What animals form ring-shaped islands atolls. Atolls. North Male Atoll

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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 46 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 1830 m, but sometimes it reaches 90 m.

Structure.

The main material from which coral reefs are built is 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 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 island 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 scaevola shrubs predominate ( Scaevola frutescens). This is followed by forests, mainly from halophytes such as silver messerschmidia ( Messerschmidia argenta) and pandanus roofing ( Pandanus tectorius). Even farther from the coast, there are fewer halophytes, and cordia appear ( Cordia), pisonia large ( Pisonia grandis), ochrosia ( Ochrosia) and other types. In the center, in more mesophytic conditions, the primary vegetation probably consisted of trees such as splendid coetard ( Guetta speciosa), hibiscus lime-shaped ( Hibiscus tiliacens), ficuses, pisonias, pandanuses, Asian barringtonia ( Barringtonia asiatica), terminals ( Terminalia), 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 between the islets are usually found suriana maritime ( Suriana maritima) and scaevola, and on the rock outcrops sourish pemphis ( Pemphis acidula). 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. The guano deposits on many of the atoll islands have been formed by sea birds such as 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 Indian Ocean are the Maldives and Laccadives; in the Pacific Ocean 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.

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 Lagoon Great 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.

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atoll is coral island, which has the form 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 an island nation located in the Pacific Ocean 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 its 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 great place m for diving, but also an excellent 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 blue hole, the clearer the water and the more breathtaking scenery you can see.

Tikehau belongs to the Tuamotu chain of atolls that cover an area in the Pacific Ocean, it is the same size as the territory 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 contains coral and volcanic islands, which are united by a triangular lagoon. It's 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, which is located in the middle of the Indian Ocean, has 1200 tiny islands of corals, 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.

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 in sea ​​waters a huge number of atolls, 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 amazing tourist facility. 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 structure 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 separated from North Male by the 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 name: 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 name: 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 name: 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 name: 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 name: 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 name: 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 name: 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 name: 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.