Coral reefs are structures built from the remains of long dead small marine organisms. The amount of reefs in the world's oceans cover nearly 10,000 square miles of the ocean's shallow water marine areas. The worlds beautiful reefs are full of a huge variety of animals and organisms that are vital to the health of the coral reef.
Types of Coral Reefs
There are three major types of coral reefs. These include fringing reefs, barrier reeds and atolls. The most common type of coral reef found in the ocean is fringing reefs. This type of coral reef occurs adjacent to land with very little separation from the shore. These develop through upward growth of reef-forming corals. Barrier reefs are broader than fringing reefs and are farther from the shore. They are usually separated from the shore by a lagoon which can be miles wide and yards deep depending on the area. Atolls are ring-shaped reefs, which enclose a central lagoon. Most atolls are far from land, such as those found in the South Pacific. In both barrier reefs and atolls parts of the coral reef may protrude above the water forming coral islands. There are two other types of reefs are patch reefs, small structures found within the lagoons of other reefs, and bank reefs which are several reef structures that have link to a coastline.
The Formation of Coral Reefs
Coral reefs are made up of animals called polyps. The major group of reef-building corals is called stony corals. The polyps of these groups secrete limestone which builds substrate up underneath them. The polyps rely on an organism called Zooxanthaellae for their nutritional needs. Mollusks and echinoderms both add their skeletal remains to the reef when they die. Algae are also involved in helping to bind sand and coral fragments together. Boring organisms help the reef develop breaking coral skeletons into the sand. Reefs do not grow in a continuous manner, instead the experience growth spurts.
Distribution of Coral Reefs
Stony coral grows in shallow waters that are clear and receive a lot of sunlight. They need to be in water that is a minimum of 64 degrees, and they thrive in 77-84 degree waters. Generally coral reefs require little wave action. The conditions that coral reefs require to grow well are only found in a few tropical and subtropical areas. The Indo-pacific region, which is from the red sea to the Central Pacific have the highest concentration of coral reefs. Another area with a medium amount of coral reefs is the Caribbean Sea.