Explanation:

Barrier reefs are separated from a mainland or island shore by a deep channel or lagoon. Their lagoons can be several kilometres wide and 30 to 70 metres deep. The best known and largest example of a barrier reef is the Australian Great Barrier Reef.?                   Platform reefs, variously called bank or table reefs, can form on the continental shelf, as well as in the open ocean, in fact anywhere where the seabed rises close enough to the surface of the ocean to enable the growth of zooxanthemic, reef-forming corals. This is the case, for example, on the east coast of the Red Sea near Jeddah.                                                                                              Atolls or atoll reefs are a more or less circular or continuous barrier reef that extends all the way around a lagoon without a central island. They are usually formed from fringing reefs around volcanic islands. Over time, the island erodes away and sinks below sea level.?  Atolls are numerous in the South Pacific, where they usually occur in mid-ocean.                                                                      A fringing reef, also called a shore reef, is directly attached to a shore, or borders it with an intervening narrow, shallow channel or lagoon. Fringing reefs follow coastlines and can extend for many kilometres. The fringing reefs of the Red Sea are "some of the best developed in the world".