Coral reefs are an attractive sight for tourists and an undesirable sight for passing ships. Many people want to visit resorts in the Pacific and Indian Oceans - the places where they are concentrated.
Definition
Several reef meanings:
- pile of stones Rocky, sandy, coral formations due to the elevation of the bottom and erosion of the banks. Heaps of remains of mollusks, algae and some reef-building organisms;
- a rocky strip hidden or protruding slightly above the water level;
- coral polyps as a perennial colony, serving as a habitat for various animals and the basis for new growths of the next generation;
- in another meaning: a reef is a device for reducing the volume of a sail in case of strong wind.
Reefs form due to the deposition of sand, erosion of certain rocks and other processes. They are formed as a result of the growth of coral polyps and combination with calcareous algae. Coral reefs are shallow, wave-resistant structures built by the release of lime by marine organisms. Polyp formations are located on underlying bases that differ in chemical properties.
Classification
Barrier reefs are located near islands far from the coast and can be separated from it by a strait. Coral is the most common. The most voluminous is the Great Barrier Reef of Australia, which stretches 1600 km along the coast.
Bordering - look like a platform like a terrace, which starts from the shore and extends deep into the ocean. They often end with a raised edge. They can be found along exposed or stable coastlines.
Atolls are ring-shaped structures, sometimes with several ring breaks, with a lagoon in shallow water, in the form of giant rings. They can easily be mistaken for islands, and only by noticing the lack of land inside can you understand that these are reefs.
Transitional types of rocky formations are characterized by similar characteristics to several corals. Some islands are distinguished by the presence of volcanic rocks in the center of the ring. In the case of others, if you examine the submerged platform from below, it may appear that it is an atoll-type reef or an underwater island.
Types of corals
There are hundreds of varieties of corals, differing in color, shape, and size. They can be round and curled, tall, fan-shaped, resembling plants. They are called tropical maritime forests because they are home to over 4,000 species of fish, 700 species of polyps and many thousands of different living creatures. Corals are classified as cnidarians: jellyfish, anemones, and Portuguese man-of-war.
Brainfish are hermaphrodites, they produce female and male cells, and their reproduction occurs as a result of mass spawning, while in other species this phenomenon is observed once a year.
There are two known ways of feeding corals. The first is with the help of stinging tentacles, catching small fish and plankton; the second is a symbiotic relationship in which algae exist inside the polyp and, through the process of photosynthesis, take food for themselves and for the polyp, and receive carbon dioxide and shelter. Most corals do not have their own shade, and zooxanthellae give them specific colors.
Conditions of existence
Corals are the most important component of the internal life of the ocean, depending on which its inhabitants live and develop. They provide economic benefits to humans equivalent to $30 billion a year through fishing, tourism, and food.
The habitat of corals is shallow water, heated to an acceptable temperature (22-27 degrees), with sufficient sunlight so that algae can synthesize nutrients and deliver them to the polyps. The Australian reef is gradually disappearing closer to Antarctica. Water level, salt percentage, temperature - all these conditions must correspond to optimal parameters for the development of polyps.
Currently, corals are threatened by ocean acidification, which is possible through the penetration of CO 2 from the atmosphere. Under the influence of carbon dioxide produced during the combustion of fuel substances, they stop growing.
WITH global warming In ocean waters, corals reject zooxanthellae algae, which gives them a peculiar brightness. In the absence of vegetation, their interaction with corals and many living organisms ceases. It is known that such reefs become colorless over time, as a result of which they die off.
The Crown of Thorns starfish is a known reef pest from the South Pacific, eating about a meter of the ecosystem every week. To combat it, chemical methods are excluded so as not to harm other inhabitants, so catching the aquatic inhabitant remains optimal.
The structure of polyps, formed over thousands of years, can be destroyed in a few minutes if fishing is carried out using explosive methods, trawlers or using cyanide.
What is a reef in terms of stability? This is an ecosystem that grows and collapses at the same time: fish and animals feed on it, acids corrode it, and the current erodes it. Visible part corals are constantly changing and over time decompose into grains of sand. But also in unfavorable conditions the reef increases up to 30 cm per year.
Australian reef
The origin of coral reefs began about 25 million years ago with the displacement of the Australian lithosphere plate. Their total global area is equal to 27 million km2. About 3,000 rocky structures and 900 offshore islands make up Australia's Great Barrier Coral Reef, one of the largest natural structures with living organisms at its core. The park, located underwater, covers an area of more than 344,000 km2.
To date, only ten percent has been studied. What a reef is is known, but the features of its coexistence with all its inhabitants and components are being studied. Eyewitnesses claim that no office equipment is able to display the natural beauty and silence of the Australian Nature Reserve.
If you dive below ten meters deep, you can see the glow of the corals and admire the number of their shades: red, green, purple, black, yellow, brown, white. The reef is about 400,000 years old and its growth has accelerated as ocean levels have risen. The new areas are located above the old ones at a depth of about twenty meters. Thousands of generations of its colonies will pass before the reef takes on new shapes and sizes.
Discoverer
In 1770, the navigator James Cook, sailing over a rocky strip of coral, unexpectedly learned what reefs were when their edges stuck into the ship and pierced its hull. The crew had to drop tons of cargo, including a heavy firearm, to lighten the ship and bring it to the shallows to repair numerous holes. The cannons, recovered from the bottom by tourists a century later, became museum exhibits, and one of them was left on Green Island.
About five hundred ships have been wrecked in the area where the reef is located, and some researchers have tried to map it. In 1970, an oil tanker sank to the bottom in this place. Torres Strait Islanders and Aboriginal Australians fished here, so Cook was not the only one to discover the reef.
Inhabitants
Six of the seven rare species of turtles live here, the most ancient sharks, including whale sharks, butterfly fish, batfish, crocodiles and many other inhabitants of amazing shape and beauty. You can find a huge flounder weighing 200 kg and 2.5 m long. Dolphins, whales, and killer whales raise their offspring near the reef. Many crustaceans build their homes here: lobsters, crabs, lobsters, shrimp. There are also deadly animals here, including blue-ringed octopuses.
Birds nest on the surface of rocky formations: petrels, frigatebirds, terns, eagles and others, up to two hundred species. Of plants, unfortunately, only 40 species are available.
Coral reefs- These are huge rocky piles formed by millions of tiny creatures - coral polyps. Reef-building coral polyps build protective skeletons for their soft bodies from limestone, calcium salts that they extract from seawater. These shells are shaped like bowls, discs or boxes. Each colony grows and develops in a specific pattern as old polyps form new individuals through budding. Old polyps gradually die off, leaving empty hard shells, and new polyps grow above them. This is how, centuries later, thousands of coral skeletons form bizarre reefs. Reef-building coral polyps build some of the toughest and most massive formations in the living world. But they themselves are very gentle creatures, capable of surviving only in warm, clean, well-warmed shallow sea water. This is partly due to the fact that each polyp contains hundreds of microscopic creatures called dinoflagellates that need sunlight for growth and development. Polyps provide their symbionts with shelter, minerals and other substances they need. They, in turn, using solar energy, create food for themselves and share it with the corals. Thus, coral polyps require sunlight to thrive.
Coral reefs- one of the richest places on Earth in terms of species diversity. The front part of the reef descends stepwise into the sea, and it is in this part that the effects of storms are most strongly felt. But on the other side of the reef, which has ledges and ridges, there is usually a shallow, calm area - a reef lagoon, protected from large waves. The cavities and crevices in the rocks of the reef provide shelter for a variety of fish, shrimp, worms, crabs and starfish, other animals, as well as algae.
Corals are very sensitive to change environment. Oil released from tankers pollutes seawater and destroys corals, which provide food for many animals. Another danger is wastewater from fields and forest clearings. They merge into rivers and then end up in the sea. Mud makes the water cloudy, and it does not allow sunlight to pass through, which is necessary for the protozoa with which corals live in symbiosis. In addition, in many parts of the world, coral skeletons are removed from the water to be sold to tourists. This trade is destroying some reefs at an alarming rate.
Another natural enemy of corals is sea stars, which eat polyps, especially in the Indian and Pacific oceans. One of these predators can destroy 4.6 square meters of coral annually. On some reefs, starfish numbers have increased significantly, partly as part of a natural cycle and partly due to human activity.
Coral reefs are second only to tropical forests in terms of the richness of their diversity of life forms. They serve as home to millions different types animals, including a third (more than 7000) of all fish species.
Coral reefs form only in tropical or subtropical shallow waters, where the average annual temperature exceeds 20 degrees.
Corals are usually named after the shape of their colonies. This shape is determined by how polyps grow and bud new ones. The curves and folds of the coral brain resemble the shape of the human brain.
Gorgonian corals have a delicate lacy shape. Finger coral looks like a hand. There are many mushroom corals.
The Great Barrier Reef stretches more than 2,000 km along the coast of northeastern Australia. It took him millions of years to reach this size. The Great Barrier Reef is much larger than any structure created by living organisms (including humans!). The 3,000 smaller reefs are now natural parks where corals and their habitats are protected.
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 the inhabitants of corals. unicellular algae(symbiont algae), 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.
An abnormal increase in temperature occurred in 1997-1998 surface waters tropical zone of the World Ocean, which led to the massive 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 porites 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 coloring remains even when the polyp retracts its tentacles.
Coral reefs are calcareous organogenic geological structures. They mainly consist of corals, which are formed with the help of small sea animals. An individual coral, also called a polyp, is cylindrical in shape with an exoskeleton. Exoskeletons give each polyp a hard external body similar to rock. Corals produce calcium carbonate from their bodies. Because the corals remain motionless, individual polyps cluster together. They form colonies that allow them to secrete calcium carbonate and form new reefs.
Corals depend on algae and in turn, the algae find shelter in coral reefs. Live corals and algae form closest to the surface of the water on top of older, dead corals. They excrete limestone during their life cycle, which helps develop reefs. Because corals require algae to survive, they are more common in calm, shallow, clear waters where there is sufficient sunlight.
Coral reefs form in waters where warm temperatures prevail ocean currents, which largely limits their distribution to no more than 30° N. w. and Yu. w. It develops rapidly along the reefs, making them one of the most diverse in the world. Overall, coral reefs attract nearly a quarter of the world's living species.
Types of Coral Reefs
Fringing reef off the coast of Eilat (Israel)
Some coral reefs take thousands of years to form. During this time they can develop into several different forms depending on location and surrounding geological features. There are 4 main types of coral reefs:
- Fringing (shore) reefs consist of platform-like coral rocks. They are usually associated with, or are located close to the shore, separated by a semi-enclosed lagoon with deeper water.
- Barrier reefs extend along island or continental shallows, in the warm waters of the Pacific, Indian and Atlantic oceans, at a distance of several to tens of kilometers from the coast. The width of barrier reefs is hundreds of meters. The distance between the reef and the shore is filled with a lagoon. The largest barrier reef on Earth is about 2000 km long, located off the eastern coast of Australia. Barrier reefs also sometimes extend above the surface of the water.
- Atolls are ring reefs that completely cover the lagoon. Lagoons inside atolls are brackish than the surrounding seawater and often attract fewer species than the surrounding coral reef.
- Intralagoonal reefs(patch reefs) form on shallow areas of the seafloor separated by deeper water from adjacent fringing and barrier reefs.
Functions of coral reefs
Coral reefs have several various functions. They help prevent sediment from washing away and damaging shorelines. Coral reefs act as a physical barrier that helps create healthier, more protected habitats near the coast. They also capture carbon dioxide, which helps create marine conditions. Coral reefs also have economic benefits for nearby settlements. They are collected for the production of medicines and jewelry. Exotic species of fish and marine plants are caught for keeping in aquariums. Also, the magnificent underwater life of coral reefs attracts tourists from all over the world.
Environmental threats to coral reefs
Many coral reefs are experiencing a phenomenon known as bleaching, in which the corals turn white and die after the algae disappear. The bleached coral weakens and eventually dies, resulting in the death of the entire reef. The exact cause of the bleaching remains unclear, although scientists speculate that it may be directly related to changes in sea temperatures. Global climate events such as El Niño and climate change have increased the temperature of the world's oceans. Following El Niño events in 1998, approximately 30% of coral reefs were permanently lost by the end of 2000.
Sedimentation also threatens coral reefs around the world. Although they only form in clean waters, soil erosion due to mining and agriculture/forestry causes rivers to carry sediment to the ocean. Natural vegetation, such as growing along waterways, acts as a barrier to precipitation. due to the construction and development of settlements, the amount of precipitation in the sea increases.
Pesticides also enter the ocean through agricultural runoff, which increases the amount of nitrogen in the sea, causing corals to become sick and die. Negligent management practices such as overfishing and uncontrolled coral harvesting also disrupt fragile marine ecosystems.
Coral reef conservation and restoration
One suggestion for saving coral reefs is to care for them like a garden. Introducing plants to remove sediment and excessive algae growth can help temporarily keep coral reef ecosystems in balance. Reducing pesticide runoff from fields can also help reduce nitrogen levels in the sea. Reducing carbon dioxide emissions from human activities can improve the overall health of coral reefs.
Coral reefs are the equivalent of underwater forests. Twenty-five percent of all marine life lives in coral reefs. The combination of plant life and colorful sea fish makes these spots a favorite dive spot for scuba divers. Large coral reefs, such as the Great Barrier Reef, are actually made up of many smaller reefs that are connected into a single ecosystem.
Reed Bank
This reef is located in the Philippines and covers an area of 8,866 square kilometers. This natural wonder is located in the South China Sea.
Chagos Archipelago
The Chagos Archipelago in the Maldives covers an area of 12,000 square meters. km. It is the second largest atoll in the world.
Saya de Mala
Saya de Mala in the Indian Ocean covers an area of 40,000 square kilometers. These are the largest flooded banks in the world. This ridge connects the Seychelles and Mauritius islands along the Mascarene Plateau. Along with its coral reefs, the marine habitat includes grasslands for the green turtle and breeding grounds for blue whales. 
Zongsha Islands
Located in the South China Sea. It is an 80 kilometer long atoll that covers an area of 6,448 square kilometers. This atoll is a disputed territory between the People's Republic of China, Taiwan and the Philippines. 
Andros Reef
Andros is a barrier coral reef in the Bahamas that stretches for more than 200 kilometers. The island lies along the edge of an ocean chasm known as the Tongue of the Ocean. The reef expands down along the chasm to a depth of 6,000 feet instead of lying flat along the ocean floor. 
Florida Reef
This is a reef system around the coast of Florida that extends from Atlantic Ocean into the Gulf of Mexico near Key West. This reef system is approximately 7,000 years old and is 322 kilometers long. 
Mesoamerican reef
The Mesoamerican barrier coral reef system extends along the eastern coast of Central America. From its northern point, the Yucatan Peninsula in Mexico, to the southern coast of Honduras, the reef reaches a total of 943 kilometers. 
Barrier Reef of New Caledonia
This coral reef is almost 1,500 kilometers in length and is located near the former French colony of New Caledonia in the Pacific Ocean. Some parts of the reef have been damaged by nickel mining, but overall the health of this reef is quite good. 
Red Sea Reef
The Red Sea coral reef off the coasts of Egypt, Israel and Saudi Arabia is approximately 5,000 to 7,000 years old. Ten percent of the 1,200 species found in this reef live only in this area. The Red Sea coral reef includes Dahab's Blue Hole, one of the most popular and dangerous dive sites in the world. 
Great Barrier Reef
The largest and most famous coral reef is the Great Barrier Reef. Over 2,500 kilometers long, it covers an area of 348,000 square kilometers and is home to more than 400 marine species. It is also one of Australia's most prominent landmarks. Unfortunately, the reef is under threat from pollution and fishing. 