what is a reef in geography

A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water.

Full Answer

What is the definition of a reef?

Rock is a legal term and does not refer to any particular type of geological formation. For example, a sandbar can be considered a rock. Reefs are formations of coral, roughly shaped like mountains, which run just below the surface of the water. Atolls are small, U-shaped islands or reefs which are made from coral.

What is the meaning of reef?

A reef is a ridge of material at or near the surface of the ocean. Reefs can occur naturally. Natural reefs are made of rocks or the skeletons of small animals called corals. Reefs can also be artificial—created by human beings.

What is the geography of coral reefs?

Coral reefs can be found in tropical destinations around the world, mostly in areas around the equator where the water is warmer. More than 100 countries have a coral reef within their borders, and over half of the world’s coral reefs are found within six countries: Australia, Indonesia, Philippines, Papua New Guinea, Fiji, and the Maldives.

What is the definition of reef crest?

The reef crest, or algal ridge, is the highest point of the reef, and is almost always exposed at low tide. The reef crest is exposed to the full fury of incoming waves, and living corals are practically nonexistent here. Small crabs, shrimps, and other animals often live in the cavities under the reef crest, protected from waves and predators.

What is a reef simple definition?

1a : a chain of rocks or coral or a ridge of sand at or near the surface of water — compare atoll, barrier reef. b : a hazardous obstruction. 2 : lode, vein.

Why is it called a reef?

reef (n. 1) "low, narrow rock ridge underwater," 1580s, riffe, probably via Dutch riffe, from a Scandinavian source such as Old Norse rif "ridge in the sea; reef in a sail," literally "rib" (see rib (n.)). Also extended to the low islands formed by coral debris or to any extensive elevation of the bottom of the sea.

What a reef is and its purpose?

Coral reefs protect coastlines from storms and erosion, provide jobs for local communities, and offer opportunities for recreation. They are also are a source of food and new medicines. Over half a billion people depend on reefs for food, income, and protection.

Is reef a land or water?

A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes—deposition of sand, wave erosion planing down rock outcrops, etc.

How is a reef formed?

Coral reefs begin to form when free-swimming coral larvae attach to submerged rocks or other hard surfaces along the edges of islands or continents. As the corals grow and expand, reefs take on one of three major characteristic structures — fringing, barrier or atoll.

Can a reef be an island?

A coral reef island is composed of rocks from coral skeletons, that is, biologically formed calcium carbonate materials derived from the adjacent coral reef and raised above sea level. Coral reef island sizes range from a few square meters to many square kilometers, and they come in all shapes and proportions.

What are the kinds of reef?

The three main types of coral reefs are fringing, barrier, and atoll. Schools of colorful pennantfish, pyramid, and milletseed butterflyfish live on an atoll reef in the Northwestern Hawaiian Islands. The most common type of reef is the fringing reef.

What kinds of reefs are there?

Scientists generally agree on four different coral reef classifications: fringing reefs, barrier reefs, atolls, and patch reefs. Fringing reefs grow near the coastline around islands and continents.

What type of reef is the most common?

Fringing reefs are the most common type of coral reef. They grow seaward near coastlines of islands and continents, usually separated from the shore by no more than a shallow lagoon.

Where are reefs found?

Coral reefs are found in shallow water where sea surface temperatures range from 68° F to 97° F. More than 90 percent of the world's coral reefs occur in the Indo-West Pacific biogeographic region. Reef systems also can be found in the West Atlantic, East Atlantic, and East Pacific oceans between 30° N and 30° S.

Are coral reefs alive?

Corals are animals However, unlike rocks, corals are alive. And unlike plants, corals do not make their own food. Corals are in fact animals. The branch or mound that we often call “a coral” is actually made up of thousands of tiny animals called polyps.

What is the largest coral reef?

the Great Barrier ReefStretching for 1,429 miles over an area of approximately 133,000 square miles , the Great Barrier Reef is the largest coral reef system in the world. The reef is located off the coast of Queensland, Australia, in the Coral Sea.

What makes a reef a reef?

A reef is a ridge of material at or near the surface of the ocean. Reefs can occur naturally. Natural reefs are made of rocks or the skeletons of small animals called corals. Reefs can also be artificial—created by human beings.

What does a reef symbolize?

Together, the circular shape and the evergreen material make the wreath a representation of eternal life. It is also a representation of faith, as Christians in Europe often placed a candle on the wreath during Advent to symbolize the light that Jesus brought into the world.

What does reef mean in sailing?

Reefing reduces the area of a sail, usually by folding or rolling one edge of the canvas in on itself and attaching the unused portion to a spar or a stay, as the primary measure to preserve a sailing vessel's stability in strong winds. Restoring full sail area is termed shaking out a reef.

What makes a coral reef?

A coral reef is made of thin layers of calcium carbonate Stony corals (or scleractinians) are the corals primarily responsible for laying the foundations of, and building up, reef structures. Massive reef structures are formed when each individual stony coral organism—or polyp—secretes a skeleton of calcium carbonate.

Why are coral reefs important?

Reefs provide a variety of economic benefits, including recreational activities, tourism, coastal protection, habitat for commercial fisheries, and preservation of marine ecosystem s. “Corals are important to us for many reasons,” Maurin says. “From a practical point of view, they can help protect coastline s from storm events, for instance, ...

What percentage of marine species live in coral reefs?

Scientists estimate that 25 percent of all marine species live in and around coral reefs, making them one of the most diverse habitats in the world. Paulo Maurin, education and fellowship coordinator for NOAA’s Coral Reef Conservation Program, says the reefs are invaluable to our planet’s biodiversity.

What will happen to coral reefs in the next few decades?

The combination of rising ocean temperatures and increased acidity will likely cause major changes to coral reefs over the next few decades and centuries. New research suggests that corals may begin to dissolveat atmospheric CO2 concentrations as low as 560 parts per million, which could be reached by the middle of this centuryif emissions are not curbed. In 2010, atmospheric carbon dioxide levels were around 390 parts per million.

What happens to corals when the water warms?

As the water warms, zooxanthellae are expelled from a coral’s tissue, causing it to lose its color and a major source of food. This process is known as “coral bleaching.”

What are rocky oceans made of?

rocky ocean features made up of millions of coral skeletons.

Do algae provide food for corals?

In return for that protection, the algae provide their host with food produced through photosynthesis. Zooxanthellae also provide corals with their striking colors. This symbiotic relationship is strongly dependent on the temperature of the surrounding water.

What is a reef?

A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes— deposition of sand, wave erosion planing down rock outcrops, etc.—but there are also reefs such as ...

Where is the coral reef located?

Coral reef at Nusa Lembongan, Bali, Indonesia. Pamalican island with surrounding reef, Sulu Sea, Philippines. A reef surrounding an islet. A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes— deposition of sand, ...

What are the major reef builders?

Corals, including some major extinct groups Rugosa and Tabulata, have been important reef builders through much of the Phanerozoic since the Ordovician Period. However, other organism groups, such as calcifying algae, especially members of the red algae Rhodophyta, and molluscs (especially the rudist bivalves during the Cretaceous Period) have created massive structures at various times. During the Cambrian Period, the conical or tubular skeletons of Archaeocyatha, an extinct group of uncertain affinities (possibly sponges), built reefs. Other groups, such as the Bryozoa have been important interstitial organisms, living between the framework builders. The corals which build reefs today, the Scleractinia, arose after the Permian–Triassic extinction event that wiped out the earlier rugose corals (as well as many other groups), and became increasingly important reef builders throughout the Mesozoic Era. They may have arisen from a rugose coral ancestor. Rugose corals built their skeletons of calcite and have a different symmetry from that of the scleractinian corals, whose skeletons are aragonite. However, there are some unusual examples of well-preserved aragonitic rugose corals in the Late Permian. In addition, calcite has been reported in the initial post-larval calcification in a few scleractinian corals. Nevertheless, scleractinian corals (which arose in the middle Triassic) may have arisen from a non-calcifying ancestor independent of the rugosan corals (which disappeared in the late Permian).

What are the different types of reefs?

Reef types include fringing reefs, barrier reefs , and atolls . A fringing reef is a reef that is attached to an island. A barrier reef forms a calcareous barrier around an island resulting in a lagoon between the shore and the reef. An atoll is a ring reef with no land present.

How are reefs built?

Many reefs are built using objects that were built for other purposes, for example by sinking oil rigs (through the Rigs-to-Reefs program), scuttling ships, or by deploying rubble or construction debris. Other artificial reefs are purpose built (e.g. the reef balls) from PVC or concrete.

Why are ancient reefs important to geologists?

Ancient reefs buried within stratigraphic sections are of considerable interest to geologists because they provide paleo-environmental information about the location in Earth's history. In addition, reef structures within a sequence of sedimentary rocks provide a discontinuity which may serve as a trap or conduit for fossil fuels or mineralizing fluids to form petroleum or ore deposits.

What is the framework of a coral reef?

Reefs are held up by a macroscopic skeletal framework. Coral reefs are an example of this kind. Corals and calcareous algae grow on top of one another and form a three-dimensional framework that is modified in various ways by other organisms and inorganic processes.

How many visitors to the Australian reef each year?

This richness and uniqueness make the reef crucial for tourism and the Australian economy—it attracts at least 1.6 million visitors every year.

Why is it important to protect coral reefs?

. . provide food and livelihoods for hundreds of millions of people around the world, they protect shorelines from erosion, and they contain compounds that are used to treat human ailments. . . .

Why is the Great Barrier Reef bleached?

This process is called bleaching because the coral becomes white. A 2018 study showed that about one-third of the Great Barrier Reef had experienced substantial damage from bleaching.

Why do corals need algae?

In this way, the algae provide food and oxygen (a byproduct of photosynthesis) for the coral, and the coral protects and provides nutrients for the algae. The algae also give coral its many colors. The coral and algae have evolved together to survive within a particular temperature range.

What is the most common pest that eats coral reefs?

One major pest species is the crown-of-thorns starfish (Acanthaster planci). A starfish may sound harmless, but these venomous creatures voraciously eat coral. Every so often, their numbers spike. Some scientists think these starfish caused over half of the reef damage from 1985 to 2012.

How much of the Great Barrier Reef has been damaged by bleaching?

A 2018 study showed that about one-third of the Great Barrier Reef had experienced substantial damage from bleaching. The researchers also found that large amounts of coral had died in the warming water almost immediately—even before there was time to expel their algal partners.

What are the threats to coral reefs?

Climate change is not the only threat to the reef. Chemical runoff and other forms of pollution, coastal development, and overfishing all can harm coral and reduce biodiversity. So can large storms such as cyclones. Species that live in the reef can also cause damage.

What is coral reef?

A coral reef is actually a complex of features, only part of which is a living coral or algal framework, although the other associated features result from this live segment . The accumulations of carbonate sandand mud provide a habitatfor sea grasses and mangrovesand for almost inconspicuous blue-green algal mats. These plants and algae trap and stabilize sediment, and their accumulations are also accreted to the whole reef complex. Stormsand surf heap up fragmental material into beachesand shoals, and the shoals may develop into low sandy or rubbly islets or cayson top of the reef.

What are the features of a coral reef?

The accumulations of carbonate sand and mud provide a habitat for sea grasses and mangroves and for almost inconspicuous blue-green algal mats. These plants and algae trap and stabilize sediment, and their accumulations are also accreted to the whole reef complex. Storms and surf heap up fragmental material into beaches and shoals, and the shoals may develop into low sandy or rubbly islets or cays on top of the reef.

How do coral polyps grow?

Initial polyps divide themselves into daughter polyps, and they divide in turn, growing into colonies that can be up to several metres in diameter, all held together in one continuous rigid calcareous skeleton. They remain attached to the seafloor and become so large and heavy that only storms disturb them. Under the right conditions, generally clear and well-circulating water that is not too rough, the corals grow profusely side by side, even on and over each other. The corals in effect build limestonebecause their skeletons are made of calcium carbonate.

How are coral reefs formed?

Coral reef, ridge or hummock formed in shallow ocean areas by algae and the calcareous skeletons of certain coelenterates, of which coral polyps are the most important. A coral reef may grow into a permanent coral island.

Why do coral reefs shape?

The shape of coral reefs, while at least in part due to the tendency of reef builders to grow upward and outward toward the prevailing winds and currents, is also the result of changes of sea level during the last 2,000,000 years or more.

How deep can coral grow?

Reef-building corals, chiefly the stony corals or Scleractinia, grow best in shallow sunlit water, between the low-water mark and a depth of 11 metres (36 feet), but they can still construct reefs in water as deep as 40 metres (about 130 feet), and they may have a sparse existence between 40 and 55 metres (130 and 180 feet).

What is the maximum temperature for coral reefs?

These corals prefer water of normal salinity with an annual maximum temperature above 22 °C (72 °F) but below 28 °C (about 82 °F). Their reef-building activities, however, may be carried on in waters whose minimum temperature in winter is not less than 15 °C (59 °F).

Where are coral reefs found?

Known coral reefs are found in the deep sea far from the continental shelves and around oceanic islands as atolls, most of which are volcanic in derivation. The few exceptions have tectonic origins where plate movements have lifted the ocean floor on the surface.

Why are coral reefs called barrier reefs?

According to this theory, coral reefs were initially fringing reefs on slanting shores, after which they became barrier reefs when the shores sank, with a water channel between them and the land. If the land is an island that sinks entirely, it results in the formation of an atoll, which means the sinking causes the thickness of the reefs.

What is the name of the mound of limestone that forms the upper surface of the ocean?

A quarter of marine species make their homes in coral reefs. A coral reef is a ridge or a mound of limestone whose upper surface is near the surface of the sea. Coral reefs are made up of calcium carbonate. The last glacial period marked the formation of coral reefs when melting ice caused the sea levels to rise and flood the continental plates.

What is the name of the channel that separates a reef from the shore?

Barrier reefs are almost the same as fringing reefs except a navigable channel, also called a lagoon, separates the reef from the shore.

Why are coral reefs important?

Importance. Coral reefs are an important factor in the ecosystem, in tourism, fisheries, and coastline protection. Coral reefs offer coastline protection to nearby islands by absorbing wave energy. The global economic value of coral reefs ranges from US $29.8 billion to US $375 billion per year.

How many theories have been proposed to explain the formation of coral reefs?

Several theories try to explain the formation of coral reefs. So far, only two have been approved as they explain the great vertical thickness of coral reefs. These two include:

Where are fringing reefs located?

Most of these reefs are composed solely of coral sand with both living and dead coral building reefs and mud. Most fringing reefs have been located in East Indies.

How are reefs formed?

In spite of this variety, the reefs share a common origin: each has been formed, over millions of years, from the skeletons and skeletal waste of a mass of living marine organisms. The “bricks” in the reef framework are formed by the calcareous remains of the tiny creatures known as coral polyps and hydrocorals, while the “cement” that binds these remains together is formed in large part by coralline algae and bryozoans. The interstices of this framework have been filled in by vast quantities of skeletal waste produced by the pounding of the waves and the depredations of boring organisms.

How is the Great Barrier Reef formed?

The water environment of the Great Barrier Reef is formed by the surface water layer of the southwestern Pacific Ocean. The reef waters show little seasonal variation: surface-water temperature is high, ranging from 70 to 100 °F (21 to 38 °C). The waters are generally crystal-clear, with submarine features clearly visible at depths of 100 feet (30 metres).

What did the Great Barrier Reef Expedition of 1928–29 contribute to?

The Great Barrier Reef Expedition of 1928–29 contributed important knowledge about coral physiology and the ecology of coral reefs. A modern laboratory on Heron Island continues scientific investigations, and several studies have been undertaken in other areas.

How is the Great Barrier Reef related to the Uplands?

The Great Barrier Reef is related in important respects to the Eastern Uplands. Lying off the Queensland coast, that great system of coral reefs and atolls owes its origin to a combination of continental drift (into warmer waters), rifting, sea-level change, and subsidence.….

What are the bricks in a reef?

The “bricks” in the reef framework are formed by the calcareous remains of the tiny creatures known as coral polyps and hydrocorals, while the “cement” that binds these remains together is formed in large part by coralline algae and bryozoans.

When did reefs grow on the continental shelf?

Borings have established that reefs were growing on the continental shelf as early as the Miocene Epoch (23.0 million to 5.3 million years ago). Subsidence of the continental shelf has proceeded, with some reversals, since the early Miocene.

How many miles is the Great Barrier Reef?

The Great Barrier Reef extends in roughly a northwest-southeast direction for more than 1,250 miles ( 2,000 km), at an offshore distance ranging from 10 to 100 miles (16 to 160 km), and has an area of some 135,000 square miles (350,000 square km). It has been characterized, somewhat inaccurately, as the largest structure ever built by living ...

What is the name of the sea animal that builds a reef around a volcano?

The top of the volcano becomes an oceanic island. In the next stage, tiny sea animals called corals begin to build a reef around the island. The type of corals that build reefs are called hermatypic corals, or hard coral s. Hermatypic corals create a hard exoskeleton of limestone (calcium carbonate).

Which island nation is made up of atolls?

Island nations made of atolls include Maldives, in the Indian Ocean, and Kiribati, in the Pacific. Tourism is a key factor in both the Maldivian and Kiritbati economies.

How do atolls form?

Atolls develop with underwater volcano es, called seamount s. First, the volcano erupts, piling up lava on the seafloor. As the volcano continues to erupt, the seamount's elevation grows higher, eventually breaking the surface of the water. The top of the volcano becomes an oceanic island.

What is an atoll?

Encyclopedic Entry. Vocabulary. An atoll is a ring-shaped coral reef, island, or series of islets. An atoll surrounds a body of water called a lagoon. Sometimes, atolls and lagoons protect a central island. Channel s between islets connect a lagoon to the open ocean or sea. Atolls develop with underwater volcano es, called seamount s.

What is the exoskeleton of coral called?

Hermatypic corals create a hard exoskeleton of limestone (calcium carbonate). Billions of these limestone exoskeletons are the reef. This coral reef, called a fringing reef, surrounds the island just below the ocean surface. The thin, shallow strip of water between the fringing reef and the island is the lagoon.

Why are atolls so popular?

The same elements that make atolls popular for nuclear testing also make them attractive to tourists. Atolls are sparse ly populated, low-lying islands whose white, sandy beaches and placid lagoons are ideally suited to the tourism industry.

Where do hermatypic corals live?

Hermatypic corals only live in warm water. An island that is located where ocean temperatures are just warm enough to support hermatypic corals is said to be at the “ Darwin point ," named after Charles Darwin. The famous naturalist was the first to outline how atolls form. Atolls and People.

Overview

See also

• Coral reef – Outcrop of rock in the sea formed by the growth and deposit of stony coral skeletons
• Reef Hobbyist Magazine
• Placer (geography) – Submerged bank or reef
• Pseudo-atoll – Island that encircles a lagoon

Biotic

Geologic

Artificial

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