Tropical coral island - formation and ecosystem

In ordinary consciousness, the island is a land area, surrounded on all sides by water. This term refers to the huge land areas, for example, Iceland, as well as tiny scraps of hardwood somewhere on the river, which can completely disappear in flood. According to their origin, the islands can be continental (created due to movement of tectonic plates), volcanic (caused by the eruption of volcanoes), washed (with a sandy base, which formed from a spit), artificial and finally emit more coral islands. If the first four groups understand that they occurred as a result of natural geotectonic processes or people's activities, what is involved in the formation of the coral island, because we know that the coral is a living organism?

In the warm waters of the tropical seas, these strange primitive creatures live, which feed on plankton, caught by their tentacles. Each such animal builds a limestone calyx for itself. The polyp dies with time, and the calyx remains. On its basis, the new polyp constructs a limestone dwelling. And now the coral colonies grow upward, rushing up to the sun toward the sun, until they reach the sea level and rise above the surface. So the coral island is formed.

It will naturally be assumed that these are low islands, since corals are marine animals, and on land they perish. The optimal depth for them is about 30-10 meters, where there are no storms and at the same time there is enough sunlight. Why, then, in real life can a coral island reach a height of several hundred meters? Because the tectonic plates of the Earth are constantly moving. Fluctuations in the level of the seabed can lift the coral reef upward or lower it into the realm of eternal darkness, by 200-300 meters. It is clear that over time the lofty island will be covered with soil and vegetation, but still its base will consist of countless limestone skeletons of long-dead polyps.

The coral island can be of two kinds: the island itself, which has a familiar form of elevation above the sea in the form of a rock, and an atoll. What are atolls and how are they formed? Quite simply, though for a long time. Atolls are very numerous in the Pacific, where volcanic activity is known to be very strong. Imagine an island that is a volcano above the water. At its base, in water, heated not only by the sun, but also by boiling magma in the bowels, polyps like to settle. They build reef around the island, encircling it like a ring. Then, after centuries of such coral activity, an eruption of the volcano takes place and ... the exploded mountain disappears in the abyss of waters. And the corals remain! From the airplane, the atoll seems to be surrounded by a blue sea ring, inside of which a lagoon is green - all that remains of the once formidable volcano.

Of course, not always the volcano sinks into the sea, and most often there are volcanic and coral islands. Examples of such bio-magmatic symbiosis we see in the state of Tonga (Polynesia), which is a conglomeration of volcanic islands surrounded by coral reefs and atolls. And an example of a classic atoll, which has an almost ideal shape of the ring, is the Bikini.

Coral island is a complex ecosystem. It can be said that reefs are the most densely populated of all marine habitats. Never falling below + 20 degrees water temperature, a shelter that can be found in coral corridors, grottoes and thickets, an abundance of food attracts many diverse creatures. Polyps absorb plankton, and they, in turn, are gnawed by colorful parrot fish, butterfly fish, and gluttonous starfish "thorn crown". In the depressions of reefs sea urchins and sea anemones settle. In the blooming coral garden, small amphiprians, known to us by the cartoon "Nemo fish," find shelter, and in the caves of dead corals they wait for their prey of moray eels. Unfortunately, because of the rapid human activity of corals is becoming less, because the polyps live only in very clean water. Even touching the coral can lead to its death. Therefore, being in tropical countries, never step on polyps, and the more so do not break fragile coral branches.