What is a Coral Reef

A coral reef   is a natural barrier made of the bodies of millions of living and dead coral polyps. Coral 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 and 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: Hard coral 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.

Who Lives There

The Great Barrier Reef is home to one of the world's most diverse range of underwater plant and animal life.

• 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 seabirds and 32 species of shorebirds

Threats to The Reef

Natural Factors

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 habitats 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 coral 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 coral 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 chances of the polyp's chances of dealing with short-term stress. If the stressful conditions persist, the polyp eventually dies.

Humans

Coral reefs take thousands of years to form. People can easily damage a reef 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 and the impact of tourism to the wellbeing of the reef is minimal.

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Pollution

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).

River Runoffs: 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.

Here are some great sites about the Barrier Reef:
Research Paper: The Great Barrier Reef, Reef Facts, Wikipedia

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