What are coral reefs? Reefs - what are they? Barrier, coral reef Which marine inhabitants reproduce to form coral reefs

Oceans and seas are the heritage of humanity, since not only do most of all species of living beings 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 a coral reef and you will see that nature is many times greater than the creation of any talented artist.

What it is?

Coral reefs are colonies of corals that sometimes form truly gigantic formations, similar in size to rocks.

Note that 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 the development and growth of young animals. Contrary to popular belief, polyps are found at all depths, not just in shallow water. Thus, the most beautiful black coral lives at such a depth that not a single ray of sunlight penetrates.

But a true coral reef can only be formed by species that live in the shallow waters of tropical seas.

What reefs are there?

There are three main types of them: fringing, barrier and atoll. As you might guess, the fringing species is found in shallow waters near the coast. The most impressive formations are the barrier reefs, which look like a breakwater. They are located along the coasts of 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, obstructing 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. Its other less significant and larger “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 coastline 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 come from, what is the mechanism of their formation?

The emergence of coral reefs

Since most polyps require a relatively shallow water environment, the ideal location for them is to have a small and flat base, preferably located near the coast. However, many scientists believe that the conditions under which the formation of a colony of polyps is possible are much more diverse.

Thus, many atolls, by all indications, should have arisen on the tops of old volcanoes, but traces of really high lava formations that could fully confirm this theory have not been found everywhere. The famous scientist Charles Darwin, traveling on the equally 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 an explanation of how the world of coral reefs arose.

"Reef" theory of Charles Darwin

Let us assume that a volcano that arose in ancient times gradually grew in size due to lava that entered the external environment as a result of numerous eruptions. As soon as about 20 meters remain from the ocean surface, optimal conditions will arise for the top of the seamount to be populated by corals. They begin to quickly expand the colony, gradually completely modifying the primary relief that arose after the eruptions.

When a young coral reef reaches a volcano, the upper part of which has almost collapsed by that time, it begins to gradually sink back into the ocean. As you dive, the corals begin to grow more intensely, and therefore the reef begins to become even more massive, remaining at approximately the same level in relation to the surface of the water.

Dynamic theory of formation

Sand begins to accumulate near the reef, most of which are the skeletons of the corals themselves, ground up by erosion and some species of sea creatures. There are more and more shallows, and the reef eventually begins to protrude above the surface of the ocean, gradually forming an atoll. suggests that the elevation of the colony of polyps above the surface of the water occurs due to constant changes in the level of the World Ocean.

Many geologists and geographers of that time immediately became interested in this theory. If it is correct, then every large coral reef should have contained at least some remnants of a volcanic core.

Is the volcanic theory of the origin of reefs true?

To test this, a test drilling was organized on the island of Funafuti in 1904. Alas, the technologies that existed at that time made it possible to reach a depth of only 352 meters, after which work was stopped, and scientists were never able to reach the supposed 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 basalt. It has been proven that the coral reef was formed more than 60 million years ago, when a colony of polyps settled on the top of an extinct volcano. Darwin was right once again.

How reefs changed during periods of falling sea levels

It is known that the ocean at 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 lower than today. Thus, all the coral reefs that formed at that time are now located 200-250 meters below the modern edge. After this mark, the formation of polyp colonies becomes impossible.

In addition, often former coral reefs (photos are 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 ocean level was at its highest, and there were no ice caps at the earth's poles yet. Note that between the ice ages, polyps did not actually form any significant colonies, since the water level changed too quickly.

Egypt is especially indicative in this regard. Coral reefs in the Red Sea are sometimes found at enormous depths, which several million years ago were the bottom of ordinary shallow seas.

Main components of a coral reef

To understand exactly how a polyp colony works, let’s take the coast of Jamaica as an example. In any photo of a classic atoll, you can first see a sand spit rising steeply from the depths. The dark stripes located parallel to the atoll are traces of coral destruction that occurred at different times due to fluctuations in ocean levels.

Sailors determine this zone by the 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 area there is a plateau where the corals are exposed at low tide. Oddly enough, in the water area of the lagoon the depth increases sharply, colonies of polyps in this area are not so developed, and during low tide they continue to remain under water. The area near the shore that is constantly exposed during low tides is called the intertidal zone. There are few corals there.

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 area. 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 wild! Yes, you cannot deny the richness of fauna in these places.

The underwater world of coral reefs

As scientists say, the Great Barrier Reef alone (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 the amazing coral reef fish - parrots. They got their name from 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 very high in calories, these fish have to constantly eat. 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 snow-white coral sand.

Recognizable and colorful inhabitants of these places are also hundreds of species. Their natural enemies sometimes become the culprits in the destruction of the reefs themselves. Thus, the Crown of Thorns star, which arrived on the Australian coast from another hemisphere, has already destroyed almost 10% of the entire Barrier Reef! Because of this, oceanographers and ichthyologists around the world have declared a real war on it: the stars are caught and destroyed.

The measures taken still have a certain effect, and therefore today the underwater world of Australia is beginning to recover.

Coral reefs are large underwater formations consisting of the skeletons of coral polyps, which are marine invertebrate animals. The order of reef-building coral polyps called madreps or stony corals—they extract calcium carbonate from seawater and create a hard, durable exoskeleton that protects their soft, baggy bodies.

Each individual coral is called a polyp. New coral polyps live on the calcium carbonate exoskeletons of their ancestors, and after death they add another exoskeleton to the existing structure. Over many centuries, the coral reef grows with each new polyp and eventually becomes a large and visible structure underwater.

Corals can be seen everywhere - from the Aleutian Islands off the coast of Alaska to the warm tropical waters of the Caribbean Sea. The largest coral reefs can be seen in the clear, shallow subtropical and tropical ocean waters, where they grow rapidly. The largest of the coral reef systems, the Great Barrier Reef of Australia, is more than 2,400 kilometers long.

Coral life

According to the non-profit environmental organization Coral Reef Alliance (CORAL), there are hundreds of species of corals in the world. Corals come in a variety of shapes and colors, from round and curled brain corals, which resemble a human brain, to tall, elegant eight-rayed Muricea corals (sea whips) and sea fans, which have intricate, brightly colored appearances. trees or plants.

In photos: Stunning new coral species in Polynesia.

Corals belong to the phylum Cnidaria. This group also includes jellyfish, anemones, Portuguese man o' war and other marine animals. Although each individual animal is considered a polyp, corals are often described as colonies consisting of thousands of polyps.

Corals feed in two different ways: some species can catch small marine organisms such as fish and plankton using stinging tentacles on the outer edges of their bodies. However, according to the US Environmental Protection Agency (EPA), most corals have a symbiotic (mutually beneficial) relationship with seaweeds known as zooxanthellae.

These algae live inside the body of the coral polyp and, through the process of photosynthesis, produce food for themselves and for the polyp. The polyps, in turn, provide the algae with a home and carbon dioxide. In addition, zooxanthellae give corals their vibrant colors—most coral polyp bodies are transparent and colorless.

Some coral species, such as brain corals, are hermaphrodites, producing both eggs and sperm at the same time. They reproduce through mass coral spawning, which in some species occurs only once a year on a specific night.

Other species, such as elkhorn coral, are dioecious and form colonies with only females or only males. Among these coral colonies, all the polyps of one particular colony produce only sperm. To continue the breeding process, they rely on a neighboring colony, which produces only eggs.

Photo of coral taken on a reef located behind Ofu Island, which is home to American Samoa National Park.

World of Coral Reefs

Most of the significant coral reefs that currently exist began to form 5,000-10,000 years ago, according to information from the CORAL organization. These formations primarily exist in warm, shallow waters that provide sufficient sunlight for the algae that provide food for the coral polyps.

Coral reefs cover less than 1 percent of the ocean floor—collectively, they would cover an area of approximately 285,000 square kilometers, which is close to the size of the state of Nevada. However, they are among the most productive and diverse ecosystems on Earth.

Approximately 25 percent of all known marine species depend on coral reefs for food, habitat and reproduction. Corals are sometimes called the "rainforests of the sea" because of their biodiversity. They are habitat for more than 4,000 species of fish, 700 species of coral, and many thousands of other plants and animals.

However, according to experts, their lives are in imminent danger.

Coral reefs are in danger

According to scientists from the Hopkins Marine Station at Stanford University, coral reefs are vital marine habitats on which many ocean species depend. In addition, they provide direct economic benefits to people totaling approximately 30 billion annually through food, fisheries and tourism.

However, coral reefs face several threats. The first threat is increasing ocean acidification, caused by the oceans absorbing huge amounts of carbon dioxide (CO2) released into the atmosphere by burning fossil fuels. This limits the corals' ability to produce the calcium carbonate exoskeletons they depend on for habitat.

Water pollution also negatively affects corals. Agricultural pesticides and fertilizers, oil and gasoline, sewage runoff, and soil from eroded land masses entering the ocean disrupt the delicate relationships that exist between the plants, corals, and other animals that are part of the reef ecosystem.

As ocean temperatures rise due to global warming, coral polyps reject the zooxanthellae they depend on for food. Once the zooxanthellae disappear, the corals also lose their bright colors, and all that remains is a white exoskeleton. This process is called coral bleaching. According to the non-profit environmental organization Coral Reef Alliance (CORAL), corals that experience bleaching usually die off.

Additionally, forms of fishing such as cyanide fishing (in which cyanide is used to make fish easier to catch), "blast fishing" using explosives, and overfishing by trawlers can destroy thousands of years old coral within minutes. reef.

"Overfishing, ocean acidification and ocean pollution are slowly killing coral reefs," Roger Bradbury, an ecologist at the Australian National University in Canberra, told the New York Times. " “Each of these factors individually is quite capable of causing the destruction of coral reefs around the world, but taken together this destruction is guaranteed.”

Coral reefs are calcareous organogenic geological structures formed by colonial coral polyps and some types of algae that can extract lime from sea water.

Coral reefs are fantastically beautiful and the most “densely populated” ecosystems of the World Ocean. The biomass of benthic invertebrate animals and fish in them is estimated at hundreds of grams per square meter of the seabed. The total number of species on coral reefs can reach or exceed one million.

The reef ecosystem owes such a vibrant life to single-celled algae (symbiont algae) living in corals, whose photosynthetic activity does not stop throughout the year.

The first corals on Earth, tabulates, appeared in the Ordovician period of the Paleozoic era approximately 450 million years ago. Together with stromatoporid sponges, they formed the basis of reef structures.

Throughout the history of their existence, corals have repeatedly experienced periods of decline and mass death - the climate has changed, and the level of the World Ocean has repeatedly risen and fallen. But neither the changing climate, nor the decrease or increase in sea level led to the complete and final death of reef-forming corals - they adapted to new conditions. A balanced reef ecosystem has great restoration potential.

In 1997-1998, there was an anomalous increase in the temperature of the surface waters of the tropical zone of the World Ocean, which led to mass death of corals in vast areas of the Indian and Pacific oceans.

Then, in the coastal areas of Bahrain, the Maldives, Sri Lanka, Singapore and near Tanzania, up to 95% of all corals in shallow reef zones died. In other tropical coastal zones, 20 to 70% of corals suffered the same fate. In the early 2000s, the tragedy repeated itself twice, especially affecting the central and southern parts of the Pacific Ocean, and by the mid-2000s, according to scientists, slightly less than half of the previously existing reefs remained on Earth.

But not in all reef areas the situation is so catastrophic. For example, in the Maldives, coral cover has been completely restored due to the rapid growth of acroporids (acroporal corals), whose growth reaches 20-25 cm per year.

A different picture is observed in the area of Bahrain and Sri Lanka, where the reefs were under very strong anthropogenic pressure.

Thus, it is not sharp climatic fluctuations, but a high level of anthropogenic pressure that leads to fatal consequences for this ecosystem.

What are coral reefs?

Coral reefs are massive deposits of calcite (limestone) formed from the skeletal remains of some colonial marine organisms - plants and animals - among which madrepore corals and coralline algae stand out. In addition to these two dominant groups of reef-forming organisms, the composition of reefs also includes a significant share of other species of animals and plants - mollusks, sponges, foraminifera and some green algae.

There are three main types of interconnected coral reefs: fringing, barrier and atoll.

Fringing or coastal reefs

Located along recently drained or stable coastlines. Such a reef is a terrace-like platform at or slightly below sea level, extending from the shore and often ending in a raised edge, heavily indented by channels, from which the slope of the reef goes quite steeply under the water, and then abruptly ends to great depths. Corals grow fastest on the outer slope of the reef and very slowly on the shallow platform.

Barrier reefs

They often surround individual islands, but are located some distance from the coast, separated from it by a strait or a calm, medium-deep lagoon. The largest and most famous is the Great Barrier Reef, a complex reef system stretching over 1,600 km along the east coast of Australia.

Atolls

Ring-shaped reefs surrounding lagoons, within which there are no land areas. They are ring-shaped with an internal shallow lagoon; ring-shaped with one or more ring breaks through which tidal waters enter the lagoon; in the shape of a half ring, quarter ring or ring-shaped, filled during high tides; or in the form of giant rings consisting of individual small atoll-like reefs fringing huge lagoons.

Types of corals

In general, hard corals that form a reef can be divided into branching, fragile corals (madrepore corals) and massive, rocky corals (brain and mendrin corals). Branching corals are usually found on shallow, flat bottoms. They are colored blue, lavender, purple, red, pink, light green and yellow. Sometimes the tops have a contrasting color, for example, green branches with purple tops.

Brain corals can reach more than 4 meters in diameter. They live at greater depths compared to branched ones. The surface of brain corals is covered with winding crevices. The predominant color is brown, sometimes in combination with green. Dense pores form a kind of bowl, the base of which consists of dead corals, and living ones are located along the edges. The edges grow, increasingly increasing the diameter of the bowl, which can reach 8 m. Living porite colonies are colored pale lilac, the tentacles of the polyps are greenish-gray.

At the bottom of bays, individual mushroom-shaped corals are sometimes found. Their lower flat part fits tightly to the bottom, and the upper part consists of vertical plates converging in the center of the circle. Mushroom coral, unlike branching and massive hard corals, which are colonies, is an independent living organism. Each such coral contains only one polyp, the tentacles of which reach a length of 7.5 cm. Mushroom corals are colored greenish and brownish. The color remains even when the polyp retracts its tentacles.

Corals are not simply calcareous structures formed by polyps. This is one of the most incredible life forms on earth. Our top 10 includes the most beautiful coral reefs in the world.

Why are corals so attractive? Firstly, with its amazing natural beauty, variety of shapes, number of colors and shades, which reaches 400. Secondly, they do not appear anywhere: corals need clean water and a warm climate. And, perhaps, the main thing is fish and other fauna of the most incredible shapes and colors, which with their presence creates a complete picture of indescribable beauty.

10. Red Sea Barrier (Egypt)

The coral reefs of the Red Sea cannot be called the most beautiful in the world, but they do have very rare and interesting shades of some colors, such as yellow, red and pink. Corals located close to the coast attract snorkelers and diving enthusiasts from many countries, especially post-Soviet ones. Frankly speaking, it was the latter fact that became the reason for inclusion in our top 10.

9. Aldabra Atoll in the Indian Ocean (Seychelles) It occupies 200 km² and is notable for the fact that it has survived to this day in almost its original condition. All thanks to the fact that, once a pirate island, it was well hidden for a long time and was a hard-to-reach place. Now the beauty of this amazing coral reef is under the protection of the local government and UNESCO. The atoll is also notable for its huge population of turtles, reaching 150 thousand individuals.

8. Roatan Island in the Caribbean Sea (Honduras)

Here is the Mesoamerican Barrier Reef, one of the largest in the world. Diving began to develop here relatively recently, some 10 years ago, and man has not yet had time to exert his detrimental influence on this beautiful underwater corner of the planet. Therefore, if you want to admire the fish surrounded by pristine beauty, hurry up!

7. Palancar Reef in the Caribbean Sea (Mexico)

The reef, stretching for 5 km, is remarkable for its structure: there are many underwater caves, branches and crevices in which you can see quite rare black corals, and at the same time get acquainted with a variety of marine life forms. Here you can find giant barracuda, moray eels, spotted eagle rays, spiny lobsters, crabs, lobsters, and many colorful tropical fish.

6. Tubbataha in the Sulu Sea (Philippines)

This is an entire national park, a World Heritage Site UNESCO. It is approximately 15 million years old, so it takes pride of place among both the most beautiful coral reefs in the world and the most ancient. In a relatively small area (7,030 hectares) there are 75% of the corals existing on the planet (almost 400 species), and about 40% of the studied reef fish (more than 500 species). About 1,000 species of marine animals are found in these waters, including dolphins, sharks and whales. The fact that the schedule of local tourist diving vessels is scheduled a year in advance suggests that Tubbataha rightly made it into our TOP 10.

5. Raja Ampat in the Indian Ocean (Indonesia)

According to some estimates, this is where the greatest diversity of marine life can be found. No wonder this place is called World Richest Reefs(English: the richest reefs in the world). There are over 1,200 species of reef fish (25 of which are endemic). The diversity of corals is so great that it is 10 times greater than all species existing in the Caribbean combined! On top of that, at least a hundred sunken ships and planes have been recorded in the surrounding area. Isn't this every diver's dream?

4. Coral reefs of the Andaman Sea (India)

At one time, they delighted the famous Jacques-Yves Cousteau, who made a documentary here. It was here that 111 species of corals were discovered, previously unknown to science. The most beautiful site is located on the territory of the Mahatma Gandhi National Marine Park. Here you can admire stingrays, dolphins, turtles, as well as schools of colorful fish swimming calmly around enthusiastic divers.

3. Apo in the South China Sea (Philippines)

It occupies 34 km² and is home to several different ecosystems. Apo owes much of its title to one of the most beautiful coral reefs on the planet to water with unique transparency. On clear and calm days, visibility can exceed 50 meters. And there is so much to see here: several varieties of sharks and rays, huge tuna, lobsters, gorgonians, as well as many sea snakes that make you flinch at every accidental touch, especially at night.

2. Belize Barrier Reef in the Atlantic Ocean (Belize)

It ranks second in the ranking of the best coral reefs in the world. Its length is 280 km, and in such a vast area there is an unimaginable diversity of living organisms. And the most interesting thing is that, according to scientists, the reef is only 10-15% studied. Therefore, among the 140 thousand divers who visit this place annually, there are many who want to become discoverers.

The highlight of this beautiful place is the so-called “Great Blue Hole”. It is a circle of blue-black color, with a diameter of 300 meters, which seems bottomless. Almost the only inhabitants of the cave (which is actually a “hole”) are sharks; they can be seen even from the surface. The spectacle is quite impressive!

1. Great Barrier Reef in the Coral Sea (Australia)

The largest coral reef in the world is also considered the most beautiful. Its area is almost 345,000 km², this miracle of nature can be seen even from space. Home to a colony of coral polyps, this aquatic oasis is considered the largest ecosystem on the planet. There are over 400 varieties of corals and more than one and a half thousand species of inhabitants, including whales and sharks, octopuses and squids, parrot fish and butterfly fish, stingrays, crustaceans, turtles... The Great Barrier Reef is rightly considered a valuable world heritage site.

Coral is a structure formed from millions of very small marine animals called polyps. The length of the polyp, which is shaped like a tube, is only an inch. At the end of this tube is a mouth surrounded by tentacles that deliver sea creatures to it. The colors of corals are very diverse, as are their shapes and sizes. They have both an internal and external skeleton. They can be soft or hard, black, smooth or prickly and other types. Some are like feathers, others are like fingers. Polyps are hollow and attach themselves to other polyps or to limestone rocks to form large structures. Almost all corals live together in groups called colonies. Very large colonies are called reefs. The polyps take calcium from seawater and turn it into limestone around the underside of their body. New polyps grow and the limestone structure becomes larger and larger.

Corals live in oceans around the world, but survive best in warm water. In tropical oceans they form large structures called atolls. Atolls grow around old volcanoes and form ring-shaped islands. Coral polyps eat small marine animals such as jellyfish larvae. Some people need seaweed to survive. Corals can reproduce by budding. Small buds appear on the body of the polyp. They grow up and separate from their parents. Corals can also lay eggs, which grow into new colonies. Some types of coral live for hundreds of years.

coral reef

A coral reef is a mountain underwater formed by the skeletons of corals. Reefs are also made up of other living things, such as seaweed or shellfish. A coral reef has vibrant colors and can grow for hundreds of years without being destroyed by the ocean. Location of coral reefs around the world.

Types of reefs:

Reef line - located near the coastline they are usually the youngest reef forms
Barrier reefs are located further from the coast they form a wall between the shallow waters near the coast and the open sea some barrier reefs are very large The longest - 2 thousand kilometers long The Great Barrier Reef on the east coast of Australia
Atolls are ring-shaped reefs. They are formed when an old volcano erupts and sinks into the sea. A reef grows upward from the edge of the volcanoes along with a lagoon formed in the middle
Most reefs need warm water to survive. They grow best in water that is at least between 16 and 20 degrees. Reefs also need enough sunlight to feed. Coral reefs can also be found in the warm ocean waters of the Pacific and Indian Oceans as well as in the Caribbean Sea and the east coast of central South America. They usually grow very slowly, no more than 10 cm per year. They can be found near the surface where they get enough sunlight

Life on coral reefs

A coral reef can have thousands of different species of corals and other organisms. This would be a record if not for tropical forests, which can support even more different organisms. This is why coral reefs are called tropical forests of the sea. Many species of fish live near coral reefs. Their bodies have the ability to change, which gives them the ability to live and find food in this area. In addition, coral reefs are home to crabs, lobsters, octopuses, starfish and other invertebrate animals.

Importance of corals and coral reefs:

Corals remove and recycle carbon dioxide, a gas responsible for the greenhouse effect.
Reefs protect islands and continents from waves and storms and allow other species to thrive in shallow waters near the coast.
A coral reef is a complex ecosystem with different species of organisms. Without reefs they would die.
Coral skeletons are used as substances for bones and other parts of our body.
Coral reefs are living laboratories for scientists and students.
The reefs attract millions of tourists every year.
People make jewelry made from coral reefs.