Fringing reef

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.

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]

EilatFringingReef
A fringing reef off the coast of Eilat, Israel

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]

Structure

Coral reef diagram
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

Coral atoll formation animation
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.
Maldives - Kurumba Island
Island with fringing reef in the Maldives
Maldives small island
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]

  • Reefs can develop vertically as far as the space below the surface allows. The reef generally grows upward from a starting point towards the surface. Once the reef crest reaches sea level the reef may begin growing seaward. Growth begins after flooding, mostly from parts of the reef that have died. Because the reef grows upward, the oldest sediments are found lower in the reef. The reef flat's age indicates when the reef reached sea level. Catch-up reefs have younger surfaces than keep-up reefs of this type.
  • Reefs can expand seaward from the shore. This requires a fairly constant sea level. If the sea level drops, the reef flat in more seaward areas slopes downward.
  • Reefs can grow atop muddy sediments which can predate the reef or accrete along with the reef's growth. These reefs also grow seaward from the shore. Older sediments are closest to shore and are not buried. Coral, seagrass and algae filter sediment before it is placed on the reef crest.
  • Reefs can form in a gradual, sporadic manner, with alternate vertical and horizontal growth episodes. In this type of fringing reef formation there are multiple separate reefs that are found parallel to the shore and the original fringing reef. These reefs become a single, large reef when reef sediments fill in the spaces between the different reefs.
  • Reefs can develop when an offshore reef grows to sea level forming a barrier. When the crest grows faster than the flat, a lagoon forms. The lagoon then fills with inshore sediments.
  • Offshore reefs can form their barrier using storms to move coral and other debris inwards. The recurring storms continually reshape the seaward side of such reefs.

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:

  • Destructive fishing practices: These include cyanide fishing, blast or dynamite fishing, bottom trawling, and muro-ami (banging on the reef with sticks). Bottom-trawling is one of the greatest threats to cold-water coral reefs.
  • Over-fishing: This affects the ecological balance of coral reef communities, warping the food chain and causing effects far beyond the directly overfished population.
  • Careless tourism: Careless boating, diving, snorkeling, and fishing happens around the world, with people touching reefs, stirring up sediment, collecting coral, and dropping anchors on reefs. Some tourist resorts and infrastructure have been built directly on top of reefs, and some resorts empty their sewage or other wastes directly into water surrounding coral reefs.
  • Marine pollution: Urban and industrial waste, sewage, agrochemicals, and oil pollution are poisoning reefs. These toxins are dumped directly into the ocean or carried by river systems from sources upstream. Some pollutants, such as sewage and runoff from farming, increase the level of nitrogen in seawater, causing an overgrowth of algae, which 'smothers' reefs by cutting off their sunlight.
  • Sedimentation: Erosion caused by construction (both along coasts and inland), mining, logging, and farming is leading to increased sediment in rivers. This ends up in the ocean, where it can 'smother' corals by depriving them of the light needed to survive. The destruction of mangrove forests, which normally trap large amounts of sediment, is exacerbating the problem.
  • Coral mining: Live coral is removed from reefs for use as bricks, road-fill, or cement for new buildings. Corals are also sold as souvenirs to tourists and to exporters who don't know or don't care about the longer term damage done, and harvested for the live rock trade.
  • Climate change: Corals cannot survive if the water temperature is too high. Global warming has already led to increased levels of coral bleaching, and this is predicted to increase in frequency and severity in the coming decades. Such bleaching events may be the final nail in the coffin for already stressed coral reefs and reef ecosystems.

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

References

  1. ^ a b c d e f Kennedy, D.M. and Woodroffe, C.D. 2002.Fringing reef growth and morphology: a review. Earth-Science Reviews. 57:255-277.
  2. ^ a b c d e 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. ^ a b c d e f g 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

External links

Aleipata Islands

The Aleipata Islands is a group of four uninhabited islands off the eastern end (the historical Aleipata region) of Upolu Island, Samoa, with an aggregate area of 1.68 km²):

Nu'utele (1.08 km²)

Nu'ulua (0.25 km²)

Namua (0.20 km²)

Fanuatapu (0.15 km²)Namua and Fanuatapu are at the outer edge of the fringing reef of Upolu, with distances of 0.7 km and 2.5 km to the Upolu mainland, respectively. Nu'utele and Nu'ulua are 4 to 6 km further south, outside of the fringing reef, at distances of 1.4 km 3.5 km off Cape Tapaga, the southeastern headland of Upolu.

These islets are remnants of eroded volcanic tuff rings. Only Namua is open for visitors (Namua Island Resort, beaches). Fanuatapu, being the easternmost island, has a lighthouse. The islands are important nesting locations for seabirds.

Amboyna Cay

Amboyna Cay, also known as An Bang Island, (Vietnamese: Đảo An Bang, Chinese: 安波沙洲; pinyin: Anbo Shazhou, Malay: Pulau Amboyna Kecil; Tagalog: Lagos) and other names is an island of the Spratly Islands group in the South China Sea located just outside (SW) of the southwest of Dangerous Ground. It is SW of Barque Canada Reef, south of the London Reefs, and NW of Swallow Reef.

With an area of 1.6 hectares (4.0 acres), it is the thirteenth largest naturally occurring Spratly island and the sixth largest amongst those occupied by Vietnam.

The island has two parts: the eastern part consists of sand and coral, and the west part is covered with guano. It has a fringing reef. An obelisk, about 2.7 m high, stands on the SW corner. There is little vegetation. It is described by some as heavily fortified. A lighthouse has been operational on the island since May 1995.

The island is also claimed by China, Malaysia, the Philippines and Taiwan.

Anuanuraro

Anuanuraro is an atoll in French Polynesia, Pacific Ocean. It is part of the Duke of Gloucester Islands, a subgroup of the Tuamotu group. Anuanuraro's nearest neighbor is Anuanurunga, which is located about 29 km to the southeast.

Anuanuraro is a small atoll. It measures 5.3 km in length, with a maximum width of 3.2 km and a land area of 2.2 km2. Its shape is roughly square and its lagoon is totally enclosed by the fringing reef.

Anuanuraro Atoll is uninhabited.

Apolima

Apolima is the smallest of the four inhabited islands of Samoa and situated in the Apolima Strait, between the country's two largest islands Upolu to the east and Savai'i to the west.

The island has one village settlement, Apolima Tai with a population of 75 (2006 Census). The small settlement is situated in the interior's flat plateau on the northern side.

Apolima is a rim of an extinct volcanic crater with a maximum height of 165 m. It is a little less than one square kilometer in size and the only access to the island is by boat.

The tiny island lies 2.4 kilometres (1.5 mi) northwest off the westernmost edge of Upolu's fringing reef and 7 km (4 mi) southwest of Savai'i island. The island's appearance is of an upturned bowl with surrounding steep cliffs and a broad opening to the sea on the northern side which is the main entry point by boat.

There are two neighbouring islands in the strait, Manono Island, which has a small population and the smaller uninhabited islet of Nu'ulopa.

Apolima island is part of the political district of Aiga-i-le-Tai.

Barber Island

Barber Island is an island south of Great Palm Island, part of the Greater Palm group in Queensland, Australia. The Aboriginal name for this island is Boodthean Island. Barber Island is one of the ten islands in the local government area of the Palm Island Aboriginal Shire Council.The surrounding waters are in the Great Barrier Reef Marine Park in the Coral Sea, which is administrated by the Great Barrier Reef Marine Park Authority (GBRMPA). The GBRMPA zoning is "Conservation Zone". In a Conservation Zone, as compared with a Buffer zone; bait netting, crabbing (trapping), and limited collecting are permitted. In a Conservation Zone, as compared with a Habitat Protection Zone, harvest fishing for sea cucumber, trochus, and tropical rock lobster are not allowed.

Barber (Boodthean) Reef is a nearshore fringing reef adjacent to the island.

Coral reef

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.

Coral belongs to the class Anthozoa in the animal phylum Cnidaria, which includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons that support and protect the coral. Most reefs grow best in warm, shallow, clear, sunny and agitated water.

Often called "rainforests of the sea", shallow coral reefs form some of Earth's most diverse ecosystems. They occupy less than 0.1% of the world's ocean area, about half the area of France, yet they provide a home for at least 25% of all marine species, including fish, mollusks, worms, crustaceans, echinoderms, sponges, tunicates and other cnidarians. Coral reefs flourish in ocean waters that provide few nutrients. They are most commonly found at shallow depths in tropical waters, but deep water and cold water coral reefs exist on smaller scales in other areas.

Coral reefs deliver ecosystem services for tourism, fisheries and shoreline protection. The annual global economic value of coral reefs is estimated between US$30–375 billion and 9.9 trillion USD. Coral reefs are fragile, partly because they are sensitive to water conditions. They are under threat from excess nutrients (nitrogen and phosphorus), rising temperatures, oceanic acidification, overfishing (e.g., from blast fishing, cyanide fishing, spearfishing on scuba), sunscreen use, and harmful land-use practices, including runoff and seeps (e.g., from injection wells and cesspools).

Gambier Islands

The Gambier Islands (French: Îles Gambier or Archipel des Gambier) are a populated (1319 people), small (30 km2 or 12 sq mi) group of islands, remnants of a caldera along with islets on the surrounding fringing reef, in French Polynesia, located at the southeast terminus of the Tuamotu archipelago. They are generally considered a separate island group from Tuamotu both because their culture and language (Mangarevan) are much more closely related to those of the Marquesas Islands, and because, while the Tuamotus comprise several chains of coral atolls, the Gambiers are of volcanic origin with central high islands.

Hauʻula, Hawaii

Hauʻula is a census-designated place and rural community in the Koʻolauloa District on the island of Oʻahu, City & County of Honolulu. In Hawaiian, hauʻula means "red hau" (hau is a type of tree: Hibiscus tiliaceus). There is a small commercial center. As of the 2010 Census, the CDP population was 4,148.A fringing reef extends off the shoreline. There are several beaches and beach parks in Hauʻula, including Hauʻula Beach Park, ʻAukai Beach Park, Kokololio Beach Park, and Mahakea Beach. Sugarcane was once grown along the narrow coastal plain inland from the highway.

The U.S. postal code for Hauʻula is 96717. There is a two-bay fire station located on Kamehameha Highway.

Kosrae International Airport

Kosrae International Airport (IATA: KSA, ICAO: PTSA, FAA LID: TTK) is an airport serving Kosrae, the easternmost state of the Federated States of Micronesia. It is located on an artificial island within the fringing reef about 150 meters from the coast and is connected to the main island by a causeway.

The airport has been continuously served by the United Airlines (formerly Continental Micronesia) Island Hopper service between Guam and Honolulu, which stops twice weekly at Kosrae in each direction. Kosrae is three jogs from both Guam and Honolulu. As of June 2015, Nauru Airlines stops at Kosrae once a week in each direction between Nauru and Chuuk.

Mombasa Marine National Park and Reserve

Mombasa Marine National Park and Reserve is a marine park and national reserve in Mombasa, Kenya. The park is 10 km² (2,500 acres) while the reserve is 200 km² (49,400 acres).It is located on the coast near tourist areas and is a popular beach because of the snorkeling and diving. It is the most heavily visited of Kenya's marine parks. It has coral reefs in its waters.

It was established as a Marine Park in 1986, and encloses part of the lagoon, back reef and reef crest habitats of the Bamburi-Nyali fringing reef.

The Marine park is characterized by warm tropical conditions varying at the surface between 25°C and 31°C during the year, stable salinity regimes and moderate nutrient levels.

Niau

Niau is a small atoll in French Polynesia, in the commune of Fakarava (Tuamotu archipelago). This atoll has a broad fringing reef, a diameter of 8 km and an area of 53 km².

Niau's lagoon is swampy, hypersaline and entirely enclosed. The narrow strip of land surrounding the lagoon is covered by marsh vegetation. The enclosed lagoon area is 33 km², making the land size at 20 km².

The lagoon has an unusual green color.

The only human settlement on Niau is Tupana, population 226 (as of 2012).

Pocklington Reef

Pocklington Reef is a coral reef and a mostly submerged atoll in the far southeast of Papua New Guinea.

It is 162.4 km from the closest island, Loa Boloba, which is a tiny coral islet within the fringing reef near Cape Deliverance, the south east point of Rossel Island (Yela) in the Louisiade Archipelago, and belongs to Milne Bay province, Samarai-Murua District, Yaleyamba Rural Local Level Government Area.

Pocklington Reef sits on top of Pocklington Ridge, which extends north-east from Rossel Island. The reef is 32 km long and up to 4 km wide. Its longer axis is north-east-south-west. The rim of the reef encloses a deep lagoon. The northern rim reaches closer to the surface, and several above water rocks with heights between 0.9 and 3 metres high lie along its length. There is a small spit of sand about the size of a football field (less than one hectare) at the north-east end.

Protanguilla

Protanguilla palau is a species of eel, the only species in the genus Protanguilla (first eel), which is in turn the only genus in its family, Protanguillidae. Individuals were found swimming in March 2010 in a deep underwater cave in a fringing reef off the coast of Palau.

Punaluu, Hawaii

Punaluʻu (pronounced [punəluʔu]) is a census-designated place and rural community in the Koʻolauloa District on the island of Oʻahu, City & County of Honolulu, Hawaii, United States. In Hawaiian, punaluʻu means "coral dived for", or in the case of the fishpond once located here, possibly "spring dived for". There is a very small commercial center located beside Punaluʻu Stream, and several condominium projects, including a high-rise building, located at Haleaha Beach and Kaluanui Beach. At the 2010 Census, the CDP had a population of 1,164.A fringing reef extends off the shoreline. There are several beaches and a beach park in Punaluʻu, including Punaluʻu Beach Park, Punaluʻu Beach, Haleaha Beach, and Kaluanui Beach. Sugar cane was once grown on the narrow coastal plain inland from the highway.

The U.S. postal code for Punaluʻu is 96717.

Raraka

Raraka, or Te Marie, is an atoll in the west of the Tuamotu group in French Polynesia. It lies 17 km to the southeast of Kauehi Atoll.

The shape of Raraka Atoll is an oval 27 km long and 19 km wide. Its fringing reef has many sandbanks and small motu (islets). This atoll has a wide lagoon with a navigable pass to the ocean.

Raraka Atoll is now uninhabited, but it is occasionally visited by islanders from neighboring atolls. There is a village called Motupapu.

Raraka Atoll in the Tuamotus should not be confused with Raraka in Malaita, Solomon Islands 09°11′S 161°01′W.

Rotuma Group

The Rotuma Group is a group of volcanic islands with Rotuma Island being the main island, located at 12°35′S 177°10′E, approximately 465 km north of Fiji.

There are some islands located at a distance between 50 m and 2 km from the main island, but still within the fringing reef: Solnohu (south), Solkope (southeast), 'Afgaha (far southeast), Husia (close southeast), as well as Hạuameamea and Hạua (close together northeast). Additionally, there is a separate chain of islands between three and six km northwest and west of the westernmost point of Rotuma Island. From northeast to southwest, those are Uea, Hafhai with nearby Hofhahoi, Hafhaveiaglolo, Hatana and Hạf’liua.The islands have an aggregate area of 44 km², of which the main island Rotuma occupies 43 km². Only the main island is permanently inhabited.

The Rotuma Group comprises a Dependency of Fiji. The population of the dependency at the 1996 census was 2810.

Rurutu

Rurutu is the northernmost island in the Austral archipelago of French Polynesia, and the name of a commune consisting solely of that island. It is situated 572 km (355 mi) south of Tahiti. Its land area is 32.7 km2 (12.6 sq mi). It is 10.8 km long and 5.3 km wide. Its highest point (Manureva) is 389 m (1,276 ft). At the 2017 census it had a population of 2,466.Geologically, Rurutu was initially formed 12 million years ago by the Macdonald hotspot, a hotspot associated with the Macdonald seamount. Over the next 10 million years, erosion shrank the island until it was almost an atoll. Then, just over a million years ago, Rurutu passed over the Arago hotspot, which lifted it roughly 150 meters. Steep sea cliffs of ancient coral lifted by the event — called makatea — now largely encircle the island. These are riddled with caves filled with concretions — indeed, Rurutu is largely unique among islands in French Polynesia in that its historic inhabitants were cave-dwelling.

Because it is endowed with a fringing reef, Rurutu has in recent years become known for whale watching: Humpback whales come and reproduce here between July and October within easy sighting distance from the beach.

Although its tiny community still subsists primarily on fishing and basic agriculture, tourism has been a growing industry, especially since François Mitterrand's visit in 1990. Whale watching season sees the bulk of tourists, but the largely untouched native culture, the white sand beaches, and the lush tropical flora draw small numbers of tourists year-round.

Sin Cowe Island

Sin Cowe Island, also known as Sinh Ton Island, (Vietnamese: Đảo Sinh Tồn; Chinese: 景宏岛; pinyin: Jinghong Dao; Tagalog: Rurok) is an island in the Spratly Islands in the South China Sea. With an area of 8 hectares (20 acres), it is the seventh largest Spratly island and the third largest of those occupied by Vietnam. It has a fringing reef which is above water at low tide.This island has been controlled by Vietnam since 1974, first by the South Vietnam's ARVN Navy, followed by the Navy of the Socialist Republic of Vietnam after 1975. The island is also claimed by China, the Philippines and Taiwan.

It is part of the Union Banks.

Waterlemon Cay

Waterlemon Cay is a small cay surrounded by a fringing reef located in Leinster Bay on Saint John, U.S. Virgin Islands. It is named after the water lemon.

The cay is surrounded by a fringing reef, and is considered to be one of the best snorkeling spots on the island. A trail leads from the sandy beach at Leinster Bay approximately 1 km (0.62 mi) along the point, from which is a ten-minute swim to the cay, where there is a small beach. The cay boasts a wide variety of reef fishes and coral, however bleaching is prevalent, and the marine life has decreased in recent times. Many attribute the depletion of Coral reefs of the Virgin Islands to high rates of erosion and runoff caused by the construction boom on the Islands.

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