Coral

For other uses, see Coral (disambiguation).
Orders
Scleractinia

Corals are gastrovascular marine cnidarians (phylum Cnidaria; class Anthozoa) existing as small sea anemone-like polyps, typically forming colonies of many individuals. The group includes the important reef builders known as hermatypic corals, found in tropical oceans, and belonging to the subclass Zoantharia of order Scleractinia (formerly Madreporaria). The latter are also known as stony corals in as much as the living tissue thinly covers a skeleton composed of calcium carbonate. A coral "head" is formed of many individual polyps, each polyp only a few millimetres in diameter. The colony of polyps functions essentially as a single organism by sharing nutrients via a well developed gastrovascular network, and the polyps are clones, each having the same genetic structure. Each polyp generation grows on the skeletal remains of previous generations, forming a structure that has a shape characteristic of the species, but subject to environmental influences.

The hermatypic corals obtain much of their nutrient requirement from symbiotic unicellular algae called zooxanthellae, and so are dependent upon growing in sunlight. As a result, these corals are usually found not far beneath the surface, although in clear waters corals can grow at depths of 60 m (200 ft). Other corals, notably the cold-water genus Lophelia, do not have associated algae, and can live in much deeper water, with recent finds as deep as 3000 m. Corals breed by spawning, with many corals of the same species in a region releasing gametes simultaneously over a period of one to several nights around a full moon.

Corals are major contributors to the physical structure of coral reefs that develop only in tropical and subtropical waters. Some corals exist in cold waters, such as off the coast of Norway (north to at least 69° 14.24' N) and the Darwin Mounds off western Scotland. The most extensive development of extant coral reef is the Great Barrier Reef off the coast of Queensland, Australia. Indonesia is home to 581 of the world's 793 known coral reef-building coral species.

Coral types

There are several other types of corals, notably the octocorals (subclass Octocorallia) and corals classified in other orders of subclass Zoantharia: to wit, the black corals (order Antipatharia) and the soft corals (order Zoanthinaria). Extinct corals include rugose corals and tabulate coral. These two groups went extinct at the end of the Paleozoic. Most other anthozoans would be treated under the common name of "sea anemone".

Geological history

Fossil coral Heliophyllum halli from the Devonian of Canada.

Although corals first appeared in the Cambrian period, some 570 million years ago, they are extremely rare as fossils until the Ordovician period, when Rugose and Tabulate corals became widespread.

Tabulate corals occur in the limestones and calcareous shales of the Ordovician and Silurian periods, and often form low cushions or branching masses alongside Rugose corals. Their numbers began to decline during the middle of the Silurian period and they finally became extinct at the end of the Permian period. The skeletons of Tabulate corals are composed of a form of calcium carbonate known as calcite.

Rugose corals became dominant by the middle of the Silurian period, and became extinct early in the Triassic period. The Rugose corals may be either solitary or colonial, and like the Tabulate corals their skeletons are also composed of calcite. The finest details of their skeletal structures are often well preserved, and such fossils may be cut and polished.

Coral skeletons in a zoological display

Scleractinian corals diversified during the Mesozoic and Cenozoic eras and are at the height of their development today. Their fossils may be found in small numbers in rocks from the Triassic period, and they are relatively common fossils in rocks from the Jurassic and Cretaceous periods as well as the Caenozoic era. The skeletons of Scleractinian corals are composed of a form of calcium carbonate known as aragonite. Although they are geologically younger than the Tabulate and Rugose corals, the aragonite skeleton Scleractinian corals does not tend to preserve well, so it is often easier to find fossils of the more ancient Tabulate and Rugose corals.

At certain times in the geological past corals were very abundant, just as modern corals are in the warm clear tropical waters of certain parts of the world today. And like modern corals their fossil ancestors built reefs beneath the ancient seas. Some of these reefs now lie as great structures in the midst of sedimentary rocks. Such reefs can be found in the rocks of many parts of the world including those of the Ordovician period of Vermont, the Silurian period of the Michigan Basin and in many parts of Europe, the Devonian period of Canada and the Ardennes in Belgium, and the Cretaceous period of South America and Denmark. Reefs from both the Silurian and Carboniferous periods have been recorded as far north as Siberia, and as far south as Australia.

Brain coral off the coast of Belize

However, these ancient reefs are not composed entirely of corals. Algae and sponges, as well as the fossilized remains of many echinoids, brachiopods, bivalves, gastropods, and trilobites that lived on the reefs help to build them. These fossil reefs are prime locations to look for fossils of many different types, besides the corals themselves.

Corals are not restricted to just reefs, many solitary corals may be found in rocks where reefs are not present (such as Cyclocyathus which occurs in the Cretaceous period Gault clay formation of England).

As well as being important rock builders, some corals are useful as zone (or index) fossils, enabling geologists to date the age the rocks in which they are found, particularly those found in the limestones of the Carboniferous period.

Environmental effects on coral

A coral reef can be an oasis of marine life.

Coral can be sensitive to environmental changes, and as a result are generally protected through environmental laws. A coral reef can easily be swamped in algae if there are too many nutrients in the water. Coral will also die if the water temperature changes by more than a degree or two beyond its normal range or if the salinity of the water drops. In an early symptom of environmental stress, corals expel their zooxanthellae; without their symbiotic unicellular algae, coral tissues are colorless, revealing the white of their calcium carbonate skeletons, an event known as 'coral bleaching'.

A combination of temperature changes, pollution, and overuse has led to the destruction of many coral reefs around the world. This has increased the importance of coral biology as a subject of study. Climatic variations, such as El Niño, can cause the temperature changes that destroy corals.

Some coral species exhibit banding in their skeletons resulting from annual variations in their growth rate. In fossil and modern corals these bands allow geologists to construct year-by-year chronologies, a kind of incremental dating, which combined with geochemical analysis of each band, can provide high-resolution records of paleoclimatic and paleoenvironamental change.

Uses

Living corals underwater are more colorful than dead coral

Coral reefs are a great source of tourism for scuba diving or snorkelling, however this has conservational implications due to damage from removal or destruction of coral.

Ancient coral reefs on land are often mined for limestone. An example of this is the quarrying of Portland limestone from the Isle of Portland.

Reddish coral is sometimes used as a gemstone especially in Tibet. Pure red coral is known as 'fire coral' and it is very rare because of the demand for perfect fire coral for jewellery-making purposes.


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Pure red coral is known as 'fire coral' and it is very rare because of the demand for perfect fire coral for jewellery-making purposes. John Deere Buck ATV. Reddish coral is sometimes used as a gemstone especially in Tibet. John Deere Gator Utility Vehicle. An example of this is the quarrying of Portland limestone from the Isle of Portland. . Ancient coral reefs on land are often mined for limestone. Quality products and superior dealer support has played a crucial part in the success of the John Deere brand.

Coral reefs are a great source of tourism for scuba diving or snorkelling, however this has conservational implications due to damage from removal or destruction of coral. As of 2004, the company employs nearly 50,000 people in 21 countries worldwide, including the United States and Canada, the United Kingdom, China, France, Germany, Spain, Italy, India, Poland, and Mexico, among many others. In fossil and modern corals these bands allow geologists to construct year-by-year chronologies, a kind of incremental dating, which combined with geochemical analysis of each band, can provide high-resolution records of paleoclimatic and paleoenvironamental change. It is one of the oldest industrial companies in the United States. Some coral species exhibit banding in their skeletons resulting from annual variations in their growth rate. It was soon taken over by Deere's son, Charles, who established marketing centers and independent retail dealers to advance the company's sales nationwide. Climatic variations, such as El Niño, can cause the temperature changes that destroy corals. In 1868, Deere's manufacturing business was incorporated under the name Deere & Company.

This has increased the importance of coral biology as a subject of study. Deere developed and began commercially manufacturing the first cast-steel plow, an advancement that aided the late 19th century and early 20th century migration into the American Great Plains. A combination of temperature changes, pollution, and overuse has led to the destruction of many coral reefs around the world. John Deere was born in Rutland, Vermont, USA on February 7, 1804 and served a four-year blacksmith apprenticeship. In an early symptom of environmental stress, corals expel their zooxanthellae; without their symbiotic unicellular algae, coral tissues are colorless, revealing the white of their calcium carbonate skeletons, an event known as 'coral bleaching'. Since it was founded in 1837, the company has established a heritage of quality products and services providing performance that endures to customers worldwide. Coral will also die if the water temperature changes by more than a degree or two beyond its normal range or if the salinity of the water drops. Additionally, John Deere manufactures engines used in heavy equipment and provides financial services and other related activities that support the core businesses.

A coral reef can easily be swamped in algae if there are too many nutrients in the water. John Deere is also a major manufacturer of construction equipment. Coral can be sensitive to environmental changes, and as a result are generally protected through environmental laws. Deere & Company (NYSE:DE) an American corporation based in Moline, Illinois is the leading manufacturer of agricultural machinery including tractors, combine harvesters, balers, and forestry equipment; and a leading supplier of equipment used in lawn, grounds and turf care such as ride-on lawn mowers, all of which are known for their distinctive green and yellow color scheme. As well as being important rock builders, some corals are useful as zone (or index) fossils, enabling geologists to date the age the rocks in which they are found, particularly those found in the limestones of the Carboniferous period. Agreentech. Corals are not restricted to just reefs, many solitary corals may be found in rocks where reefs are not present (such as Cyclocyathus which occurs in the Cretaceous period Gault clay formation of England). John Deere Health Care, Inc.

These fossil reefs are prime locations to look for fossils of many different types, besides the corals themselves. John Deere Capital Corporation. Algae and sponges, as well as the fossilized remains of many echinoids, brachiopods, bivalves, gastropods, and trilobites that lived on the reefs help to build them. AGRIS Corporation. However, these ancient reefs are not composed entirely of corals. Reefs from both the Silurian and Carboniferous periods have been recorded as far north as Siberia, and as far south as Australia.

Such reefs can be found in the rocks of many parts of the world including those of the Ordovician period of Vermont, the Silurian period of the Michigan Basin and in many parts of Europe, the Devonian period of Canada and the Ardennes in Belgium, and the Cretaceous period of South America and Denmark. Some of these reefs now lie as great structures in the midst of sedimentary rocks. And like modern corals their fossil ancestors built reefs beneath the ancient seas. At certain times in the geological past corals were very abundant, just as modern corals are in the warm clear tropical waters of certain parts of the world today.

Although they are geologically younger than the Tabulate and Rugose corals, the aragonite skeleton Scleractinian corals does not tend to preserve well, so it is often easier to find fossils of the more ancient Tabulate and Rugose corals. The skeletons of Scleractinian corals are composed of a form of calcium carbonate known as aragonite. Their fossils may be found in small numbers in rocks from the Triassic period, and they are relatively common fossils in rocks from the Jurassic and Cretaceous periods as well as the Caenozoic era. Scleractinian corals diversified during the Mesozoic and Cenozoic eras and are at the height of their development today.

The finest details of their skeletal structures are often well preserved, and such fossils may be cut and polished. The Rugose corals may be either solitary or colonial, and like the Tabulate corals their skeletons are also composed of calcite. Rugose corals became dominant by the middle of the Silurian period, and became extinct early in the Triassic period. The skeletons of Tabulate corals are composed of a form of calcium carbonate known as calcite.

Their numbers began to decline during the middle of the Silurian period and they finally became extinct at the end of the Permian period. Tabulate corals occur in the limestones and calcareous shales of the Ordovician and Silurian periods, and often form low cushions or branching masses alongside Rugose corals. Although corals first appeared in the Cambrian period, some 570 million years ago, they are extremely rare as fossils until the Ordovician period, when Rugose and Tabulate corals became widespread. Most other anthozoans would be treated under the common name of "sea anemone".

These two groups went extinct at the end of the Paleozoic. Extinct corals include rugose corals and tabulate coral. There are several other types of corals, notably the octocorals (subclass Octocorallia) and corals classified in other orders of subclass Zoantharia: to wit, the black corals (order Antipatharia) and the soft corals (order Zoanthinaria). .

Indonesia is home to 581 of the world's 793 known coral reef-building coral species. The most extensive development of extant coral reef is the Great Barrier Reef off the coast of Queensland, Australia. Some corals exist in cold waters, such as off the coast of Norway (north to at least 69° 14.24' N) and the Darwin Mounds off western Scotland. Corals are major contributors to the physical structure of coral reefs that develop only in tropical and subtropical waters.

Corals breed by spawning, with many corals of the same species in a region releasing gametes simultaneously over a period of one to several nights around a full moon. Other corals, notably the cold-water genus Lophelia, do not have associated algae, and can live in much deeper water, with recent finds as deep as 3000 m. As a result, these corals are usually found not far beneath the surface, although in clear waters corals can grow at depths of 60 m (200 ft). The hermatypic corals obtain much of their nutrient requirement from symbiotic unicellular algae called zooxanthellae, and so are dependent upon growing in sunlight.

Each polyp generation grows on the skeletal remains of previous generations, forming a structure that has a shape characteristic of the species, but subject to environmental influences. The colony of polyps functions essentially as a single organism by sharing nutrients via a well developed gastrovascular network, and the polyps are clones, each having the same genetic structure. A coral "head" is formed of many individual polyps, each polyp only a few millimetres in diameter. The latter are also known as stony corals in as much as the living tissue thinly covers a skeleton composed of calcium carbonate.

The group includes the important reef builders known as hermatypic corals, found in tropical oceans, and belonging to the subclass Zoantharia of order Scleractinia (formerly Madreporaria). Corals are gastrovascular marine cnidarians (phylum Cnidaria; class Anthozoa) existing as small sea anemone-like polyps, typically forming colonies of many individuals.

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