Coral Reefs Formation Types – Coral 102


There are several types of reef systems in the world’s oceans. The three major types of coral reefs around the world are atolls, fringing reefs and barrier reefs.

coral reef structures

Atolls are a roughly circular (annular) oceanic reef system surrounding a central lagoon.  They have a central lagoon that contains no significant land mass. The central lagoon is often deep (less than 25 m), but this is not a prerequisite. If land does exist, it sits atop a part of the encircling reef and is comprised solely of carbonate material derived from the reef. As originally defined for Pacific reefs, the term implies a specific genetic origin around a volcanic island. Caribbean and Atlantic atoll-like reefs are not of this type, and tend to form around isolated highs formed by local tectonics.

The Pacific Ocean is home to far more atolls than any of the other ocean basins, but the Indian Ocean also contains numerous examples this reef type. Only a relative few such reef formations occur in the tropical western Atlantic, or “Greater Caribbean” region however.  The three best examples (Glover’s, Lighthouse, and Turneffe) can be found just off the the Belize barrier reef.

Barrier Reef – a reef system that parallel the shore and is separated from it by a wide lagoon that contains at least some deep portions.  Great Barrier in Australia is World’s largest.  Barrier reefs are often some distance from the coast. Some barrier reefs are attached to fringing reefs on shelving coastlines. In other cases these reefs may have developed in offshore places. Sometimes a lagoon separates a barrier reef from the coast.

Fringing Reef – a reef system that grow fairly close to (or directly from) the shore, with an entirely shallow lagoon or no lagoon at all Florida’s coral reef system most closely resembles a barrier reef, however, the reefs are closer to shore and they lack the shallow inshore lagoons found on most barrier reefs so it is more aptly named a bank reef.  This type of reef is directly attached to the shore. Fringing reefs grow quickly in shallow water but their growth further away from shore is slower. Fringing reefs have a shallow platform that spreads outward to a sharply defined edge. Imagine the reef like a shelve with an edge that drops down to the sea floor.

coral reef-types

Florida also has patch reefs, which grow between the reef tract and the land in shallower waters. Patch reefs are typically small (the size of your back yard or a small home). You will see these up and down the coast from Sebastian Inlet and South.  The term “patch reef” is commonly used to refer to comparatively small, isolated outcrops of coral surrounded by sand and/or seagrass.  They are all through the Florida Keys.

More than 45 species of stony corals and 37 species of octocorals(soft corals) are found along the Florida Reef Tract. Each kind lives in a separate colony that is shaped differently. The colonies take on the various hues of the algae that live within them. Corals can generally be divided into two main categories: stony corals and octocorals (sea fans and other soft corals). Marine sponges are also very important within the coral reef community and over 70 species can be found along the Florida Reef Tract.

Stony corals are the major reef architects. Polyps, the living portion of corals, extract calcium from seawater and combine it with carbon dioxide to construct the elaborate limestone skeletons that form the reef backbone.Florida’s most common reef-building corals are brain, star, elkhorn and staghorn. Brain coral is dome-shaped and has the waves, folds and ridges that resemble those of a human brain. Star coral is also dome-shaped, but has a distinctive star pattern on its surface that is caused by the accordion-like folds within its polyp cups. Elkhorn and staghorn corals are so named because their branchlike projections resemble the antlers of those animals. In recent years, corals have experienced declines due to a combination of factors, including coral disease and damage from hurricanes. In 2006, elkhorn and staghorn coral were listed as threatened species under the Endangered Species Act. To restore these corals that were once so abundant, coral nurseries have become established along Florida’s coast and in the Florida Keys. Nurseries are growing new colonies and successfully out-planting them to locations where they had once flourished.

Octocorals, some of which are also called gorgonians, look like strange trees and shrubs, although they too are composed of living polyps. Unlike stony corals, octocorals are unable to build thick limestone skeletons, but are supported by an internal structure composed of a horn-like substance called gorgonin.

The most common octocorals in Florida are sea fans and sea whips. Sea fans are pale lavender or green fan-shaped corals. Their fans flutter in the ocean current like lace curtains. Sea whips have long feathery branches that spread in all directions. They can be orange, lilac, purple, yellow, brown or buff.


Along the northern extension of the Florida Reef Tract, the reefs generally occur in a series of one to three discontinuous reef lines (terraces) that parallel the shoreline, extending north from Miami-Dade County to Martin County. Different reef organisms characterize the type of habitats found along Florida reefs, typically transitioning from a cover of algae and small octocorals nearshore to numerous octocorals and varied hard coral populations at the outer reefs. The various reef architectural and compositional components create an environment that is ecologically diverse and productive, one that supports many other aquatic plants and animals that make southeast Florida reefs their home.

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About daniellesdives

diving enthusiast
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