What are atolls in biology. Atolls and islands of the Republic of Maldives. See the meaning of Atoll in other dictionaries

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An atoll is a coral island that has the appearance of a full or partial ring. In other words, the atolls include turquoise lagoons, colorful reefs, which are smoothly combined with marine life and are reminiscent of the wild life of Robinson Crusoe. In this collection you can admire the most beautiful atolls in the world.

Tuvalu is island nation, which is located in pacific ocean, on the way between Hawaii and Australia. This atoll is the second least populated sovereign state in the world, followed by the Vatican. Due to the fact that the country is fairly remote, few tourists visit it.

Bikini Atoll is famous for interesting historical facts. Firstly, the model bathing suit was named after this atoll. Secondly, nuclear weapons were tested in this place from 1946 to 1958. The indigenous people of this place were resettled even before the start of the tests. Today, the islands are completely safe to visit. Many tourists come here for diving, during which you can see the sunken ships.

Tubbataha Reef is one of the best diving spots in the world. It is located in the Philippines and consists of two atolls: North and South. They are divided among themselves by a channel, the width of which is 8 kilometers. Coral reefs are not only a great place for diving, but also a great habitat for exotic fish.

Reef Lighthouse can be considered the most popular among the world's atolls. This is due to the fact that it contains a large blue hole. Right in the center of the atoll. This real paradise, which has not yet been explored for divers. They come here from all over the world. The deeper you dive into the blue hole, the clearer the water and the more breathtaking scenery you will be able to see.

Tikehau belongs to the Tuamotu chain of atolls, which cover an area in the Pacific Ocean, it is the same size as the territory of Western Europe. This place attracts tourists due to its white and pink sandy islands, inside which there are turquoise lagoons that are inhabited by all kinds of exotic fish. The research team of Jacques Cousteau, who visited here, concluded that this place is the largest concentration of fish in French Polynesia.

Europeans first visited the island in 1606. On this moment Carelyn belongs to the Republic of Kiribati. Despite the fact that man has been developing his activities on this island for more than 300 years, it belongs to the most pristine tropical islands in the world and the most pristine atolls. Caroline Island and its neighboring island Frint has become home to the world's largest crab population. The islands have a height of 6 meters above sea level, and, therefore, it is in danger of disappearing under water because of that. That the sea level is constantly rising. Scientists have calculated that the islands can completely disappear under water in 2025.

Aitutaki is composed of coral and volcanic islands, which are united by a triangular lagoon. This is a classic palm island with turquoise shallow water, corals, exotic fish. The most popular island is Tapuaetai, which is located in the southeastern part of the lagoon.

Aldabra is one of Outer Islands Seychelles, the distance to which is more than 1100 kilometers from Mahe. This is the most big Island on Seychelles. After Kiritimati, it is the second largest atoll in the world. Due to the fact that access to the Aldabra atoll is difficult, it is practically untouched by civilization. Approximately 152,000 giant tortoises can be found on its territory.

Rangiroa is one of the largest atolls in the world and the largest in the Tuamotu archipelago. This place is ideal for divers due to the fact that the deep lagoon is full of marine life. Here you can meet sharks, sea ​​turtles and dolphins.

A tiny country in the Maldives that sits in the middle indian ocean in its composition has 1200 tiny coral islands, which are grouped into 26 atolls. Tourists come here to explore the alluring depths that are accessible due to good visibility. When exploring the depths, you can get acquainted with the sunken ships that guides will show you.

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 is made up of three parts: outer slope of the reef, reef platform and 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 the subsidence of the volcanic base under water, if such subsidence does not occur, then a nuclear atoll is formed with 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

- (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, 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. Dictionary 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 a coral atoll in the tropics, white sand beaches shaded by a coconut tree whose leaves rustle softly under…

What is an atoll? The atoll is a ringed coral reef that partially or completely surrounds the lagoon. In other words, an atoll is a narrow stretch of land that borders and is surrounded by water at the same time. This is what distinguishes an atoll from an ordinary island. While an island is just a piece of land surrounded by water, an atoll contains a body of water within it.

Another curious detail about atolls is the fact that they are not actually made of soil, but of coral. The corals have to grow fast enough to replace parts of the atoll that are destroyed by erosion in order for the atoll to remain intact. Since corals thrive only in warm waters, atolls can only be found in the tropics and subtropics. Hence, the atolls are unique coral land masses consisting of a crystal clear lagoon and spectacular colorful reefs teeming with amazing marine life. Sounds exciting, doesn't it?!

Let's go on an amazing journey through the tropics. From the stunning Aitutaki Atoll in the Cook Islands to the extraterrestrial beauty of atolls in the Maldives, here are 25 of the world's most astounding atolls.

25. Takapoto, French polynesia

Takapoto, measuring 20 kilometers by 7 kilometers, is an atoll located in the Tuamoto archipelago in French Polynesia. atoll discovered Dutch navigator Jacob Le Maire in 1616, currently home to about 380 people.

24. Aitutaki, Cook Islands


Approximately 2,000 people live on Aitutaki Atoll. It is the second most visited island in the Cook Islands. The atoll, which the authorities have saved from mass tourism, is famous for its turquoise waters of the central lagoon and picturesque beaches lined with palm trees.

23. Ulithi, Caroline Islands


Ulithi, part of the Federated States of Micronesia, is an atoll of 40 islets surrounding one of the largest lagoons in the world. The atoll was the main base for the US Navy during the Great Patriotic War. Several sunken ships are still at the bottom of this lagoon.

22. Tubbataha Reef, Philippines


Tubbataha Reef, located in the middle of the Sulu Sea (Sulu Sea), is a marine and bird sanctuary, consisting of two large atolls - North and South Atoll. This protected area boasts amazing biodiversity and contains 75 percent known to science coral species and 40 percent of reef fish species.

21. Tarawa, Kiribati


Tarawa is an atoll and the capital of the Republic of Kiribati, located in the central Pacific Ocean. The atoll, which is home to almost 60,000 people, boasts a wide reef teeming with fish and a large lagoon spanning over 500 square kilometers.

20. Tikehau, French Polynesia


Tikehau, located 340 kilometers northeast of Tahiti on the Tuamotu Islands, is an oval-shaped atoll and tourist destination famous for pink sandy beaches lined with coconut palms and stunning marine life and flora.

19. Maafushi, Maldives


Maafushi, which is part of the Kaafu Atoll, is one of the inhabited islands in the Maldives. The atoll was badly damaged by the 2004 tsunami but quickly recovered. Nowadays, Maafushi boasts a thriving local economy based on fishing and tourism.

18. St. Francois Atoll, Seychelles


Saint Francois Atoll, consisting of the two islands of Saint Francois and Bijoutier, is an uninhabited atoll in the western Indian Ocean. The atoll is home to numerous species of birds, including the Fairy Tern, Curlew, Turnstone, Tules and so on.

17. Rangiroa, French Polynesia


, one of the largest atolls in the world, consists of approximately 415 tiny islets and shoals, with a total area of ​​​​about 170 square kilometers. In the center of the atoll, there is a large lagoon where black pearl oysters are bred.

16. Palmyra Atoll, North Pacific Equatorial Region


Palmyra Atoll, located between Hawaii and American Samoa, is an unoccupied atoll consisting of an extensive reef, lagoons and 50 islets. The atoll is officially administered by the United States and is covered with coconut, scaevola, and pisonia trees.

15. Nukuoro, Federated States of Micronesia


Surrounding a lagoon 6 kilometers in diameter, Nukuoro is a remote atoll with a population of nearly 400 people. There is no tourism on the island, except for occasional visits by passing sailing yachts.

14. Ontog Java Atoll, Solomon Islands


Ontong Java Atoll is sometimes also called Lord Howe Atoll. It is a large shoe-shaped atoll, consisting of more than 120 low-lying islets. There are two large villages on the atoll - Luaniua and Pelau - where most of the population of the atoll.

13. Nukumanu, Papua New Guinea


Nukumanu is a medium-sized atoll in Papua New Guinea located in the southwestern Pacific Ocean, 4 degrees south of the equator. The atoll consists of 20 sandy islands surrounding a large lagoon.

12. Lihou Reef, Coral Sea Islands Territory


Lihou Reef, located in the Coral Sea, northeast of Queensland, Australia, is the second largest atoll in the world in terms of total area. Surrounding a 2,500 square kilometer lagoon, the atoll is an important nesting site for many bird species.

11. Cayo Bolivar, Colombia


Cayo Bolivar, located 25 kilometers from San Andrés, a Colombian coral island in the Caribbean, is an uninhabited atoll consisting of two islands - East and West Cay. Its diversity of marine life and beautiful beaches have made it popular place for tourist excursions.

10 Aldabra, Seychelles


Aldabra, uninhabited and extremely isolated, is a large atoll virtually untouched by man. Known as one of the "crown jewels" of the Indian Ocean, it has a distinct island fauna, including the largest population of giant tortoises in the world.

9. Ari Atoll, Maldives


Ari Atoll is a natural atoll located in the Maldives. This is one of the largest atolls in the world and is located in the western part of the archipelago. More than 20 islands are scattered here, most of which were developed for tourist resorts, and each of them is autonomous and has places for living and recreation.

8. Bangaram Atoll, India


Bangaram Atoll, located in the Union Territory of Lakshadweep, India, is a popular tourist destination offering numerous recreational activities including scuba diving or snorkeling and deep sea fishing. It features white sandy beaches, a tranquil lagoon and stunning coral reefs.

7. Chagos Islands, British Territory in the Indian Ocean


The Chagos Islands are a group of seven consisting of more than 60 individual tropical islands in the Indian Ocean. These reefs, notable for their amazing biodiversity, are home to at least 371 coral species, 784 fish species and 2 turtle species.

6. Pearl and Hermes Atoll, Hawaii


Pearl and Hermes Atoll, which is part of the Northwest Islands Hawaiian archipelago, is a small Hawaiian atoll named after two English whaling ships, which were wrecked on this atoll in 1822. Once the center of the pearl trade, the atoll is now a bird sanctuary.

5. Osprey Reef, Coral Sea Islands Territory

Osprey Reef, part of the northwestern group of islands in the Coral Sea, is an oval-shaped submerged atoll. The depth of the waters surrounding this atoll is 2 kilometers and the slopes of its reef are home to a variety of marine life, including the rare dwarf nautilus pompilius.

4. Diego Garcia Atoll, British Indian Ocean Territory


Diego Garcia Atoll, located in the central Indian Ocean just 7 degrees south of the equator, was settled by the French in the 1790s and was later ceded to the British crown. It has the largest continuous landmass of any atoll in the world.

3. Kwajalein Atoll, Marshall Islands


Kwajalein, which is part of the Republic of the Marshall Islands, is one of the largest atolls in the world, judging by the area body of water which it surrounds. It consists of 97 islands and islets, and its land area is 16 square kilometers. It surrounds a giant lagoon with an area of ​​2174 square kilometers.

2. Kure Atoll, Hawaii


Kure Atoll, politically part of Hawaii, is the most northern atoll in the world. This atoll is sometimes also called ocean island. It is home to hundreds of thousands of seabirds and numerous marine animals, including the monk seal.

1. Ducie Island, Pitcairn Islands


Ducie Island, located in the South Pacific Ocean, is a small uninhabited atoll on the Pitcairn Islands. Despite the sparse vegetation, the atoll is home to a range of bird species. More than 90 percent of the world population of Murphy's Typhoon nests on Ducie.

Charles Darwin's theory of the formation of atolls

famous biologist C. Darwin in 1842 formulated immersion theory. It explains how atolls are formed, namely, the uplift and subsidence of the crust. Earth in the oceans. According to him, atolls are formed in 3 stages:

1. fringing reef(the volcano fades, the bottom settles);
2. barrier reef(continuation of subsidence);
3. atoll.

Also, Darwin believed that under all lagoons lies stone foundation. Subsequently, his theory was confirmed.

Fresh water, flora and fauna of the atolls

In fact, streams, rivers and similar sources fresh water there isn't. Where does it come from on the coral islands drinking water ? Drinkable water to the atolls bring the rains. What about flora? Seeds of plants with a high level of survival, fall into a mixture of old coral and sand. Mainly coconuts. Over time, shrubs and palm trees begin to sprout. If speak about fauna, then its presence is not typical for atolls. But, there are a large number of different insects and many kinds fish.

The famous bathing suit "bikini" named thanks to the sensational, at one time, atomic testing on an atoll called Bikini. Countries like Tuvalu And Kiribati, are located entirely on the atolls. And, here, the atoll, on which the human foot has never set foot - Caroline. It is part of the state Kiribati. But, soon, it will be flooded due to the constant rise water level in the global ocean.

The most famous atoll in the world is Lighthouse having annular form. At its center is the famous Big lagoon blue hole . And the largest atoll on Earth is Kiritimati. The second largest atoll is Aldabra where they found their home more150 thousand giant turtles. The largest raised atoll is considered Niue where the country with the same name is located.

"The coral islands, erected by small cranium-skinned animals, present us with the largest buildings on the globe, amazing the human mind," wrote the famous Russian navigator F. F. Bellingshausen. Indeed, the activity of corals, which erected dozens of large and hundreds of small islands of Oceania, built the Great Barrier Reef, the construction volume of which exceeds 100,000 times the Great Chinese wall(the size of the reef: 2000 kilometers long, 2000 meters high and up to 150 kilometers wide) causes both admiration and amazement.

"Tiki" - a statue from the Marquesas Islands

And after them comes the question: how did the corals manage to build islands and reefs, and in particular ring atolls in the ocean? Here is what Darwin wrote in his diary after he managed to examine coral islands and reefs (during his world travel on the Beagle): "Such formations, no doubt, occupy an important place among the amazing phenomena of the globe. These are not curiosities that immediately catch the eye, but rather a miracle that amazes us after some thought. We are surprised when travelers tell about huge heaps of some ancient ruins. But how insignificant are the largest of them, when compared with the colossal amount of matter formed here from various tiny animals. On all the islands, on the smallest particles and large fragments of rock, there is a single seal that speaks of that they were once created by an organic force.

Measuring the depth at a distance of only a little more than a mile from the coast, Captain Fitz Roy lowered a lot, seven thousand two hundred feet long, but did not reach the bottom. Therefore, we must consider this island as the top of a high mountain; to what depth the work of coral organisms extends is completely unknown. If it is correct to assume that the rock-forming polyps continue to build them up while the volcanic base of the island gradually subsides intermittently, then it is likely that the coral limestones must be of enormous thickness. We know some islands in the Pacific, such as Tahiti and Eimeo... which are surrounded by coral reefs separated from the shore by channels and pools of calm water. Various factors control the growth of the most productive coral species in these situations. Therefore, if we suppose that such an island, after long successive interruptions, has sunk a few feet... the work of the corals will continue upward from the base of the surrounding reef. Over time, the central landmass would sink below sea level and disappear, and the corals would complete the circular wall. Wouldn't it be a lagoon island then? From this point of view, we must consider the lagoon island as a monument, built by myriads of tiny architects to mark the place where the earth was buried in the depths of the ocean.

This diary entry, dated April 12, 1836, contains the key to Darwin's theory of the origin of coral reefs, which he later developed in the book "The Structure and Distribution of Coral Reefs" and the world-famous "Naturalist's Voyage Around the World on the Beagle". First, corals that live only in shallow water (at depths of no more than 50-60 meters) begin their activity around the coastal shallows of an island or mainland (this is how the Great Barrier Reef was formed near the coast of Australia). But here the bottom - and with it the island surrounded by reefs - slowly begins to sink. Corals need the sun, they cannot live at great depths - and small builders begin to erect their buildings in order to remain in shallow water as before.

The island sinks more and more - and the space between it and the coral reef fringing it becomes wider and wider, which turns into a barrier reef. Little builders continue their titanic work, they build a solid wall on the foundation formed by their predecessors - corals. The sinking of the bottom continues, and the sinking of the island and coral structures continues. “As the barrier reef slowly sinks, corals will continue to grow rapidly upwards, but as the island sinks, the water will grab the shore span by span, and here at first individual mountains (peaks) form separate islands within one big reef, and in the end the last most high peak. The moment this happens, a real atoll is formed," Darwin wrote.

Darwin's theory of atoll formation, like his ingenious theory of evolution, has been controversial. Some scientists, including the greatest geologist Charles Lyell, admitted that Darwin was right. Others have come out with sharp criticism of his theory. So, the famous Alexander Agassiz announced that "Darwin made observations on the move during his voyage and did not want to stop anywhere", all the facts on which he builds the theory of the formation of atolls are taken "second hand", and therefore the theory is also vicious, their explaining. According to Agassiz, barrier reefs have grown on the coastal terraces that the activity has created. sea ​​waves. This explains the even flat bottom of the lagoons of coral atolls.

A detailed and reasoned criticism of Darwin's theory was made by John Murray. Firstly, Murray noted, in a number of places there are coral reefs that rise above sea level to a rather high altitude (on the Palau Islands in Micronesia - up to 150 meters, in Hawaii, on the island of Kauai, they find the remains of corals at an altitude of over a kilometer) . The corals themselves, the inhabitants of shallow waters, could not "grow" their buildings to such a height - obviously, here we are dealing with land uplift. But Darwin's theory suggests the opposite process: the slow and steady sinking of the islands, the tombstones of which are coral atolls. Murray's second important argument, which cast doubt on Darwin's theory, was the existence of places where there were fringing reefs, barrier reefs, and atolls at the same time: Darwin, on the other hand, assumed a gradual evolution going on for many decades, during the sinking of the island to the bottom.

Murray put forward his hypothesis: the land does not sink into the ocean, as the creator of the theory of evolution suggested, but, on the contrary, rises. When the top of the uplifted seamount reaches shallow depths where corals can settle, these little builders take up residence there and begin to create a reef that gradually expands outwards. But the growth rate of corals on the outer and inner parts of the reef is not the same. Corals in the inner part of the reef die off, the limestone that is part of this reef is dissolved and washed out. As a result, a "hole" is formed inside the reef, the depression is a lagoon. And on the edges of the reef, coral activity is in full swing, they continue to build up the reef - and thereby more and more strengthen the isolation of the lagoon. Ultimately, a barrier reef with a lagoon, or coral atoll, is formed.

Darwin, objecting to Murray, pointed out that the geological data on the structure of the bottom of the lagoons indicate that they do not "deepen" with time, but, on the contrary, are filled with sediments. Moreover, the waters of the lagoons, supersaturated with calcium carbonate, can in no way be a limestone solvent. (Murray believed that first a limestone bank is formed, and then, when the limestone dissolves, a lagoon.)

In 1915, R. Daly, a professor at Harvard University, put forward an original hypothesis called the "glacial control hypothesis". For, according to her, all existing atolls in the ocean are very young structures erected by corals in the Quaternary period. During the glaciation, the level of the World Ocean dropped by about 60-80 meters. The depth of the lagoons of coral atolls is approximately the same. The lowering of the ocean level led to the death of numerous coral colonies; the turbidity and cooling of the water during the Ice Age also led to the death of corals. Meanwhile, the ocean continued its activity - waves, ebbs and flows formed ledges and platforms along the coasts of the continents and islands (only at a lower, "glacial" sea level). But now the period of the last glaciation is over, the ice began to melt, and the level of the World Ocean is steadily rising, flooding the recently formed ledges and platforms. Favorable conditions were again created for the corals, and they were not slow to take advantage of this. The platforms that the ocean flooded served as the basis for their structures. Where these platforms were narrow, fringing reefs appeared; where they were wide, barrier reefs appeared. Atolls, on the other hand, were formed on the tops of mountains cut in glacial period abrasion - "smoothing" activity of waves.

Daly, it would seem, explained not only the origin various kinds coral structures and the flat shape of the bottom of the lagoons of the atolls, but also the fact that all the lagoons, both in the center of the atoll and behind the reefs, have approximately the same depth - and it is equal to the magnitude of the sea level rise in the post-glacial period (60-80 meters). However, careful measurements of the lagoons have shown that this is not so: in fact, their depth varies over a very wide range and varies from 60 to 180 meters.

Thus, the question of whose hypothesis is right remained open - right up to the very recent years when the deep drilling of the atolls began and people were finally able to find out their true history.