What is the Great Barrier Reef?

Some common questions about the Great Barrier Reef

• What is the Great Barrier Reef?
• How old is the Barrier Reef?
• What is coral?
• What makes up a coral reef?
• Types of coral reef

What is the Great Barrier Reef?

The Great Barrier Reef is the largest coral reef system in the world. In fact, it is the largest natural feature on earth and can be seen from space.

It is home to thousands of marine animals and a truly beautiful place.

Located off the North Queensland Coast of Australia it is a playground for whales, dlophins and tourists alike.

The Great Barrier Reef is a system of coral reefs that supports the planet's most complex ecosystem. (An ecosystem is the term used to describe a 'society' of plants and animals that are dependant on and interact with one another for survival).

Over time, the coral reefs grow and join together making larger reefs that get to support more and more life.

The Great Barrier Reef is made up of a few thousand separate coral reefs, cays, islands and lagoons making it by far the largest reef system in the world.

Sections of the Great Barrier Reef

How old is it?

It's thought that the Great Barrier Reef originated around half a million years ago, but it's widely accepted that the present structure that we know and see is between 6000 and 8000 years old, having become established since the last ice age.

Coral growth rates vary immensely, from just one centimeter a year to maybe 15 or 20 cm/year, depending on the species. But the larger hard corals, that make up the basis of reef systems, have the slowest growth rates. This explains why coral reefs can take hundreds or even thousands of years to develop.

Since the origins of the Reef first began many millennia ago, sea levels have fluctuated greatly over long periods of time due to shifting continents and ice ages of varying time spans.
Because coral can't survive out of water, if the sea level drops and exposes a living coral reef, then that reef will die very quickly.
If the sea level rises again, new coral reefs will form on top of the old ones, and so the cycle starts over. This cycle happens over thousands and thousands of years.

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What is coral?

Coral is actually an animal, not a type of sea-plant that it was once thought of.

There are two types of coral - hard and soft coral. The hard corals are the ones that you probably associate with coral reefs, but the soft corals are equally as abundant.

Both types of coral share the same body, called a polyp.
A polyp is similar to a very small sea anemone with a tubular body and tentacles around its mouth.
The polyps of hard corals secrete a type of calcium that builds up over time to form a hard skeleton around the polyp, forming the recognizable structure that we see.

Coral polyps are very simple organisms that feed on microscopic plankton floating around in the sea. They use the fine tentacles to catch the plankton, and feeding usually occurs during the night.

The food that is caught is passed down through the body of the polyp to its digestive system, but this isn't the only way that energy is gained; algae lives inside the walls of the polyp body and because algae is a plant, it photosynthesises to create sugars that also help feed the polyp, supplying it with much of its nutrition.
In most cases, it's actually the algae that give corals their color.

As different corals grow and join together, a reef forms. Different types of coral such as brain coral, fan coral and fire coral can all live together to form a typical coral reef.

Above, many different types of coral make up a reef

What makes up a coral reef?

The term coral reef is used to describe an area of numerous corals that have grown and joined together, and support other animal and plant life.

Coral Reefs are only found in warmer tropical waters, and the water also needs to be free of pollutants.
All corals are very sensitive to any kind of change in water temperature and pollution, and a reef can be very easily and quickly destroyed, either by natural events or (more commonly) human activities.
A reef that might have taken hundreds of years to grow can be completely destroyed in under a year if water conditions deteriorate enough.

Types of coral reef

The main types are platform reef, fringing reef, barrier reefs and atolls.
The pictures below show the different types of reef:

A platform reef forms when coral reaches the surface of the sea it branches out and grows horizontally. The familiar flat structures form just beneath the surface.

A fringing reef is one that grows away from, but very close to, an area of mainland or island coast.

A barrier reef grows further out from the mainland. Sometimes the area between the reef and the mainland will silt up, forming a lagoon.

An atoll is formed when a reef grows in a pyramid shape, rather like a volcano. A lagoon forms in the center of the surrounding reef, and smaller reefs may grow within this lagoon.

 

Related pages

Great Barrier Reef facts and figures

Great Barrier Reef history - how and when it began