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The Great Barrier Reef
The Great Barrier Reef is located off the coast of Queensland, Australia. It is the largest coral reef in the world, with a length of over 2000 kilometers and has the most diverse range of underwater animals anywhere in the world. The actual reefs are made of billions upon billions of minuscular animals call coral polyps that live together and construct this beautiful underwater habitat. This underwater ecosystem is home to creatures as small as microscopic plankton to massive whales weighing over a hundred tonnes.
The Great Barrier Reef is the only living organizing on the planet that is visible from space.
Great Barrier Reef Facts
The Great Barrier Reef is a collection of over 2,900 individual coral reefs and 900 idyllic white-beached islands located along the north eastern coastline of Australia. It is the world's largest coral reef. It is so large, in fact, that it is the only living organism visible from space. In terms of size, it is as big as Germany or Japan and half as big as Texas.
The Great Barrier Reef is renowned for the abundance of exotic plant and animal life. These range from microscopic planktons, to breathtaking corals, colourful fish, and a huge assortment of other marine creatures. It is estimated that about 10% of the world's entire fish species live in the area of the Great Barrier Reef. It is claimed that the Great Barrier Reef alone has more different types of fish than the entire Caribbean Ocean.
The Great Barrier Reef is listed as one of the Seven Wonders of the Natural World and was declared a World Heritage area in 1975. It is one of the most popular tourist destinations in Australia. Over two million tourists visit the area each year.
It is ideal place for snorkelling, scuba diving, sailing, whale and dolphin watching and lots more. There is also an underwater observatory from where you can see the fantastic underwater biodiversity.
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.
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.
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.
A saltwater coral reef is a natural barrier made of the bodies of billions of living and dead coral polyps. Despite looking like plants, corals are actually colonies of tiny animals related to jellyfish and sea anemones. The stunning array of colours and shapes are created by nearly 600 different varieties of coral found in the Great Barrier Reef. Coral polyps grows just below the surface to a depth of up to 60m in warm climates where there is clear salt water and sunlight.
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 of a straight pin.
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.
Coral polyps are usually nocturnal. They stay inside their protective cases during the day and extend their tentacles out to feed in the night. They feed on various small organisms, from microscopic plankton to tiny 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.
Most colour in coral is due to the presence of tiny symbiotic algae, called, zooxanthellae that live inside the coral and give them their distinctive shades of colours ranging from yellow to brown. The coral and zooxanthellae live in a mutually beneficial relationship. The coral provided the algae with a protective environment and nutrients and in return the zooxanthellae uses photosynthesis to produce glucose, glycerol, and amino acids which it shares with the coral. It has been estimated that the zooxanthellae shares as much as 90% of this material with the coral. This mutual relationship is vital for a healthy coral reef.
Why do Corals Look Washed Out Underwater?
A coral may look 'washed out' and rather drab underwater (when scuba diving for example). This is because as water depth increases the visible colours in the light spectrum decreases. So some corals may look 'washed out'. Exposure to artificial light, like a camera flash, sometimes displays the true vibrant colours of many corals.
The coral can regulate the population of algae it hosts. It does this by controlling the amount of light and nutrients it makes available to the zooxanthellae. In times of physical stress, usually caused by environmental factors, the coral may resort to a mass expulsion of its zooxanthellae population. This leads the coral to have a white appearance and is referred to as coral bleaching. The coral cannot survive for long without its zooxanthellae and will die.
Not all coral colour is due to the presence of zooxanthellae. Some corals which usually live closer to the surface of the ocean, have their own natural pigmentation to protect them from the damages of direct sunlight. These corals usually have bright pink, blue and purple colours.
Coral Reproduction Coral Spawning
While corals can be either male or female, many corals are hermaphrodites. While cross-fertilization is the predominated method of fertilization, some corals and are capable of self-fertilising their eggs and even cloning themselves.
Means of Reproduction
• Spawning - where eggs and sperm are released by coral polyps into the water at the same time to increase the chances of cross fertilization.
• Brooding - Here the egg and sperm are fertilised within the parent coral polyp and the resulting baby coral known as a larvae is released in to the surrounding water when it is relatively well developed.
• Budding - is where the young polyp grows out of an adult polyp. The new polyp is a clone of its parent.
• Parthenogenesis - in this process the egg grows into a new coral without fertilization and the offspring is a clone of the parent.
• Coral Bail - is when a piece breaks off from its parent, then regrows any missing body parts to become a fully viable new polyp. It is a clone of its parent.
Formation of New Coral Colonies
A coral egg, once fertilised, develops into larva called a planula that drifts around in the water until it finds a suitable place to establish itself. It takes only a single coral polyp floating in the sea to attach itself successfully to a suitable surface, such as a rock, to start up a brand new coral colony.
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 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.
The Great Barrier Reef has the world's most diverse range of underwater animals. These include:
• 1,625 species of fish, including sharks
• 360 types of coral
• 3,000 molluscs (like clams and the sea slug)
• 215 species of birds
• 14 species of sea snake
• 6 out of the worlds 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)
Unlike on land, the sea 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. The Great Barrier Reef is home to a wide variety of underwater vegetation.
There are 15 species of sea grasses on the Great Barrier Reef.
See grasses grow in shallow water where sunlight reaches them as they require sunlight for photosynthesis. They are true plants (unlike seaweed and algae) with roots, flowers and seeds. Since they are true flowering plants (angiosperms), male flowers release pollen into the water where they are moved by waves and ocean currents and encounter female flowers to pollinate. These flowers then develop seeds which when released can float many miles before settling onto the sea floor and germinating into new plants. Phenomenally, one square meter of sea grass can generate up to 10 litres of oxygen a day. Vast sea grass meadows cover such huge areas that they are visible from outer space. They 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. Large algae are called macroalgae.
Although sometimes classified as plants they are not true plants because they lack roots, stems and leaves. 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. Red and brown algae are found closer to the shore while red and green algae are more prevalent in offshore areas.
Algae play an important role in the ecology of the reef. They are major reef formers and create habitats for numerous invertebrates and vertebrates. In addition they are a major food source 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.
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.
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