Coral Reef - Types

Types

The three principal reef types are:

• Fringing reef – this type is directly attached to a shore, or borders it with an intervening shallow channel or lagoon.
• Barrier reef – a reef separated from a mainland or island shore by a deep channel or lagoon
• Atoll reef – this more or less circular or continuous barrier reef extends all the way around a lagoon without a central island.

Other reef types or variants are:

• Patch reef – this type is an isolated, comparatively small reef outcrop, usually within a lagoon or embayment, often circular and surrounded by sand or seagrass. Patch reefs are common.
• Apron reef – a short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore
• Bank reef – a linear or semicircular shaped-outline, larger than a patch reef
• Ribbon reef – a long, narrow, possibly winding reef, usually associated with an atoll lagoon
• Table reef – an isolated reef, approaching an atoll type, but without a lagoon
• Habili – this is a reef in the Red Sea that does not reach the surface near enough to cause visible surf, although it may be a hazard to ships (from the Arabic for "unborn").
• Microatoll – certain species of corals form communities called microatolls. The vertical growth of microatolls is limited by average tidal height. By analyzing growth morphologies, microatolls offer a low-resolution record of patterns of sea level change. Fossilized microatolls can also be dated using radioactive carbon dating. Such methods have been used to reconstruct Holocene sea levels.

• Cays – are small, low-elevation, sandy islands formed on the surface of coral reefs. Material eroded from the reef piles up on parts of the reef or lagoon, forming an area above sea level. Plants can stabilize cays enough to become habitable by humans. Cays occur in tropical environments throughout the Pacific, Atlantic and Indian Oceans (including the Caribbean and on the Great Barrier Reef and Belize Barrier Reef), where they provide habitable and agricultural land for hundreds of thousands of people.

• When a coral reef cannot keep up with the sinking of a volcanic island, a seamount or guyot is formed. The tops of seamounts and guyots are below the surface. Seamounts are rounded at the top and guyots are flat. The flat top of the guyot, also called a tablemount, is due to erosion by waves, winds, and atmospheric processes.