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The Great Barrier Reef The Great Barrier Reef extends more

than 1,250 miles (2,012 km) off Australia's northeast coast. It is a chain of 2,900 indi­vidual coral reefs, and it is the largest system of reefs in the world.

Formed over millions of years, coral reefs are made from coral-brilliantly colored sea polyps that grow in large colo­nies. Within the coral's tissues live micro­scopic algae that make food for the coral. As coral die, their hard skeletons remain. New coral attach and grow on top of the old skeletons. After many years, a complex structure of live and dead coral is formed. This structure is a reef.

The Great Barrier Reef is home to a spectacular array of species-anemones, sponges, worms, lobsters, crayfish, prawns, crabs, birds, mammals, and fish. These species provide food for humans and, along with the beauty of the reef itself, attract tourists, which is good for

Australia, Oceania, and Antarctica

Environmental Case Study

Australia's economy. The reef also protects coastal towns from storms, and it prevents shores from eroding.

The Great Barrier Reef has always been subject to damaging forces of nature, such as predators, floods, and storms. But today the reef, like other reefs around the world, is in danger of being destroyed. Overfishing, damage by tourists, pollu­tion, and warming ocean waters are all taking a toll.

Bleaching Probably the greatest threat to the long-term health of the Great Bar­rier Reef is warming ocean waters. Coral live only in clear, unpolluted water. Coral is also extremely sensitive to changes in temperature. When the water is too pol­luted or too warm, the coral may become stressed and die. Even slightly warmer temperatures can cause the coral to cast out their algae. Algae not only feed the

The Great Barrier Reef



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Environmental Case Study continued

coral, they also give it its brilliant color. Without the algae, the coral turns a bleached white.

Coral can often recover from a short period of bleaching, but if the bleaching is severe or prolonged, the coral will slowly starve to death. Scientists fear that if ocean waters warm too much, bleaching will cause the Great Barrier Reef to become a massive underwater graveyard.

Lately, bleaching has been happening more frequently. In 1998 warm water led to a severe episode of bleaching. Soon after, in the summer of 2002, the reef suf­fered its worst episode of bleaching ever­between 60 percent and 95 percent of the reefs were affected.

Warm water is not the only cause of bleaching. Other causes include increased ultraviolet light from the sun and pollution from farms, households, and industries.

Damage from Trawling Prawn travyl-ing involves dragging a net along the sea floor to catch prawns (shrimplike crea­tures). Trawling causes massive damage to seabed life. For every pound of prawns caught, 13 pounds of fish and other marine animals are picked up. The animals, which

are often injured in the nets, are thrown overboard and may not survive.

The Australian government has increased fines for illegal prawn trawling. It has also paid for equipment such as radar to catch offenders. The government now requires all trawlers in the Great Barrier Reef Marine Park to use special devices that keep species other than prawns out of their nets.

Tourists About two million people visit the Great Barrier Reef each year. They come to swim, snorkel, scuba dive, and fish. Tourists can cause great damage to the reefs. People sometimes break off pieces of coral for souvenirs, touch reefs while snorkeling or scuba diving, drag diving gear or boats over reefs, and drop anchors on them.

The Great Barrier Reef Marine Park encourages tourists to act responsibly, and requires permits for certain activities. The Australian government has declared one­third of the reef off-limits to fishing.

After the widespread coral bleaching in 1998, scientists began the first thorough studies of coral reefs around the world. These studies continue today.

-,. I It's a Fact"')' -


1. The first European visitor to the Great Barrier Reef was the British explorer Captain James Cook, who navigated it (and ran his ship aground on it) in 1770. He began the work of charting channels and passages through the reefs.

2. Coral reefs harbor an astonishing diversity of living things. They have ~ been called "the rain forests of the sea." The Great Barrier Reef con-tains some 400 species of coral, 4,000 species of mollusks, and 1,500 species of fish, as well as many different kinds of turtles, seabirds, r:

and mammals. :"i

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."' .. " ... ( Storms and Starfish ) ...... ".

Some of the greatest threats to the Great Barrier Reef are as old as the reefs themselves. Tropical storms, cyclones, waves, and floods can seriously damage coral reefs.

Also damaging to the reef is a strange creature known as the crown-of-thorns starfish. Covered by long, sharp spines, the starfish prowls the reef, searching for coral to eat. When it finds a tasty morsel of coral, the starfish extrudes its stomach through its mouth, releases digestive juices that break down the coral, and feasts on the partly digested coraL

Scientists watch the Great Bar­rier Reef for outbreaks of crown­of-thorns starfish. When too many starfish threaten areas of the reef that are important to science or tourism, scientists inject the starfish with a drug that kills them but does not harm other plants or animals. J

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~ Review the Facts Directions: Read the information about the Great Barrier Reef and examine the map. Then answer these questions.

1. Listing What are three benefits of the Great Barrier Reef?




Environmental Case Study continued

2. Determining Cause and Effect How does prawn trawling endanger coral reefs?

3. Identifying What are three ways tourists can damage coral reefs?




4. Explaining What happens to coral during bleaching?

5. Stating What are three causes of coral bleaching?




6. Describing How do scientists manage crown-of-thorns starfish?


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Creating a Coral Display

'# For Investigation • magazines

Many organizations around the world are at work to save coral reefs and other ocean ecosystems. Form a team of three or four students, and choose one of the organizations listed below or another that you know about. Work together to create a classroom learning center about the organization.

• posterboard or butcher paper

• paints or markers • audiocassette player or

videocamera (optional) • access to library and/or

Internet resources

Reef Check:

The Nature Conservancy:

The Coral Reef Alliance:

The Ocean Conservancy:

The National Marine Sanctuaries Foun-dation:

What to Do

1. Use the Internet or library resources to research the organization you have chosen. Find out about its activities to protect coral reefs or other ocean ecosystems as well as its members, home office, and sources of funding.

2. Find ways to present your informa­tion that will be interesting to your classmates. You could create a mural, a collage, an annotated map, or a poster. You could write a script and make an audio or video recording.

3. Make a fact sheet about the organiza­tion. Include photographs of its mem-bers at work.


Assessment Checklist Assess your project using the checklist below:

D Describes how the organization is working to save ocean ecosystems

D Engaging display, with interesting and accurate descriptions

D Includes photos or drawings that show members at work

D Includes background information about the organization

D Well organized and logically developed

4. Set up your display on a table or desk in your classroom.


Take turns "hosting" your presentation, and visit the displays of other groups.