1988 The Barrier Reef World Draft Ed

Rationale

The study of coral reefs is important for providing a clear, scientifically-testable record of climatic events over the past million years or so. This includes records of recent major storms and human impacts that are recorded by the changes in coral growth patterns.

Reefs occupy less than 0.2% of the seabed. Yet they run along more than 150 000 km of coastline in more than 100 countries and territories. By their massive formation between the surface and the first few tens of meters deep, coral reefs are a very effective for absorbing elements coming from the ocean. They absorb waves energy and contribute to environmental protection through the reduction of coastal erosion. They reduce the damage in case of storms, hurricanes, and in some way, the energy of tsunamis. In doing so, they protect both ecosystems located between the reefs and coasts, such as seagrass and lagoon for example, and human settlements located by the sea. Their impact is so effective that the man mimics immersing concrete structures along some of our fragile coasts. Without this protective role, our Queensland coastline would be a different looking place.

Coral cays are small islands formed of dead coral or coral shingle, either as a result of an old reef being elevated above the sea and then weathered, or from storms tossing coral rubble into a sand cay or reef flat.
From the air, coral cays can be seen forming at one end of reefs. Also, if you have studied another unit in this series called Coastal Physics, you will remember that waves as they pass around a reef bend. This process is called refraction.
A coral reef is living, growing and constantly changing. Waves, especially storm waves, are continually breaking up both living and dead coral and other limestone secreting organisms. Also, thousands of parrot fish are constantly chewing at the coral and breaking it down.
The rubble produced in this way is constantly being ground up and shifted by waves, tides and winds. Over a long period of time this coral rubble can be transported around the cay in the direction of the longshore drift and thrown up as sand by the wind, waves and currents onto the reef top on the sheltered or lee side.
When the rubble and sand are washed together in one spot they form a sand spit which may eventually develop into a true coral island called a cay.
Sand cays are small islands composed of sand which has been deposited by the slowing down of converging currents, and shaped by the action of wind, waves and currents.
Sand cays are often tempory, especially very small ones which appear and disappear, and when present, constantly change size and shape.

Heron Island, North West Island and Green Island are examples of the many sand cays that are found off Queensland's coast.