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Types of Coral Reef

There are three types of coral reef: fringing, barrier and atoll reefs.

Fringing reefs

Fringing reefs

  • These grow from a shore/coastline or are adjacent to (next to) one.
  • They are very sensitive to human activity.
  • The Bahamas has one of the world’s most extensive coral reef systems with lots of fringing reefs.
Barrier reefs

Barrier reefs

  • Barrier reefs are linear reefs (generally parallel to a shore).
  • They are separated from the shore by a lagoon
  • The Great Barrier Reef in Queensland, North East Australia is the world’s largest coral reef system and an example of a barrier reef.
  • Barrier reefs are sensitive to human activity
Atoll reefs

Atoll reefs

  • Atoll reefs are often circular.
  • They surround deep lagoons.
  • They are found mid-ocean.
  • Most of the world’s atolls are found in:
    • The Pacific Ocean: for example, Funafuti. Funafuti is a small coral atoll that’s only 20 meters (66 ft) wide at the narrowest parts, and about 400 meters (1300 ft) at the widest part of the island.
    • The Indian Ocean: for example, The Maldives. The Maldives is made up of about 1,200 tiny coral islands grouped into 26 atolls.
How do atoll reefs form?

How do atoll reefs form?

  • Corals start to grow around a volcanic island, which forms a fringing reef.
  • The reef continues to expand over hundreds of thousands of years.
  • As the reef expands, the interior island starts to subside.
  • The fringing reef becomes a barrier reef.
  • Eventually, the island will completely subside beneath the water.
  • This leaves a ring of coral with a lagoon in the centre (atoll reef).
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