![]() ![]() Water properties such as temperature and chemical composition tend to dictate the health of a reef. Each sedentary animal that is part of a reef possesses a hard exoskeleton that contributes to its strength and rock-like appearance, but it is the algae beneath the surface that gives each polyp its color.Ĭoral reefs vary greatly in size and type, but all are highly sensitive to changes in the water. Algae, which live protected in coral polyps, make much of the food consumed by a reef. This hard substance is also found in many rocks and minerals.Ĭorals and algae have a mutually beneficial or symbiotic relationship. These sessile or immobile creatures cluster with other corals to form colonies and bind themselves together to form a reef by secreting calcium carbonate. Polyps are small marine invertebrates that are unable to move. As you will read, the Great Barrier Reef is the largest in the world by both length and area.Ī coral reef is a submerged oceanic structure made of many different polyps. Nearly all of the world’s coral reefs, particularly the largest reefs, are located in the tropics. ![]() Additionally, the islands are of higher elevation and have a wide reef-front terrace.Covering only about one percent of the ocean floor, reefs are home to an estimated 25 percent of the world's marine species, from fish to sponges. However, it is generally a pseudo-atoll since it has a ring of islands that look like atolls but had a very different mode of formation. Pseudo-Atollīermuda, an island country in the North Atlantic Ocean, is sometimes referred to as the northernmost atoll. Ultimately, the island sinks below the sea and the barrier reef becomes an atoll. The barrier reef has a deeper lagoon and protects it from harsh waves and wind. ![]() As the top subsides to become a guyot, fringing reef becomes a barrier reef. As it erodes, the top is made flat by the ocean waves. Over the years, the volcanic island will erode and sink to the seafloor through a process known as subsidence. The shallow strip of water between the island and the fringing reef is the lagoon. At this point, the coral reef is known as a fringing reef and surrounds the island just below the water surface. These corals begin to build reefs around these islands, creating a hard exoskeleton of limestone. The next stage of the formation of an atoll involves tiny sea animals known as corals. The top of this volcano is what is known as the oceanic island. As it continues to erupt, the seamount increases in elevation and finally breaks to the surface of the water. When this volcano erupts, it spills lava on the floor of the sea. The development of an atoll starts with an eruption of an underwater volcano known as a seamount. The closest atoll to the Equator is Kiribati’s Aranuka. Those in the extreme south are Elizabeth Reef and Middleton Reef, both of which belong to the Coral Sea Island. Kure Atoll together with those of the Northwestern Hawaiian Islands are the extreme northern atolls. Those in the Atlantic Ocean are relatively smaller with the notable ones located in the eastern part of Nicaragua. Quite a number of atolls are also concentrated in the Indian Ocean. The majority of the known atolls are found in the Pacific Ocean where they are mainly concentrated in the Marshall Island, Caroline Island, Tuamotu Island, Coral Sea Island, and other island groups such as Tokelau, Tuvalu, and Kiribati. Thus, atolls can only be found in the subtropical and tropical regions. Distribution of AtollsĬorals that are able to build reefs mainly thrive in warm waters of the oceans in the tropical and subtropical regions. Atolls are mostly hidden by ocean waves, with some wrecking canoes and ships. The modern definition of atoll describes it as an annular reef that has enclosed a lagoon in which there is no raised mass of land projecting into the body of water. It is usually formed from a fringing reef around a volcanic island. An atoll is a type of coral reef with a coral rim that partially or completely surrounds a water body known as a lagoon. There are four types of coral reefs including table reef, barrier reef, fringing reef, and atoll. One of the most common features that characterize oceans or seas are the coral reefs. ![]() What Is An Atoll? Atolls of the Maldives. ![]()
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