Formation of Coral Reefs

Coral reefs are among the world's more impressive eco-systems. A coral reef is the accumulation of hundreds and in some cases, thousands of years of coral colony growth. There are different types of coral reef formation, such as fringing reefs, barrier reefs and atoll reefs. The coral uses hard surfaces in the ocean as a base.

  1. Coral Build Up

    • Coral reefs are a mixture of a build up of dead corals and other organisms with limestone skeletons, held together by algae. The living coral consists of hundreds of thousands of coral polyps. These are soft bodied invertebrate animals. Corals take calcium carbonate from the water to form hard shell-like skeletons. Every polyp links its skeleton to other skeletons, thereby building up a colony of coral polyps. They continually create new skeletons at their base and sides, which extend the colony upwards and outwards. The colony continues to grow upon the skeleton that is already dead and turned into coralline limestone. A coral reef consists of many colonies, as well as the other organisms that make up the reef environment.

    Habitat

    • Coral reefs form in shallow water with maximum depths of around 200 feet. They are found in water temperatures between 64 and 91 degrees Fahrenheit. Whether they reside in cool, temperate water or warmer, tropical water depends on the species of coral that exist on the reef.

    Fringing Reefs

    • Fringing reefs form along coastlines and continental shelves, in shallow waters. The coral polyp colonies build on top of hard surfaces provided by the coast and grow upwards towards the surface, building further upon the colony as it dies. These fringing reefs project outwards from the shore and are found in the tropical water zones around the world.

    Barrier Reefs

    • Barrier reefs are formed parallel to coastlines, separated by a lagoon that develops between fringing reef and the land. The reef continues to grow offshore until it reaches the continental shelf. It is also possible for barrier reefs to originate offshore, if the sea bed is shallow enough to allow coral growth. The coral then grows upwards, pushing the oceanic island down, forming its own structure, and creating the lagoon between the reef and the shore. The most famous barrier reef is the Great Barrier Reef in Australia, which is large enough to be seen from space.

    Atoll Reefs

    • An atoll is a ring of reef, often found encircling an island of sand or coral rubble. A coral atoll will generally have a shallow, sheltered lagoon in the middle of the ring. There are channels that provide access to the open ocean as well as fresh and colder water for the lagoons. Atolls are built off the top of extinct submarine volcanoes. Once existing as fringing reefs around the volcanoes, the coral colonies continue to grow towards the surface, as the volcano sinks further into the ocean. This means that the visible atoll is based around the coral with little evidence of the submerged volcano. The majority of the world's atolls are found in the Pacific "Ring of Fire" due to their relationship with volcanoes.