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How are coral reefs formed, what are their main types, and why are coral reefs important?

author:Extraordinary says energy

Often referred to as the "rainforest of the sea," coral reefs are considered the most productive ecosystems in the world, known for their biodiversity and various ecosystem services. Coral reefs are mainly formed by calcium carbonate produced by the colony of coral polyps that build them. Coral reefs cover about 109,800 square miles, or just 0.1 percent of the ocean's surface. The economic value of global coral reefs is estimated to be between $29.8 billion and $375 billion per year, and about 500 million people worldwide depend on them for their livelihoods. However, human activities currently pose a serious threat to coral reefs, resulting in a decline of about 50 per cent in their populations.

01 Formation and types of coral reefs

It is thought that ice melting during the last glacial period caused sea levels to rise and the continental shelf to be flooded, creating coral reefs. Sir Charles Darwin outlined the theory of atoll formation in his book The Structure and Distribution of Coral Reefs. According to the theory, the gradual subsidence and tectonic uplift of the earth's crust under the vast ocean led to the formation of atolls. Darwin also proposed three stages of atoll formation: first, the extinction of volcanic islands; Second, the subsidence of the island and seabed led to the formation of marginal reefs around the extinct volcanic islands; Third, as it continues to sink, the marginal reef gradually becomes a barrier reef and finally an atoll.

Depending on the formation pattern, we can find three different types of coral reefs in different parts of the planet. These are edge reefs, barrier reefs, and atolls.

- Edge reef

How are coral reefs formed, what are their main types, and why are coral reefs important?

Divers explore the edge coral reefs of the Red Sea

Marginal reefs, also known as coastal reefs, are located on the continental edge or near the coast of volcanic islands. This type of reef extends several miles from the coast, with a shallow channel in the middle separating the reef edge from the shore. Marginal reefs are considered the most common and youngest of the three reef types, consisting mainly of coral sand, mud, dead coral, and living coral colonies. Marginal coral reefs are found off the coast of Florida, Mannar Bay, and the New Hebrides Society Islands. Along the Red Sea coast you can see the most developed edge coral reefs in the world.

- Barrier Reef

How are coral reefs formed, what are their main types, and why are coral reefs important?

Aerial view of the Great Barrier Reef, Australia

The barrier reef is considered the largest of the three reef types, and these large linear reef groups develop along the continental coastal edge. The coral reef is almost parallel to the coast, separated from the mainland by a large and deep lagoon. Because these reefs take more time to form than marginal reefs, barrier reefs are rare. The most famous example of this type of reef is the 1400-mile-long Great Barrier Reef off Australia's northeast coast. Some other notable coral reefs include Belize Barrier Reef and New Caledonia Barrier Reef.

- Atolls

How are coral reefs formed, what are their main types, and why are coral reefs important?

Aerial view of the Pacific atore

Atolls, usually located in the center of the sea, are horseshoe-shaped coral reefs that partially or wholly surround a deep central lagoon. Atolls are formed when volcanic islands are surrounded by marginal coral reefs and sink into the sea. The edge reef continues to grow and forms a circle around the central lagoon. This circular ring is broken in some places, forming a channel that allows the movement of the water, which in turn connects the central lagoon to the open sea. Most known atolls are located in the South Pacific Ocean, mainly in the Caroline Islands, the Marshall Islands, the Cook Islands, French Polynesia and Micronesia. Some of the famous atolls in the Indian Ocean include the Chagos Archipelago, Maldives, Seychelles and Cocos Island.

02 Conditions required for coral reef formation

Reef-building corals are extremely sensitive to temperature fluctuations and are commonly found in tropical and subtropical oceans, where annual water temperatures range from 79 to 81 degrees Fahrenheit. Corals also need a suitable range of salinity for reef building. It is estimated that if the salinity is below 20ppt for more than a day, it will lead to the death of corals and other coral reef-related organisms. Polyps have a symbiotic relationship with the tiny zooxanthellae, which are found in the tissues of polyps and provide nutrients to polyps. Because of this important relationship between polyps and zooxanthellae, coral reefs are often found in clear, sediment-free shallow waters that absorb more sunlight.

In addition to these three main classical reef types, scientists and researchers have also discovered a number of other types of reefs. These reef types include platform reefs, patch reefs, apron reefs, ribbon reefs, shore reefs, microatolls, etc.

03 Biodiversity of coral reefs

How are coral reefs formed, what are their main types, and why are coral reefs important?

Coral reefs support the diversity of marine life and are also spawning grounds for many fish species

The complex and diverse habitats of coral reefs are home to a variety of marine life. Coral reef ecosystems support about 250,000 known marine species on Earth, including 4,000 species of fish, 700 species of corals and many other aquatic plants and animals, the study said. Different organisms, such as cyanobacteria, phytoplankton, seagrasses, micro-algae, and macroalgae, play the role of autotrophs in coral reef ecosystems. Coral reefs provide ideal habitat and safe refuge for many fish, echinoderms, sponges, turtles, crustaceans, molluscs, anemones, and a variety of other marine animal species.

Some of the famous fish found in coral reef ecosystems include cardinalfish, butterflyfish, parrotfish, stickleback, rabbitfish, small tropical fish, trumpetfish, etc. Different sharks such as carpet sharks, bamboo sharks, white-tipped sharks, and nurse sharks can also be observed on the reef. In addition, coral reef ecosystems are important habitats for several species of seabirds. For example, Hawaii's Midway Atoll is home to more than 3 million seabirds, including large numbers of black-backed albatrosses and black-footed albatrosses.

04 The importance of coral reefs

How are coral reefs formed, what are their main types, and why are coral reefs important?

Coral reefs are rich in fish life and provide fishing opportunities for communities, thus supporting their livelihoods.

Coral reefs provide a variety of ecosystem services, such as shoreline protection, fisheries and tourism. More than 500 million people depend on coral reefs for ecosystem services, and the global economic value of coral reefs ranges from $29.8 billion to $375 billion annually. As low-wave peak breakwaters, coral reefs absorb 97% of wave energy, protecting coastlines from tropical storms and wave action. This helps prevent significant property damage and loss of life. In addition, the reef provides about 6 million tons of fish per year. Well-managed coral reefs produce an average of 15 tonnes of seafood per square kilometre per year. Coral reef fisheries in Southeast Asia alone have been recorded to earn about $2.4 billion annually from seafood.

05 Threats to coral reefs

How are coral reefs formed, what are their main types, and why are coral reefs important?

The process by which coral reefs lose their color is known as coral bleaching, which occurs due to ocean acidification

However, despite the multiple ecosystem services of coral reefs to humans and other life forms, they are highly threatened by climate change, increased greenhouse gas emissions, ocean warming and acidification, pollution and various other anthropogenic activities. Worldwide, coral reefs are greatly affected by global warming and climate change, which has led to a warming of the Earth's atmosphere and an increase in the surface temperature of seawater. Microscopic zooxanthellae that live in the tissues of polyps are very sensitive to high temperatures. Therefore, a slight change in sea temperature causes corals to expel zooxanthellae, which can lead to bleaching of coral tissue. When exposed to warm waters for several days, these bleached corals die, turning the reef into a barren habitat.

Human activities, such as the overburning of fossil fuels, increase the process of carbon dioxide, destroying corals' ability to build calcium carbonate exoskeletons. This makes coral reefs more vulnerable to disease and ultimately destroys their structures. In addition, coral reefs face serious threats from a variety of local sources, such as pollutants discharged into the ocean, the growth of harmful algae and bacteria, increased sediments, coral exploitation, toxic chemicals, marine litter, destructive fishing practices and irresponsible tourism. Makes seawater acidic. Carbonic acid formed during acidification.

How are coral reefs formed, what are their main types, and why are coral reefs important?

Beautiful coral reefs around Lombok, Indonesia

As mentioned above, coral reefs are highly productive aquatic ecosystems, known for their rich biodiversity and range of ecosystem services they provide. Researchers believe that the combination of rising surface water temperatures and ocean acidification will lead to significant changes in coral reefs in the coming decades. To help address this, many countries have passed legislation aimed at reducing greenhouse gas emissions. Over the past few decades, Earth's coral reefs have seen unprecedented deaths, and researchers have begun "coral farming" to restore damaged reefs.

Source: Coral Reefs - WorldAtlas

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