Coral reef

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See also: fringing reef, coral atoll, structure and distribution of coral reefs Coral reefs
Most were created after the last glacial period when ice melt caused a rise sea level and flooding on the continental shelves. This means that most coral reefs are less than 10,000 years. As communities of coral reefs have been established on the shelves, they have constructed reefs that grew up, the pace of rising sea levels. Reefs that has not kept pace may be drowned reefs, covered with water until there was not enough light for the survival of others.
Coral reefs are also found in the deep sea far from continental shelves and around oceanic islands such as atolls. The vast majority of these islands of the ocean reef are of volcanic origin. The few exceptions are of tectonic origin, where plate movement lifted the ocean bottom to the surface.
In 1842, Charles Darwin published his first monograph, structure and distribution of coral reefs. There, he outlined his theory of the formation of coral atolls, he conceived an idea for the voyage of the Beagle. His theory was that the atolls were formed by uplift and subsidence of the crust beneath the oceans. Darwin’s theory describes a sequence of three stages of the formation of atolls. It begins with a fringing reef forms around a volcanic island off the island and grants the ocean floor. As subsidence continues, the fringing reef becomes a barrier reef, and, finally, a coral atoll.
Darwin’s theory begins with a volcanic island off
As the island and lost on the ocean floor, coral growth built a fringing reef, often including a shallow lagoon between the land and the main reef
As subsidence continues the fringing reef becomes a barrier reef further from lagoon shore with more and more inside
Finally, the well of the island under the sea and the reef is an atoll surrounding a lagoon open
A fringing reef may take ten thousand years to form, and an atoll may take up to 30 million years
A small atoll in the Maldives.
Darwin predicted that in each lagoon is a base of bedrock the remains of the original volcano. drilling that followed proved correct. Darwin’s theory followed from his understanding that the coral polyps grow in the clean seas of the tropics where the water is agitated, but can live only in a limited water depth, starting just below the tide low. When the level of the underlying land remains the same, the corals grow around the side to form what he called fringing reefs, and may eventually develop from the bank to become a barrier reef. When the field is increasing, fringing reefs may develop around the coast, but raised reefs above sea level dies and becomes white limestone. The disappearance of the earth slowly, the fringing reefs to keep pace with growth from the top on a base of dead coral, forming a barrier reef enclosing a lagoon between the reef and the shore. A coral reef can encircle an island, and once the wells of the island below sea level to an almost circular atoll of coral growth continues to monitor the level of the sea, forming a central lagoon. barrier reefs and atolls are generally not form complete circles, but are split in places by the storms. If the earth disappear too quickly or rising sea levels too quickly, the coral dies because it is below the depth of living.
In general, the two major variables determining the geomorphology, or form, coral reefs are the nature of the underlying substrate on which they rest, and the history of changes in sea level relative to the substrate.
As an example of how reefs Reefs are formed on continental shelves, the structure of current living reefs of the Great Barrier Reef began to grow about 20,000 years. The sea level was then 120 meters (390 feet) lower than it is today. As sea level rose, water and coral encroached on what had been the hills of the coastal plain. In 13,000 years the sea level was 60 meters (200 feet) lower than today, and the hills of the coastal plain were, by then, the continental islands. As rising sea level has continued most of the continental islands were submerged. The corals could then invade the hills, forming the islands and reefs present. The sea level on the Great Barrier Reef has not changed significantly in the last 6000 years, and age structure of reef life currently estimated at between 6,000 and 8,000 years. Although the Great Barrier Reef formed along a continental shelf, and not around a volcanic island, the same principles apply as described by Darwin’s theory above. The Great Barrier Reef development was halted at the stage of the reef, since Australia is not about to plunge. She formed reefs in the world biggest obstacle 3001000 feet (330-1100 meters) from shore, and 2,000 km (1,200 miles) long.
Healthy coral reefs grow horizontally from January to March cm (0 39. 1. 2 inches) per year, and vertical growth of 1-25 inches (0. 412) a year, but they are limited to higher growth at a depth of 150 meters (490 ft) because they need sunlight, and can not grow above sea level.

Types The three types of reefs are major
a Fringing reef reef that is directly connected to a land border or with a shallow channel or lagoon.
Barrier Reef a reef separated from the mainland or island shore by a lagoon.
Atoll Reef A barrier reef more or less circular or continuous stretching around a lagoon without a central island.
Other reef types or variants are:
Patch Reef isolated comparatively small reef outcrops, usually in a lagoon or bay, usually circular and surrounded by sand or seaweed. reefs are frequent.
apron reef looks like a small reef fringing reef, but more sloping, extending downward and a point or edge of the peninsula.
Bank reefs linear or semi-circular shaped-outline, larger than a reef.
Ribbon Reef A long and narrow, somewhat winding reef, usually associated with an atoll lagoon.
; Table isolated reef reef, approaching an atoll type, but without a lagoon.
inhabited Cay in the Maldives
microatolls certain species of coral communities form called microatolls. The vertical growth of microatolls is limited by average tidal height. By analyzing the different growth morphologies, microatolls can be used as a hard low-resolution models of sea level change. microatolls fossils can be dated by radiocarbon dating. These methods have been used to reconstruct the sea level of the Holocene.
Cays small, low-lying, sandy island formed on the surface of a coral reef. Material eroded from lots of coral on the parts of the reef or lagoon, forming a zone of altitude. Plants can stabilize cays enough for them to be habitable by humans. Cays occur in tropical environments in the Pacific, Atlantic and Indian Ocean (including the Caribbean and the Great Barrier Reef and Belize Barrier Reef) where they provide living space and agricultural land for hundreds of thousands of people. The surrounding reef ecosystems also provide food and building materials for the Islanders.
When a coral reef can not follow the sinking of a volcanic island, a seamount Marine Guyot or formed. Seamounts and seamounts are below the surface of the ocean and can accommodate many species, depending on their location and depth. Seamounts are rounded at the top and seamounts are flat. The flat top of the Guyot, also called tablemount, due to erosion by waves, winds and phenomena atmosphériques.Distribution

Location of coral reefs.
Border for 20 C isotherms. Most corals live this limit. Rating cooler waters caused by ascending the southwest coast of Africa and off the coast of Peru.
This map shows areas of upwelling in red. Coral reefs are not found in coastal areas where cooler nutrient-rich upwellings are
Coral reefs are estimated to cover 284,300 km ² (109,800 square miles), which is a little less one percent of the area occupied by the world’s oceans. The Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) account for 91. 9% of the total. Southeast Asia accounts for 32. 3% of that figure, while the Pacific including Australia accounts for 40. 8%. Atlantic and Caribbean coral reefs only account for 7. 6%.
Although corals exist in both temperate and tropical waters, reefs in shallow waters only form in an area extending from 30 N to 30 S of the equator. Tropical corals do not grow at depths of more than 50 meters (160 ft). The optimum temperature for most of the coral reef is 2627 C, and some reefs exist in waters below 18 C. However reefs in the Persian Gulf have adapted to temperatures of 13 C in winter and 38 ° C été.coralliens />
Coral reefs are rare along the U.S. west coast and along the West African coast. This is mainly due to strong upwelling and cold coastal currents that reduce water temperatures in these areas (respectively Peru, Benguela and Canary Islands rivers). The corals are rarely found along the coasts of South Asia from the eastern tip of India (Madras) on the border of Bangladesh and Myanmar. They are rare along the coast around north-eastern South America and due to the release of freshwater from the Amazon and Ganges Rivers respectively in Bangladesh.
Reefs reefs and major areas of the world’s reefs
The Great Barrier Reef – largest coral reef system in the world, Queensland, Australia.
Belize Barrier Reef – the second largest the world, stretching from southern Quintana Roo, Mexico along the coast of Belize to the Bay Islands of Honduras.
The New Caledonia Barrier Reef – the second longest barrier reef double in the world with a length of about 1500 kilometers (930 miles).
The Andros, Bahamas Barrier Reef – the third largest in the world after the east coast of Andros Island , Bahamas between Andros and Nassau.
Red Sea Coral Reef – located off the coast of Israel, Egypt, Sudan, Eritrea, Djibouti, Somalia, Jordan, Saudi Arabia and Yemen.
Pulley Ridge – deepest photosynthetic coral reef, Florida.
numerous reefs scattered over the Maldives.
Ghe Raja Ampat Islands in Indonesia ‘s West Papua province has the highest diversity of marine connues.Biologie

Anatomy of a coral polyp.
See also: Coralcoralliens
Live should be regarded as small live animals included in the calcium carbonate. It is a mistake to think of coral as plants or rocks. Coral is formed from the accumulation of individual animals, polyps, arranged in various forms. The polyps are usually small, but they can vary in size from a pinhead to a foot in diameter. Coral polyps grow with calcium carbonate other organizations filed, based on coral as a skeleton beneath and around them, pushing the “coral head” or top and toward the outside polyps. Waves, herbivorous fish (such as parrots), sea urchins, sponges and other forces and organisms break down the coral skeletons into fragments that settle into spaces in the reef structure. Many other organisms living in the reef community contribute calcium carbonate skeleton in the same way. coralline algae are important contributors to the structure of coral reef in the parts subjected to greater forces by waves (such as the reef front facing the open ocean). The limestone deposit in the leaves of algae on the surface of coral, which strengthen it.
Reef-building corals or hermatypic only found in the photic zone (more than 50 m deep) the depth to which sunlight penetrates enough water for photosynthesis. Coral polyps are not photosynthesis, but they have a symbiotic relationship with unicellular organisms called zooxanthellae, these cells in the tissues of coral polyps carry out photosynthesis and produce more organic nutrients that are then used by the coral polyps. Because of this relationship, coral reefs grow much faster in clear water, which admits more sunlight. Indeed, the relationship is responsible for coral reefs in the sense that without their symbionts, coral growth is too slow for the corals to form structures impressive reef. Corals get up to 90% of their nutrients from their zooxanthellae symbionts.

Table coral polyps Focus arranged on a coral, waving their tentacles. There may be thousands of polyps on a single branch of coral.
Corals can reproduce sexually and asexually. An individual polyp may use both reproductive modes within its lifetime. Corals reproduce sexually by either internal or external fertilization. Reproductive cells are on the mesentery membranes that radiate inward from the layer of tissue that lines the cavity of the stomach. Some corals are hermaphroditic mature adults, others are exclusively male or female. Some even change sex as they grow.
Fertilized eggs develop in the interior of the polyp for a period ranging from several days to several weeks. Subsequent development produces a tiny larva called planula. Externally fertilized eggs develop during spawning synchronized. egg output Polyps and sperm into the water at the same time. The eggs are scattered over a vast territory. The spawning depends on four factors: the time of year water temperature, and tidal and lunar cycles. Spawning is most effective when there is little variation between high and low tides. The less water movement, the greater the chances of fertilization. ideal time occurs in spring. Release of eggs or larvae planulae usually occurs during the night and sometimes in phase with the lunar cycle (36 days after full moon). The period of release to settlement lasts only a few days, but some planulae can survive afloat for several weeks (7, 14). They are vulnerable to heavy predation and adverse environmental conditions. For the lucky few who survive to attach to the substrate, the challenge comes from competition for food and space.
There are about a thousand species of corals that build different forms such as wrinkled brain, cabbage, senior tennis, deer wood strands of wire, and pillars.

Brain coral staghorn coral
wire spiral pillar coral
Coral

paradox paradox Darwin Darwin
Coral. . . seems to grow when ocean waters are warm, low, clear and agitated, a fact that Darwin had already noted his passing by Tahiti in 1842.
This is a fundamental paradox, shown quantitatively by the seeming impossibility of balance the inputs and outputs that control nutrient metabolism of coral polyps.
Recent oceanographic research has highlighted the reality of this paradox by stating that the oligotrophic ocean photic zone persists until ‘at the reef crest wave battered. When you approach the edges of reefs and atolls in the near-desert of the open sea, the virtual absence of living matter is suddenly a multitude of life without transition. So why is there something rather than nothing, and more specifically, where do the nutrients necessary for the proper functioning of this machine are amazing coral reefs? Francis Rougerie
During his voyage on the Beagle, Darwin described tropical coral reefs as an oasis in the desert of the ocean. He reflected on the paradox of tropical coral reefs, which are among the richest ecosystems and most diverse on earth, flourish when they are surrounded and supported by the tropical ocean waters that provide little nutrients. It was a challenge for scientists to explain this paradox.
Coral reefs cover just under one percent of global ocean surface, but they support more than one quarter of all marine species. This large number of species results in complex food webs with large predatory fish eat smaller fish that eat zooplankton forage even smaller and so on. However, all food chains ultimately depend on plants, which are the primary producers. And primary productivity on a coral reef is very high, resulting in a typical biomass production of 5-10g C m2 day1.
Tropical waters are often described as clear. Because they are deficient in nutrients and plankton to drift. The sun shines all year round in the tropics, the warming of the surface layer of the ocean so it is less dense than the subsurface layers. The warming of the water is separated from the water fountain with a stable thermocline, where temperatures can change quickly. This keeps the waters warm surface floating above the cooler deeper waters. There is little exchange between these layers. Organisms that die in aquatic environments in general at the bottom of where they decompose. This decomposition releases nutrients as nitrogen, phosphorus and potassium. These nutrients, N, P and K are necessary for plant growth, but in the tropics, they are not directly recycled to the surface.
The plants are the base of the food chain, and the necessary light and nutrients, they are growing. In the ocean of these plants are mainly a type of plankton, microscopic phytoplankton that drift in the water column. They need sunlight for photosynthesis, carbon fixation of powers, so they are only found in surface waters. But they also needed nutrients. Phytoplankton use nutrients rapidly in surface waters, and in the tropics these nutrients are generally not replaced due to the thermocline.
Coral polyps
The situation of coral reefs is different. The lagoons are formed by the upward growth of coral reefs filled with material eroded from the reef and the island. They became refuges for marine life, providing protection against waves and storms.
More importantly, the nutrients are recycled, and not as they are lost in the open ocean. In coral reefs and lagoons, producers include phytoplankton and marine worms, algae, coralline algae, especially types of small algae called grass, spending their nutrients for the corals. Phytoplankton are eaten by fish and crustaceans, which also pass nutrients along the food chain. Recycling so that fewer nutrients are needed overall to support the community.
Corals harbor many symbiotic organisms. In particular, there is a remarkable symbiosis between coral and algae, microscopic, single cell known as a dinoflagellate zooxanthellae. The fact endosymbiotic zooxanthellae with coral polyp, which is, she lives in the tissues of the polyp. There, it absorbs solar energy with special pigments, using photosynthesis to provide the polyp with organic nutrients as glucose, glycerol and amino acids. Zooxanthellae can provide up to 90% of energy needs of corals. In return, as an example of mutualism, coral provides the zooxanthellae, averaged one million per cubic centimeter of coral, a relatively safe place to live and a steady supply of carbon dioxide needed for photosynthesis.
The corals are nocturnal eaters. Here in the darkness the coral polyps have extended their tentacles to feed on zooplankton
The color of coral depends on the type they host zooxanthellae corals
also absorb nutrients, including nitrogen and phosphorus directly into the water. Many corals extend their tentacles into the night to take the zooplankton that brush when the water is choppy. Zooplankton provides the polyp with nitrogen, and the actions of the nitrogen polyps with zooxanthellae, which also require this element. The pigments of different species of coral zooxanthellae provide their different colors. Coral loses its zooxanthellae becomes white and is said to be bleached, a condition which, unless corrected may lead to the death of coral.
A 2001 paper reported that sponges are another key to explain Darwin’s Paradox. These sponges live in the crevices of coral reefs. They are efficient filter feeders, and in the Red Sea they consume about sixty percent of the phytoplankton that drift by. The sponges absorb nutrients phytoplankton are then excreted in a form, the coral can use.
Researchers in 2002 explained why coral thrives better in rough water. They found the surface roughness of coral is the key. Normally there is a boundary layer of still water over a submerged object, which acts as a gate. But when the waves breaking on the coral very rough edges of the boundary layer is disrupted, allowing access to the corals and few nutrients that are there. The researchers say that the turbulent water promotes rapid growth of coral and thousands of branches. While ecosysemss reefs are great at recycling, with waste of a species to become the food of another, the researchers also say that without the gains nutrition coral rough surfaces, even the most efficient recycling would leave corals who want to nutrients.
In 2004, another agency symbiotic bacteria called cyanobacteria, was found to provide soluble nitrates for the reef by nitrogen fixation.
Coral reefs are often dependent on other habitats such as seagrasses and mangroves in the surrounding area for the supply of nutrients. seaweed and mangroves supply and dead animals that are rich in nitrogen and also serve to feed the fish and animals of the reef by providing wood and vegetation. The reefs in turn protect mangroves and seagrass beds from waves and produce sediment mangroves and seagrass beds in the root zones in.

ecosystems of coral reefs contain number of distinct areas that represent different types of habitats for fish and invertebrates. Usually, three main zones are recognized: the reef show (outermost part of the deepest and the reef), reef crest (zone shallower and closer to the ocean waves break) and back reef (behind reef crest and closer to the coast, with calm waters protected) which is also frequently called the reef lagoon.
The three areas are physically and ecologically interconnected to some extent with the life of coral and ocean processes ample opportunities for exchange of ocean water, sediment, nutrients, and marine life from each other.
Thus, they should normally be regarded as integral elements the ecosystem of coral reefs, each playing a role in supporting fish assemblages that characterize diverse and abundant coral reefs.
Most coral reefs are in shallow waters less than fifty meters deep. Some are on tropical continental shelves where fresh, nutrient-rich upwelling does not occur, as the Great Barrier Reef. Others are in the depths of the ocean surrounding the islands and atolls that, as the Maldives. The reefs surrounding the islands are formed when the islands disappear in the ocean, and atolls are formed when an island in the subsidies below the sea surface
Moyle and Cech are six major areas, While most reefs have only some areas.
water in the surface area of the reef is often agitated. This diagram represents a reef on a continental shelf. The waves travel in water left on the ground outside the reefs until they meet the slope of coral reefs or before. Then, the waves pass over the shallow reef crest. When a wave enters shallow water, the shoals, which is, it slows down and increases the wave height.
The reef surface is the shallowest part of the reef. It is subject to the constant rise and the waves rise and fall of tides. When the waves of the water passes over the shallow areas, they stand, as shown in the diagram at right. This means that the water in the surface area of the reef is often agitated. These are the precise conditions under which coral growth. Superficiality means that there is much light for photosynthesis, and agitated the water promotes the ability of coral to feed on plankton. However other organisms such as fish and invertebrates, should be able to withstand robust to flourish in this area.
The gross floor reef is the bottom of the shallow sea around a reef. This field applies to the reefs on the continental shelves. The reefs around the tropical islands and atolls drops abruptly to great depths, and not a floor outside the reefs. Usually sand, soil outside the reefs often supports seagrasses that are important feeding areas for reef fish.
The reef is falling for his first 50 meters, a habitat for many reef fish that find shelter on the cliff and plankton in the water nearby. The landing zone is mainly applicable to reefs around oceanic islands and atolls.
The reef face is the area above the ground or coral the reef.

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