Coral reef. The great Coral reef. The underwater world of coral reefs

The Oceans and seas are the heritage of mankind as they live in not only a large part of all known (and unknown) species of living beings. In addition, only in the murky depths of the sea waters sometimes you can see such paintings whose beauty is sometimes able simply to overwhelm even the most indifferent person. View of the coral reef, and you will see that the nature is many times greater than the creation of any talented artist.

What is it?

Coral reefs are called colonies of corals, which form sometimes really gigantic structures, the size is similar with the rocks.

Note that these corals, which can form reefs, are the Scleractinia, class Anthozoa, phylum Cnidaria. Single individuals form a giant colony of polyps and calcareous colonies older individuals provide support for the development and growth of young animals. Contrary to popular belief, polyps occur at all depths and not only in shallow water. So, beautiful black coral dwells at a depth which does not penetrate no ray of sunlight.

But the real coral reef can be formed only in those species that live in shallow waters of tropical seas.

What reefs exist?

There are three main types: fringing, barrier and atolls. As you might guess, on the margin of the kind found in shallow water near the coast. The most impressive formations are the barrier reefs, which are similar to groyne. They are found along the coasts of continents or large Islands. As a rule, they are very important. Firstly, there is a shelter of millions of species of living beings, and secondly, these formations play an important role in shaping the region's climate, letting the ocean currents.

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The largest and Most famous is the Great barrier reef which stretches for 2000 km, forming the Eastern edge of the Australian continent. Others are not so significant and large his “relatives” are located along the coast of the Bahamas, and Western Atlantic.

Atolls – this small island has a circular shape. Their coast protected by coral reefs, forming a natural barrier that does not allow the strong tidal and ocean currents wash away the fertile layer of the land surface. Where do come from reefs, what is the mechanism of their formation?

The Appearance of coral reefs

As most of the polyps need in a relatively shallow environment perfect for them is the presence of a small and flat base, preferably located near the coast. However, many scientists believe that the conditions under which the formation of colonies of polyps, much more diverse.

So, many atolls all signs had to occur on the peaks of old volcanoes, but not everywhere found traces of really high lava formations that could completely prove this theory. The famous scientist Charles Darwin, travelling on the equally famous ship "HMS Beagle", were engaged not only in shaping the evolutionary view of the development of mankind. Along the way, he managed to make many discoveries, one of which was an explanation of how did the world's coral reefs.

“Reef” the theory of Charles Darwin

Suppose that in ancient times the volcano was gradually increased at the expense of lava that fell into the environment as a result of numerous eruptions. As soon as the surface of the ocean will be about 20 meters, there will be optimal conditions for the settlement of the tops of a submarine mountain of coral. They begin to quickly build up a colony gradually completely altering the primary relief that arose after the eruption.

When a young coral reef reaches critical mass, the volcano, the upper part of which had already almost collapsed, starting to dive back into the ocean. As you dip the corals begin to grow more intense, and because the reef starts to become more massive still and remained at the same level relative to the surface of the water.

Dynamic theory of the formation

Close to the reef begins to build up in the sand, most of which – the coral skeletons themselves, ground erosion, and some types of sea creatures. Banks are becoming more reef over time begins to protrude beyond the surface of the ocean, gradually forming the Atoll. The dynamic model suggests that the elevation of a colony of polyps over the surface of the water is due to the constant changes in Global sea level.

Many geologists and geographers of the time immediately became interested in this theory. If it is true, then every large coral reef had to carry at least some remnants of a volcanic core.

True if the volcanic theory of the origin of reefs?

To test this, in 1904, on the island of Funafuti in the Pacific was organized by test drilling. Alas, but existing technologies allowed to reach a depth of only 352 meters, then the work was stopped, and the intended kernelscientists to get so and failed.

In 1952 the Americans with the same objective began drilling in the Marshall Islands. At a depth of about 1.5 kilometers, scientists have found a layer of volcanic basalt. It was proved that the coral reef was formed over 60 million years ago when a colony of polyps settled on top of an extinct volcano. Darwin was once again right.

How did the reefs in periods of falling global sea level

It is Known that the amplitude of the ocean in different periods reached one hundred meters. The current level stabilized only six thousand years ago. Scientists believe that 15 thousand years ago the sea level was at least 100-150 meters below modern. Thus, all coral reefs, which were formed at that time are now 200-250 meters below the modern edge. After this point the formation of colonies of polyps is not possible.

In addition, often former coral reefs (photo is in the article), which were formed in still more ancient periods, find on the current land. They were formed in those days when the ocean level was as high as possible, and ice caps at earth's poles was not. Note that between the glacial periods polyps is not actually formed a little bit of important colonies, as the water level is too quickly changed.

Especially revealing in this respect, Egypt. Coral reefs in the Red sea can sometimes find in the vast depths that few million years ago was the bottom of a conventional shallow seas.

Main components of the coral reef

To understand how specifically organized colony of polyps, for example, consider the coast of Jamaica. On any photo of a classic Atoll first visible rising abruptly from the depths of the sand spit. Dark bands are parallel to the Atoll – the traces of the destruction of corals that occurred in different geological periods due to fluctuations in the level of the ocean.

Sailors this zone is determined by the surf: even at night the sound of the surf that is heard long before the appearance of the shore, warning of the presence of reefs. After the protected area starts on the plateau on which the corals are opened during low tide. Oddly enough, but in the waters of the lagoon depth increases dramatically, colony polyps in that area is not so developed, during low tide, they remain under water. Land near the coast, which is constantly open during low tide, called littoral. Corals there are few.

The largest and Most branching corals grow on the outer edges, which look out into the ocean. The greatest concentration of marine species occurs in the area of the intertidal zone. By the way, whom do you meet by visiting a coral reef? The underwater world of Egypt and other popular tourist countries so rich that your eyes will scatter! Yes, the richness of the fauna of these places will not refuse.

The Underwater world of coral reefs

As scientists say, there is only one Great Barrier reef (which we have already spoken) lives almost two thousand species of fish! Imagine how many lives worms, sponges and other invertebrates?

The Most colorful inhabitants are awesome fish coral reef parrot. Its name they got for a specific type of “bill”, which is a variation of the jaw plate. The jaws of these “parrot” is so strong that they can easily tear and grind whole blocks of coral.

As the polyps are not too high in calories, these fish have to eat constantly. Year, one population can destroy several tons of coral. Digested their remains are released into the environment in the form of sand. Yes, “parrot” play an important role in the formation of the amazingly beautiful beaches of white coral sand.

Recognizable and colorful inhabitants of these places are also hundreds of species of sea urchins. Their natural enemies, the starfish sometimes become perpetrators of the destruction of the reefs themselves. So, crown of Thorns, who arrived on the Australian coast from the other hemisphere, has destroyed almost 10% of the Barrier Reef! Because of this, oceanographers and ichthyologists around the world have declared her the real war: the stars are caught and destroyed.

The carried out activities give a certain effect, but because today the underwater world of Australia begins to recover.