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Coral reefs


The first photo is Playa Grande, the famous beautiful beach on the north coast of the Dominican Republic, the photo was taken some time ago. In the second photo - he is, the photo was taken just the other day (the author of the photo is Denis Tumarkin). How did it happen, what happened? The beach is washed away by storms. Local residents claim that in November, storms will wash the beach again, but these assurances look like an attempt to give out wishful thinking. In the same way, Playa Punta Rusia and Playa Granja were destroyed by storms, the observation deck on the northern highway between Gaspar Hernandez and Rio San Juan was severely damaged, and the Monte Cristi promenade was damaged.

Water is a tough thing, any natural scientist can appreciate it, taking a ride in a boat to meet even a small one and a half meter wave. Storms, oceanic storms - break rocks, wash off beaches, destroy coasts. It’s easy. But not everywhere. Where there are barrier coral reefs, storm waves lose their strength on the way, and the damage they do to the coast is no longer so fatal. Yes, of course, storms also cause damage to the reef, but a lively, prosperous reef - a self-healing structure - if the conditions are ideal.

The increase in temperature and acidity of the waters of the oceans, ocean pollution by agricultural and industrial wastes, and many other cute things that modern civilization does with the environment - all these factors increase the destruction of barrier reefs. Such a global problem is quite global. Affecting all countries where coral reefs protect the coast. From Australia to Belize. Yes, in general, all countries are affected: in addition to protecting coasts, corals play a significant role both in the mechanism of atmospheric oxygen reduction and in the mechanism of reproduction of marine food resources.

The logical conclusion is that to solve the problem, its causes must be eliminated. And here a new problem comes out - the problem of inertia in the thinking of most of the world's inhabitants. Most of the inhabitants of the planet are sure that “the oxygen is produced by the tree, the fish is taken from the supermarket, the beach was washed away by the will of Fate, and you don’t need to interfere in Nature’s affairs at all, she’s smart, she’ll do everything herself, she knows better”, this whole blizzard - you see what am I talking about? Just the average citizen does not want to hear that the well-being and prosperity surrounding him is illusory, and is already crumbling like a house of cards. The average person is very upset and annoyed by people, even just forcing the average person to distract from the archival and pressing issues of enrichment and arrangement of the mink, for the sake of boring and insignificant issues such as the survival of the species Homo sapiens. It is only natural that those people who raise such questions are considered by the layman to be crazy, obsessed, crazy, etc. But here's the thing: the question of how to make sure that storms do not destroy another beautiful beach, the layman’s answer is to rely on the will of God (gods, Doom, Fate, constellations, weather on Mars), the answer is those who the layman considers crazy - build an artificial reef.

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Formation Conditions

Most of the coral reefs that we observe today formed after the ice age, when ice melting led to sea level rise and flooding of the continental shelf. This means that their age does not exceed 10,000 years. Based on the shelf, the colonies began to grow up and reached the surface of the sea. Coral reefs are also found far from the continental shelf around the islands and in the form of atolls. Most of these islands are of volcanic origin. Rare exceptions have arisen as a result of tectonic shifts. In 1842, Charles Darwin in his first monograph, The Structure and Distribution of Coral Reefs, formulated an immersion theory that explains the formation of atolls by raising ru en and subsidence ru en Earth's crust under the oceans. According to this theory, the process of formation of the atoll goes through three successive stages. First, after the volcano damps and the bottom settles, a fringing reef develops around the formed volcanic island. With further subsidence, the reef becomes a barrier and, finally, turns into an atoll.

According to Darwin's theory, a volcanic island first appears

As the bottom settles, a fringing reef forms around the island, often with a shallow intermediate lagoon

During subsidence, the fringing reef grows and becomes a large barrier reef with a large and deeper lagoon.

Finally, the island hides under water, and the barrier reef turns into an atoll enclosing an open lagoon

According to Darwin's theory, coral polyps thrive only in the clear tropical seas of the tropics, where water is actively mixed, but can exist only in a limited range of depths, starting just below low tide. Where the level of the underlying land permits, corals grow around the coast, forming coastal reefs that can eventually become a barrier reef.

Darwin predicted that under each lagoon there should be a stone base, which is the remains of a primary volcano. Subsequent drilling confirmed his hypothesis. In 1840, on the Hao Atoll (Tuamotu Island), using primitive drill at a depth of 14 m, exclusively corals were discovered. In 1896-1898, while trying to drill a well to the base of Funafuti Atoll (Tuvalu Island), the drill sank to a depth of 340 m in a homogeneous thickness of coral limestone. The 432 m deep well on the elevated atoll of Quito-Daito-Shima (Ryukyu Island) also did not reach the bedrock of the atoll. In 1947, a well with a depth of 779 m was drilled on Bikini, reaching the Early Miocene deposits, about 25 million years old. In 1951, two wells 1266 and 1389 m deep on the Envetok Atoll (Marshall Islands) passed Eocene limestones about 50 million years old and reached indigenous basalts of volcanic origin. These findings indicate the volcanic genesis of the base of the atoll.

Where the bottom rises, coastal reefs can grow along the coast, but, rising above sea level, corals die and become limestone. If the land settles slowly, the rate of growth of fringing reefs over old, dead corals is sufficient to form a barrier reef surrounding the lagoon between the corals and the ground. Further lowering of the ocean floor leads to the fact that the island is completely hidden under water, and on the surface there remains only a reef ring - the atoll. Barrier reefs and atolls do not always form a closed ring, sometimes storms break walls. A quick rise in sea level and subsidence of the bottom can suppress coral growth, then coral polyps will die and the reef will die. Corals living in symbiosis with zooxanthellae may die due to the fact that enough light will no longer penetrate to the depth for photosynthesis of their symbionts.

If the bottom of the sea under the atoll rises, an island atoll will arise. An annular barrier reef will become an island with several shallow passages. With a further rise in the bottom, the passages will dry out and the lagoon will turn into a relict lake.

The growth rate of corals depends on the species and ranges from a few millimeters to 10 cm per year, although under favorable conditions it can reach 25 cm (acropores).

The first corals on Earth appeared about 450 million years ago. The extinct tabuli along with stromatoporid sponges formed the basis of reef structures. Later (416

416-359 million years ago) four-rayed corals of rugose appeared; the reef area reached hundreds of square kilometers. 246–229 million years ago, the first corals appeared, living in symbiosis with algae, and in the Cenozoic era (about 50 million years ago), maderepores corals, which exist today, appeared.

During the existence of corals, the climate has changed, sea level has risen and decreased. The last strong decline in ocean level occurred 25-16 thousand years ago. About 16 thousand years ago, the melting of glaciers led to an increase in the level of the ocean, which reached modern about 6 thousand years ago.

Formation conditions [edit |