Oceans and seas are the property of mankind, since not only most of all species of living creatures known (and unknown) to science live in them. In addition, only in the gloomy depths of sea waters can one sometimes see such pictures, the beauty of which can sometimes simply stun even the most indifferent person. Look at the coral reef and you will see that nature is many times superior to the creation of any talented artist.
What is this?
Coral reefs are called colonies of corals, which sometimes form really giant formations, similar in size to rocks.
Note that the true corals that can form reefs are Scleractinia belonging to the class Anthozoa, phylum Cnidaria. Single individuals form giant colonies of polyps, and calcareous colonies of older individuals provide support for development andyoung growth. Contrary to popular belief, polyps are found at all depths, not just in shallow water. So, the most beautiful black coral lives at such a depth that no sunbeam penetrates.
But a real coral reef can only be formed by those species that live in the shallow waters of tropical seas.
What reefs exist?
There are three main varieties: fringing, barrier and atolls. As you might guess, the fringing variety is found in shallow water near the coast. The most impressive formations are barrier reefs, which look like a breakwater. They are located along the coast of the continents or large islands. As a rule, they are very important. Firstly, millions of species of living beings find refuge there, and secondly, these formations play an important role in shaping the climate of the region, preventing ocean currents.
The largest and most famous is the Great Barrier Reef, which stretches for 2000 km, forming the eastern edge of the Australian mainland. Other not so significant and large "relatives" are located along the coast of the Bahamas, as well as in the western part of the Atlantic.
Atolls are small ring-shaped islands. Their coast is protected by coral reefs, which form a natural barrier that prevents strong tides and ocean currents from washing away the fertile layer from the land surface. Where do reefs even come from, what is the mechanism of their formation?
The emergence of coralreefs
Since most polyps need a relatively shallow water environment, it is ideal for them to have a small and flat base, preferably close to the coast. However, many scientists believe that the conditions under which the formation of a colony of polyps is much more diverse.
Thus, many atolls by all indications should have arisen on the tops of old volcanoes, but far from everywhere traces of really high lava formations have been found that could fully confirm this theory. The famous scientist Charles Darwin, traveling on the no less famous Beagle ship, was engaged not only in the formation of an evolutionary view of the development of mankind. Along the way, he managed to make many discoveries, one of which was the explanation of how the world of coral reefs arose.
"Reef" theory of Charles Darwin
Suppose that a volcano that arose in antiquity gradually increased due to lava, which fell into the external environment as a result of numerous eruptions. As soon as there is about 20 meters left to the ocean surface, optimal conditions will arise for the colonization of the top of the seamount with corals. They begin to quickly build up a colony, gradually completely changing the primary relief that arose after the eruptions.
When a young coral reef reaches a critical mass, the volcano, the upper part of which by that time had almost collapsed, begins to gradually sink back into the ocean. As you divecorals begin to grow more intensively, and therefore the reef begins to become even more massive, remaining approximately at the same level in relation to the surface of the water.
Dynamic Formation Theory
Sand begins to accumulate near the reef, most of which is the skeletons of the corals themselves, ground up by erosion and some types of sea creatures. There are more and more shallows, the reef eventually begins to protrude above the surface of the ocean, gradually forming an atoll. The dynamic model suggests that the rise of a colony of polyps above the surface of the water is due to the constant change in the level of the World Ocean.
Many geologists and geographers of that time immediately became interested in this theory. If she is correct, then every great coral reef must have contained at least some remnants of a volcanic core.
Is the volcanic theory of the origin of reefs true?
To test this, in 1904 a test drilling was organized on the island of Funafuti in the Pacific Ocean. Alas, the technologies that existed at that time made it possible to reach a depth of only 352 meters, after which the work was stopped, and scientists could not reach the alleged core.
In 1952, the Americans began drilling in the Marshall Islands for the same purpose. At a depth of about 1.5 kilometers, scientists found a layer of volcanic bas alt. It has been proven 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 right once again.
Howreefs changed during periods of sea level decline
It is known that the amplitude of ocean fluctuations in different periods reached one hundred meters. The current level stabilized only six thousand years ago. Scientists believe that 15 thousand years ago, the ocean level was at least 100-150 meters lower than today. Thus, all the coral reefs that formed at that time are now 200-250 meters below the modern edge. After this mark, the formation of polyp colonies becomes impossible.
In addition, often former coral reefs (the photo is in the article), which were formed in even more ancient periods, are also found on the current land. They were formed at a time when the level of the ocean was at its highest, and there were no ice caps at the Earth's poles yet. Note that between the ice ages, the polyps actually did not form any significant colonies, as the water level changed too quickly.
Egypt is especially indicative in this regard. Coral reefs in the Red Sea are sometimes found at great depths, which a few million years ago were the bottom of ordinary shallow seas.
Main components of a coral reef
To understand exactly how a polyp colony works, consider the coast of Jamaica as an example. In any photo of a classic atoll, a sandbar rising steeply from the depths is first visible. The dark stripes running parallel to the atoll are traces of coral destruction that occurred in different geological periods due to ocean level fluctuations.
Sailors determine this zone by breakers: even at night, the sound of the surf, which is heard long before the shore appears, warns of the presence of reefs. After the protected zone, a plateau begins, on which the corals open at low tide. Oddly enough, but in the water area of the lagoon, the depth increases sharply, the colonies of polyps in this area are not so developed, at low tide they continue to remain under water. The area near the coast, which is constantly open at low tide, is called the littoral. There are few corals.
The largest and most branched corals grow on the outer edges that face the open ocean. The highest concentration of marine life is observed in the littoral region. By the way, who can you meet when visiting a coral reef? The underwater world of Egypt and other popular tourist countries is so rich that your eyes will run wide! Yes, you can’t deny these places the richness of the fauna.
Underwater world of coral reefs
According to scientists, only one Great Barrier Reef (which we have already talked about) is home to almost two thousand species of fish! Can you imagine how many worms, sponges and other invertebrates live there?
The most colorful inhabitants are amazing coral reef fish - parrots. They got their name for a specific type of "beak", which is a modified jaw plate. The jaws of these "parrots" are so strong that they can easily tear off and grind entire blocks of coral.
Since polyps are not too high in calories, thisfish have to eat all the time. In a year, one population can destroy several tons of corals. Their digested remains are released into the external environment in the form of sand. Yes, yes, "parrots" play an important role in the formation of 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 - starfish - sometimes become responsible for the destruction of the reefs themselves. So, the star Crown of Thorns, which arrived on the Australian coast from another hemisphere, has already destroyed almost 10% of the entire Barrier Reef! Because of this, oceanologists and ichthyologists around the world declared a real war on her: the stars are caught and destroyed.
The measures taken still give a certain effect, and therefore today the underwater world of Australia is beginning to recover.
