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What is a reef? It is like an underwater city mostly found in warm, salty, shallow waters. Instead of housing made of mortar and bricks, the reef is a series of rigid, water-resistant structures, mostly coral.
Coral reefs are formed from the skeleton-like calcium carbonate of invertebrates (coral are related to jellyfish and sea anemones and have no backbone). Coral has many nooks and crannies, so when it is part of a reef, it creates a home for tons of fish and other undersea organisms. How cool, a coral hotel!
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A Sumptuous Environment
The Great Barrier Reef runs along the coast of Queensland in northeastern Australia. It also stretches out and away, between 10 and 100 miles from the coast. At its widest point, it is 45 miles across and in its entirety covers an area of approximately 133,000 square miles (344,400 square km). It also happens to be about 1,250 miles (or 2,000 km) long, which is like a drive from Colorado to Indiana. It is so large that it can be seen from space.
The United Nations Educational, Scientific and Cultural Organization (UNESCO) watches over the reef and has it classified it as a World Heritage site in order to protect it.
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Polyps Are Perfect
Hard coral are actually creatures made from polyps. This free-swimming larvae-type creature attaches itself to hard surfaces, mostly rocks. Polyps look like tubes where they attach with tentacles at the other end to gather food. They are all the same as the parent polyp and reproduce asexually. That means they have no sex organs and reproduce in binary fission or splitting, also called “budding." During the process of binary fission, an organism duplicates its genetic material (DNA) and then divides into two parts, creating what is called two daughter cells.
Polyps get together into colonies, deposit calcium carbonate, and these deposits make chambers that grow up and up and look like feathery fans, or they can resemble plates, antlers or even brains.
Reef building coral also have zooxanthellae (pronounced zoh-uh-zan-THEH-lee), tiny algae in its tissue, and that gives them color. They are usually green or brown, although some are a brilliant coral color.
The zooxanthellae are symbiotic. Single-celled algae, they have the ability of photosynthesis and covert light and chemical elements into energy. This process provides food for the coral, while the coral provide them protection and a nutrient rich environment that helps them to stick around.
Even if a polyp dies, living ones form a thin layer over the skeleton and continue growing. Soon sponges and other algae arrive. It is home!
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Happy 18 Millionth Birthday
The polyps that are reef building collect limestone, siphoning it out of the water as if with a straw, which gives them their hard, armor skeleton. Polyps die, other colonies build, the skeleton becomes another layer and this is what forms the reef.
Animals live in there, materials drop in there and then after a few mudslides, the reef becomes a great limestone wall. In the northern end of the Great Barrier Reef, the base of the fabulous coral wall is about 18 million years old.
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The native peoples of Australia, the Aborigines, have known about the reef forever. It was not until 1928 that Great Britain started the Great Barrier Reef Expedition. Charles Maurice Yonge and his scientist friends studied and researched the area, and this lead to his publication, A Year on the Great Barrier Reef.
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Great Barrier Reef Home Life
Some 1,500 species of fish and crustaceans call the reef home, which is more than any other marine habitat. A few of the dwellers are dolphins and whales further out. Residents such as the Dugong, a sea mammal related to the elephant, grow 7 to 11 feet long, weigh 500-925 pounds (230-420 kg) and hang around for about 73 years just grazing on grasses by warm water coral.
Giant clams some three feet across (1 m) and up to 500 pounds call the reef home, as do squid, octopus and other shelled animals. Some smaller ones who inhabit the reef include:
- Sea snakes
Of course, it is the corals that are most often recognized—about 400 different species.
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The Crown of Thorns (their technical name is Acanthaster planci) is a serious predator with a voracious appetite for the coral. This large starfish and will grow up to about 18 inches (45 cm) across. They eat corals faster than they grow—not to mention that chemicals from their stomach slowly break down living polyps—until only an empty skeleton is left behind.
Crown of Thorns feed in a weird way because parts of their stomach, called gastric folds, come through their mouths and turn inside out, smothering the coral. Their digestive enzymes then spread to the coral and this helps them to absorb the digested tissue of its prey, outside the stomach.
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In addition to the Crown of Thorns, which can have a boom period of reproduction, other things destroy the reef. A partial list includes the following:
Too many tourists create stress, frighten nesting animals, and make noise and pollution
- Litter, other garbage and even sunscreen in the water
- Oil spills and accidents
- Fishing, nets and boat anchors
- Agriculture and industry chemicals
- Dirt and materials from rivers
- Warmer climate, air pollution and gases and rising water levels
- Coral bleaching—too warm water means algae leave, turning coral white and stressed
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Once a year the reef is assessed, like a kind of extensive doctor’s report. Although every year there are about four cyclones, they had a neutral impact for summer 2013-14; there were relatively few coral bleaching and plume episodes, and sea surface temperatures remained near average according to Queensland Park and the Eye on the Reef programs.
- Algone: Zooxanthellae
- Expedition 325: Great Barrier Reef Environmental Changes
- Encyclopedia.com: Photosynthesis
- NOAA Coral Reef Conservation: Coral Reefs
- The University of Glasgow Story: Charles Maurice Yonge
- Wildscreen: Crown of Thorns
- Eye on the Reef Monitoring Program
- Earthducation: Great Barrier Reef
- National Geographic: Dugong
- Henzel, Cynthia Kennedy. Barrier Reef. Edina, MN: ABDO Publishing Company, 2011. Book.