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 three main types of coral reef recognized by most coral reef scientists. It is distinguished from the other main types (barrier 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.

Contents

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]

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. 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]

Structure

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]

Threats

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

Related Research Articles

Atoll Ring-shaped coral reef

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.

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.

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.

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.

Marine ecosystem Ecosystem in saltwater 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 a colloquial, Australian term for a submarine groundwater discharge, a freshwater spring flowing from the seabed.

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

A term typically used by Earth scientists, a sabkha is a coastal, supratidal mudflat or sandflat in which evaporite-saline minerals accumulate as the result of semiarid to arid climate. Sabkhas are gradational between land and intertidal zone within restricted coastal plains just above normal high-tide level. Within a sabkha, evaporite-saline minerals sediments typically accumulate below the surface of mudflats or sandflats. Evaporite-saline minerals, tidal-flood, and aeolian deposits characterize many sabkhas found along modern coastlines. The accepted type locality for a sabkha is at the southern coast of the Persian Gulf, in the United Arab Emirates. Sabkha is a phonetic translation of the Arabic word used to describe any form of salt flat. A sabkha is also known as a sabkhah,sebkha, or coastal sabkha.

Coral island

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.

The Great Barrier Reef, the world's largest reef system, stretching along the East coast of Australia from the northern tip down to the town of Bundaberg, is composed of roughly 2,900 individual reefs and 940 islands and cays that stretch for 2,300 kilometres (1,616 mi) and cover 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 in northeast Australia. A large part of the reef is protected by the Great Barrier Reef Marine Park.

Kadmat Island village in India

Kadmat Island, also known as Cardamom Island, is a coral island belonging to the Amindivi subgroup of islands of the Lakshadweep archipelago in India. Measuring 9.3 kilometres (5.8 mi) in length, the island has a lagoon with a width of 1.5 kilometres (0.93 mi) covering an area of 25 square kilometres (9.7 sq mi). The ecological feature of the island is of coral reef with seagrass, and marine turtles which nestle here. The Ministry of Environment and Forests (India) has notified the island as a marine protected area for ensuring conservation of the island's animal, plant, or other type of organism, and other resources.

<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.

Florida Reef Coral barrier reef along the Florida Keys

The Florida Reef is the only living coral barrier reef in the continental United States. It is the third largest coral barrier reef system in the world. It lies a few miles seaward of the Florida Keys, is about 4 miles wide and extends 270 km (170 mi) from Fowey Rocks just east of Soldier Key to just south of the Marquesas Keys. The barrier reef tract forms a great arc, concentric with the Florida Keys, with the northern end, in Biscayne National Park, oriented north-south and the western end, south of the Marquesas Keys, oriented east-west. The rest of the reef outside Biscayne National Park lies within John Pennekamp Coral Reef State Park and the Florida Keys National Marine Sanctuary. Isolated coral patch reefs occur northward from Biscayne National Park as far north as Stuart, in Martin County. Coral reefs are also found in Dry Tortugas National Park west of the Marquesas Keys. There are more than 6,000 individual reefs in the system. The reefs are 5,000 to 7,000 years old, having developed since sea levels rose following the Wisconsinan glaciation.

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 Factors which adversely affect tropical 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

Marine habitats are habitats that support marine life. Marine life depends in some way on the saltwater that is in the sea. A habitat is an ecological or environmental area inhabited by one or more living species. The marine environment supports many kinds of these habitats.

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

An algae scrubber is a water filtering device which uses light to grow algae; in this process, undesirable chemicals are removed from the water. Algae scrubbers allow saltwater, freshwater and pond hobbyists to operate their tanks using natural filtration in the form of primary production, much like oceans and lakes.

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.

References

  1. 1 2 3 4 5 6 Kennedy, D.M. and Woodroffe, C.D. 2002.Fringing reef growth and morphology: a review. Earth-Science Reviews. 57:255-277.
  2. 1 2 3 4 5 Castro, Peter and Huber, Michael E. 2008. Marine Biology. 7ed. McGraw-Hill, New York
  3. Zubi, Teresa. 2007. Ecology, Coral Reefs. http://www.starfish.ch/reef/reef.html Accessed on March 30, 2008
  4. Australian Museum. 2004. geoscience: the Earth, Great Barrier Reef. http://www.amonline.net.au/geoscience/earth/barrier_reef.htm Accessed on March 30, 2008.
  5. McClanahan, T. R.; Young, T. P. (1996). East African Ecosystems and Their Conservation. New York: Oxford University Press. p. 70. ISBN   978-0-19-510817-0.
  6. Albert, U., Udy, J., Baines, G. and McDougall, D. 2007. Dramatic tectonic uplift of fringing reefs on Ranongga Is., Solomon Islands. Coral Reefs 26:983.
  7. 1 2 3 4 5 6 7 Tomascik, T. and Sander, F. 1987. Effects of eutrophication on reef-building corals: II. Structure of scleractinian coral communities on fringing reefs, Barbados, West Indies. Marine Biology. 94:53-75