid ring-shaft, closing the inner water space - the lagoon. This is a reef ring itself and called the atoll.
The sizes and shapes of the atolls are diverse: the diameter varies from 2-3 to several tens of kilometers. Suvodiv Atoll in the Maldives group reaches 217 km in circle with diameter to 71 km and consists of 102 coral islets. In the Marshall Islands group there are atolls reaching over 100 km in diameter. The form of the atoll in the plan is more or less round or oval, then triangular, quadrangular or incorrectly vane or angular. The smallest atolls of the lagoon is sometimes missing, replaced by a dry saucer-shaped depression. If the lagoon is developed, then its depth is always insignificant - no more than 70-80 m, and small atolls are several meters. The bottom of the lagoon is usually quite flat, slightly concave, smooth, usually folded with coral sand, and closer to the middle - the finest limestone. In cases where the reef ring is broken in several places by channels connecting the lagoon with an open sea, the depth of the lagoon always exceeds the depth of these channels. Thus, if the surface "part of the atoll is not solid, then the underwater part is usually a continuous reefal shaft, protruding the edge of the underwater volcanic elevation of the bottom of the sea. If oceanic waters can be freely penetrated through the wide channels inside the lagoon," then corals can develop in the lagoon. Here and there are reef islets. Separate islands, forming an atoll ring, are often like an atoll in a miniature, having their own lagoon in the middle, or represent an incomplete ring, opens toward the main lagoon with a wide channel. Such second order atolls are called atoll he mi.
In the structure and relief of the atoll ring there is a distinctly expressed zonal structure. You can select the following zonal elements:
1. Outdoor (oceanic) slope, steeply falling to significant depths of several hundred meters. The angle of fall often exceeds 45 °, and in the upper part of the slope, where there is a particularly intense reproduction of corals, it is often even a canopy.
2. Lime-algae comb forming the outer edge of the surface of the reef and is distinctly expressed only on its side. This comb is the highest part of the reef and is complicated mainly by lime deposits of algae . The comb is absent on the atolls of the seas of Indonesia and the Red Sea, where such a powerful surf is never observed as on the atolls of the open ocean. The strength of the surf is such that it makes the reef completely inaccessible from the windward side, with the exception of those places where he is broken by the channels. The surf destroys the construction of corals and makes their development almost impossible to a depth of 2-3 m. But algaeit is growing up in such conditions and, as it was already indicated, it can remain alive above sea level, wetting only by splashes. A bikini atoll in the Marshall Islands group, an algae comb, painted in red or pink color, reminds its asymmetric profile by Coustle and rises by 0.6-1.0 m above the reef plateau located behind it.
On the outer, the viscous side of the ridge is sometimes observed; Equal stuffing grooves and the ridiculous increases that are absent on the part-ridge facing the lagoon. In addition to the Marshall Islands, similar grooves are observed on the funfuti atoll in the group of Islands of Ellis, on Ra-Roya in the Tuamot group, on Onotoa in Gilbert Islands.
3. The reef plateau lies behind the algae ridge; It usually reaches several hundred meters wide, has an uneven surface and is mainly formed by dead coral reefs and rhyhydrated dedrites who are undergoing cementation and inlaid limestone algae. Sometimes the plateau is partially occupied and living corals, which near the algae ridge find favorable life conditions with plenty of water from the ocean water. These colonies of corals often have the form of micate-shaped micate-shaped buildings, in which living polyps are located at the edges, and these edges are a little rising over, the central part. The microatile height is usually only a few decimeters, and the diameter varies from several decimeters to several meters. At the reef plateau there are islands folded by coral sand.
4. The indoor slope of the reef rings is much more gentle than the outer slope. Its upper part is formed by sand blown from the islands. On the slope there are colonies of living corals with flat vertex surfaces, which almost reaches the surface of the water.
5. Laguna. The bottom of the lagoon is sometimes flat and covered with limestone sand unknown power. But from the sandy bottom often steep tubers of living corals. In the lagoon enamel (Marshall Islands), Emery counted about 2300 such colonies.
Atolls are extremely widespread within the tropical belt of the Pacific and Indian Oceans. In the Indian Ocean, between 70 and 100 ° C. D. Atolls are dominant form of islands. These include groups of the Lakkadiv and Maldives, Chagos Islands, etc. In the Pacific Ocean, the atales include all the islands of Tuamot, Tokelau, Phoenix, Central Polynesian sprays, Ellis, Gilbert, Marshall, Hawaiian Islands and many others. As you can see, the atoll islands are grouped into archipelagoes that occupy extensive spaces. Outdoken Ocean, real atolls are rare. It can be noted their presence in the seas of Indonesia, as well as several typical atolls known in the Red Sea.
Real atolls rise only a few meters above the ocean, and some do not even perform on the surface at all, representing underwater banks. But along with it there are both atolls that have undoubtedly experienced some raising since their formation. They rise to a significantly greater height above sea level than normal reefs, their lagoon often has the kind of dry depressions with an underground flow through cracks in reef limestone. Examples of raised atolls can serve numerous small islands of Central Polynesian Sporads, Christmas Island in the Indian Ocean (height 364 m), some of Luaita Islands, Eua Island (329 m) in the Tonga Archipelago, etc. As already mentioned, on the slopes of such raised atolls Reef limestone are located in several tiers, forming as far as a number of terraces. Of particular interest are raised atols for understanding their genesis, since the erosion of reef limestone occasionally reveals their foundation, usually from volcanic rocks. Such formations are scheduled for a number of transitions to high volcanic islands with modern boundary or barrier reefs. Such transitional formations are the so-called almost-atolls. An example of an almost-atoll is the atoll of Truk in the Caroline Islands group, in whose lagoon, reaching 63 km in the diameter, rises a number of islands of volcanic origin, one of which reaches 530 m of heights. Al-Atoll Ermite with four volcanic islands is known on Admiralty Islands.
The question of the origin of the atolls is still decided by researchers in different ways. In the first half of the last century, the satellite of the Russian navigator O. E. Kotsebu I. F. Eshcholz expressed his eyes that the formation of the atolls occurs on the mountain peaks rising from the bottom of the ocean. This view of I. F. Eshcholts was further developed in the views of a number of Naturalists of the XIX century., Which believed that coral reefs of the atolls of their ring-shaped form repeat the same shape of the edge of the volcanic crater, on which they laid. With this opinion, it was not kniting, however, the fact that the size of many atolls is much higher than the variations of the craters of the famous volcanoes of the globe.
The slender theory of formoll formation was given in 1842. Ch. Darwin after his observations over the structure and life of coral reefs during the world travel on the Beagle ship. According to Darwin, the foundation of each atoll must be the island, most often representing the top of a volcano rising from the bottom of the sea. The corals settled in the outskirts of this island formed the originating reef, closely adjacent to the shore. With the then slow down the bottom of the sea followed, the initial island was gradually immersed and decreased in height and in the diameter. As reef, the corals are immersed all the time it was adjusted to the sea level, but the growth of reef on the parties took place only on the outside facing the open sea. In this regard, the channel was to form between the reef ring and decreasing in the size of the island. The reef turned in this way in the barrier. Later, the island could completely disappear under water, and only the reef, constantly awaited from above the live corals, remained in the form of a ring on the spot of the sunken island.
Darwinov Theory of the Origin of Atolls, developed and complemented later by D. Dan, was taken some time by all unconditionally and admitted universal. It was confirmed by the fact that the dead reefs, leaving for depths, were observed, on which corals live can no longer, as well as the presence of the almost-atolls described above. However, a number of new facts caused criticism of this theory and made it doubt its universal application.
An important event of the second half of the last century was a round-the-world oceanographic expedition of the student's research ship "Challenger" (1868-1872). The participant of this expedition D. Mörrery proposed a new theory of origin of coral reefs and atolls. According to this theory, ring reefs are formed on underwater volcanic hills, dedicated to sites, where the bottom of the sea rises. When the vertex of this hill reaches such a depth that the shallow-armed naval bottom organisms can already settle on it, their lime skeletons are beginning to accumulate, to which the remains of dying plankton organisms are also joined - the sinks of the Foraminiferator, Pateropod, etc., due to these sediments, the volcanic surface. Hill rises even more. More deep seats of the sea, lime precipitates are usually not achieved, aimed soluble with sea water when lowering. When this way, underwater elevation approaches the sea level so much that the reef-forming corals can settle on it, the latter begin to build their buildings across the entire space. However, at the external edges, the reef corals formed in this way are in more favorable conditions, receiving consistently fresh water and abundant food, so the growth of reef here is faster. In the inner parts, corals began to die, and the limestone of dead reefs gradually soluble with sea water. So the lagoon is formed here. On very small atolls, as already mentioned, the lagoons may not be, since the surf waves fills it with the damaged products of the destruction of the outer parts of the reef. The larger the size of the atolls, the stronger the accumulative activity of the surf lags behind the dissolving and eroding action of seawater and the greater and deeper the lagoon.
As can be seen from the above, the theory of Mörray, as opposed to the theory of Darwin, suggests a relatively very small power of coral reef limestone, not exceeding several tens of meters. As we will see below, drilling at some atolls in some cases did not confirm this assumption. There are Mörery's theory and other weaknesses. For example, it excites doubt the possibility of the formation of a lagoon with a dissolving action of seawater.
Finally should be outlined Glycio-Evstobatic theory Reefs proposed by R. A. Dali. The views of the latter are based on the fact that a large number of laguns have a depth of about 60 m. The level of the bottom of these lagoon is thinking by the author as an abrasive surface that has formed during the quarterly glaciation, when the World Ocean level was euvatically reduced due to exemptions from it-significant water volume, Swimming on a land in the form of powerful stals of the ice of continental and mountain glaciation. Lowering the water temperature of the ocean during the maximum of glaciation in more remote from the equator the outskirts of the modern coral distribution range should cause them to die here , and they are preserved alive only in a few "shelters" (refugium) near the equator. In the postgrade of the warming of climate and the stabilization of glaciers, the sea level Evstically rose, corals spread from these shelters and took their buildings the abrasive surfaces of the level reduction time. Dali indicates the vastness of the atolls and barrier reefs, which reach large sizes in the equatorial areas than in the outskirts of their range, and explains this greater ancient first. He also admits that the role and movement of the earth's crust could play, but does not give them much importance.
As it was possible to make sure of the above, the solution of the question of which of the proposed theories is most complied with the well-known facts, it requires primarily the determination of the power of coral limestones, which occur on the volcanic foundation or thicker of shallow sedimentary formations. So, according to Dae's theory, the coral formation power cannot be greater than the water layer returned to the ocean as a result of the melting of glaciers. On the other hand, the theory of lowering (Darwin, Dan) requires high power of the strata of coral limestone. This issue could be allowed only by drilling at the atolls. For the first time, such drilling was carried out in 1896-1899. Funafuti's atoll in the Ellis islands group, rising from the depths of 5000 m. At low, the drilling technique managed to drill only to a depth of 300 m with a little, although the foundation of coral formations was not yet reached. The well revealed coral rocks overlapped with sandstones, fragments of the skeletons of the simplest, sinks of bivalves and brickelogs of mollusks. The presence of coral rocks at depths exceeding the possibility of growth of corals, indicates the lowering of the reef construction as it increases (, p. 18). This spoke in favor of the theory of Darwin.
According to Vivald's research in the Indian Ocean, a decrease in surface waters in the area of \u200b\u200bthe Lakkadiv and Maldives reached 8-9 ° at the period, i.e., the water temperature was below 18 ° - the limit of the possible existence of coalles.
At a later time, drilling on reefs and atolls was carried out in many areas, and its results in most cases speak in favor of Darwin theory of lowering. So, drilling to Quito Daito Tzima south of Japan showed the spread of the newest PLO-Pleistocene coral limestone to a depth of 103 m, that is, to a depth of a slightly larger, desired Evstico theory of Dale. This drilling conducted to a depth of 432 m has not reached the foundation of reef limestone. Two drilling lined in the lagoon of the Large Barrier Reef Queensland showed the spread of the latest reef limestone to the depths of 123 and 145 m. On. Maratouz northeast of Borneo (Kalimantana) Corals were until the very end of the well - to a depth of 429 m, on the OUP in the group of the Hawaiian Islands - to 319 m, on the Bikini Atoll in the Marshall Islands group, 777 m took the deepest of four wells, without reaching the base of coral formation. Magnetic survey on bikini showed an allegedly volcanic base of the atoll at depths from 1250 to 3950 m. All these facts indicate a significant amount of lowering the bottom of the sea. It is impossible, however, not to say about the Bermuda islands, the structure of which reveals consent to the Glyatio-Evstust-Caucasian theory of Dale. It turned out that the reefs of Bermuds rest on the platform at a depth of 75 m, and the seismic exploration in 1952 showed the presence of an alignment surface at this level under all this archipelago.
| Previous |
Coral reefs call structures from organogenic limestones formed by polyps and other rhyme-forming organisms and populated numerous forms of corals, algae and other living organisms.
It should be especially noted that Mad Pageor corals and coral algae play a dominant role in the construction of coral reefs. In addition to these two main "builders" reefs, other organisms - sponges, mollusks, foraminifera, etc. take part in its construction.
All varieties of buildings created by corals and other rhyme-forming organisms can be divided into several main types. Distinguish coastal reefslocated directly on the shores of the islands or mainland, barrier reefswho are disturbing from the shore at some distance and atoll - Ring-shaped coral islands. Finally, there are also significant coral banks that arise on the shallows, and dense coral settlements in the lagunis and bays.
Three types of reefs generate a variety of transitional forms. Furming reef near one part of the coast further can go to the barrier reef, and their border is difficult to distinguish. Some of the islands could actually be considered atolls if it were not for the presence in the center of the reef ring of one or several dissected solids of volcanic rocks. Immersed (flooded) reefs serve as indicators of underwater platforms located near the water surface, which contributes to the growth of corals, but it is more likely that they are flooded atolls or islands.
The process of the formation of all these coral buildings was interested in geologists and zoologists for a very long time, especially the origin of the ring-shaped islands - atolls seemed especially incomprehensible. A few theories were proposed explaining the formation of these islands, and many of them are pretty naive. So, until the middle of the XIX century, the opinion was dominated that the atolls are coral fours of the craters of underwater volcanoes.
The first convincing theory of origin of coral buildings of various types was nominated by C. Darwin. In his book "Building and spreading coral reefs", published in 1842, Ch. Darwin gave not only a detailed description of various coral buildings, but also showed how one type of coral settlements as it turns into another. Darwin collected a huge material concerning the livelihoods of organisms forming coral reef, their relationship to the conditions of the external environment, growth intensity and distribution in the World Ocean.
Part of the information he received from the captains of ships, furring the tropical latitudes of the oceans and the seas, and from scientists who studied corals.
He spent the most valuable observations during the round-the-world travel on Beagle. According to Darwin, the first stage of the formation of coral islands is opportuning coastal reef
. Corals in this case use the banks of the islands as a support, or, as experts, the substrate say. If the conditions favors the development of corals, and the island does not experience lifting or lowering, the reef remains the busty coastal reef.
In cases where the bottom of the sea as a result of the processes occurring in the earth's crust begins to rise and the island, as it were, comes out of the water, the bordering reef grow along its new coastline. Reef sites that are outside the water are dying, and with the seaside reef increases and increases, but the overall picture does not change.
It is very different about the cases when the seabed is lowered and the island is immersed in water. The rhyme-forming organisms require a lot of food and pure sea water rich in oxygen. Thanks to this, the rise of reef, which was previously the island, always follows its periphery washed by the sea, and almost does not go to the inner part of the resulting ring, where water is less saturated with oxygen due to heating in the sun and smaller mixing with the air of the surf waves. So arises barrier Reef
. The longer this process lasts, the further the barrier retreats from the island. Finally, this moment comes when the island is finally immersed in the sea, and the barrier reef turns into atoll
- Ring island with a prisoner inside his lagoon.
Coral buildings in different parts of the ocean make it possible to trace all stages of gradual turning of the coastal reef into the atoll. Riga growth up sharply limited to the sea level, but no matter how fast the seabed lowered, corals always have time to grow to the upper boundary at which they can exist. Some of the modern coral islands rise from the bottom of the sea to a considerable height.
Later, some researchers put forward other theories of the origin of the coral islands. The fact is that the theory of Darwin is based on one indispensable condition - the lowering of the seabed. Opponents of this theory argued that the relationship between raising and lowering the seabed is much more complicated than C. Darwin believed.
In this regard, other theories of the formation of reefs and the atolls were put forward, relied on volcanic activity in the earth's crust or tied to cooling and warming in the climate of the Earth. However, they all had weaknesses in their bases. Darwin knew how to prove the legality of his theory: to organize drilling of some atolls to get samples to study the soil at depths of 200 or more meters. If at all the depth of the atoll is composed of coral limestone, then its theory will receive irrefutable proof.
Darwin's dream was carried out only in the middle of the XX century. In 1951, two very deep drilling were produced on an enywlock atoll (Marshall O-Wa).
It turned out that coral limestone was littered with a basalt layer only at a depth of 1266 and 1380 m. The calculations were shown that the reef, which gave rise to this atoll, was born 60 million years ago. It is clear that the accumulation of such powerful limestone could only occur as a result of a long dive of the bottom of the ocean.
It is very likely that the most common way to formollov was the immersion of volcanic islands. Interesting discovery on the seabed of a large number of flat-term underwater mountains (called guyotes), similar to deep immersed atolls. At least one of them was raised shallow corals.
From the review of fossil reef literature, it follows that the formation of reefs was mainly in those geological epochs when the weak immersion of the earth's crust prevailed (or a slow rise in the sea level).
In geological periods, which were characterized by a raising coral structures or their rapid immersion, the reefs almost did not develop.
Recently, many new data appeared on geomorphology, oceanography, paleontology and biology of modern rhyme-forming animals. All of them are used to clarify Darwinian theory.
ArticlesThere are three kinds of islands: mainland, volcanic and coral. The formation of the islands occurred not only many thousand years ago, but now new island territories arise.
How did the mainland islands formed?
The mainland islands were formed due to the movement of the tectonic plates of the earth's crust. Once the islands were part of large continents. Vertical movements of tectonic plates together with a raising of the world's ocean form formed faults in the continent. The nature of the mainland islands and the nature of the nearest mainland to them are almost identical. The mainland or continental islands are located within the single shelf, or are separated with the mainland deep fault. Continental Islands include Greenland, New Earth, Madagascar, British Islands, etc.
How are the volcanic islands formed?
In the oceans there are constantly volcanic activity. The erupting volcano highlights a huge amount of lava, which, frozen when contact with water and air, forms new volcanic islands. Such islands are experiencing greater aquatic erosion and gradually go under the water. Volcanic islands are often significantly removed from the mainland and form a unique environmental system. An example of volcanic islands can serve as a chain of the Hawaiian Islands.
How are Coral Islands formed?
Such islands are capable of forming only in equatorial and tropical latitudes. Shames are populated by corals and polyps, which are rooted for the seabed. Over time, the lower part of the corals hardens, forming a solid foundation of the island. Such a base begins to delay the sand, which the ocean bears with its flow. Coral reefs are formed, which are populated by the wonderful animals of the ocean. An excellent example of such islands is a big barrier reef near the banks of Australia.
Coral reefs and islands In education, the main role is played by solid polypnyaks of coral polyps (see) and the products of their destruction. Although coral polyps are distributed in the seas of all belts and are found on all sorts of depths, from the lower boundary of the tumps to huge ocean depths, however, their mass development is limited to a relatively narrow horizontal and vertical limits. This applies especially to those from K. polyps forming a colony equipped with a dense lime skeleton, which, developing in huge masses, lead to the formation of powerful lime deposits - K. Reefs and islands. These animals find conditions favorable for their development, in layers are relatively shameless: from the line of low tide up to 20-30 seedlings, below this depth of living K. Polyps participating in the construction of K. Reefs are found only as an exception (to a depth of about 90 m ); In general, below 20-30 seeds we find only the dead masses of K. polypnyakov. The most powerful growth of corals is limited to even closer limits - from the line of low tide to 10-15. In the horizontal direction, the propagation area of \u200b\u200bcorals, reefs, is limited to a narrow strip on both sides of the equator; Only from the Bermuda islands there are significant coral formations at 32 ° C. sh. Within the specified belt K. Reef and O-Wa are not common; The studies of the American zoologist Dana showed that K. Reefs and O-BA are found only there, where the sea water temperature does not fall below 20 ° C, (known, however, the case of finding reef corals with a slightly low temperature, about 18 ° C). Therefore, we do not find significant K. formations at the Western shores of America, Africa and Australia; Due to the existence of cold flows here - a line connecting points where the temperature does not fall below 20 ° C ("isocrum 20 °"), approaching the equator and only at the Zap. The shores of America are weakly developed by K. Reefs between California and Gvestville. Meanwhile, the eastern shores of all these continents are obscured by numerous and extensive K. buildings. FIG. 1. General view of the coastal and barrier reef. The most developed K. Buildings in Great Ocean, where they are found in all typical forms (coastal reefs, barrier reefs and K. O-Great - see below). In the central and southern part, the atolls predominate (the islands of lowland, Alice, Gilbert, Marshal, as well as Caroline); Coastal reefs are fought by O-in Elizabeth, the on-line of marigors, friendship, new hebritis, Solomon, Sandwich, Mariana and some of the Chinese Sea; In the Australian seas there are barrier reefs and part of the atoll (the most important reefs at the eastern shore of Australia, the Western New Caledonia and the reef of Fiji Islands) are found. From the East Asian Islands, coral education (especially coastal reefs) are located in the Philippine O-Wah, Borneo, Java, Kependals, Timor, and others. In Indian Ocean South Coast of Asia, in general, poor coral formations; Significant coastal reefs are used by individual items of South-Zap. and south-east. the shores of Ceylon; In the O-Wax of Maldives, Lacdiiv and Chagos (Chagos) are extensive K. Education in the form of atolls; In the western part of the Indian Ocean, the O-VA is bordered mainly by coastal reefs (Seychelles, Mauritius, partly Bourbon); Part of Madagascar bordered by coastal reefs, Comoros - Barrier, East Coast Africa represents extensive coastal reefs. K. Reefs are replete in the Red Sea, where there is a little interrupted coastal reef from Suez to the Bab El Mandeb along the African coast; In addition, there are formations similar to barrier reefs, and on the Walter - and the atoll. K. Reefs are also common in the Persian Gulf. IN Atlantic Ocean Significant K. Buildings are in the East. The shores of America, here significant reefs are found at the shores of Brazil, on the shores of Yucatan and Florida, Cuba, Jamaica, Haiti, in the Bahamas and Bermuda O-Wah; There are coastal and barrier reefs, and in Bermuda O-Wah and Atoll. The main role in the formation of K. construction is played by polypnias of a number of forms from a group of 6-beam or multigructure polyps (Hexactinia s. PolyActinia), especially the Astraeidae families (Astrangia, Meandrina, Diploria, Astrangia, Cladocora, and others), 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-ray polyps with a limestone (for example, Heliopora, Tubipora) take part in the formation of K. O-Gossi and reefs (eg Heliopora, Tubipora), as well as horn polypnias of the Gorgonide. In addition to the actual coral polyps, representatives of one group of hydraulices, characterized by lime deposits - Hydrocorallinae (MillePora, etc.) have important importance in the formation of reefs and OGs. Finally, a significant component of the mass of reefs and octs make up the masses of limestone algae, NalliP and partly Coraline. Finally, the composition of coral buildings includes mollusc shells, lime skeletons of Mshanok (Bryozoa), Cinelene's sinks (Rhizopoda) and radiolarium (Radiolaria) and others. Solids of animals; These extraneous elements can sometimes make a very significant part of the mass of coral buildings. The composition of the reefs and octs in different seas is significant differences; So, in the Red Sea predominant and constitute the main mass of polypnia Porites, Madrepora and Stylophora, in the reefs of Mauritius Island - Porites and MontiPora, on Ceylon - Madrepora and Poecilopora, in Singapore - Madrepora, on Sandwich O-Wah - Poecillopora, Zap. The shores of America - Porites and Poecillopora, Florida - Porites, Madrepora and Meandrina, etc. For the most part, the base of K. Reef or Islands serve solid rocks - underwater mountains or coastries of continents and islands. Grinding ground, especially Ilova, adverse for the development of corals. However, the newest studies of the Slyuer at the shores of Java showed that K. Reefs may occur both at the bottom covered with sludge if there are sinks, stones or pieces of pembol, to which young corals can be attached. As the last and increase in the severity of the colony of polyps sitting on a piece of pembol, etc., the base is deeper and deeper and deeper into il, meanwhile, coral polyps continue to multiply successfully and grow up. Reaching its foundation of a more dense soil, the young reef gets a dense foundation, relying on which, he can successfully increase further. Some polyps, according to other studies, can successfully grow on a ground of gravel if it is fastened with algae (as follows: Psammocora, MontiPora, Lophoseris in the eastern shore of Africa). Most coral polyps find the most favorable conditions in the upper layers, where there is a strong movement of water, and only some, more fragile forms are looking for protection from the surf. At the same time, most of them tend to light (represents positive heliotropism - see). Therefore, polypnias are continuously growing upwards, meanwhile as part below the lying die. Thus, the living colonies of polyps form, so to speak, live boring on the dead mass of reef containing various cavities, emptiness. Powerful masses of coral buildings are compacted due to the fact that the empty gaps between individual polypnomas and their branches are gradually filled with coral chips and other lime deposits. A strong surf, the action of which polypnias is exposed, blends the significant masses of them and the movement of water fragments are abrained into a smaller material. The process of destruction and changes in reef under mechanical action of waves strongly contributes to various marine animals, ruling coral buildings; These are the drilling sponges, some mollusks (eg lithodomus) and partly crustaceans. Some fish feeding on with corals bristle branches and, shredy them, give rise to the formation of a thin lime alley, which also cements polypnyakov fragments. Some role in the formation of this subtle il is also played by the doctures, in many cars on K. Reiffes, from where hundreds of centners of some species are born annually into China called Trepenga. The growth of K. polypnyakov is performed with different speeds. Branchy tree shapes are most rapidly growing; So in one case, on the remnants of a broken vessel in 64, Madrepora rose by up to 16 ft.; Madrepora Alcicornis in Haiti for 3 months formed a branch of 7-12 cm long; Usually, branchy polypnias are lengthened to a smaller value. Much more slowly, the increase in massive polypnias, what are the Astraea, Meandrina, etc.; So, the case is known when Meandrina increased by 6 inches in 12 years, usually the polypnyak thickens per year on a small part of the inches. K. Polyps can live only below the low-end features, and for the most part even a short stay outside the water entails the death of animals (only some forms, like Porites, Goniastraea, Coeloria, Tubipora, can remain alive outside the water. The polyps themselves can, therefore, to build their buildings only to the bottom line of the mist and any elevation of reefs and the islands above this level can only be caused by the action of other factors. Slices of polypnias, broken down, are thrown by sea to the surface of the reefs and, gradually sticking out, give rise to the surface parts of K. buildings. And here, the gaps are performed smaller fragments, k. sand and other dense remnants of animals and individual pieces are finally cemented, merging into a solid rock, due to the release of lime from the solution in water. Another reason that can cause a strong increase in K. Buildings over the sea is a negative oscillation of the sea level, thanks to which K. Buildings can rise to 80 or more over the UR. seas. The dissolution of the part of dead polypnias in water containing carbon dioxide occurs as under the UR. sea \u200b\u200band on the surface of the surface parts of K. Buildings. The accumulation of K. Sand on the surface K. O-GWI can reach such sizes that real dunes are formed, which, under the influence of dominant winds, are gradually moving inside the country, falling asleep plantations and farms; So it was, for example, at Paget Parish in Bermuda O-Wah, where the movement of the "sandy glacier", as the moving dune was called, covered farm, managed to stop only the planting of trees. The surface of K. O-GOB and reefs, covering a layer of humus, gives the soil on which often very luxurious tropical vegetation develops. K. Buildings are found in a wide variety of forms that can be reduced to the three main types: 1) coastal reefs, 2) barrier reefs and 3) separate K. O-Wa and Mel. Coastal reefs are formed in cases when K. The buildings are directly adjacent to the shores of the islands or the mainland and focus them, interrupting in those places where the streams and rivers flow (as the polyps for the most part cannot live in muddy and especially in desalinated water) or where the development of them is hampered or the structure of the bottom ( For example, a cool break). Coastal reefs may or remain under water, or, due to the indicated reasons, becomes supervised. Ruiter's research over the formation of K. Reefs off the coast of O-Vi Krakataau, after the famous eruption of this volcano, proved that reefs may arise at some distance from the coast and gradually grow towards it. The study of the bottom surrounding the coastal reef shows that it gradually decreases towards the open sea. Barrier reefs (also underwater or surface) stretch along the shores of O-Wa or the mainland, remaining separated from them a relatively shallow canal of various widths (10-15 and 50 nautical miles). Channel depth can be very different, but always relatively small. Sometimes the bottom dries on the bottom when the depth of it is somewhat large and even can reach 40-50 soot. Meanwhile, outside the reef of depth is relatively high and can reach several hundreds of seeds, and the outer edge of the reef falls into depth. In places, barrier reefs are interrupted. Sometimes they surround from all sides o-in. In some cases, barrier reefs achieve huge sizes; So in the East. The banks of Australia from Cape Car Sunday (24 o 40 "Yu. Sh.) to South. New Guinea shores stretches" Big Australian Reef "with a length of about 1725 km, separated from the bank of the channel in 25-160 km of width; the main passage of him with the lighthouse lies Under 11 ° 35 "Yu. sh. (Raines Inlet), channel depth 10-60 soot., And outside the reef, there are more than 300 soot. A very diverse form represents K. O-VA (and individual mels); Molds are dominated by rounded, oblong, ring-shaped ("Atolls") and semi-lunk. The most distinctive appearance have the atoll; This is a ring-shaped sushi band, a width is usually not more than 100-200 m, the surrounding central pool ("lagoon"), which is usually connected to the surrounding sea by several aisles lying on the side opposite to the opposite of the dominant winds. Rarely (eg whitsunday island) Atolls represent a solid continuous ring. The size of the lagoon is very different and the diameter of them can reach 75 km. And more (and the diameter is 30-45 km. It is often found). The depth of the lagoon is generally insignificant, usually somewhat large, but can reach the coarse up to 50; Meanwhile, from the outside of the atoll, we find, as at barrier reefs, mostly very significant depths. The bottom of the lagoon is covered (as well as the channel of barrier reefs) K. Sand and limestone and represents relatively few living corals, an advantage of more gentle forms. Sometimes small o-was can be in the lagoon. The height of the ataolls above sea level is mostly insignificant, not more than 3-4 m; Sometimes, through the atoll, the waves of the surf beyond the lagoon. The atoll side is generally above. Comparatively rare K. O-Wa reaches a significant height above sea level (which is explained by the negative fluctuation of the sea level: the reefs formed are extended from the sea). So at the Vikanoro, according to Darwin, the wall K. Reef reaches 100 m of the embroidered, according to the methium, in low-lying O-Wah, rocks from K. Limestone embroidered in 80 m. Sometimes the submarine atol, such, for example, a big reef In O-Wah, Chagos, lying at a depth of 5-10 soot. Under the sea level. Extremely ordinary and other forms of octoral and shames, which sometimes also achieve significant sizes; So reef lying to the two main islands of the Fiji Group, represents the surface of about 3000 square meters. English miles; K. Bank of Saya de Malha, to St. Madagascar, stretches from 60 ° 20 "c. D. Up to 62 ° 10" (according to Greenwich) and from 8 ° 18 "Yu. Sh. Up to 11 ° 30", and then Yu lies Nazareth Bank (NazarethBank) about 400 km long. The sea, crowded by K. Rifami, represent generally significant hazards for navigation, especially since K. O-Wa and reefs are often cool raised from a significant depth and nothing indicates the proximity of the reefs, except Burunov in case of excitement. On the other hand, the barrier reefs allow in some cases the ships to safely pass along the coast while in the open sea is a strong bad weather. The fence of shores reefs prevents the blurring action of waves on the shore. In addition, thanks to the reefs, in some cases, the erosion products brought from sushi are deposited from the coast and determine the significant increase in sushi; So, Tahiti surrounds the sushi band wide from 0.5 to 3 eng. The miles that occurred this path and covered with rich vegetation. Along with the process of education K. O-GOB (for example, Florida), in other places (for example, on Bermuda O-WAH) we meet the phenomenon of their destruction; In these cases, the formation of caves (sometimes stalactite and stalagmite), arches, etc.; At the same time, a special red soil is observed on the surface of the O-WA, in which the residue from the erosion is seen, dissolving the lime of reef. The peculiar structure of K. Reefs and O-Great Patriotic War, important and tremendous distribution were initiated by their interest in these formations, especially the atales; To explain the form of the last one, they resorted (from Steffens, in 1822) to the hypothesis that the atolls crowned underwater crater; Others believed that K. Polyps, by virtue of a special instinct, build their arrangements in the form of a ring to use the protection against the surf. The theory of K. Education, given by Darwin, explained the mysterious fact of the existence of K. Buildings at large depths, where corals building reefs cannot live, explained the reason for the considerable thickness of K. sediments (which was confirmed by the way, and the newest drilling experiments on K. Rifa), as well as the form of K. Buildings and the relationship between them. Despite a number of new objections, Darwin's theory remains dominant. The theory of Darwin is so called. Immersion theory (Senkungstheorie), the essence of which is as follows. If K. buildings arise from the shore of the O-Wa or the mainland, where the water level remains more or less permanent (the bottom does not ignore), then it should give rise to the coastal reef. If the bottom is descended, the reef will continue to grow up and should take the character of the barrier reef separated from the sushi channel. This will be facilitated by the fact that K. Polyps will find better conditions for life on the outside of reef, which will therefore grow stronger. If finally, with further immersion of O-in, surrounded by an annular reef, it will completely disappear under the surface of the sea, on the spot it will remain atoll (underwater or surface, depending on the speed of immersion). Such an explanation of the origin of the K. Buildings and the relationship between them explains the many of their features and relies on a number of various facts. However, the extensive K. Education, in the form of barrier reefs, is observed in such places where it is obviously happening, on the contrary, the atoll is also observed in such locations. In general, it is necessary to recognize that various forms of K. builds can occur in and otherwise, in addition to the bottom of the bottom, for example, on underwater banks and mountains, and the form of O-GBIs (including the atolls) is sometimes determined by the direction of marine currents or those that the corals of this reef grow more successfully at the edges of it than in the middle, the average dying and subjected to the destructive action of flows and water containing carbon dioxide, which leads to the formation of the lagoon. Be that as it may, the latest objections against Darwin's theory are represented by addresses and amendments to it than a new explanation that could completely replace this Darwin. Extensive K. Education existed in former geological periods and in many sediments we find explicit traces of reefs. In the most ancient periods, K. Reef occupied, relatively, very extensive area. Paleozoic reef corals found in Scandinavia and Russia far in 60 ° C. sh. And some kind of childbirth even on Spitsbergen, new land and Barents O-Wah; Lithostrotion was during the nonsense expedition (NARES) found from from 81 ° C. sh. In the Silurian and Devonian period, the corals were overcome in the seas on Shir. Canada and Scandinavia. In later geological periods, we see that K. Reefs are increasingly retreating to the equator, which stood, in all likelihood, due to the decrease in the sea temperature under high latitudes. In the Triassic period, the reefs were abundant in Central and Southern Europe; In the Jurassic period, the extensive K. Sea occupied a significant part of Western and Central Europe, and traces of reefs remained in England, France, Germany and Switzerland. In the chalk period there were few reefs here, but they have abounded in Southern Europe. In Eocene, they were abounded in southern Europe, but they met in England, in Miocene they were only in South and Central Europe, and in Pliocene reefs at the present over the course of Europe no longer found. Literature. The most important writings about K. Rifakh and O-Wah: Darwin, "On the Structure and Distribution of Coral Reefs" (I-E ed., 1842); Dana, "Corals and Corals Islands" (1872); Semper, "Die Palau-Inseln" (LPC., 1873); Semper, "Die Natürlichen Existenzbedingungen Der Thiere" (LPC., 1880); REIN, "DIE BERMUDASINSELN UND IHRE KORALLENRIFFE" (Berl., 1881); Guppy, "Salomon-Islands" (Lond., 1887); Langenbeck, "Die Theorien Über Die Enttehung Der Koralleninseln" (LPC., 1890); Böttger, "Geschichtliche Darstelung Unserer Kenntnisse und Meinungen Von Der Korallenbauten" ("Zeitschrift Für Naturwissenschaften" t. LXIII); Murray and Irvine, "CORAL REEFS AND OTHER CARBONATE OF LIME FORMATIONS IN MODERN SEAS" ("NATURE", XLII; other articles in the same journal); Sluiter, "Einiges Über Die Enttehung d. KorallenRiffe in D. java see" ("Biol. Centralblatt", BD. IX); Kent, "The Great Barrier Reef of Australia" (1893); A number of work on the corals in the reports "Challenger" and others. Good reports of the most important data from Keller, "Leben des Meeres" (Edition unfinished), Marschell in Thierleben Bram (BD. X; New edition, ends in Russian), as well as Kingsley, "The Riverside ZOOLOGY" (t. i); Heilprin, "The Distribution of Animals" (1887) and Nicholson article in Encyclopedia Britannica. N. Knipovich.
Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron. - S.-PB.: Brockhauses-Efron. 1890-1907 .
Watch what is "coral reefs and islands" in other dictionaries:
In education, the main role is played by solid polypnyaks of coral polyps (see) and the products of their destruction. Although coral polyps are distributed in the seas of all belts and are found on all sorts of depths, from the lower boundary of the tumps to huge ... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron
Coral reefs, underwater or partially oversized limestrokes, which are generated mainly by skeletons of colonial coral polyps (see coral polyps) in shallow-water sections of the tropical seas. Within the ecosystem (see ... ... encyclopedic Dictionary
Construction of organogenic limestone, located near the sea level or at small depths in the coastal area of \u200b\u200bthe tropical seas or in shallow warm seas. They are massive deposits of calcite (limestone), ... ... Geographic Encyclopedia
Loading...
