The Great Barrier Reef is the largest coral reef in the world. It is made up of a collection of over 2,900 individual coral reefs and 600 idyllic islands located along the north eastern coastline of Australia.
The Great Barrier Reef ecosystem is home to plants and animals as small as microscopic plankton to massive whales weighing hundred tonnes. It has the most diverse range of underwater animals found anywhere on earth.
This world heritage site has many attractions and things to do such as snorkelling, scuba diving, swimming, sailing, whale and dolphin watching and lots more. Over two million tourists visit the area each year to enjoys these wonders of nature.
Location of the Great Barrier Reef
The Great Barrier Reef (marked in grey on the map) is located between 15 to 150 kilometres off the north-eastern coast of Queensland, Australia in the Coral Sea in the Pacific Ocean. It extends from the tip of Cape York Peninsula in the north to Bundaberg in the south.
Length of the Great Barrier Reef
The Great Barrier Reef is 2,300 km (1,450 miles) long. This is about the same distance along the west coast of North America starting at Vancouver and ending in San Diego. The width of the reef varies from between 60 to 250 kilometres wide. To provide a scale of the sheer magnitude of this reef; the Belize Reef in the Caribbean, which is the second longest reef in the world, is just 290 km.
Size of the Great Barrier Reef
The total area of the Great Barrier Reef is 344,000 sq kilometres. It has an average depth of 35 meters in its in-shore waters. The outer reefs extends over 2000 metres. Coral however do not live at these great depths. In terms of size, it is as big as Germany or Japan and half as big as Texas. It is so large, that it is the only living organism on the planet that is visible from space.
Structure of The Great Barrier Reef What is the Great Barrier Reef Made of?
Coral reefs, such as The Great Barrier Reef, are natural underwater ecosystems built from calcium carbonate structures made from the accumulation of the bodies of billions tiny animals known as coral polyps. In fact, most of the coral structure is made up the calcified remains of dead coral polyps. Only the topmost layers are alive. With the right amount of sunlight, water conditions and temperature, and over long periods of time, corals form the structures the make up the beautiful reefs we see today.
An individual polyp has a tubular body with tentacles surrounding the mouth at the upper end. The polyp lives inside a stony translucent (see-through) limestone case made of calcium carbonate. It constructs this case by extracting calcium from the water.
Corals can live individually or on large colonies containing thousands of polyps. The brain coral, for example, is made up of thousands of little polyps no bigger than the size of a pinhead.
The Great Barrier Reef has the world's most diverse range of underwater animals. These include:
• 1,625 species of fish
• 360 types of coral
• 3,000 types of molluscs (like giant clams and the sea slug)
• 215 species of birds
• 14 species of sea snake
• 6 out of the world's 7 species of sea turtle (all listed as threatened)
• 630 species of echinoderm ( starfish, sea urchins)
• 30 species of cetaceans (whales and dolphins)
• 22 species of sea birds and 32 species of shorebirds
• 30 species of dolphins and whales
• 133 species of sharks and rays
• 1,300 species of crustaceans (crabs, prawns)
• 450 species of hard coral
• 40 species of sea anemones
• 150 species of soft coral and sea pens
• 100 jelly fish (blue bottle, box jellyfish)
The Great Barrier Reef does not have sea-forests with underwater trees and scrubs. The most prevalent type of plants are sea grasses. It also contained various types of algae such as seaweed, which are not true plants at all. Mangroves, which are actually terrestrial plants that is they grow above the surface of the sea but have their roots in it, are also considered part of the Great Barrier Reef flora.
Fifteen species of sea grasses grow in the Great Barrier Reef. Sea grasses are true plants (unlike seaweed and algae) with roots, flowers and seeds. They are most often found in shallow and protected lagoons referred to as back reefs which are usually found between a coral reef and the shore. Vast sea grass meadows are home to a diverse community of organisms and an important food source for turtles, dugongs, fish, octopuses, squids, cuttlefish, snails, oysters, sponges, shrimps, sea fleas, worms, urchins, anemones, micro-algae, crabs, polychaetes, clams, diatoms, dinoflagellates, copepods and many other creatures.
Seaweeds are marine algae. Like plants, seaweeds require sunlight for photosynthesis. Since they don't have roots they require a hard surface such as dead coral or rock to attach themselves to. There are over 400 species of marine algae growing in the Great Barrier Reef. Algae are major reef formers and create habitats for numerous numerous animals. They are also a major source of food for a large variety of herbivores, fishes, crabs, sea urchins and zooplankton. They also leak organic carbon into the water which is consumed by bacteria who in turn are consumed by many filter feeders.
Mangroves are plants that grow along many parts of the coastline along the Great Barrier Reef. There are 39 species of these plants that cover an area of approximately 3800 km2 of coastline. These represent almost all of the mangroves species found in Australia and half all mangrove species in the world. Mangroves provide a important buffer between land and reef. They benefit the reef by stabilizing shorelines, improving water quality by filtering out land runoff and pollutants. The extensive prop root systems of mangroves provide nursery habitats and protection for many reef animals.
The age of the Great Barrier Reef is about 6,000 to 8,000 years. 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 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.
The Great Barrier Reef is a very sensitive ecosystem. Many natural factors affect its heath.
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 act as a means of natural population control by eating coral polyps and making room for new coral to form.
Once in about every 17 years or so crown of thorns starfish appear in plague proportion, denuding vast tracts of the reef. It is thought that these outbreaks are related to increased rainfall and nutrient flows from flooded rivers.
The symbiotic algae which usually resides with the coral can sometimes put strain on the host causing it to eject the algae. Mass expulsions of the algae is known as coral bleaching (because the algae contribute to coral's 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. A coral bleaching event in 2002 affect nearly 50% of the coral on the Great Barrier Reef.
These reefs take thousands of years to form. People can easily damage them by:
• Walking on them
• Dropping anchors on them
• Dragging diving gear over them
• Breaking them and taking them 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.
The Great Barrier Reef is a protected wilderness areas and a World Heritage Site since 1975. It is strictly managed to minimise human induced pollutants. However the reef straddles an area with significant human activity which invariably results in human environmental damage. There are over 12 ports along the Great Barrier Reef with thousands of sea-going vessels travelling about it each day. Over 6,500 large ships also navigate through it each year.
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 on Great Barrier Reef
Sediments, nutrients, fertilisers, pesticides, toxic chemicals, sewage, rubbish, detergents, heavy metals and oil run into rivers and out to the Great Barrier Reef, where they can threaten plants and animals on the reef.
The Great Barrier Reef was sighted by various European explorers from as early as the 17th century but none of them provided it with a name remembered today.
It was Matthew Flinders, who was the first to survey the entire Australian coastline between 1801 and 1803, who gave it a name that stuck. He actually called it the Extensive Barrier Reef. Over time this name morphed into The Great Barrier Reef.
• Great – It is the largest and longest coral reef in the world being over 2,300 kms in length and covering an area of approximately 344,400 km²
• Barrier – The reef acts as massive a natural barrier protecting the coastline and is separated from the coastline by a deep channel of water.
• Reef – A natural underwater ridge just below the surface close to a shoreline is called a reef.
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