What is the Great Barrier Reef?
The Great Barrier Reef Queensland, Australia
The Great Barrier Reef is a coral reef which stretches along the east coast of Queensland Australia. It is the world's largest coral reef and the only living organism large enough to be visible from space. It is over 2,000km (1,250 miles) long and between 60 kilometres to 250 kilometres wide. It is made up of a collection of over 2,900 individual reefs very close to each other. It was declared a World Heritage area in 1975.
Over 1.6 million tourist visit the the Great Barrier Reef each year and over 6,000 ships navigate through it each year. It is ideal for water sports such as sailing, snorkelling, and diving. There is also an underwater observatory from where you can see the fantastic underwater biodiversity.
Where is Barrier Reef Located?
Extent of the Great Barrier Reef
What is a Coral Reef?
A coral reef is a natural barrier made of the bodies of millions of living and dead coral polyps.
Corals are ancient animals related to jellyfish and anemones. An individual coral is known as a polyp. Coral polyps grows just below the surface to a depth of up to 60 m in warm climates where there is clear salt water and sunlight. It is made of two parts:
Coral polyps: The colourful part of the coral is made up of millions of different sorts of marine polyps. These are soft-bodied invertebrate animals which have no backbone. An individual polyp has a tubular body with tentacles surrounding the mouth at the upper end. They form the living part of the coral. These polyps feed on various small organisms, from microscopic plankton to small fish. The polyp's tentacles grab onto their prey and kill them using stinging cells called nematocysts. The tentacles then contract to bring the prey into the stomach. Once digested, the stomach reopens and the waste products are eliminated. The polyp lives inside a stony limestone case it makes by extracting calcium from the water. Symbiotic algae live on the coral and transform sunlight into sugars through photosynthesis. The coral host help itself to some of the sugars and contributes some colour to the coral.
Hard corals: These are the remains of the cases dead polyps which have accumulated over the eons to form the solid portions and some the frameworks of some of the delicate and intricate structure of the of the reef.
How Old is the Great Barrier Reef?
The present Great Barrier Reef is about 6,000 to 8,000 years old
The original coral reefs started forming in the Pacific Ocean, in the Coral Sea, sometime between 58 and 48 million years ago. There were many reefs formed and then destroyed and reformed over the ensuing millions of years. When Australia drifted to its present position, the sea levels were altered around the area accelerating the formation of more coral reefs. The present coral reef is believed the have had two major phases of development. The first was about 600,000 years ago. This reef died due to changes in sea level and climate. The second phase started about 20,000 years ago when new coral started to grow on top of the remains of the older reef. As the sea levels rose, at end of the last glaciation period, the rising sea water started to cover low lying hills along the east coast of Australia. The coral reefs slowly started growing on this newly submerged land. Around 13,000 years ago the sea level stabilized. The current Great Barrier Reef configuration is about 6,000 to 8,000 years old.
Who Lives in the Great Barrier Reef?
The Great Barrier Reef has the world's most diverse range of underwater plants and animals
- • 1500 species of fish
- • 360 different types of coral
- • 5,000 molluscs (like clams and the sea slug)
- • 500 species of seaweed
- • 215 species of birds
- • 17 species of sea snake
- • 6 species of sea turtle (all listed as threatened)
- • 400 species of marine algae
- • 600 species of echinoderm ( starfish, sea urchins)
- • 30 species of cetaceans (whales and dolphins).
- • 22 species of sea birds and 32 species of shorebirds
Plants of the Great Barrier Reef
Sea Grasses: There are 15 species of seagrasses on the Great Barrier Reef. They are true plants, unlike seaweed and algae, because they have roots, flowers and seeds. They are the only flowering plants found in the sea. They are an important food source for turtles and dugongs. Vast meadows of them cover such huge areas that they are visible from outer space.
Seaweed There are over 400 species of marine algae. Red and brown algae are found closer to the shore while red and green algae are more prevalent in offshore areas.
Natural Threats to the Great Barrier Reef
Environmental: Coral is very sensitive changes to temperature, nutrient and water quality. Just a 1 or 2 degree change in the water temperature has been known to stress coral and cause coral bleaching. It is feared that global warming may severely impact the reef.
Crown of Thorns: These starfish destroy coral by eating it. It was once thought of as a great risk to the reef but recent research has shown that it is actually native to this habitat and may actually act as a means of natural population control by eating coral polyps and making room for new coral to form. Once in a bout every 17 years they appear to plague proportions denuding vast tracts of the reef. It is thought that these outbreaks are related to increased rainfall and nutrient flows from flooded rivers.
Algae: The symbiotic algae which usually resides with the coral can sometimes put strain on the host causing it to to eject the algae. Mass expulsions of the algae is known as coral bleaching (because the algae contribute to coral's brown colouration). This ejection seems to increase the polyp's chances of dealing with short-term stress. If the stressful conditions persist, the polyp eventually dies.
Human Threats to the Great Barrier Reef
These reefs take thousands of years to form. People can easily damage them by carelessness such as by:
- Walking on them
- Dropping anchors on them
- Dragging diving gear over them
- Breaking them and taking them home as souvenirs
- Knocking and grounding boats on them
Fortunately strict guidelines are presently enforced on all tour operators to ensure the protection of this vital natural asset.
Environmental Threats to the Great Barrier Reef
The Great Barrier Reef is a protected wilderness areas and since 1975 is now being strictly managed to minimise human induced pollutants. However the reef straddles an area with significant human activity.
Oil Spills and Ships Running Aground: Busy shipping channels traverse the reef and occasionally mishaps occur. Most recently bulk coal carrier Shen Neng 1 ran aground about 70km east of Great Keppel Island damaging its hulk and leaked a quantity of fuel oil into the water (The light blue area in the photograph on the left is caused by sand stirred up by the grounded vessel and not the actual fuel oil which was quickly contained).
Dumping and River Run-offs: Sediments and nutrients, fertilisers, pesticides, toxic chemicals, sewage, rubbish, detergents, heavy metals and oil run into rivers and out to the Great Barrier Reef lagoon, where they can threaten plants and animals on the reef.
How to Get to the Great Barrier Reef
Great Barrier Reef Attractions
Our Other Fascinating Pages
Australia has many animals found nowhere else in the world...View More
Great Barrier Reef
The Great Barrier Reef, Australia is the largest coral reef in the world...View More
The people migrated here from all over the world...View More
Aborigines - The First Australians
The Aborigines were the first people to come to Australia...View More