The Great Barrier Reef is the biggest group of coral reefs in the world.
It stretches along the coast on the north-east part of Australia. It is called the Great Barrier Reef because it creates a barrier between the Pacific Ocean and the coast.
The Great Barrier Reef is a scattering of thousands of individual reefs. The reefs is on the World Heritage List made by UNESCO, because of its size and its many different plants and fishes. The reef lies in the Great Barrier Reef Marine Park, the worlds largest marine park. It has an area of nearly 350 000 square kilometres. The reef region is 260 000 square kilometres. The reef region is a popular tourist attraction because of its warm climate, sandy beaches, colourful wildlife, tropical islands and ideal conditions for water sports.
The Great Barrier Reef stretches north and north-west from Gladstone, Queensland, to a point in the Gulf of Papua. The Great Barrier Reef is longer than 2000 kilometres and consists of nearly 3000 different reefs. An average reef is about 110 square kilometres in area. The area that The Great Barrier Reef lies in has relatively shallow waters of about 40 metres deep.
The Great Barrier Reef consists of billions of smal animals called coral polyps and plants called coralline algae. The coral reef is built up by dead corals, with a thin outside of living corals. A coral reef includes many species of corals, such as staghorn coral, brain coral, honeycomb coral and mound coral. Almost 1500 of 3000 kinds of fish known to live in the seas around Australia are found in the reef region. Angelfish, cod, manta rays, mackerel, butterfly fish and surgeon fish all live in reef waters. Other animals that live in the reef waters include crabs, shrimps, crayfish, sea urchins, sea stars, sea cucumbers, soft corals, sea fans, sponges, sea anemones and worms.
Experts think that parts of the Great Barrier Reef could be as much as 18 million years old. But the most of it have developed over the last 2 million years. The reefs on the top are only a few thousands years old, but most of these reefs are built upon a foundation of older reefs.
Sea level was more than 130 metres below todays level about 20 000 years ago. The existing reefs were at this time limestone hills rising from the plain. The sea level started to raise about 18 000 years ago, and the hills were covered with water. Corals began to grow again. The old reefs often provided the most suitable foundations for this new growth. When the land was covered by the rising sea, a number of mountain ranges were cut of from the main land to become continental islands. There are 616 islands in the reef region.
The climate of the Great Barrier Reef varies. In the north there is tropical conditions and high humidity and a wet season around January. In the south it is cooler, subtropical to temperate conditions. The water temperature in the south seldom falls below 20 C.
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