Fringing reef

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A fringing reef off the coast of Eilat, Israel EilatFringingReef.jpg
A fringing reef off the coast of Eilat, Israel

A fringing reef is one of the four main types of coral reef recognized by most coral reef scientists. It is distinguished from the other main types (barrier reefs, platform reefs and atolls) in that it has either an entirely shallow backreef zone (lagoon) or none at all. If a fringing reef grows directly from the shoreline (see photo, right) the reef flat extends right to the beach and there is no backreef. In other cases (e.g., most of the Bahamas), fringing reefs may grow hundreds of yards from shore and contain extensive backreef areas with numerous seagrass meadows and patch reefs.

Coral reef Outcrop of rock in the sea formed by the growth and deposit of stony coral skeletons

A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.

Atoll Ring-shaped coral reef, generally formed over a subsiding oceanic volcano, with a central lagoon and perhaps islands around the rim

An atoll, sometimes called a coral atoll, is a ring-shaped coral reef including a coral rim that encircles a lagoon partially or completely. There may be coral islands or cays on the rim. The coral of the atoll often sits atop the rim of an extinct seamount or volcano which has eroded or subsided partially beneath the water. The lagoon forms over the volcanic crater or caldera while the higher rim remains above water or at shallow depths that permit the coral to grow and form the reefs. For the atoll to persist, continued erosion or subsidence must be at a rate slow enough to permit reef growth upward and outward to replace the lost height.

The Bahamas Country in North America

The Bahamas, known officially as the Commonwealth of The Bahamas, is a country within the Lucayan Archipelago. The archipelagic state consists of more than 700 islands, cays, and islets in the Atlantic Ocean, and is located north of Cuba and Hispaniola, northwest of the Turks and Caicos Islands, southeast of the U.S. state of Florida, and east of the Florida Keys. The capital is Nassau on the island of New Providence. The designation of "the Bahamas" can refer either to the country or to the larger island chain that it shares with the Turks and Caicos Islands. The Royal Bahamas Defence Force describes the Bahamas territory as encompassing 470,000 km2 (180,000 sq mi) of ocean space.


This type of coral reef is the most common type of reef found in the Caribbean and Red Sea. Darwin believed that fringing reefs are the first kind of reefs to form around a landmass in a long-term reef growth process. [1]

Red Sea Arm of the Indian Ocean between Arabia and Africa

The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. To the north lie the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez. The Red Sea is a Global 200 ecoregion. The sea is underlain by the Red Sea Rift which is part of the Great Rift Valley.

Charles Darwin British naturalist, author of "On the origin of species, by means of natural selection"

Charles Robert Darwin, was an English naturalist, geologist and biologist, best known for his contributions to the science of evolution. His proposition that all species of life have descended over time from common ancestors is now widely accepted, and considered a foundational concept in science. In a joint publication with Alfred Russel Wallace, he introduced his scientific theory that this branching pattern of evolution resulted from a process that he called natural selection, in which the struggle for existence has a similar effect to the artificial selection involved in selective breeding.

Barrier reef

Sometimes it is hard to tell the difference between fringing reefs and another type of reef called a barrier reef. One of the ways that these two types of reefs are separated is based on the depth of the lagoon in the back reef which is the area near to shore. Barrier reefs have at least some deep portions; fringing reefs do not. Another major difference is that barrier reefs tend to be much farther away from shore than fringing reefs. [1]


Diagram of a fringing coral reef Coral reef diagram.jpg
Diagram of a fringing coral reef

There are two main components that make up a fringing reef, the reef flat and the reef slope.

Reef flat (back reef)

The reef flat is the shoreward, flat, broadest area of the reef. The reef flat is found in fairly shallow water, and can be uncovered during low tide. This area of the reef is only slightly sloped towards the open ocean. [2]

Since the reef flat is adjacent or nearly adjacent to land, it sustains the most damage from runoff and sediments. Typically, few of the flat's corals are alive. Seagrasses, seaweeds, and soft corals are often found there. [2]

Reef slope (fore reef)

The reef slope is found at the outer edge of the fringing reef, closest to the open ocean. This area of the reef is often quite steep and descends either to a relatively shallow sand bottom or to depths too great to allow the growth of coral. [2]

Coral grows much more abundantly on this slope, both in numbers and in species diversity. This is mostly because runoff and sediments are less concentrated here. Greater wave action disperses pollutants and carries nutrients to this area. [2] In addition a common feature on the fore reef is spur and groove formations which transport sediment downslope in the groove.

The upper portion of this slope is called the reef crest. The crest has the best balance between sunlight and waves, so coral grows fastest here. The base of the slope receives the least sunlight and has the least growth out of the whole slope. [2]

Location of fringing reefs

Fringing reefs are located near shore in the tropics in many areas and are the most common reef type. Coral reefs are found in the tropics in which the water is between 18 and 30 °C (64 and 86 °F). [3]

Many of the Great Barrier Reef's components are actually fringing reefs. Of the close to 3400 individual reefs, 760 are actually fringing reefs. [4]

Near Msambweni, Kenya the reef, which stretches from Msambweni to Malindi in the north, is the world's largest continuous fringing reef. [5]

Reef growth

This dynamic animation shows the dynamic process of coral atoll formation. Corals (represented in tan and purple) settle and grow around an oceanic island, forming a fringing reef. In favorable conditions, the reef expands, and the interior island subsides. Eventually the island completely subsides beneath the water, leaving a ring of growing coral with an open lagoon in its center. The process of atoll formation may take as long as 30,000,000 years. Coral atoll formation animation.gif
This dynamic animation shows the dynamic process of coral atoll formation. Corals (represented in tan and purple) settle and grow around an oceanic island, forming a fringing reef. In favorable conditions, the reef expands, and the interior island subsides. Eventually the island completely subsides beneath the water, leaving a ring of growing coral with an open lagoon in its center. The process of atoll formation may take as long as 30,000,000 years.
Island with fringing reef in the Maldives Maldives - Kurumba Island.jpg
Island with fringing reef in the Maldives
A coral atoll in the Maldives Maldives small island.jpg
A coral atoll in the Maldives

Keep-up: These reefs grow at the same rate that sea level rises. [1]

Catch-up: These reefs initially grow more slowly than sea level rises, but eventually catch up when the rise in sea level slows or stops. [1]

Give-up: These reefs are not able to grow fast enough and are "drowned out". [1]

Reef development

The most important determinant of reef growth is available space as determined by sea level changes. Sea level changes are mostly due to glaciation or plate tectonics. There are six different major ways in which fringing reefs grow and develop. [1]

Effect of tectonic activity

Tectonic activity can have very detrimental effects. An earthquake on Ranongga Island in the Solomon Islands moved 80% of its fringing reef permanently above sea level. Northern reefs became elevated 1m above the high tide water height, whereas on the south side reefs moved 2 to 3m above the water height. [6]


As with other types of reefs, there are many reasons of fringing reef destruction, such as:

Species diversity

The backreef area has the least species diversity, which increases seaward towards the reef crest. Some of this difference is due to eutrophication from increased nutrients, sediments and toxicity due to domestic and industrial wastes. [7]

More macrophytes live on the bottom due to the increases in nutrients. They also feel that this increase in nutrients has caused an increase in the number of phytoplankton that are present above the coral reef. The increase in phytoplankton has led to reduced light reaching the coral species and has also led to a greater number of larger invertebrates to be found. [7]

The sediments that are present within the environment cause increased turbidity and may smother some organisms. The corals present on the fringing reefs use four processes to get rid of sediments which include polyp distension, tentacular movement, ciliary action and mucus production. The corals that are present then are thus likely those that can get rid of the sediments the best. [7]

Bloodling also known as brooding corals have higher growth and reproduction rates than others. [7]

In the area of the reef closest to the shore there is generally a lot of fleshy algae which forms on sand and coral rubble. These types of algae include Lyngbia sp. and Oscilatoria sp. [7]

Over recent years the dominant species in the reef flat have been affected by environmental changes. On fringing reefs in Barbados, species such as Diploria strigosa , Palythoa mamillosa, and Diadema antillarum are found. [7]

The reef crest's most common species is Porites porites , a type of stony coral, although there are also significant areas covered in flesh-like algae. [7]

See also

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The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,300 kilometres (1,400 mi) over an area of approximately 344,400 square kilometres (133,000 sq mi). The reef is located in the Coral Sea, off the coast of Queensland, Australia. The Great Barrier Reef can be seen from outer space and is the world's biggest single structure made by living organisms. This reef structure is composed of and built by billions of tiny organisms, known as coral polyps. It supports a wide diversity of life and was selected as a World Heritage Site in 1981. CNN labelled it one of the seven natural wonders of the world. The Queensland National Trust named it a state icon of Queensland.

Estuary A partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea

An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea.

Lagoon A shallow body of water separated from a larger body of water by barrier islands or reefs

A lagoon is a shallow body of water separated from a larger body of water by barrier islands or reefs. Lagoons are commonly divided into coastal lagoons and atoll lagoons. They have also been identified as occurring on mixed-sand and gravel coastlines. There is an overlap between bodies of water classified as coastal lagoons and bodies of water classified as estuaries. Lagoons are common coastal features around many parts of the world.

Reef A bar of rock, sand, coral or similar material, lying beneath the surface of water

A reef is a bar of rock, sand, coral or similar material, lying beneath the surface of water. Many reefs result from natural, abiotic processes—deposition of sand, wave erosion planing down rock outcrops, etc.—but the best known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and coralline algae.

A carbonate platform is a sedimentary body which possesses topographic relief, and is composed of autochthonic calcareous deposits. Platform growth is mediated by sessile organisms whose skeletons build up the reef or by organisms which induce carbonate precipitation through their metabolism. Therefore, carbonate platforms can not grow up everywhere: they are not present in places where limiting factors to the life of reef-building organisms exist. Such limiting factors are, among others: light, water temperature, transparency and pH-Value. For example, carbonate sedimentation along the Atlantic South American coasts takes place everywhere but at the mouth of the Amazon River, because of the intense turbidity of the water there. Spectacular examples of present-day carbonate platforms are the Bahama Banks under which the platform is roughly 8 km thick, the Yucatan Peninsula which is up to 2 km thick, the Florida platform, the platform on which the Great Barrier Reef is growing, and the Maldive atolls. All these carbonate platforms and their associated reefs are confined to tropical latitudes. Today's reefs are built mainly by scleractinian corals, but in the distant past other organisms, like archaeocyatha or extinct cnidaria were important reef builders.


Crustose is a habit of some types of algae and lichens in which the plant grows tightly appressed to a substrate, forming a biological layer of the adhering organism. Crustose adheres very closely to the substrates at all points. Crustose is found on rocks and tree bark. Some species of marine algae of the Rhodophyta, in particular members of the order Corallinales, family Corallinaceae, subfamily Melobesioideae with cell walls containing calcium carbonate grow to great depths in the intertidal zone, forming crusts on various substrates. The substrate can be rocks throughout the intertidal zone, or, as in the case of the Corallinales, reef-building corals, and other living organisms including plants, such as mangroves and animals such as shelled molluscs. The coralline red algae are major members of coral reef communities, cementing the corals together with their crusts. Among the brown algae, the order Ralfsiales comprises two families of crustose algae.

Marine ecosystem Any ecosystems in the marine environment

Marine ecosystems are the largest of Earth's aquatic ecosystems and are distinguished by waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 70% of the surface of the Earth and account for more than 97% of Earth's water supply and 90% of habitable space on Earth. Marine ecosystems include nearshore systems, such as the salt marshes, mudflats, seagrass meadows, mangroves, rocky intertidal systems and coral reefs. They also extend outwards from the coast to include offshore systems, such as the surface ocean, pelagic ocean waters, the deep sea, oceanic hydrothermal vents, and the sea floor. Marine ecosystems are characterized by the biological community of organisms that they are associated with and their physical environment.

Wonky hole is the Australian term for a submarine freshwater spring on the seabed.

Sabkha a salt lake above the tide line, formed along arid coastlines and characterized by evaporite-carbonate deposits with some siliciclastics

Sabkha is a phonetic translation of the Arabic word used to describe any form of salt flat. Geographically, sabkhas can be sub-divided into two broad categories.

A coral island is a type of island formed from coral detritus and associated organic material. They occur in tropical and sub-tropical areas, typically as part of coral reefs which have grown to cover a far larger area under the sea.

<i>The Structure and Distribution of Coral Reefs</i> book by Charles Darwin

The Structure and Distribution of Coral Reefs, Being the first part of the geology of the voyage of the Beagle, under the command of Capt. Fitzroy, R.N. during the years 1832 to 1836, was published in 1842 as Charles Darwin's first monograph, and set out his theory of the formation of coral reefs and atolls. He conceived of the idea during the voyage of the Beagle while still in South America, before he had seen a coral island, and wrote it out as HMS Beagle crossed the Pacific Ocean, completing his draft by November 1835. At the time there was great scientific interest in the way that coral reefs formed, and Captain Robert FitzRoy's orders from the Admiralty included the investigation of an atoll as an important scientific aim of the voyage. FitzRoy chose to survey the Keeling Islands in the Indian Ocean. The results supported Darwin's theory that the various types of coral reefs and atolls could be explained by uplift and subsidence of vast areas of the Earth's crust under the oceans.

Coastal fish

Coastal fish, also called inshore fish or neritic fish, inhabit the sea between the shoreline and the edge of the continental shelf. Since the continental shelf is usually less than 200 metres deep, it follows that pelagic coastal fish are generally epipelagic fish, inhabiting the sunlit epipelagic zone. Coastal fish can be contrasted with oceanic fish or offshore fish, which inhabit the deep seas beyond the continental shelves.

Coral reef protection Modifying human activities to reduce impact on coral reefs.

Coral reef protection is the process of modifying human activities to avoid damage to healthy coral reefs and to help damaged reefs recover. The key strategies used in reef protection include defining measurable goals and introducing active management and community involvement to reduce stressors that damage reef health. One management technique is to create Marine Protected Areas (MPAs) that directly limit human activities such as fishing.

Environmental issues with coral reefs

Human impact on coral reefs is significant. Coral reefs are dying around the world. Damaging activities include coral mining, pollution, overfishing, blast fishing, the digging of canals and access into islands and bays. Other dangers include disease, destructive fishing practices and warming oceans. Factors that affect coral reefs include the ocean's role as a carbon dioxide sink, atmospheric changes, ultraviolet light, ocean acidification, viruses, impacts of dust storms carrying agents to far-flung reefs, pollutants, algal blooms and others. Reefs are threatened well beyond coastal areas. Climate change, such as warming temperatures, causes coral bleaching, which if severe kills the coral.

Marine habitats A habitat that supports marine life

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Algae scrubber A biological water filter that uses light to grow algae which removes undesirable chemicals from aquarium water

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The Virgin Islands Patch Reefs are numerous, small subtropical coral reef ecoregions. These reefs are located on all three islands; St. John, St. Thomas, and St. Croix. Of the three islands St. Croix, has an established barrier reef. It is approximately 20 meters deep and covers 485 sq km.

Coral reefs of the Virgin Islands

One of the marine ecosystems found in the Virgin Islands are the coral reefs. These coral reefs can be located between the islands of St. Croix, St. Thomas, and St. John. These coral reefs have an area of 297.9 km2, along with other marine habitats that are in between. The way these coral reefs grow are by coral larvae swimming freely and attaching themselves to hard surfaces around the islands and start to develop a skeleton on the outside of their skin to protect themselves from predators but also allow a new place for other coral larvae to attach to and grow on. These corals can form into three different structures; fringing reefs, which are reefs that are close to the shore, barrier reefs, which are reefs that are alongside the shore and is separated by deep water, and an atoll reef which is a coral reef that circles a lagoon or body of water.


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