What are atolls in biology. Atolls and islands of the Republic of Maldives. How are atolls formed?

ATOLL
ring-shaped coral reef surrounding the water area. Coral reefs are common in tropical and subtropical latitudes, most widely in the Pacific and Indian Oceans. The word "atoll" comes from the name used by the peoples of Oceania for the reefs that form a chain small islands, towering 4-6 m above the water surface. Sometimes reefs are flooded, and between their individual parts there are deep straits. The lake-like waters within the atolls are called lagoons. Usually their depth is 18-30 m, but sometimes it reaches 90 m.

Structure. The main material from which they are built Coral reefs, is a limestone formed as a result of the accumulation of skeletons of marine animals and plants containing calcium carbonate, mainly corals and coralline algae. Islets scattered along the reefs usually consist of limestone fragments and crumbs - products of wave activity. Often, small dunes are formed from this material under the influence of wind. The outer coast of most of the atoll islands is a rather narrow strip of fringing reefs, often with an even border of massive pink calcareous algae and steep, narrow beaches composed of limestone fragments. Behind the coastal ridge of the beach, coarse-grained material is replaced by crushed stone, which is further replaced by gravel as it is crushed. In the center of the islet there is often a depression filled with saline soil stained with humus. The interior of the islet is usually composed of coarse-grained coral sand or fine gravel, while the central parts of the beach are composed of fine calcareous sand. If the atoll is completely raised above sea level, then the limestones composing it usually erode and form a rough surface - "macatea". The groundwater level is very close there, and small wells are often dug near the center of the islands. If the island is large or there is a lot of rainfall, then the groundwater is almost fresh, but if it is small or located in an area with little rainfall, then the groundwater is brackish or saline.
Flora. The vegetation cover is the most remarkable characteristic of the surface of the atolls. It is sparse and most often consists of several species of widespread herbaceous plants and tree species that live in the coastal strip. In the distribution of vegetation, a certain zonality is observed in the direction from the outer edge of the atoll to the inner one. She may be in in general terms described for the entire Indo-Pacific region, where atolls are especially numerous, and their flora is of the same type. The outer zone is represented by shrubs, among which the shrub scaevola (Scaevola frutescens) predominates. This is followed by forests, mainly from such halophytes as silver messerschmidia (Messerschmidia argenta) and roofing pandanus (Pandanus tectorius). Even farther from the coast, there are fewer halophytes, and cordia (Cordia), large pisonia (Pisonia grandis), ochrosia (Ochrosia) and other species appear. In the center, in more mesophytic conditions, the primary vegetation cover probably consisted of such trees as the magnificent leopard (Guettarda speciosa), lime-shaped hibiscus (Hibiscus tiliacens), ficus, pisonia, pandanus, Asian barringtonia (Barringtonia asiatica), terminalia (Terminalia) and etc. On most of the islands, these forests were subsequently replaced by plantations of coconut palms and breadfruit. The inner zone of the beaches is characterized by a narrow strip of trees such as hernandia, calophyllum, pandanus, thespesia, cordia. On sandbars Suriana maritima and scaevola are usually found between the islets, and sour pemphis (Pemphis acidula) at rock outcrops. In places, in the inner parts of the islets, waterlogged depressions are found, and in some of them they are confined to hard rocks. In such conditions, some tree species typical of mangrove swamps are found. Other islets are swampy and treeless, dominated by grasses and sedges. On inhabited islands, soil is taken out of these depressions and filled with humus, and then used to grow taro, sugar cane and other plants. Due to the salinity of the soil, few (except those listed above) cultivated plants can grow on low coral islets. Taro, breadfruit and coconuts are the main food of the population, in addition, coconuts are a source of drinking water.
Other natural resources. The vast majority of the atolls are inhabited, and there, crop production depends on the potential fertility of nutrient-poor saline soils. The main crop is coconuts. Along with the above plants, the basis of the diet of the population is fish and shellfish, which abound in lagoons, reefs and adjacent open water areas. Other trade items are guano, pearls, shells for making buttons and dried holothurians. The most fertile are the large atolls that rise above sea level, especially if they are confined to very humid areas. They feature much more lush vegetation, richer flora, and a much more diverse array of crops. Apparently, all this is associated with lower soil salinity. On the uplifted atolls, there are often large deposits of phosphorites (probably formed from ancient deposits of guano). Such atolls include the islands of Makatea, Nauru, Ocean, Angaur. Guano deposits on many atoll islands were formed as a result of the life of sea birds - gannets, frigatebirds, terns and tropical birds that breed here. In addition to the listed birds and land crabs, including the palm thief, the terrestrial fauna is poor: rats dominate, and fruit bats (fruit-eating bats) are numerous in the western Pacific Ocean. The waters abound with turtles, spiny lobsters, giant bivalves, and many kinds of fish. The rich fauna of the reefs includes many species of invertebrates.
famous atolls. The largest groups of atolls in the Indian Ocean are the Maldives and Laccadives; in the Pacific Ocean - the Caroline, Marshall, Gilbert Islands in Micronesia, Tuamotu and others in Polynesia; a large number of atolls scattered throughout Melanesia. IN Atlantic Ocean there are several atolls in the Lesser Antilles group, in addition, the Bahamas include a number of atolls that are not typical. The largest atoll in terms of area (with a relatively small lagoon in the center) is Christmas Island in the equatorial Pacific Ocean. The largest lagoon is apparently located on Kwajalein Atoll (Marshall Islands), although lagoons of almost the same size are found on some other atolls.
See also CORAL REEFS.
LITERATURE
Ravikovich A.I. Recent and fossil reefs. M., 1954 Geography of the atolls of the southwestern part of the Pacific Ocean. M., 1973

Collier Encyclopedia. - Open society. 2000 .

Synonyms:

See what "ATOLL" is in other dictionaries:

Modern Encyclopedia

- (Atoll) lagoon reef, a special kind of island. A ring-shaped strip of land surrounding an inland shallow lake or lagoon. Usually A. rises above sea level by several meters. The depth in the lagoon is small; 60 150 m (30 80 sea fathoms), while ... ... Marine Dictionary

Coral island, reef Dictionary of Russian synonyms. atoll n., number of synonyms: 9 bikinis (5) ... Synonym dictionary

atoll- a, m. atoll m., eng. Coral island. Atolian oh, oh. Sometimes the tentacles of an octopus were pushed into the hole, which, apparently, methodically ransacked the atoll jar. A. Kim Fish Simplicitas. // NM 1997 4 102. Lex. Dal: atol; Toll 1863: atoll; SAN 1891 ... Historical Dictionary of Gallicisms of the Russian Language

Atoll- (from the Malay adol closed), a coral building with a shallow lagoon in the middle, connected to the ocean through one or more straits. The base of an atoll is usually the summit of an underwater volcano. Distributed in tropical latitudes ... ... Illustrated Encyclopedic Dictionary

A coral structure, in the form of a solid or broken ring, surrounding a shallow lagoon. The base of an atoll is usually the summit of an underwater volcano. Widespread in the tropical latitudes of the Pacific and Indian Oceans … Big Encyclopedic Dictionary

ATOLL, a ring-shaped CORAL REEF surrounding a shallow LAGOON. The reef appears initially as a frame for an island that slowly sinks into the water, usually volcanic origin. As the island sinks, the coral continues to grow... Scientific and technical encyclopedic dictionary

ATOLL, atoll, husband. (Malay). Annular coral island. Explanatory Dictionary of Ushakov. D.N. Ushakov. 1935 1940 ... Explanatory Dictionary of Ushakov

ATOLL, a, husband. Ring-shaped coral island. | adj. atoll, oh, oh. Explanatory dictionary of Ozhegov. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 ... Explanatory dictionary of Ozhegov

With a group of islets (motu), separated by straits. These straits connect the ocean with the lagoon. If there are no straits, then the land forms a continuous ring, in which case the water in the lagoon may be less salty than in the ocean. An elevation at the bottom of the ocean is usually shaped like a cone formed by an extinct volcano.

A typical atoll consists of three parts: the outer slope of the reef, the reef platform and the lagoon. The height of the atoll usually does not exceed 3-4 meters above the mean ocean level. Atolls can have a variety of configurations and sizes. One of the largest atolls on Earth - Kwadzhelein (Menshikov) in the Marshall Islands archipelago - reaches 2336 km², of which 92% is in a lagoon stretching for 300 km. The total area of 92 islands of this atoll is 14.5 km². Another large atoll - Rangiroa (Rangiroi) in the Tuamotu archipelago - occupies 1639 km², and its 241 islets occupy 43 km². The coral reefs of such large atolls frame an uplift on the ocean floor, which is a volcanic plateau, and not a cone of a single volcano. With the exception of small atolls, reefs usually make up a few percent of the area of the atolls themselves, and land is often only a fraction of a percent. In the case of the small Pangelai atoll, reefs and land cover 3 out of 4 km² of the atoll area.

Atolls are usually formed by fouling a volcanic island with a coral reef, forming a ring belt. Often this is accompanied by subsidence of the volcanic base under water, if such subsidence does not occur, then a nuclear atoll is formed with a volcanic island inside the lagoon. A slight decrease in the water level (or uplift of the tectonic base of the atoll) leads to the transformation of the coral reef into an atoll. Further land uplift may lead to the formation of an uplifted atoll. If the atoll submerges under water, then an underwater bank (that is, a shallow) is formed, which can be called a submerged atoll.

Illustrations

Literature

Ignatiev G.M. Tropical Islands of the Pacific Ocean. Moscow, publishing house "Thought", 1978, 270 p.
Scott G. A. J., Rotondo G. M. "A model for the development of types of atolls and volcanic islands on the Pacific lithospheric plate". USA, Washington D.C.: Smithsonian Institution, 1983.
Rapaport Moshe. "Population pressure on cowl atolls: trends and approaching limits". USA, Washington D.C.: Smithsonian Institution, 1990.

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See what "Coral Atoll" is in other dictionaries:

Atoll (eng. Atoll) Atoll is a coral island, having the form of a continuous or discontinuous ring surrounding the lagoon. Atoll (Scotland) historical area in the center of Scotland, in the mountains north of Perthshire ... Wikipedia

Ring-shaped coral reef surrounding the water area. Coral reefs are common in tropical and subtropical latitudes, most widely in the Pacific and Indian Oceans. The word atoll comes from the name used by the peoples ... ... Collier Encyclopedia

Coral island, reef Dictionary of Russian synonyms. atoll n., number of synonyms: 9 bikinis (5) ... Synonym dictionary

ATOLL, a ring-shaped CORAL REEF surrounding a shallow LAGOON. The reef appears initially as a frame for an island slowly sinking into the water, usually of volcanic origin. As the island sinks, the coral continues to grow... Scientific and technical encyclopedic dictionary

ATOLL, atoll, husband. (Malay). Ring-shaped coral island. Explanatory Dictionary of Ushakov. D.N. Ushakov. 1935 1940 ... Explanatory Dictionary of Ushakov

ATOLL, a, husband. Ring-shaped coral island. | adj. atoll, oh, oh. Explanatory dictionary of Ozhegov. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 ... Explanatory dictionary of Ozhegov

Husband. coral island with an open ring; a ringed, lagoonal ridge, an island gradually carved out by the smallest skull-skinned animals, with a lake or a lagoon in the middle (it is permissible to transform a lagoon into a Russian lagoon). Dahl's Explanatory Dictionary. IN AND. Far... ... Dahl's Explanatory Dictionary

- [Malay adol closed] coral island in the form of a narrow annular ridge of reef limestone (coral barrier) that closes the inner lagoon. The outer slope is steep (about 45 60°), sometimes even overhangs. On the inside of the ring, often ... ... Geological Encyclopedia

Books

50 Most Beautiful Islands, Mason, Anthony. Island of dreams - what do we mean by this concept? The simplest answer is coral atoll in the tropics white sand beaches shaded by a coconut tree whose leaves rustle softly under…

Coral reefs - formed a unique ecosystem of the oceans. These calcareous geological structures are formed in tropical seas in shallow water and cover an area of more than 27 million square meters. km (mainly in the seas of the Indian and Pacific Oceans). - an amazing and lengthy process that has not been fully studied. And today we will get acquainted with different theories and find out how the “birth” of a reef occurs.

During the formation of coral reefs, madrepore corals form entire colonies of various shapes and sizes. This process is based on several forms, thanks to which reefs can be divided into types.

Studying corals, scientists for many years cannot come to a single version that can fully confirm how the formation of atolls and coral banks located in the Pacific, Indian and Atlantic oceans took place. Until now, many questions regarding the reasons for which the coral reef formation and platforms for them.

There are various scientific theories. Some of them complement each other, while others are completely opposite to the first. What provisions of the existing theories are relevant today and are taken into account?

The formation of coral reefs according to Darwin's theory

The first to speak possible reasons influencing the formation of coral reefs, is Charles Darwin. While traveling around the world, he met various fossil marine organisms located on high altitudes in the Andes. He made the assumption that their formation is associated with vertical uplift of some parts of the earth's surface.

It was not even assumed at that time that a displacement of some sections of the earth's crust could occur. His theory was based on two premises. One of them says that the platforms on which the coral reef formation , gradually dropped.

This caused the corals to grow upwards at the same rate as the platforms were sinking. This theory has been around for more than a century and a half. It fully explained the formation of atolls and coastal and barrier reefs.

Big barrier reef

According to Darwin's theory, atolls are a kind of development of coral construction, consisting of successive stages. Initially, a reef forms around the volcano in shallow water, thereby creating a coastal coral reef. As the volcano sinks into the sea, the corals grow upwards, keeping it at the same level.

But, coral reef formation and their growth occurs not only upwards, but also towards the sea. This causes a channel to form between the reef and land. And when it reaches a certain width, it turns from coastal to barrier.

Further, the volcano descending into the sea, in the end, completely disappears in sea depths ah, after which there remains a ring of formed corals, called an atoll. In the Pacific and Indian Oceans, you can find hundreds of different atolls with completely different diameters.

The coral reef is home to numerous marine animals and plants.

There are small coral reef formation , whose diameter does not exceed one kilometer. And there are also such atolls, the diameter of which reaches 160 kilometers. The most common are atolls, the diameter of which is within 30 kilometers.

Darwin's theory, which was perfectly able to explain the presence of a huge number of atolls in sea waters, was preceded by a different version. It was believed that the atolls were formed using reefs growing along the edge of craters. extinct volcanoes which subsequently completely sank into the sea.

But, this version could only explain the formation of coral reefs on the crater of the volcano, which was at a suitable depth. To explain why a huge number of craters of volcanoes are located at the same depth, according to this theory, was impossible.

Deep exploration and reef drilling support Darwin's suggestion that coral limestone is found on older volcanic rocks. In addition, the study of coral limestone taken from deep sea wells confirms the fact that it was once at or slightly above sea level.

However, not everyone coral reef formation was confirmed by Darwin's theory. So, the Great Barrier Reef is not just a simple coral reef. giant size. It is a single complex, consisting of a significant number of corals, different in shape and formation.

This is where I want to end the first part of the article, and if you want to know about the conditions favorable for the growth of corals and about the methods of reproduction of coral polyps, read the continuation of the article.

In more detail, with various types corals, these articles will introduce you.

Maldives - unique creation nature and an amazing tourist site. Located in the Indian Ocean near India, the state is a Muslim republic. At the same time, respect for tourists is so strong that due attention is paid to the main Christian holidays. The Republic of Maldives consists of several atolls, which, in turn, include numerous islands. Only 10 groups of atolls out of 20 are open for tourists to visit. At the same time, almost every hotel in the Maldives occupies a separate island, which gives tourists a sense of peace and serenity. However, for fans active rest there is something to do - there are plenty of opportunities for this on the islands, including diving, for which it is Island state visited by divers from all over the world. For all the exoticism, holidays in the Maldives are distinguished by the highest level of service.

In the material on Tourister.ru we will talk about the structure of the Republic of Maldives - atolls and islands with their description and detailed information. Also you can explore detailed maps of atolls : , , And .

Kaafu Atoll (North Male)

Kaafu Atoll (South Male)

The atoll is divided from North Male Vadu Strait and stretches from west to east for 19 km and from north to south for 36 km. Only three islands of the pearl chain are occupied by local natives, the remaining 19 paradise turned into resorts and delight travelers from all over the world with gentle lagoons and marvelous beaches.

South Male is possible.

Vaavu Atoll

Alternative title: Felidhu

Located 65 km from the capital Maldives- Male (90 minutes by speedboat or 5 hours by boat). The atoll is an interesting geographical phenomenon, as it consists of two atolls: the main Vavu and a round one, 9 kilometers in diameter, located next to the main atoll. Five inhabited islands with a population of about 2,300 people, make Vaavu Atoll the smallest administratively in the Maldives. In addition to these five, there are about 14 other islands, but most of them are almost undeveloped by tourists compared to the islands of other atolls. Vaavu Atoll is considered one of the the best places for diving in the Maldives.

The Fotteyo Kandu dive site is considered the best in the country and one of the top five in the world. Vaavu Atoll was opened to tourists in 1975, and has become a favorite with many organizers of various cruises and safaris in the Maldives. The reefs of the eastern side of the atoll are in an untouched state and are perfect for lovers of not only diving, but also snorkeling. There are a lot of sharks here, there is a chance to see hammerhead fish and other equally interesting fish.

Look detailed map atoll and read about tourist islands Wow you can.

Meemu Atoll

Alternative title: Mulaku

The atoll stretches for 50 kilometers from north to south and 30 kilometers wide, containing eight fishing islands and two resorts. There are excellent places for recreation and diving, which is confirmed by numerous cruises.

View a detailed map of the atoll and read about tourist islands Meem can.

Seenu Atoll

Alternative title: Addu

Most southern atoll, located right at the equator, stretching for 15 km from north to south and 18 km from west to east. It consists of 5 islands: northern Midu and western Hitado, Gan, Feidu and Marado, united by bridges. On the island of Gan, an airport and resort hotel, and large Khitadhoo ranks 2nd in terms of population after Male - 12,000 inhabitants. Green and pretty, Feidou and Marado rustle with plantations of coconut palms, nature has endowed them with small bays where fishing villages have settled down. A pleasant surprise awaits the guests of the hotel in Ghana - at any time they can visit the nearby islands and get acquainted with the life of local aborigines.

View a detailed map of the atoll and read about tourist islands Seenu can.

Faafu Atoll

Alternative title: Northern Nilande (Nilandhe Atholhu Uthuruburi)

A small atoll, has an oval shape and the second name is North Nilande. It stretches for 21 km from west to east and 45 km from north to south, containing five fishing islands and only one resort, relatively recently opened to travelers.

View a detailed map of the atoll and read about tourist islands Faafu can.

Dhaalu Atoll

Alternative title: Nilande South (Nilandhe Atholhu Dhekunuburi)

Dhaalu Atoll is located 150 km north of Male and 5 km from Faafu Atoll. It is also known as Nilandhe Atholhu Dhekunuburi (South Nilade Atoll). It is separated from North Nilade (Faafu Atoll) by the Strait of Deburieiterei Kandu. The airport and other atolls can be reached by seaplane or speedboat.

Dhaalu Atoll, 38 km long and 23 km wide, has about 46 islands, many of which are uninhabited. Seaplane transfer takes 40 minutes. For tourism, Dhaalu Atoll was opened quite recently. The islands open to tourists are located in the northern part of the atoll and provide excellent diving opportunities. The main island is Kudahuwadhoo. This is a fairly large island. developed infrastructure and a population of 1500 people.

The main reefs, interesting and accessible for diving, are located along the northern and northeastern parts of the islands. There are practically no shallow reefs inside the atoll.

Relatively clean from coral thickets, the lagoon allows you to safely go on a tour of the islands on a boat. Dhaalu Atoll still keeps the ruins of ancient monasteries and mosques. On the islands where he lives indigenous people Souvenirs are much cheaper than in the capital.

View a detailed map of the atoll and read about tourist islands Dhaalu is possible.

Alif Atoll

Alternative title: Ari (Ari), also the northern and southern parts are called Alif Alif and Alif Dhaal

The atoll stretches for 33 km from west to east and 96 km from north to south. The atoll is divided into two honors: Alif Alif (northern) and Alif Daal (south). In the northern part, in addition to the main atoll, there is a small Radsu atoll, and in the southern part, the capital Mahibadhoo. The atoll includes 70 islands, but only 18 of them are inhabited, and 25 have been turned into resorts. Once upon a time, local natives hunted sharks and turtles, but since sea hunting is banned, they have been busy servicing tourist hotels.

Baa Atoll

Alternative title: Malosmadulu (Maalhosmadulu Dhekunuburi)

It is an administrative unit of the Republic of Maldives, together with Horseborough Atoll, with the capital Eidafushi. The atoll stretches for 32 km from west to east and 42 km from north to south and includes 10 inhabited islands. Local aboriginals trade fishing, at the same time mastering more profitable tourism professions. Undersea world amazingly varied and surprising interesting places for diving. Marvelous corals, as yet untouched by divers, as well as dozens of fish species await ocean treasure hunters!

Lhaviyani Atoll

Alternative title: Miladunmadulu Uthuruburi

The atoll is 120 km away from the Maldivian capital, and therefore travelers arrive to rest by seaplane. The atoll stretches for 35 km from north to south and 37 km from west to east. Products and goods are brought here on dhoni, sailing such a considerable distance for 8 hours. Fadiffoulou contains 6 fishing and 4 resort islands.

View a detailed map of the atoll and read about tourist islands Lhaviyani is possible.

Coral is a structure made up of millions of very small marine animals called polyps. The polyp, which is tube-shaped, is only an inch long. At the end of this tube is a mouth surrounded by tentacles that bring sea creatures to it. The color of corals is very diverse, as well as their shapes and sizes. They have both an internal and an external skeleton. They can be soft or hard, black, smooth or prickly and other types. Some are like feathers, others are like fingers. The polyps are hollow and attach themselves to other polyps or to limestone rocks to form large structures. Almost all corals live together in groups called colonies. Very large colonies are called reefs. Polyps take calcium from sea water and turn it into limestone around the lower part of their body. New polyps grow and the limestone structure gets bigger and bigger.

Corals live in oceans all over the world, but survive best in warm water. In tropical oceans, they form large structures called atolls. Atolls grow around old volcanoes and form ring-shaped islands. Coral polyps eat small marine animals such as jellyfish larvae. Some people need seaweed to survive. Corals can reproduce by budding. Small buds appear on the body of the polyp. They grow up and separate from their parents. Corals can also lay eggs that grow into new colonies. Some types of coral live for hundreds of years.

coral reef

A coral reef is an underwater mountain formed by coral skeletons. Reefs are also made up of other living things such as seaweed or shellfish. The coral reef has vibrant colors and can grow for hundreds of years without being destroyed by the ocean. Location of coral reefs around the world.

Reef types:

Reef line - located near the coast line they are usually the youngest reef forms
Barrier reefs are located farther from the coast, they form a wall between shallow water near the coast and open sea some barrier reefs are very large The longest is 2 thousand kilometers long The Great Barrier Reef is on east coast australia
Atolls are ring-shaped reefs. They form when old volcano erupts and sinks into the sea The reef grows upward from the edge of the volcanoes along with the lagoon formed in the middle
Most reefs need warm water to survive They grow best in water that is at least between 16 and 20 degrees. Reefs also need enough sunlight to eat. Coral reefs can also be found in warm ocean waters Pacific and Indian Oceans as well as in the Caribbean Sea and the east coast of the central part South America They usually grow very slowly, no more than 10 cm per year. They can be found near the surface where they get enough sunlight.

Life on coral reefs

A coral reef can have thousands of different types of corals and other organisms. This would be a record if not for the rainforests, which can contain even more different organisms. That is why coral reefs are called tropical forests seas. Many fish species live near coral reefs. Their bodies have the ability to change, which makes it possible for them to live and find food in this area. In addition, coral reefs are home to crabs, lobsters, octopuses, starfish and other invertebrates.

Significance of corals and coral reefs:

Corals remove and recycle carbon dioxide, a gas that is responsible for the greenhouse effect.
Reefs protect islands and continents from waves and storms and allow other species to thrive in the shallow waters near the coast.
A coral reef is a complex ecosystem with many different types of organisms. Without reefs, they would die.
Coral skeletons are used as substances for bones and other parts of our body.
Coral reefs are living laboratories for scientists and students.
The reefs attract millions of tourists every year.
People make jewelry made from coral reefs.