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Understanding the Different Types of Reefs

Understanding the Different Types of Reefs

Written by Nevin
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Published on September 1, 2009
two scuba divers with fish, reef, coral, and turtle

Reefs are often referred to as the rainforests of the oceans, often playing host to an extraordinary variety of marine plants and animals.  Here is a brief compilation of the different types of reefs you may encounter on your dives which may help broaden your knowledge of this hobby and help you appreciate the reef ecosystems all the more.

Types of Reefs

Biotic Reefs

Biotic Reefs are created through natural processes and comprise primarily of Coral Reefs and Oyster Reefs.

Oyster Reefs

Oyster reefs are often referred to as oyster bars and are common submerged habitats in the found in near shore areas and estuaries, but grow especially vigorously near river mouths where waters are brackish and less than 10 meters deep. Oysters reproduce and settle on the shells of other oysters and thus, over time, the oysters may form massive reef structures consisting of staggering numbers of individuals. These Oyster reefs play host to several species of breeding fish, smaller organisms and snails often forming a complete microhabitat.

Coral Reefs

Coral reefs are the most popular form of biotic reefs found in the world today, which are formed with a combination of the growth of coral and algae. Corals need warm water between 18°C and 30°C and bright sunlight. Most coral reefs lie between the latitudes of 30 degrees north and south where sea temperatures are warmest.  There are three main types of Coral Reef:  Fringing, Barrier Reefs and Atolls.

Fringing Reefs

A fringing reef is a submerged platform of living coral that extends from the shore to the sea. It is the most commonly found type of coral reef that can develop in shallow waters (usually 10m) along the coast of tropical islands or continents. The corals grow upwards to sea level or just below and outwards towards the open ocean. Fringing reefs are generally narrow platforms a short distance from shore and don’t contain a substantial lagoon. Fringing reefs are also formed on top of a harder substrate material like limestone or volcanic rock.

Barrier Reefs

A barrier reef is a fringing reef that is separated from the mainland or the island by a deep lagoon. Corals grow on both the calm waters of the lagoon as well as the seaward reef front. The most popular Barrier Reef is Australia’s Great Barrier reef that is the largest reef system in the world. The other popular barrier reef is the Belize barrier reef which is the second largest in the world stretching from Mexico along the coast of Belize to the Bay Islands of Honduras.

Atolls

An atoll is a circular barrier reef forming an island that encircles completely or partially a central lagoon. Parts of the reef may emerge from the water as small islets. It is said that atolls form due to the gradual sinking of oceanic islands over thousands of years. The fringing reef around the island gradually grows as the central parts crumble and build onto the edges, forming a barrier reef until the central portion is completely submerged  thus emerging a circular atoll.

Abiotic Reefs

Abiotic reefs are a result of a manmade/non living process either influencing the creation of the reef, such as erosion, sand depositing, dumping rocks, underwater blasting etc. The abiotic reefs also consist of Artificial Reefs created with the intent to break waves, reduce erosion or increase the bio diversity promoting marine life in areas of generally featureless bottom. Shipwrecks and sunken oil rigs also contribute to the formation of Abiotic Artificial reefs. Often artificial reefs are created deliberately for diving, but double as reef conservation measures as well by creating a habitat for reef creatures.