> The Great Barrier Reef

> The Great Barrier Reef is a chain of at least 2900 coral reefs off the north-eastern coast of Australia. At 2000 km long and 72km across at its widest point, it is the world's largest coral reef system and the biggest structure made by living things.

> Coral is made up of the skeletons of millions of tiny marine animals called polyps, both dead and alive. The coral of the Great Barrie Reef has been growing for two million years and is more than 500m thick in places. The dead skeletons form the main structure of the reef, while it is the living polyps that give the reef its amazing variety of colors. Coral needs special conditions to grow: salt water which must be clear enough to allow sunlight to pass through it and a temperature of 17.5ºC or more. The water must also be shallow, because sunlight cannot reach beyond 30m. These conditions are found in the warm waters of the Australian coastline.

> Of the 400 different types of coral on the Barrier Reef, the major varieties are the curiously shaped 'horn', 'brain' and 'table' corals, all named for the way they look. One of the most spectacular sights on the reef takes place once a year when almost one Third of the reef's corals reproduce. This takes place over several nights in November or December after the full moon. It has been described as looking like a giant underwater snowstorm.

> Providing shelter to a huge number of living things, the reef is home to 1500 types of fish, 500 types of seaweed, 215 types of bird, 16 types of sea snake, six types of turtle and many more varieties of sea plants and animals. Visitors to the reef are often scared by the possibility of meeting a hungry shark. Fortunately sharks are rarely seen and most sharks only feed on fish. However, there are other creatures that pose a threat to divers and people snorkeling. Scorpion fish have highly poisonous spines but are brightly colored and easily avoided, while the dangerous stone fish waits on the bottom and can be stepped upon. Certain kinds of jellyfish can also give a nasty sting.

> Many visitors come to the reef to try and spot whales. In the winter months, many whales travel from the cold waters of Antarctica to the reef to mate and to give birth to their young.

> The reef's islands form important nesting sites for sea birds and are visited by six of the world's seven types of sea turtle. Rather than give birth at sea, turtles lay eggs a little inland, on the islands' sandy beaches.

> The Great Barrier Reef is a World Heritage listed and protected area, where the only industry is tourism. Many thousands of people visit the area each year to view the reef's extraordinary collection of life by diving, snorkeling or looking through glass-bottomed boats.

> From: Senior English Reader Book 3A (上海外语教育出版社）