The multi-colored coral formations of the Great Barrier Reef comprise living polyps of the family Coelenterata.
These are polyps which excrete lime, forming a hard exterior.
The colors of coral come from live polyps. They turn white when they die.
Some of the corals may have the shells of different-colored clams embedded in them.
The colorful corals are a habitat of equally colorful fish. There are an estimated 1500 species of fish in the Great Barrier Reef as well as innumerable molluscs and crustaceans.
Types of islands
The true coral islands are called cays and have been formed by dead coral ground down to sand by the action of the sea. They are low-lying islands which may or may not have vegetation.
Some large cays have been developed as tour destinations and even as island resorts such as Heron Island off Gladstone.
South of the Great Barrier Reef are vegetated sand islands, such as Fraser Island (Australia’s fourth largest island) north of the Sunshine Coast or North Stradbroke off the Gold Coast.
Closer to shore along the Queensland coast are continental islands which in ages past could have been land peaks which eventually became encircled by water. These include Great Keppel, the Whitsundays, Hinchinbrook and Dunk.
These continental islands may have fringing reefs as well but, strictly speaking, are not part of the great Barrier Reef.
