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

An ecosystem (or ecological system) is a system that environments and their organisms form through their interaction.[2]: 458  The biotic and abiotic components are linked together through nutrient cycles and energy flows.

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. Coral reefs first appeared 485 million years ago, at the dawn of the Early Ordovician, displacing the microbial and sponge reefs of the Cambrian.

Sometimes 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.

Shallow tropical coral reefs have declined by 50% since 1950, partly because they are sensitive to water conditions. They are under threat from excess nutrients (nitrogen and phosphorus), rising ocean heat content and 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).

Ocean acidification is the ongoing decrease in the pH of the Earth's ocean. Over the past 200 years, the rapid increase in anthropogenic CO2 (carbon dioxide) production has led to an increase in the acidity of the Earth’s oceans. Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05. Carbon dioxide emissions from human activities are the primary cause of ocean acidification, with atmospheric carbon dioxide (CO2) levels exceeding 410 ppm (in 2020). CO2 from the atmosphere is absorbed by the oceans. This chemical reaction produces carbonic acid (H2CO3) which dissociates into a bicarbonate ion (HCO) and a hydrogen ion (H+). The presence of free hydrogen ions (H+) lowers the pH of the ocean, increasing acidity (this does not mean that seawater is acidic yet; it is still alkaline, with a pH higher than 8). Marine calcifying organisms, such as mollusks and corals, are especially vulnerable because they rely on calcium carbonate to build shells and skeletons.

Most coral reefs were formed after the Last Glacial Period when melting ice caused sea level to rise and flood continental shelves. Most coral reefs are less than 10,000 years old. As communities established themselves, the reefs grew upwards, pacing rising sea levels. Reefs that rose too slowly could become drowned, without sufficient light. Coral reefs are also found in the deep sea away from continental shelves, around oceanic islands and atolls. The majority of these islands are volcanic in origin. Others have tectonic origins where plate movements lifted the deep ocean floor.

In The Structure and Distribution of Coral Reefs, Charles Darwin set out his theory of the formation of atoll reefs, an idea he conceived during the voyage of the Beagle. He theorized that uplift and subsidence of Earth's crust under the oceans formed the atolls. Darwin set out a sequence of three stages in atoll formation. A fringing reef forms around an extinct volcanic island as the island and ocean floor subside. As the subsidence continues, the fringing reef becomes a barrier reef and ultimately an atoll reef.

Darwin predicted that underneath each lagoon would be a bedrock base, the remains of the original volcano. Subsequent research supported this hypothesis. Darwin's theory followed from his understanding that coral polyps thrive in the tropics where the water is agitated, but can only live within a limited depth range, starting just below low tide. Where the level of the underlying earth allows, the corals grow around the coast to form fringing reefs, and can eventually grow to become a barrier reef.

A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into coastal lagoons (or barrier 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.

Where the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies. If the land subsides slowly, the fringing reefs keep pace by growing upwards on a base of older, dead coral, forming a barrier reef enclosing a lagoon between the reef and the land. A barrier reef can encircle an island, and once the island sinks below sea level a roughly circular atoll of growing coral continues to keep up with the sea level, forming a central lagoon. Barrier reefs and atolls do not usually form complete circles but are broken in places by storms. Like sea level rise, a rapidly subsiding bottom can overwhelm coral growth, killing the coral and the reef, due to what is called coral drowning. Corals that rely on zooxanthellae can die when the water becomes too deep for their symbionts to adequately photosynthesize, due to decreased light exposure.

Zooxanthellae are photosynthetic cells that live in coral tissues and provide them with nutrients and color.

The two main variables determining the geomorphology, or shape, of coral reefs are the nature of the substrate on which they rest, and the history of the change in sea level relative to that substrate.

The approximately 20,000-year-old Great Barrier Reef offers an example of how coral reefs formed on continental shelves. Sea level was then 120 m (390 ft) lower than in the 21st century. As sea level rose, the water and the corals encroached on what had been hills of the Australian coastal plain. By 13,000 years ago, sea level had risen to 200 feet lower than at present, and many hills of the coastal plains had become continental islands. As sea level rise continued, water topped most of the continental islands. The corals could then overgrow the hills, forming cays and reefs. Sea level on the Great Barrier Reef has not changed significantly in the last 6,000 years. The age of living reef structure is estimated to be between 6,000 and 8,000 years. Although the Great Barrier Reef formed along a continental shelf, and not around a volcanic island, Darwin's principles apply. Development stopped at the barrier reef stage, since Australia is not about to submerge. It formed the world's largest barrier reef, 980 to 3,280 ft) from shore, stretching for 1,200 miles.

Healthy tropical coral reefs grow horizontally from approximately 1/2 to nearly 1 1/20 inches per year, and grow vertically anywhere from approximately .25 to 9 3/4 inches per year; however, they grow only at depths shallower than 490 feet because of their need for sunlight, and cannot grow above sea level.

coral reefs are made up of coral skeletons from mostly intact coral colonies. As other chemical elements present in corals become incorporated into the calcium carbonate deposits, aragonite is formed. However, shell fragments and the remains of coralline algae such as the green-segmented genus Halimeda can add to the reef's ability to withstand damage from storms and other threats.

Spalding lists four main reef types that can be clearly illustrated – the fringing reef, barrier reef, atoll, and "bank or platform reef"—and notes that many other structures exist which do not conform easily to strict definitions, including the "patch reef".

A fringing reef, also called a shore reef, is directly attached to a shore, or borders it with an intervening narrow, shallow channel or lagoon.It is the most common reef type. Fringing reefs follow coastlines and can extend for many kilometres. They are usually less than 328 feet wide, but some are much wider. Fringing reefs are initially formed on the shore at the low water level and expand seawards as they grow in size. The final width depends on where the sea bed begins to drop steeply. The surface of the fringe reef generally remains at the same height: just below the waterline. In older fringing reefs, whose outer regions pushed far out into the sea, the inner part is deepened by erosion and eventually forms a lagoon. Fringing reef lagoons can become over 328 feet wide and several metres deep. Like the fringing reef itself, they run parallel to the coast. The fringing reefs of the Red Sea are "some of the best developed in the world" and occur along all its shores except off sandy bays.

Barrier reefs are separated from a mainland or island shore by a deep channel or lagoon. They resemble the later stages of a fringing reef with its lagoon but differ from the latter mainly in size and origin. Their lagoons can be several kilometres wide and 98 to 229 feet deep. Above all, the offshore outer reef edge formed in open water rather than next to a shoreline. Like an atoll, it is thought that these reefs are formed either as the seabed lowered or sea level rose. Formation takes considerably longer than for a fringing reef, thus barrier reefs are much rarer.

The best known and largest example of a barrier reef is the Australian Great Barrier Reef. Other major examples are the Mesoamerican Barrier Reef System and the New Caledonian Barrier Reef. Barrier reefs are also found on the coasts of Providencia, Mayotte, the Gambier Islands, on the southeast coast of Kalimantan, on parts of the coast of Sulawesi, southeastern New Guinea and the south coast of the Louisiade Archipelago.

Platform reefs, variously called bank or table reefs, can form on the continental shelf, as well as in the open ocean, in fact anywhere where the seabed rises close enough to the surface of the ocean to enable the growth of zooxanthemic, reef-forming corals. Platform reefs are found in the southern Great Barrier Reef, the Swain and Capricorn Group on the continental shelf, about 62 to 125 miles from the coast. Some platform reefs of the northern Mascarenes are more 700 miles from the mainland. Unlike fringing and barrier reefs which extend only seaward, platform reefs grow in all directions. They are variable in size, ranging from a few hundred feet to many miles across. Their usual shape is oval to elongated. Parts of these reefs can reach the surface and form sandbanks and small islands around which may form fringing reefs. A lagoon may form In the middle of a platform reef.

Platform reefs are typically situated within atolls, where they adopt the name "patch reefs" and often span a diameter of just a few dozen feet. In instances where platform reefs develop along elongated structures, such as old and weathered barrier reefs, they tend to arrange themselves in a linear formation. This is the case, for example, on the east coast of the Red Sea near Jeddah. In old platform reefs, the inner part can be so heavily eroded that it forms a pseudo-atoll. These can be distinguished from real atolls only by detailed investigation, possibly including core drilling. Some platform reefs of the Laccadives are U-shaped, due to wind and water flow.

Atolls or atoll reefs are a more or less circular or continuous barrier reef that extends all the way around a lagoon without a central island. They are usually formed from fringing reefs around volcanic islands. Over time, the island erodes away and sinks below sea level. Atolls may also be formed by the sinking of the seabed or rising of the sea level. A ring of reefs results, which enclose a lagoon. Atolls are numerous in the South Pacific, where they usually occur in mid-ocean, for example, in the Caroline Islands, the Cook Islands, French Polynesia, the Marshall Islands and Micronesia.

Atolls are found in the Indian Ocean, for example, in the Maldives, the Chagos Islands, the Seychelles and around Cocos Island. The entire Maldives consist of 26 atolls.

Coral reefs are estimated to cover about 109,800 sq miles, just under 0.1% of the oceans' surface area. The Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) account for 91.9% of this total. Southeast Asia accounts for 32.3% of that figure, while the Pacific including Australia accounts for 40.8%. Atlantic and Caribbean coral reefs account for 7.6%.

Corals exist both in temperate and tropical waters, shallow-water reefs form only in a zone extending from approximately 30° N to 30° S of the equator. Tropical corals do not grow at depths of over 160 feet. The optimum temperature for most coral reefs is 79 to 81 °F, and few reefs exist in waters below 64 °F. When the net production by reef building corals no longer keeps pace with relative sea level and the reef structure permanently drowns a Darwin Point is reached.

Reefs in the Persian Gulf have adapted to temperatures of 55 °F in winter and 100 °F in summer. 37 species of scleractinian corals inhabit such an environment around Larak Island.

Deep-water coral inhabits greater depths and colder temperatures at much higher latitudes, as far north as Norway. Although deep water corals can form reefs, little is known about them.

The northern most coral reef on Earth is located near Eilat, Israel. Coral reefs are rare along the west coasts of the Americas and Africa, due primarily to upwelling and strong cold coastal currents that reduce water temperatures in these areas (the Humboldt, Benguela, and Canary Currents, respectively). Corals are seldom found along the coastline of South Asia—from the eastern tip of India (Chennai) to the Bangladesh and Myanmar borders, as well as along the coasts of northeastern South America and Bangladesh, due to the freshwater release from the Amazon and Ganges Rivers respectively.

When alive, corals are colonies of small animals embedded in calcium carbonate shells. Coral heads consist of accumulations of individual animals called polyps, arranged in diverse shapes. Polyps are usually tiny, but they can range in size from a pinhead to 12 inches across.

Reef-building or hermatypic corals live only in the photic zone (above 229 feet), the depth to which sufficient sunlight penetrates the water.

Coral polyps do not photosynthesize, but have a symbiotic relationship with microscopic algae (dinoflagellates) of the genus Symbiodinium, commonly referred to as zooxanthellae. These organisms live within the polyps' tissues and provide organic nutrients that nourish the polyp in the form of glucose, glycerol and amino acids. Because of this relationship, coral reefs grow much faster in clear water, which admits more sunlight. Without their symbionts, coral growth would be too slow to form significant reef structures. Corals get up to 90% of their nutrients from their symbionts. In return, as an example of mutualism, the corals shelter the zooxanthellae, averaging one million for every cubic centimetre of coral, and provide a constant supply of the carbon dioxide they need for photosynthesis.

The varying pigments in different species of zooxanthellae give them an overall brown or golden-brown appearance and give brown corals their colors. Other pigments such as reds, blues, greens, etc. come from colored proteins made by the coral animals. Coral that loses a large fraction of its zooxanthellae becomes white (or sometimes pastel shades in corals that are pigmented with their own proteins) and is said to be bleached, a condition which, unless corrected, can kill the coral.

There are eight clades of Symbiodinium phylotypes. Most research has been conducted on clades A–D. Each clade contributes their own benefits as well as less compatible attributes to the survival of their coral hosts. Each photosynthetic organism has a specific level of sensitivity to photodamage to compounds needed for survival, such as proteins. Rates of regeneration and replication determine the organism's ability to survive. Phylotype A is found more in the shallow waters. It is able to produce mycosporine-like amino acids that are UV resistant, using a derivative of glycerin to absorb the UV radiation and allowing them to better adapt to warmer water temperatures. In the event of UV or thermal damage, if and when repair occurs, it will increase the likelihood of survival of the host and symbiont. This leads to the idea that, evolutionarily, clade A is more UV resistant and thermally resistant than the other clades.

Clades B and C are found more frequently in deeper water, which may explain their higher vulnerability to increased temperatures. Terrestrial plants that receive less sunlight because they are found in the undergrowth are analogous to clades B, C, and D. Since clades B through D are found at deeper depths, they require an elevated light absorption rate to be able to synthesize as much energy. With elevated absorption rates at UV wavelengths, these phylotypes are more prone to coral bleaching versus the shallow clade A.

Clade D has been observed to be high temperature-tolerant, and has a higher rate of survival than clades B and C during modern bleaching events.

Reefs grow as polyps and other organisms deposit calcium carbonate, the basis of coral, as a skeletal structure beneath and around themselves, pushing the coral head's top upwards and outwards. Waves, grazing fish (such as parrotfish), sea urchins, sponges and other forces and organisms act as bioeroders, breaking down coral skeletons into fragments that settle into spaces in the reef structure or form sandy bottoms in associated reef lagoons.

Typical shapes for coral species are named by their resemblance to terrestrial objects such as wrinkled brains, cabbages, table tops, antlers, wire strands and pillars. These shapes can depend on the life history of the coral, like light exposure and wave action, and events such as breakages.

Corals reproduce both sexually and asexually. An individual polyp uses both reproductive modes within its lifetime. Corals reproduce sexually by either internal or external fertilization. The reproductive cells are found on the mesenteries, 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 species change sex as they grow.

Internally fertilized eggs develop 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 synchronized spawning. Polyps across a reef simultaneously release eggs and sperm into the water en masse. Spawn disperse over a large area. The timing of spawning depends on time of year, water temperature, and tidal and lunar cycles. Spawning is most successful given little variation between high and low tide. The less water movement, the better the chance for fertilization. The release of eggs or planula usually occurs at night and is sometimes in phase with the lunar cycle (three to six 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. During this process, the larvae may use several different cues to find a suitable location for settlement. At long distances sounds from existing reefs are likely important, while at short distances chemical compounds become important. The larvae are vulnerable to predation and environmental conditions. The lucky few planulae that successfully attach to substrate then compete for food and space.

Corals are the most prodigious reef-builders. However many other organisms living in the reef community contribute skeletal calcium carbonate in the same manner as corals. These include coralline algae, some sponges and bivalves. Reefs are always built by the combined efforts of these different phyla, with different organisms leading reef-building in different geological periods.

Coralline algae are important contributors to reef structure. Although their mineral deposition rates are much slower than corals, they are more tolerant of rough wave-action, and so help to create a protective crust over those parts of the reef subjected to the greatest forces by waves, such as the reef front facing the open ocean. They also strengthen the reef structure by depositing limestone in sheets over the reef surface.

"Sclerosponge" is the descriptive name for all Porifera that build reefs. In the early Cambrian period, Archaeocyatha sponges were the world's first reef-building organisms, and sponges were the only reef-builders until the Ordovician. Sclerosponges still assist corals building modern reefs, but like coralline algae are much slower-growing than corals and their contribution is (usually) minor.

In the northern Pacific Ocean cloud sponges still create deep-water mineral-structures without corals, although the structures are not recognizable from the surface like tropical reefs. They are the only extant organisms known to build reef-like structures in cold water.

Bivalves Oyster reefs are dense aggregations of oysters living in colonial communities. Other regionally-specific names for these structures include oyster beds and oyster banks. Oyster larvae require a hard substrate or surface to attach on, which includes the shells of old or dead oysters. Thus reefs can build up over time as new larvae settle on older individuals. Crassostrea virginica were once abundant in Chesapeake Bay and shorelines bordering the Atlantic coastal plain until the late nineteenth century. Ostrea angasi is a species of flat oyster that had also formed large reefs in South Australia.

Hippuritida, an extinct order of bivalves known as rudists, were major reef-building organisms during the Cretaceous. By the mid-Cretaceous, rudists became the dominant tropical reef-builders, becoming more numerous than scleractinian corals. During this period, ocean temperatures and saline levels—which corals are sensitive to—were higher than it is today, which may have contributed to the success of rudist reefs.

Coral reefs form some of the world's most productive ecosystems, providing complex and varied marine habitats that support a wide range of organisms. Fringing reefs just below low tide level have a mutually beneficial relationship with mangrove forests at high tide level and sea grass meadows in between: the reefs protect the mangroves and seagrass from strong currents and waves that would damage them or erode the sediments in which they are rooted, while the mangroves and sea grass protect the coral from large influxes of silt, fresh water and pollutants. This level of variety in the environment benefits many coral reef animals, which, for example, may feed in the sea grass and use the reefs for protection or breeding.

Reefs are home to a variety of animals, including fish, seabirds, sponges, cnidarians (which includes some types of corals and jellyfish), worms, crustaceans (including shrimp, cleaner shrimp, spiny lobsters and crabs), mollusks (including cephalopods), echinoderms (including starfish, sea urchins and sea cucumbers), sea squirts, sea turtles and sea snakes. Aside from humans, mammals are rare on coral reefs, with visiting cetaceans such as dolphins the main exception. A few species feed directly on corals, while others graze on algae on the reef. Reef biomass is positively related to species diversity.

The same hideouts in a reef may be regularly inhabited by different species at different times of day. Nighttime predators such as cardinalfish and squirrelfish hide during the day, while damselfish, surgeonfish, triggerfish, wrasses and parrotfish hide from eels and sharks.

The great number and diversity of hiding places in coral reefs, i.e. refuges, are the most important factor causing the great diversity and high biomass of the organisms in coral reefs.

Coral reefs also have a very high degree of microorganism diversity compared to other environments.

Reefs are chronically at risk of algal encroachment. Overfishing and excess nutrient supply from onshore can enable algae to outcompete and kill the coral. Increased nutrient levels can be a result of sewage or chemical fertilizer runoff. Runoff can carry nitrogen and phosphorus which promote excess algae growth. Algae can sometimes out-compete the coral for space. The algae can then smother the coral by decreasing the oxygen supply available to the reef. Decreased oxygen levels can slow down calcification rates, weakening the coral and leaving it more susceptible to disease and degradation. Algae inhabit a large percentage of surveyed coral locations. The algal population consists of turf algae, coralline algae and macro algae. Some sea urchins (such as Diadema antillarum) eat these algae and could thus decrease the risk of algal encroachment.

Sponges are essential for the functioning of the coral reef system. Algae and corals in coral reefs produce organic material. This is filtered through sponges which convert this organic material into small particles which in turn are absorbed by algae and corals. Sponges are essential to the coral reef system however, they are quite different from corals. While corals are complex and many celled while sponges are very simple organisms with no tissue. They are alike in that they are both immobile aquatic invertebrates but otherwise are completely different.

There are several different species of sea sponge. They come in multiple shapes and sizes and all have unique characteristics. Some types of sea sponges include; the tube sponge, vase sponge, yellow sponge, bright red tree sponge, painted tunicate sponge, and the sea squirt sponge.

Over 4,000 species of fish inhabit coral reefs. The reasons for this diversity remain unclear. Hypotheses include the "lottery", in which the first (lucky winner) recruit to a territory is typically able to defend it against latecomers, "competition", in which adults compete for territory, and less-competitive species must be able to survive in poorer habitat, and "predation", in which population size is a function of post settlement piscivore mortality. Healthy reefs can produce up to 35 tons of fish per square feet each year, but damaged reefs produce much less.

Sea urchins, Dotidae and sea slugs eat seaweed. Some species of sea urchins, such as Diadema antillarum, can play a pivotal part in preventing algae from overrunning reefs. Researchers are investigating the use of native collector urchins, Tripneustes gratilla, for their potential as biocontrol agents to mitigate the spread of invasive algae species on coral reefs. Nudibranchia and sea anemones eat sponges.

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. Animals boring into the rock include sponges, bivalve mollusks, and sipunculans. Those settling on the reef include many other species, particularly crustaceans and polychaete worms.

Coral reef systems provide important habitats for seabird species, some endangered. For example, Midway Atoll in Hawaii supports nearly three million seabirds, including two-thirds (1.5 million) of the global population of Laysan albatross, and one-third of the global population of black-footed albatross. Each seabird species has specific sites on the atoll where they nest. Altogether, 17 species of seabirds live on Midway. The short-tailed albatross is the rarest, with fewer than 2,200 surviving after excessive feather hunting in the late 19th century.

Sea snakes feed exclusively on fish and their eggs. Marine birds, such as herons, gannets, pelicans and boobies, feed on reef fish. Some land-based reptiles intermittently associate with reefs, such as monitor lizards, the marine crocodile and semiaquatic snakes, such as Laticauda colubrina. Sea turtles, particularly hawksbill sea turtles, feed on sponges.

Since their emergence 485 million years ago, coral reefs have faced many threats, including disease, predation, invasive species, bioerosion by grazing fish, algal blooms, and geologic hazards. Recent human activities present new threats. From 2009 to 2018, coral reefs worldwide declined 14%.

Human activities that threaten coral include coral mining, bottom trawling, and the digging of canals and accesses into islands and bays, all of which can damage marine ecosystems if not done sustainably. Other localized threats include blast fishing, overfishing, coral overmining, and marine pollution, including use of the banned anti-fouling biocide tributyltin; although absent in developed countries, these activities continue in places with few environmental protections or poor regulatory enforcement. Chemicals in sunscreens may awaken latent viral infections in zooxanthellae and impact reproduction. However, concentrating tourism activities via offshore platforms has been shown to limit the spread of coral disease by tourists.

Greenhouse gas emissions present a broader threat through sea temperature rise and sea level rise, resulting in widespread coral bleaching and loss of coral cover. Climate change causes more frequent and more severe storms, also changes in ocean circulation patterns, which can destroy coral reefs. Ocean acidification also affects corals by decreasing calcification rates and increasing dissolution rates, although corals can adapt their calcifying fluids to changes in seawater pH and carbonate levels to mitigate the impact. Volcanic and human-made aerosol pollution can modulate regional sea surface temperatures.

Corals respond to stress by "bleaching", or expelling their colorful zooxanthellate endosymbionts. Corals with Clade C zooxanthellae are generally vulnerable to heat-induced bleaching, whereas corals with the hardier Clade A or D are generally resistant, as are tougher coral genera like Porites and Montipora.

Every 4–7 years, an El Niño event causes some reefs with heat-sensitive corals to bleach, with especially widespread bleachings in 1998 and 2010. However, reefs that experience a severe bleaching event become resistant to future heat-induced bleaching, due to rapid directional selection. Similar rapid adaption may protect coral reefs from global warming.

Marine protected areas (MPAs) are areas designated because they provide various kinds of protection to ocean and/or estuarine areas. They are intended to promote responsible fishery management and habitat protection. MPAs can also encompass social and biological objectives, including reef restoration, aesthetics, biodiversity and economic benefits.

The effectiveness of MPAs is still debated. For example, a study investigating the success of a small number of MPAs in Indonesia, the Philippines and Papua New Guinea found no significant differences between the MPAs and unprotected sites. In some cases they can generate local conflict, due to a lack of community participation, clashing views of the government and fisheries, effectiveness of the area and funding. In some situations, as in the Phoenix Islands Protected Area, MPAs provide revenue to locals. The level of income provided is similar to the income they would have generated without controls. Overall, it appears the MPA's can provide protection to local coral reefs, but that clear management and sufficient funds are required.

The Caribbean Coral Reefs - Status Report 1970–2012, states that coral decline may be reduced or even reversed. For this overfishing needs to be stopped, especially fishing on species key to coral reefs, such as parrotfish. Direct human pressure on coral reefs should also be reduced and the inflow of sewage should be minimized. Measures to achieve this could include restricting coastal settlement, development and tourism. The report shows that healthier reefs in the Caribbean are those with large, healthy populations of parrotfish. These occur in countries that protect parrotfish and other species, like sea urchins. They also often ban fish trapping and spearfishing. Together these measures help creating "resilient reefs.

Protecting networks of diverse and healthy reefs, not only climate refugia, helps ensure the greatest chance of genetic diversity, which is critical for coral to adapt to new climates. A variety of conservation methods applied across marine and terrestrial threatened ecosystems makes coral adaption more likely and effective.

Designating a reef as a biosphere reserve, marine park, national monument or world heritage site can offer protections. For example, Belize's barrier reef, Sian Ka'an, the Galapagos islands, Great Barrier Reef, Henderson Island, Palau and Papahānaumokuākea Marine National Monument are world heritage sites.

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. Australia compiled a Coral Reef Resilience Action Plan. This plan consists of adaptive management strategies, including reducing carbon footprint. A public awareness plan provides education on the "rainforests of the sea" and how people can reduce carbon emissions.

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. Their cultural traditions allow line fishing, but no net or spear fishing. Both biomass and individual fish sizes are significantly larger than in places where fishing is unrestricted.

Increased levels of atmospheric CO2 contribute to ocean acidification, which in turn damages coral reefs. To help combat ocean acidification, several countries have put laws in place to reduce greenhouse gases such as carbon dioxide. Many land use laws aim to reduce CO2 emissions by limiting deforestation. Deforestation can release significant amounts of CO2 absent sequestration via active follow-up forestry programs. Deforestation can also cause erosion, which flows into the ocean, contributing to ocean acidification. Incentives are used to reduce miles traveled by vehicles, which reduces carbon emissions into the atmosphere, thereby reducing the amount of dissolved CO2 in the ocean. State and federal governments also regulate land activities that affect coastal erosion. High-end satellite technology can monitor reef conditions.

The United States Clean Water Act puts pressure on state governments to monitor and limit run-off of polluted water.

Coral aquaculture, also known as coral farming or coral gardening, is showing promise as a potentially effective tool for restoring coral reefs. The "gardening" process bypasses the early growth stages of corals when they are most at risk of dying. Coral seeds are grown in nurseries, then replanted on the reef. Coral is farmed by coral farmers whose interests range from reef conservation to increased income. Due to its straight forward process and substantial evidence of the technique having a significant effect on coral reef growth, coral nurseries became the most widespread and arguably the most effective method for coral restoration.

Coral gardens take advantage of a coral's natural ability to fragment and continuing to grow if the fragments are able to anchor themselves onto new substrates. This method was first tested by Baruch Rinkevich in 1995 which found success at the time. By today's standards, coral farming has grown into a variety of different forms, but still has the same goals of cultivating corals. Consequently, coral farming quickly replaced previously used transplantation methods or the act of physically moving sections or whole colonies of corals into a new area. Transplantation has seen success in the past and decades of experiments have led to a high success and survival rate. However, this method still requires the removal of corals from existing reefs. With the current state of reefs, this kind of method should generally be avoided if possible. Saving healthy corals from eroding substrates or reefs that are doomed to collapse could be a major advantage of utilizing transplantation.

Coral gardens generally take on the safe forms no matter where you go. It begins with the establishment of a nursery where operators can observe and care for coral fragments. It goes without saying that nurseries should be established in areas that are going to maximize growth and minimize mortality. Floating offshore coral trees or even aquariums are possible locations where corals can grow. After a location has been determined, collection and cultivation can occur.

The major benefit of using coral farms is it lowers polyp and juvenile mortality rates. By removing predators and recruitment obstacles, corals are able to mature without much hindrance. However, nurseries cannot stop climate stressors. Warming temperatures or hurricanes can still disrupt or even kill nursery corals.

Technology is becoming more popular in the coral farming process. Teams from the Reef Restoration and Adaptation Program (RRAP) have trialed coral counting technology utilizing a prototype robotic camera. The camera uses computer vision and learning algorithms to detect and count individual coral babies and track their growth and health in real time. This technology, with research led by QUT, is intended to be used during annual coral spawning events and will provide researchers with control that is not currently possible when mass producing corals.

Efforts to expand the size and number of coral reefs generally involve supplying substrate to allow more corals to find a home. Substrate materials include discarded vehicle tires, scuttled ships, subway cars and formed concrete, such as reef balls. Reefs grow unaided on marine structures such as oil rigs. In large restoration projects, propagated hermatypic coral on substrate can be secured with metal pins, superglue or milli put. Needle and thread can also attach A-herma type coral to substrate.

Another possibility for coral restoration is gene therapy: inoculating coral with genetically modified bacteria, or naturally-occurring heat-tolerant varieties of coral symbiotes, may make it possible to grow corals that are more resistant to climate change and other threats. Warming oceans are forcing corals to adapt to unprecedented temperatures. Those that do not have a tolerance for the elevated temperatures experience coral bleaching and eventually mortality. There is already research that looks to create genetically modified corals that can withstand a warming ocean. Madeleine J. H. van Oppen, James K. Oliver, Hollie M. Putnam, and Ruth D. Gates described four different ways that gradually increase in human intervention to genetically modify corals. These methods focus on altering the genetics of the zooxanthellae within coral rather than the alternative.

(REF:"How Reefs Are Made". Coral Reef Alliance. 2021. Archived from the original on 30 October 2021.) (REF:Lee, Jeong-Hyun; Chen, Jitao; Chough, Sung Kwun (1 June 2015). "The middle–late Cambrian reef transition and related geological events: A review and new view". Earth-Science Reviews. 145: ) (REF:Coral reefs NOAA National Ocean Service. )(REF:Spalding, Mark, Corinna Ravilious, and Edmund Green (2001). World Atlas of Coral Reefs. Berkeley, CA: University of California Press and UNEP/WCMC ISBN ) (REF: Greenfield, Patrick (17 September 2021). "Global coral cover has fallen by half since 1950s,)(REF: Danovaro, Roberto; Bongiorni, Lucia; Corinaldesi, Cinzia; Giovannelli, Donato; Damiani, Elisabetta; Astolfi, Paola; Greci, Lucedio; Pusceddu, Antonio (April 2008). "Sunscreens Cause Coral Bleaching by Promoting Viral Infections". Environmental Health Perspectives.)(REF: Minato, Charissa (1 July 2002). "Urban runoff and coastal water quality being researched for effects on coral reefs")(REF: "The Sixth Status of Corals of the World: 2020 Report". GCRMN.)(REF: Webster, Jody M.; Braga, Juan Carlos; Clague, David A.; Gallup, Christina; Hein, James R.; Potts, Donald C.; Renema, Willem; Riding, Robert; Riker-Coleman, Kristin; Silver, Eli; Wallace, Laura M. (1 March 2009). "Coral reef evolution on rapidly subsiding margins". Global and Planetary Change. 66)(REF: Tobin, Barry (2003) [1998]. "How the Great Barrier Reef was formed". Australian Institute of Marine Science. Archived from the original)(REF: Four Types of Coral Reef Archived 24 October 2012 at the Wayback Machine Microdocs, Stanford Education)(REF: Hallock, Pamela (1997), "Reefs and Reef Limestones in Earth History", Life and Death of Coral Reefs, Boston, MA: Springer US)(REF: Hopley, David (ed.) Encyclopedia of Modern Coral Reefs Dordrecht: Springer)(REF: Stoddart, D. R. (November 1969). "Ecology and morphology of recent coral reefs". Biological Reviews. 44)(REF: National Oceanic and Atmospheric Administration. Coral Reef Information System Glossary, 2014)(REF: Types of Coral Reefs Archived September 13, 2017, at the Wayback Machine at"What are Coral Reefs". Coral Reef Information System (CoRIS). National Oceanic and Atmospheric Administration)(REF: Are corals animals or plants? NOAA: National Ocean Service)(REF: Sorokin, Yuri I. (1993). Coral Reef Ecology. Germany: Springer-Verlag, Berlin Heidelberg.)(REF: Coral Reef Protection: What Are Coral Reefs?. US EPA.)

Broken Coral   10/7/13

Broken Coral

Broken Coral is sold assorted type and size. Cannot provide a specific size or type. The type can vary from picture.


One half pound of Broken Coral pieces 1/2 inch up to 5 inches........ $9.95

Cats Paw Coral 11/7/13

Stylophora common name cat's paw coral

These are in the genus of colonial stony corals part of the family Pocilloporidae. They are native to the Red Sea, the Indo-Pacific region and eastwards as far as the Pitcairn Islands.

Members of this genus are branching corals. The finger-like branches vary in width and have blunt tips. The growth forms and colors are variable depending on many factors, including the level of light and the amount of water movement. The color may be orange, pink, magenta, purple, green or brown.

Scientific classification

Domain: Eukaryota

Kingdom: Animalia

Phylum: Cnidaria

Class: Hexacorallia

Order: Scleractinia

Family: Pocilloporidae

Genus: Stylophora

Schweigger, 1820

(REF: Hoeksema, B. (2018). "Stylophora Schweigger, 1820". WoRMS. World Register of Marine Species.)(REF: Sprung, Julian (1999). Corals: A quick reference guide. Ricordea Publishing.)

coral branches shape can vary.


One 5 to 7 inch Cats Paw Coral branch .... $31.00


One 7 to 9 inch Cats Paw Coral......$42


One 9 to 11 inch Paw Coral ......$67.95


One 11 to 13 inch Cats Paw Coral Branch..... $96

Table Coral  10/7/13

Table Coral

Coral cluster shape can vary.


One Table Coral Cluster 7 to 10 inches..... $44.95


One Table Coral 10 to 12 inches ....$63

Brownstem Coral

Brownstem Coral

Coral cluster shape can vary.


One Brownstem Coral cluster 6 to 8 inches..... $27


One Brownstem Coral cluster 8 to 10 inches .... $31


One Brownstem Coral cluster 10 to 12 inches .....$52

Green Fire Coral

Green Fire Coral

Coral cluster shape can vary.


One Green Fire Coral cluster 5 to 7 inches..... OUT OF STOCK


One Green Fire Coral cluster 6 to 8 inches..... OUT OF STOCK


One Green Fire Coral cluster 8 to 10 inches ..... $45


One Green Fire Coral cluster 10 inches or greater... $59

Octopus Coral

Octopus Coral

  • The Octopus Coral branch shape can vary

  • 0C1-100 One Octopus Coral 10 to 12 inches..... OUT OF STOCK OC2-100 One Octopus Coral 12 to 15 inches..... OUT OF STOCK OC3-100 One Octopus Coral 15 to 17 or more inches..... OUT OF STOCK

    Elkhorn Coral Cluster

    Coral Clusters can vary in shape.


    One Elkhorn Coral branch 5 to 7 inches....$24


    One Elkhorn Coral branch 7 to 9 inches....$45


    One Elkhorn Coral branch 9 to 11 inches.....$69

  • ELK4-100
  • One Elkhorn Coral  12 to 15 inches.....OUT OF STOCK
  • Stag Horn Coral

    Stag Horn Coral

  • Stag Horn Coral branch shape can vary

  • SH1-100 One Stag Horn Coral 7 to 10 inches ..... OUT OF STOCK


    One Stag Horn Coral branch 10 to 12 inches......OUT OF STOCK


    One Stag Horn Coral 12 to 14 inches .....OUT OF STOCK


    One Stag Horn Coral 14 to 16 inches .....OUT OF STOCK

    Birdnext Coral

    Bird nest Coral

    Bird nest Coral clusters can vary in shape.


    One Bird nest Coral cluster 5 to 7 inches ..... OUT OF STOCK


    One Bird nest Coral cluster 7 to 9 inches ..... $42


    One Birdnest Coral cluster 9 to 11 inches .....OUT OF STOCK


    One Birdnest Coral cluster 11 inches or more...... OUT OF STOCK

    Branch Coral

    Branch Coral cluster created designs

    Branch Coral designed creations vary in shape


    One Branch Coral designed 7 to 10 inches ....$45


    One Branch Coral created design 10 to 12 inches ....OUT OF STOCK


    One Branch Coral created design 12 to 15 inches ..... $105

    Blue Ridge Coral

    Blue Ridge Coral

    Coral Cluster shape can vary. There will be some calcium deposit on base of coral, where it was attached.


    One Blue Ridge Coral cluster (natural color) 5 to 7 inches ...... $38


    <p><b>One Blue Ridge Coral cluster 7 to 10 inches</b> .... $45</p>


    One Blue Ridge Coral cluster 10 to 12 inches.... $59


    One Blue Ridge Coral cluster 12 to 14 inches.... $84

    Red Pipe Organ Coral

    Red Pipe Organ Coral

    Coral cluster shape will vary. There can be calcium deposits on the cluster base; where it was attached.


    One Red Pipe Organ Coral 5 to 7 inches...$26

    Lace Coral

    Lace Coral cluster

    Coral Cluster shapes can vary.


    One Lace Coral cluster 5 to 7 inches.... $24


    One Lace Coral cluster 7 to 9 inches.... $31


    Bowl Coral cluster

    Coral Cluster shapes can vary. Measured across bowl


    One Bowl Coral cluster 5 to 7 inches..... $29


    One Bowl Coral cluster 7 to 9 inches..... $42



    One Mushroom Coral piece 4 to 5 inches..... OUT OF STOCK


    One 5 to 6 inch Mushroom Coral piece.... $8.95


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