How the Great Barrier Reef Works

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.

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.

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.

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.

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.

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.