How the Great Barrier Reef Works

By: Jennifer Horton
Marine Life Image Gallery The Great Barrier Reef's 3,000 reefs host a variety of marine life. See more pictures of marine life.
Jeff Hunter/Getty Images

Early explorers saw the Great ­Barrier Reef not as a natural wonder of the world, but as a labyrinth. The collection of more than 3,000 reefs and 600 islands along the northeast coast of Australia caused many shipwrecks before it was mapped in th­e 1800s [source: Australian Government].

The first recorded "discovery" of the reef occurred when Lieutenant James Cook crashed into it in 1770 [source: sail on, the reef has caused many shipwrecks, which continue to be popular dive sites for the millions of tourists who explore the reef's waters every year.


Spanning 1,250 miles (2,000 kilometers) from north to south, the Great Barrier Reef is often called the largest living organism in the world [source: polyps that build on top of one another and stick together with coralline algae. The Great Barrier Reef contains more than 400 different kinds of coral species -- ten times the amount in the entire Atlantic Ocean [source: Sammon].

This underwater Eden hosts much more than an abundance of coral. You'll find a greater diversity of life on a single coral wall than you will on an entire continent [source: Chadwick]. So far, 1,500 species of fish have been spotted on the reef, and new ones are found every year [source: Chadwick].

Although some sections of the Great Barrier Reef may be 2 million years old, most scientists agree that the majority of it is a mere 500,000 years old. That's young by coral reef standards. Since then, its growth has been interrupted several times by sea-level changes that occurred during the ice ages. The structure of the current reef is approximately 6,000 to 8,000 years old, and is growing on top of older reefs that formed during a period of higher sea levels [source: CRC].

In this article, you'll learn about the different islands and reef types that make up the Great Barrier Reef. Who lives there? What threats face it? And how does Australia oversee every square mile of it?­

On the next page, you'll find out about the islands and reefs comprising this marine wonderland.


Reef Types in the Great Barrier Reef

Several different types of reefs are found within the Great Barrier Reef Marine Park. This aerial photograph shows how the reefs get farther from the mainland as you move south.
AFP/Getty Images

Although it is called the "Great Barrier Reef" and is often referred to simply as "the reef," both titles are misleading. The names suggest the existence of a single barrier reef, but the ecosystem really is made up of a number of different reefs -- only some of which are true barrier reefs. The rest are a combination of barrier, fringing, platform and patch reefs. Not sure which is which? We can tell you.

  • Barrier reefs form along the outermost edges of the continental shelf (the underwater border of a continent) and are separated from land by a wide, deep lagoon. They echo the coastline and sometimes break the water's surface at their shallowest areas.
  • Fringing reefs resemble barrier reefs in that they also parallel coastlines, but they hug the shore more. They border islands or extend outward from the mainland and are separated from land only by a narrow, shallow lagoon.
  • Platform and patch reefs are both small, isolated reefs that grow on top of the continental shelf, often on underwater hills that provide a good surface for coral growth. Platform reefs tend to be oval in shape and anywhere from 1.9 miles to 6.2 miles (3 km to10 km) long [source: CRC]. Patch reefs are smaller and shallower than platform reefs.
  • Ribbon reefs are long, narrow reefs (hence the ribbon name) that develop along the edge of the continental shelf. These reefs lack a lagoon. They may be up to 16 miles (25 kilometers) long but only 1,640 feet (500 meters) wide [source: Microsoft Encarta].

If you were to fly over the Great Barrier Reef, you would notice that its topography changes as you travel south. The reef is sometimes characterized as having three major sections: Far Northern, Cairns/Central, and Mackay/Capricorn (farthest south).


The northernmost section is known for having the most diversity due to its remote location and nearness to the equator. Here, the ribbon reefs dominate. Their windward sides deflect strong waves and currents, providing a calm inner section wtih scattered fringing reefs and patch reefs.

As the plane headed south, you would approach the central section. You would see the continental shelf widen and find that the reefs are farther from the mainland. The broad, shallow area created by the wider shelf hosts patch reefs and small coral islands. This section is the most accessible and gets the most tourist traffic.

Many low lying islands called coral cays are found throughout the Great Barrier Reef region.
Martin Barraud/Getty Images

Moving on to the southern section, the shelf continues to widen before narrowing and bringing the reefs back closer to land. Many submerged platform and patch reefs dot the underwater landscape. If you kept heading south, you'd see the reefs gradually disappear as the shelf narrows and temperatures dip to levels unsuitable for coral growth.

Scattered among the 3,000-plus reefs are low-lying coral or sand islands called cays. These cays support many different types of plant communities including mangrove, rainforest and grassy, depending on the rainfall they receive. The islands form from debris such as coral sand, shells and hard algae piling up against the tops and edges of the reefs.

Both the reefs and the cays benefit from this arrangement. Barrier reefs enable inner sea grass beds and mangroves to thrive by buffering them from rough seas. In turn, these formations prevent contaminants from entering the fragile ecosystem and smothering the coral by capturing nutrients and sediments in runoff. They also serve as a nursery for many of the reef's residents. You'll meet some of those interesting residents next.


Great Barrier Reef Fish and Other Animals

Coral reefs host vast amounts of life, including silvertip sharks like this one.
Jeff Hunter/Getty Images

The tropical location of the Great Barrier Reef is ideal for more than just the 2 million tourists who visit each year [source: coral growth. And where there's an abundance of healthy coral, you can bet there's a lot of other marine life as well. Reefs host more animal species than any other marine ecosystem [source: Microsoft Encarta].

Along with the 1,500 species of fish mentioned earlier, the reef also hosts more than 200 species of birds, 4,000 types of mollusks, 30 species of whales and dolphins, and six species of sea turtles [source: worms from 103 different species, and 250 types of shrimp on a single reef [source: Chadwick].


The Great Barrier Reef is one of the few places where you might see a dwarf goby fish smaller than your fingernail, a whale shark bigger than your car and an overstuffed giant grouper on just one dive. The "non-fish" species are equally as stunning. Giant clams, whose rainbow-colored mantles are as unique as fingerprints, can reach up to 4 feet (1.2 meters) in length and weigh more than 440 pounds (200 kilograms) [source: National Geographic].

While you'll want to give all animals in the Great Barrier Reef some space, you may want to cut a wider berth around some, like the 20 species of sea snakes, some of which possess venom 20 times stronger than the most poisonous land snake [source: octopus. At a mere five to 20 centimeters, this poisonous mollusk has surprised greedy divers who try to sneak shells into their wetsuits only to be bitten by the venomous octopus lurking inside [source: Zell]. Coral, too, can pack a serious punch. Just barely brushing up against the stinging fire coral will leave you with a burning itch.

The crown-of-thorns starfish destroys entire coral colonies.
Norbert Wu/Getty Images

Another marine creature is deadly not to people but to the reef itself. The crown-of-thorns starfish, which feeds on coral, has devastated the reef on two separate occasions since the early 1960s. During an outbreak, thousands of these starfish descend on the reefs and feast on the fragile polyps, leaving a path of destruction in their wake. Algae often colonize the resulting coral graveyard, preventing the coral from swiftly recovering.

Reefs hit by the crown of thorns, one of the largest starfish in the ocean, can take more than 10 years to regenerate [source: Sammon].

Damage caused by starfish notwithstanding, the Great Barrier Reef has fared relatively well in comparison to other coral reefs; its reefs are ranked among the world's least threatened [source: Microsoft Encarta]. You'll find out how the reef has managed to stay out of danger on the next page.


Great Barrier Reef Marine Park

The Great Barrier Reef Marine Park is classified into zones that permit certain activities and ban others. Scuba divers enjoy access to much of the park.
Pete Atkinson/Getty Images

With the invention of oil drilling, and you understand why Australia designated it a marine park in 1975.

The federal government and the Queensland state government work together to manage the park's daunting 132,973 square miles (344,400 square kilometers). The Great Barrier Reef Marine Park Authority is in charge of protecting the reef.


Despite the fact that the park does not include the northernmost section of the reef, it is the largest marine protected area in the world [source: Great Barrier Reef: Review]. In addition to the reef itself, the park encompasses several other marine communities including mangroves, estuaries, sea-grass beds and deep ocean troughs.

When the marine park was created, officials divided it into particular zones that outlined what activities could or couldn't be carried out there. Zones ranged from general use zones, where fishing, swimming, boating and most other activities were permitted, to scientific research zones, which were off-limits to anyone other than the scientists involved. In light of global warming and reports of animal populations declining in the reef, the Australian government decided to review the marine park's setup.

The marine park is now classified into 70 distinct habitat types, and at least 20 percent of each habitat type is designated a "no-take" zone. "No-take," as its name suggests, means that nothing can be removed from the area, so activities like fishing and shell collecting are forbidden. Before the review, less than 5 percent of the park was protected by a no-take clause. Now, 33 percent of the park is protected in this way [source: Great Barrier Reef: Zoning]

Tourists aren't the only ones that flock to the marine park. Scientists find its relatively pristine reefs and abundant marine life ideal for research. For example, scientists from the Australian Institute of Marine Science even pinpointed the protective coating secreted by coral that is exposed to air and are working with a pharmaceutical company to use it to develop sunscreen [source: Sammon].

The myriad reefs and cays of the Great Barrier Reef would take a lifetime to explore, but that doesn't prevent people from trying. If you want to explore the reef a little more, follow the links on the following page.


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More Great Links

  • Australian Government Culture and Recreation Portal. "Great Barrier Reef." Dec. 30, 2007. (April 22, 2008)
  • Chadwick, Douglas H. "Kingdom of Coral: Australia's Great Barrier Reef." National Geographic. January 2001. (April 21, 2008)
  • Coleman, Neville. "Australia's Great Barrier Reef." Chartwell. 1990.
  • CRC Reef Research Centre. "What is the Great Barrier Reef?" (April 22, 2008)
  • Great Barrier Reef Marine Park Authority. "Review of the Great Barrier Reef Marine Park Act 1975." (April 22, 2008)
  • Great Barrier Reef Marine Park Authority. "Zoning Plan Frequently Asked Questions." December 2003. (April 23, 2008) Dec2003.pdf
  • Microsoft Encarta Online Encyclopedia. "Great Barrier Reef." 2007. (April 22, 2008)
  • National Geographic Society. "Giant Clam." 2008. (April 24, 2008)
  • Sammon, Rick. "Seven Underwater Wonders Of The World." Thomasson-Grant. 1992.
  • Zell, Len. "Diving and Snorkeling Great Barrier Reef." Lonely Planet. 2006.