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From Wikipedia, the free encyclopedia

Coral reefs are aragonite structures produced by living organisms. In most reefs the predominant organisms are colonial cnidarians that secrete an exoskeleton of calcium carbonate. The accumulation of this skeletal material, broken and piled up by wave action and bioeroders, produces massive calcareous formations that make ideal habitats for living corals and a great variety of other animal and plant life.

Ocean habitats
	Littoral zone
	Intertidal zone
	Neritic zone
	Continental shelf
	Kelp forests
	Coral reefs
	Fishing banks
	Continental margin
	Pelagic zone
	Straits
	Seamounts
	Hydrothermal vents
	Cold seeps
	Demersal zone
	Benthic zone
Aquatic ecosystems
Aquatic layers
Wild fisheries
Land habitats

Contents 1 Formations 2 Distribution 3 Biology 4 Ecology and biodiversity 5 Threats 5.1 Overfishing 5.1.1 Aquarium fish 5.2 Pollution 5.2.1 Organic pollutants 5.2.1.1 Soil runoff 5.2.1.2 Windborne 5.2.1.3 Sewage 5.2.1.4 Mines 5.2.2 Non-organic 5.3 Global warming 5.4 Ocean acidification 5.5 Mangroves and seagrassbeds 5.6 Coral mining 5.7 Other physical destruction 6 Destruction worldwide 6.1 Threatened species 7 Protection and restoration 7.1 Protected areas 7.2 Restoration technologies 7.3 Organizations 8 Reefs in the past 9 References 9.1 General references 10 External links

[edit] Formations

Coral reefs can take a variety of forms, defined in following:

• Fringing reef – a reef that is directly attached to a shore or borders it with an intervening shallow channel or lagoon.
• Barrier reef – a reef separated from a mainland or island shore by a deep lagoon (see Great Barrier Reef).
• Patch reef – an isolated, often circular reef, usually within a lagoon or embayment.
• Apron reef – a short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore.
• Bank reef – a linear or semi-circular shaped-outline, larger than a patch reef.
• Ribbon reef – a long, narrow, somewhat winding reef, usually associated with an atoll lagoon.
• Atoll reef – a more or less circular or continuous barrier reef extending all the way around a lagoon without a central island.
• Table reef – an isolated reef, approaching an atoll type, but without a lagoon.

BVI salts ponds were all shallow and mostly hypersaline and their waters were generally well mixed. They exhibited large variations in salinity, both temporally and spatially among ponds. -http://www.biology-online.org/

[edit] Distribution

Coral reefs are estimated to cover 284,300 square kilometres, with the Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) accounting for 91.9% of the total.^{[citation needed]} Southeast Asia accounts for 32.3% of that figure, while the Pacific including Australia accounts for 40.8%. Atlantic and Caribbean coral reefs only account for 7.6% of the world total.^[1]

Coral reefs are either restricted or absent from the west coast of the Americas, as well as the west coast of Africa. This is due primarily to upwelling and strong cold coastal currents that reduce water temperatures in these areas.^[2] Corals are also restricted from off the coastline of South Asia from Pakistan to Bangladesh.^[1] They are also restricted along the coast around north-eastern South America and Bangladesh due to the release of vast quantities of freshwater from the Amazon and Ganges Rivers respectively.^{[citation needed]}

Although corals are found in temperate and tropical waters, shallow-water reefs are formed only in a zone extending at most from 30°N to 30°S of the equator. This zone is very important to whales because many types of plankton live there. Tropical corals do not grow at depths of over 50 m (165 ft). Temperature has less of an effect on the distribution of tropical coral, but it is generally accepted that they do not exist in waters below 18 °C.^[3], and that the optimum temperature is 26-27 °C for most coral reefs. The reefs in the Persian gulf however have coral adapted to changing temperatures of 13 °C in winter and 38 °C in summer, thus having significantly colder and hotter ambient environments respectively than most coral reefs. ^[4]Also, deep water coral is more exceptional still as it can exist at greater depths and colder temperatures. Although deep water corals also form reefs, very little is known about them.^[5]

Famous coral reefs and reef areas of the world include:

• The Great Barrier Reef - largest coral reef system in the world, Queensland, Australia;
• The Belize Barrier Reef - second largest in the world, stretching from southern Quintana Roo, Mexico and all along the coast of Belize down to the Bay Islands of Honduras.
• The New Caledonia Barrier Reef - second longest double barrier reef in the world, with a length of about 1500 km.
• The Andros, Bahamas Barrier Reef - third largest in the world, following along the east coast of Andros Island, Bahamas between Andros and Nassau.
• The Red Sea Coral Reef - located off the coast of Israel, Egypt and Saudi Arabia.
• Pulley Ridge - deepest photosynthetic coral reef, Florida
• Many of the numerous reefs found scattered over the Maldives

[edit] Biology

The building blocks of coral reefs are the generation of reef-building, and other organisms that are composed of calcium carbonate. For example, as a coral head grows, it lays down a skeletal structure encasing each new polyp. Waves, grazing fish (such as parrotfish), sea urchins, sponges, and other forces and organisms break down the coral skeletons into fragments that settle into spaces in the reef structure. Many other organisms living in the reef community contribute their skeletal calcium carbonate in the same manner. Coralline algae are important contributors to the structure of the reef in those parts of the reef subjected to the greatest forces by waves (such as the reef front facing the open ocean). These algae contribute to reef-building by depositing limestone in sheets over the surface of the reef and thereby contributing also to the structural integrity of the reef.

Reef-building or hermatypic corals are only found in the photic zone (above 50 m depth), the depth to which sufficient sunlight penetrates the water for photosynthesis to occur. The coral polyps do not photosynthesize, but have a symbiotic relationship with single-celled organisms called zooxanthellae; these cells within the tissues of the coral polyps carry out photosynthesis and produce excess organic nutrients that are then used by the coral polyps. Because of this relationship, coral reefs grow much faster in clear water, which admits more sunlight. Indeed, the relationship is responsible for coral reefs in the sense that without their symbionts, coral growth would be too slow for the corals to form impressive reef structures. Corals can get up to 90% of their nutrients from their zooxanthellae symbionts.^[6]

Corals can reproduce both sexually and asexually. An individual polyp may use both reproductive modes within its lifetime. Corals reproduce sexually by either internal or external fertilization. The reproductive cells are found on the mesentery membranes that radiate inward from the layer of tissue that lines the stomach cavity. Some mature adult corals are hermaphroditic; others are exclusively male or female. A few even change sex as they grow.

Internally fertilized eggs are brooded in the polyp for a period ranging from days to weeks. Subsequent development produces a tiny larva, known as a planula. Externally fertilized eggs develop during a synchronized spawning. Polyps release eggs and sperm into the water simultaneously. This spawning method disperses eggs over a larger area. Synchronous spawning depends on four factors: time of year, water temperature, and tidal and lunar cycles. Spawning is most successful when there is little variation between high and low tides. The less water movement there is over the reef, the better the chance that an egg will be fertilized. Ideal timing occurs in the spring, release of eggs or planula larvae usually occurs at night and is sometimes in phase with the lunar cycle (3-6 days after a full moon). The period from release to settlement lasts only a few days, but some planulae can survive afloat for several weeks (7, 14). They are vulnerable at this time to heavy predation and adverse environmental conditions. For the lucky few which survive to attach to substrate, the challenge comes from competition for food and space.

[edit] Ecology and biodiversity

Coral reefs support an extraordinary biodiversity; although they are located in nutrient-poor tropical waters. The process of nutrient cycling between corals, zooxanthellae, and other reef organisms provides an explanation for why coral reefs flourish in these waters: recycling ensures that fewer nutrients are needed overall to support the community.

Cyanobacteria also provide soluble nitrates for the coral reef through the process of nitrogen fixation. Corals absorb nutrients, including inorganic nitrogen and phosphorus, directly from the water, and they feed upon zooplankton that are carried past the polyps by water motion.^[7] Thus, primary productivity on a coral reef is very high, which results in the highest biomass per square meter, at 5-10g C m^-2 day^-1.^[8] Producers in coral reef communities include the symbiotic zooxanthellae, sponges, marine worms, seaweed, coralline algae (especially small types called turf algae), ... although scientists disagree about the importance of these particular organisms.^[7]

Coral reefs often also depend on other habitats as seagrass meadows and mangrove forests in the surrounding area for the supply of nutrients. Seagrass and mangroves supply dead plants and animals, which are rich in nitrogen and also serve to feed fish and animals from the reef by supplying wood and vegetation to eat. Reefs in turn protect mangroves and seagrass from fierce waves and produce sediment for the mangroves and seagrass to root in.^[9]

Coral reefs are home to a variety of tropical or reef fish which can be distinguished. These include:

• fish that swim right adjust the coral (such as Labridae and parrotfish) These types of fish feed either on small animals living near the coral, seaweed, or on the coral itself. Fish that feeds on small animals include cleaner fish (these fish eat them from between the jaws of larger predatory fish), bullet fish and Balistidae (these eat sea urchins) while fish eating seaweed include the Serranidae. Serranidae even tend to cultivate the weed by removing creatures feeding on it (as sea urchins), and they even remove inedible seaweeds. Fish that eats coral includes the parrotfish and butterflyfish.
• fish that swim above and in the surrounding area of the coral reef. these include predatory fish as eg pompanos, groupers, Horse mackerels, certain types of shark, Epinephelus marginatus, barracudas, snappers, ...) They also include herbivorous and plankton-eating fish. Fish eating seagrass include Horse mackerel, snapper, Pagellus, Conodon, ... Fish eating plankton includes Caesio, manta ray, chromis, Holocentridae, pterapogon kauderni, ...

Generally, fish that swim in coral reefs are just as colourful as the reef itself. Examples are the beautiful parrotfish, angelfish, damselfish, Pomacanthus paru, Clinidae and butterflyfish. At night however, some change colour to a more less catchy colour. Also, it should be noted that besides colourful fish swapping their colour to that of the environment, other fish (eg predatory and certain herbivorous fish as Lampanyctodes hectoris, Holocentridae, pterapogon kauderni, ...) as well as aquatic animals (Comatulida, Crinoidea, Ophiuroidea, ...) emerge and become active and certain go to rest.

Other fish groups found on coral reefs include groupers, grunts and wrasses. Over 4,000 species of fish inhabit coral reefs.^[1] It has been suggested that the high number of fish species that inhabit coral reefs are able to coexist in such high numbers because any free living space is rapidly inhabited by the first planktonic fish larvae that occupy it. These fish then inhabit the space for the rest of their life. The species that inhabit the free space are random and have therefore been termed "a lottery for living space".^[10]

Reefs are also home to a large variety of other organisms, including sponges, Cnidarians (which includes some types of corals and jellyfish), worms, crustaceans (including shrimp, cleaner shrimps, spiny lobsters and crabs), molluscs (including cephalopods), echinoderms (including starfish, sea urchins and sea cucumbers), sea squirts, turtles such as the sea turtle, green turtle and hawksbill turtle and sea snakes. Aside from humans, mammals are rare on coral reefs, with visiting cetaceans such as dolphins being the main group. A few of these varied species feed directly on corals, while others graze on algae on the reef and participate in complex food webs.^[7][1]

These other organisms also have their part in the food-chain of the reef. Sea urchins for example eat seaweed, while the Hawksbill turtle eats sponges. Nudibranchia eat sponges too, as well as sea anemones. Dotidae and sea slugs eat seaweed.

A number of invertebrates, collectively called cryptofauna, inhabit the coral skeletal substrate itself, either boring into the skeletons (through the process of bioerosion) or living in pre-existing voids and crevices. Those animals boring into the rock include sponges, bivalve molluscs, and sipunculans. Those settling on the reef include many other species, particularly crustaceans and polychaete worms.^[2]

Researchers have found evidence of algae dominance in locations of healthy coral reefs. In surveys done around largely uninhabited US Pacific islands, algae consists of a large percentage of the surveyed coral locations. ^[11] The algae population consists of turf algae, coralline algae, and macroalgae.

[edit] Threats

Human activity may represent the greatest threat to coral reefs living in Earth's oceans. In particular, global warming, coral mining, pollution (organic and non-organic/chemical), over-fishing, blast fishing and the digging of canals and access ways into islands and bays are the most serious threats to these ecosystems. Runoff from agricultural areas may also threaten reefs by encouraging the growth of harmful algae.^[13]

In order to find answers for these problems, researchers are currently working to determine the degree various factors impact the reef systems. The list of factors is long but includes the oceans acting as a carbon dioxide sink, changes in Earth's atmosphere, ultraviolet light, ocean acidification, biological virus, impacts of dust storms carrying agents to far flung reef systems, various pollutants, impacts of algal blooms and others. Reefs are threatened well beyond coastal areas and so the problem is broader than factors from land development and pollution though those are too causing considerable damage.

[edit] Overfishing

The live food fish trade has been implicated as a driver of decline due to the use of cyanide and disaster for people living in the tropics. Hughes, et al., (2003), writes that "with increased human population and improved storage and transport systems, the scale of human impacts on reefs has grown exponentially. For example, markets for fishes and other natural resources have become global, supplying demand for reef resources far removed from their tropical sources."^[14]

Overfishing (and particularly selective overfishing) also creates another problem. They promote the abundant growth of certain fish and organisms that can be damaging to the reef if they appear in great numbers. For example the fishing of bullet fish, Balistidae and other natural predators as lobsters ^[15] promote the population growth of sea urchins. Also, acanthaster planci, Drupella, tapiro, Terpios, and Rhodactis have been known to destroy reefs when their population became too big.

[edit] Aquarium fish

The hobby of keeping saltwater aquaria has experienced an increase in world popularity since the 1990s. Beyond sales of aquaria, air pumps, food, medications and other supplies, the primary product of the aquarium industry is fish. However, the world market is limited in the diversity of collected species. For example, among 4000 coral reef fish species, only 200–300 are exploited. Selection of species results from a demand for fish being highly colorful and being able to be maintained and fed in aquaria. The last point is very important in the choice of imported species.

Although a few fish species (e.g. Pomacentridae) can be reproduced in aquaria, 95% of exploited fish are directly collected in the coral environment. Intense sampling of coral reef fish, especially in South-East Asia (including Indonesia and the Philippines), has caused great damage to the environment. A major catalyst of cyanide fishing is poverty within fishing communities. In areas like the Philippines where cyanide is regularly used to catch live aquarium fish, the percentage of the population below the poverty line is 40%.^[16] In such developing countries, a fisherman might resort to such unethical practices in order to prevent his or her family from starving.

Most, 80–90%, of aquarium fish exported from the Philippines are captured with sodium cyanide.. This toxic chemical is dissolved in sea water and released into fish shelters. It has a rapid narcotic effect on fish, which are then easily captured. However, most fish collected with cyanide die a few months after capture from extensive liver damage. Moreover, other fish species that are not interesting for the aquarium market also die in the field.^[17]

[edit] Pollution

Coral reefs are biological assemblages adapted to waters with low nutrient content, and the addition of nutrients (called eutrofication) favors species (as algae, seaweed, ...) that disrupt the balance of the reef communities. ^[18]Some algae are toxic, and both plants reduce the levels of sunlight and oxygen, killing of other marine organisms as fish and coral. Especially the addition of nutrients such as phosphates and nitrates are very damaging to reefs. High nitrate levels are toxic to corals, while phosphates slow down the growth of coral skeleton.

Poor water quality has also been shown to encourage the spread of infectious diseases among corals.^[19]

[edit] Organic pollutants

[edit] Soil runoff

Extensive and poorly managed land development can threaten the survival of coral reefs. Runoff caused by farming and construction of roads, buildings, ports, channels, and harbors, can carry soil laden with carbon, nitrogen, phosphorus, and minerals. This nutrient-rich water can cause fleshy algae and phytoplankton to thrive in coastal areas, known as algal blooms, which have the potential to create hypoxic conditions by using all available oxygen.

[edit] Windborne

In addition to local soil runoff, additional soil (sand) is blown in from other regions. Dust from the Sahara moving around the southern periphery of the subtropical ridge moves into the Caribbean and Florida during the warm season as the ridge builds and moves northward through the subtropical Atlantic. Dust can also be attributed to a global transport from the Gobi and Taklamakan deserts across Korea, Japan, and the Northern Pacific to the Hawaiian Islands.^[20] Since 1970, dust outbreaks have worsened due to periods of drought in Africa. There is a large variability in the dust transport to the Caribbean and Florida from year to year;^[21] however, the flux of dust is greater during positive phases of the North Atlantic Oscillation.^[22] Dust events have been linked to a decline in the health of coral reefs across the Caribbean and Florida, primarily since the 1970s.^[23] Studies have shown that corals can incorporate dust into their skeletons as identified from dust from the 1883 eruption of Krakatoa in Indonesia in the annular bands of the reef-building coral Montastraea annularis from the Florida reef tract.^[24] The relative abundance of chemical elements, particularly metals, has been used to distinguish soil derived from volcanic dust from mineral dust.^[25]

[edit] Sewage

Another major pollutant is those generated by the people themselves. Most islanders use traditional sewage which often goes unfiltered into the sea. Filtering the sewage is something which is normally done in the first world, but in developing countries, this very important step is often skipped. Also, most experts now agree that composting toilet alongside a ecological sanitation approach is best followed in small island nations, yet these countries already implemented such system and for the moment prefer to keep using it.

[edit] Mines

Copper, gold,and other mines inland where minerals are collected also form a major center of pollution. Most of the pollution is simply soil, which ends up in rivers flowing to the sea and ultimately covers the coral, but small mineral fractions may also introduce trouble. Copper, a common industrial pollutant, has been shown to interfere with the life history and development of coral polyps.^[26]

[edit] Non-organic

Leaked oil and chemicals (e.g. from detergents, paints, ...) flowing into the sea from factory outlets are another key threat.

Chemical fertilizers (based on ammonium nitrate) are another pollutant.

Radioactive waste is often dumped by the USA near its military installations (Mororua, Fangataufa, Johnston Atoll, ... Also, nuclear tests (eg at Kwajalein, Bikini, Enewetak) may also caused some nuclear pollution, yet compared to the other forms of pollution noted, they remain only small.

[edit] Global warming

Global warming introduces sea level rise, effectively asking the coral to grow faster to keep up. Also, the sea temperature increases, which is very disturbing to the coral. This was seen during the 1998 and 2004 El Niño weather phenomena, in which sea surface temperatures rose well above normal, many tropical coral reefs were bleached or killed. Some recovery has been noted in more remote locations, but global warming could negate some of this recovery in the future. High seas surface temperature (SSTs) coupled with high irradiance (light intensity), triggers the loss of zooxanthellae, a symbiotic algae, and its dinoflagellate pigmentation in corals causing coral bleaching. Zooxanthellae provide 95% of the energy to the coral host. Reefs can often recover from bleaching if they are healthy to begin with and water temperatures cool. However, recovery will not be possible if CO₂ levels rise to 500 ppm because there will not be enough carbonate ions lefct in the oceans for corals to grow.^[27]Refer to Hoegh-Guldberg 1999 for more information.

Global warming is also the basis of a new emerging problem: increasing coral diseases. Due to global warming (which is the main cause of coral bleaching), corals have been weakened. In their weakened state, the coral is much more prone to disease. As such, coral diseases have been beginning to spread more rapidly. These include Black band disease and White band disease. With the projected 2°C temperature increase, it is likely that coral will not be able to adapt enough physiologically or genetically to keep up with climate change^[28]

[edit] Ocean acidification

A related problem to global warming is ocean acidification, which is caused by one and the same problem; namely increasing CO₂ emissions.

The decreasing ocean surface pH is of increasing long-term concern for coral reefs.^[29] Increased atmospheric CO₂ increases the amount of CO₂ dissolved in the oceans.^[30] Carbon dioxide gas dissolved in the ocean reacts with water to form carbonic acid, resulting in ocean acidification. Ocean surface pH is estimated to have decreased from approximately 8.25 to 8.14 since the beginning of the industrial era,^[31] and it is estimated that it will drop by a further 0.3 - 0.4 units by 2100 as the ocean absorbs more anthropogenic CO₂.^[32] Under normal conditions, the conditions for calcium carbonate production are stable in surface waters since the carbonate ion is at supersaturating concentrations. However, as ocean pH falls, so does the concentration of this ion, and when carbonate becomes under-saturated, structures made of calcium carbonate are vulnerable to dissolution. Research has already found that corals experience reduced calcification or enhanced dissolution when exposed to elevated CO₂.^[33]

[edit] Mangroves and seagrassbeds

Within the last 20 years, once prolific seagrassbeds and mangrove forests, which absorb massive amounts of nutrients and sediment have been destroyed. Both the loss of wetlands, mangrove habitats and seagrassbeds are considered to be significant factors affecting water quality on inshore reefs.^[34]

[edit] Coral mining

Coral mining is another threat, conducted by the villagers themselves, as well as large-scale companies. Mining is often done for construction purposes, and is of particular value as these rocks can be obtained up to 50% cheaper than other rocks (eg from quarries).^[4] The coral rocks are ground and mixed with other materials as cement in order to make concrete. Ancient coral reef material used for construction is known as "coral rag".

[edit] Other physical destruction

Dynamite fishing is extremely destructive method. Sticks of dynamite, grenades, or home-made explosives are activated and thrown in the water. This method of fishing not only kills the fish within the main blast area, but also takes the lives of many reef animals that are not edible or wanted. The blast also kills the corals in the area, eliminating the very structure of the reef, destroying the habitat for fish and other animals important for the maintenance of a healthy reef.^[35]

Other types of fishing like muro-ami and kayakas kills all fish in certain areas, causing havoc on the ecosystem of the reef.^[35]

Boats and ships require an access point into bays and islands to load/unload cargo/people. For this, often parts of the reef are chopped away to clear a path. Alhough this seems but minor destruction of the reef, it can have additional negative consequences. These are altered water circulation and altered tidal patterns, which cause a turnaround in the reefs supply of nutrients; hereby sometimes destroying a great part of the reef and its ecosystem.

Fishing boats and other large vessels cause a form of destruction in shallow waters known as grounding. Two types of damage can occur. Collision damage occurs when a coral reef is crushed and split by a vessel's hull into multiple fragments. Scarring occurs when boat propellers tear off the live coral and expose the skeleton. The physical damage can be noticed as striations in the reefs.

Mooring also causes considerable damage. To reduce the amount of (considerable) devastation which may occure, mooring buoys have been invented. They are already placed in most major wetparks and marine sanctuaries. Most buoys are of the Halas Mooring Buoy System-type. ^[36]

Construction also takes its toll. Besides the previous discussed problem of using corals as construction material, the buildings themselves are often also placed right unto the reef, which causes even more destruction. This as it hinders the aquatic life and may alter water circulation and tides (which bring the nutrients for the reef). Buildings often placed include tourist resorts, airports, docks, and dwellings. The main reason why people build on top of reefs (despite possible problems of moist) is simply because of the lack of space.

[edit] Destruction worldwide

Southeast Asian coral reefs are at risk from damaging fishing practices (such as cyanide and blast fishing), overfishing, sedimentation, pollution and bleaching. A variety of activities, including education, regulation, and the establishment of marine protected areas are under way to protect these reefs. Indonesia, for example has nearly 33,000 square miles (85,000 km²) of coral reefs. Its waters are home to a third of the world's total corals and a quarter of its fish species. Indonesia's coral reefs are located in the heart of the Coral Triangle and have been victim to destructive fishing, unregulated tourism, and bleaching due to climatic changes. Data from 414 reef monitoring stations throughout Indonesia in 2000 found that only 6% of Indonesia's coral reefs are in excellent condition, while 24% are in good condition, and approximately 70% are in poor to fair condition (2003 The Johns Hopkins University).

On September 24, 2007, Reef Check (the world’s largest reef conservation organization) stated that only 5% of Philippines 27,000 square-kilometers of coral reef are in "excellent condition": Tubbataha Reef, Marine Park in Palawan, Apo Island in Negros Oriental, Apo Reef in Puerto Galera, Mindoro, and Verde Island Passage off Batangas. Philippine coral reefs is second largest in Asia.^[37]

General estimates show approximately 10% of the coral reefs around the world are already dead.^[38][39]Problems range from environmental effects of fishing techniques, described above, to ocean acidification.^[40] Coral bleaching is another manifestation of the problem and is showing up in reefs across the planet.

[edit] Threatened species

The global standard for recording threatened marine species is the IUCN Red List of Threatened Species.^[41] This list is the foundation for marine conservation priorities worldwide. A species is listed in the threatened category if it is considered to be critically endangered, endangered, or vulnerable. Other categories are near threatened and data deficient. By 2008, the IUCN had assessed all known reef-building corals species as follows^[42]

Group	Species	Threatened	Near threatened	Data deficient
Reef-building corals	845	27%	20%	17%

According to the IUCN, the primary threats to coral reefs are bleaching and disease which has been linked to an increase in sea temperatures. Other threats include coastal development, coral extraction, sedimentation and pollution. The coral triangle (Indo-Malay-Philippine archipelago) region has the highest number of reef-building coral species in threatened category as well as the highest coral species diversity. The loss of coral reef ecosystems will have devastating effects on many marine species, as well as on people that depend on reef resources for their livelihoods. Various chemicals are dropped into the sea this kills off the reefs. ^[42]

[edit] Protection and restoration

Inhabitants of Ahus Island, Manus Province, Papua New Guinea, have followed a generations-old practice of restricting fishing in six areas of their reef lagoon. While line fishing is permitted, net and spear fishing are restricted based on cultural traditions. The result is that both the biomass and individual fish sizes are significantly larger in these areas than in places where fishing is completely unrestricted.^[43][44]

It is estimated that about 60% of the world's reefs are at risk due to destructive, human-related activities. The threat to the health of reefs is particularly strong in Southeast Asia, where an enormous 80% of reefs are considered endangered.

[edit] Protected areas

Many governments worldwide take measures to protect their coral reefs.

One method of coastal reef management that has become increasingly prominent is the implementation of Marine Protected Areas (MPAs). MPAs have been introduced in Southeast Asia and elsewhere around the world to attempt to promote responsible fishery management and habitat protection. Much like the designation of national parks and wild life refuges, potentially damaging extraction activities are prohibited. The objectives of MPAs are both social and biological, including restoration of coral reefs, aesthetic maintenance, increased and protected biodiversity, and economic benefits. Conflicts surrounding MPAs involve lack of participation, clashing views and perceptions of effectiveness, and funding.

Biosphere reserves are other protected areas that may protect reefs.

Also, Marine parks, as well as world heritage sites can provide protection for coral reefs. World heritage designation is something that is not immediately thought of for the protection of coral reefs, yet also play a vital role. For example the Chagos archipelago, Sian Ka'an, the Great Barrier Reef, Henderson Island, the Galapagos islands, Belize's Barrier reef and Palau have been designated as protected by nominating it a world heritage site.

In Australia, the Great Barrier Reef is protected by the Great Barrier Reef Marine Park Authority, and is the subject of much legislation, including a Biodiversity Action Plan.

[edit] Restoration technologies

Low voltage electrical currents applied through seawater crystallizes dissolved minerals onto steel structures. The resultant white carbonate (aragonite) is the same mineral that makes up natural coral reefs. Corals rapidly colonize and grow at faster than normal rates onto these coated structures. The change in the environment produced by electrical currents also accelerates formation and growth of both chemical limestone rock and the skeletons of corals and other shell-bearing organisms. Within the vicinity of the anode and cathode is a high pH environment which inhibits the growth of filamentous and fleshy algae, which compete with coral for space. This, and the increased growth rates cease when the mineral accretion process stops.^[45]

The effects of mineral accretion is, however, only temporary. During the process the settled corals have an increased growth rate, and size, and density, but after the process is complete the corallites are comparable to naturally growing corallites in growth rate and density, and are about the same size or slightly smaller.^[45]

In large restoration projects, depending on the type of coral, placement of propagated hermatype coral coral unto substrate is often done through the use of metal pins, superglue or milliput ^[46]. A-hermatype coral can also be placed unto substrate using needle and thread ^[47]. Also, to restore large sections of broken coral reef, concrete has also been used. Finally, special structures as reef balls can be placed to provide corals an ground base to grow on.

[edit] Organizations

Organizations which currently undertake coral reef/atoll restoration projects using simple methods of plant propagation:

• Coral Cay
• Counterpart ^[48]
• U.S. Coral Reef Task Force (CRTF)
• National Coral Reef Institute (NCRI)
• US Department of Commerce’s National Oceanic and Atmospheric Administration (NOAA): Coral Reef Conservation Program
• National Center for Coral Reef Research (NCORE)
• Reef Ball
• Southeast Florida Coral Reef Initiative (SEFCRI)
• Foundation of the peoples of the South Pacific
• WorldFishCenter: promotes sustainable mariculture techniques to grow reef organisms as tridacnidae

Organizations which carry out research to better understand the workings of coral reefs:

• Tropical Marine Research Unit

Organizations which promote interest, provide knowledge bases about coral reef survival, and promote activities to protect and restore coral reefs:

There are separate layers of the ocean otherwise called as “zones”. The first zone is the Erysipelas Zone , this is where most of the visible light exists. Second is the Mesosphere Zone the light that penetrates to this depth is extremely faint. Then the Bathysphere Zone, here the only visible light is that produced by the creatures themselves. Fourth, the Abyssinia Zone, the water temperature is near freezing, and there is no light at all, very few creatures can be found at these very low depths. Lastly, the Hadalpelagic Zone, these areas are mostly found in deep water trenches and canyons.

[edit] Reefs in the past

Throughout the Earth history, from a few thousand years after hard skeletons were developed by marine organisms, there were almost always reefs formed by reef-building organisms in the ancient seas. The times of maximum development were in the Middle Cambrian (513-501 Ma), Devonian (416-359 Ma) and Carboniferous (359-299 Ma), due to Order Rugosa extinct corals, and Late Cretaceous (100-65 Ma) and all Neogene (23 Ma - present), due to Order Scleractinia corals.

Not all reefs in the past were formed by corals: in the Early Cambrian (542-513 Ma) resulted from calcareous algae and archaeocyathids (small animals with conical shape, probably related to sponges) and in the Late Cretaceous (100 - 65 Ma), when there also existed reefs formed by a group of bivalves called rudists; one of the valves formed the main conical structure and the other, much smaller valve acted as a cap.

[edit] References

[edit] General references

[edit] External links

Wikimedia Commons has media related to: Coral reefs

• How Coral Reefs Work
• Reef Fest Concert Series Non-profit effort to benefit coral reef conservation globally, starting in 2008, the International Year of the Reef
• International Year of the Reef in 2008
• Moorea Coral Reef Long Term Ecological Research Site (US NSF)
• ARC Centre of Excellence for Coral Reef Studies
• NOAA's Coral-List Listserver for Coral Reef Information and News
• NOAA's Coral Reef Conservation Program
• Exhibition of the Mexican Caribbean coral reef biodiversity aquarium in Xcaret Mexico
• NOAA's Coral Reef Information System
• NOAA Report: The State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States: 2005
• ReefBase: A Global Information System on Coral Reefs
• National Coral Reef Institute Nova Southeastern University
• Global Coral Reef Alliance
• Global Coral Reef Monitoring Network (GCRMN)
• Marine Aquarium Council
• NCORE National Center for Coral Reef Research University of Miami
• The Coral Reef Alliance (CORAL)
• Science and Management of Coral Reefs in the South China Sea and Gulf of Thailand
• A special report on the plight of the planet's coral reefs—and how you can help—from Mother Jones magazine
• A guide to finding sources and literature about coral reefs
• NBII portal on coral reefs
• Microdocs: 4 kinds of Reef & Reef structure

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