Coral Reefs

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Sea bass flock to a tropical coral reef in the Red Sea.
Sea bass flock to a tropical coral reef in the Red Sea.
Michael Lang/Smithsonian Institution

Coral reefs pulsate with colors and movement. They support more species per square meter than any other ocean ecosystem. Because of this phenomenal diversity, coral reefs have been called the rainforests of the sea.

The corals themselves form the basic reef structure. Tiny coral polyps leave behind limestone skeletons, which build up over the centuries…layer by layer. Abundant sunlight and warm water supply food for the sponges, algae, fishes, and thousands of other species who gradually move in.

Coral reefs that took millions of years to build have been disappearing within just decades as a result of human activities. It is up to us to help preserve those that remain.

"In a world of doom and gloom, it is important to know that reefs with exuberant coral growth and abundant fish populations still exist."

– Dr. Nancy Knowlton, Smithsonian Institution

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Cool Stuff

Cool Stuff

Colorful fishes throng a reef in the Northwestern Hawaiian Islands.

Back in the day—that is, the Cretaceous, when dinosaurs roamed the earth around 65 million years ago—clams, not corals, were building all the reefs. Check out photos of bizarre and beautiful coral reef life of today. And, once you find out how corals reproduce, you’ll never see a full moon the same way again.

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Sections

Ecosystem Basics

A variety of organisms make their home on this tropical coral reef in Indonesia.

Coral reefs are the big cities of the sea, housing about a quarter of all marine species. Corals—which are living animals—form the foundation of these cities. Different kinds of corals live in the colder waters of the deep sea. One place to find them is on the hidden underwater peaks called seamounts.

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Featured Creatures

Close-up photograph of translucent coral polyps, showing the symbiotic algae living inside.

Photosynethic algae, or zooxanthellae, live inside the tissue of every tiny coral polyp. The coral gives the algae a home. In return, the algae provide the coral with food. Also, this is your chance to meet a moray eel—a type of bony fish and denizen of coral reef crevices.

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Science

The sun sets over the Smithsonian’s marine field station at Carrie Bow Cay, Belize. For more than three decades, it has been home to the Smithsonian’s Caribbean Coral Reef Ecosystem Program.

Take a look at some of the clever ways scientists are studying coral reefs—including the use of satellites in outer space and creature “apartment buildings” that are placed in the reefs themselves. Also, get a behind-the-scenes glimpse at one of the most important coral collections in the world.

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Threats & Solutions

These bleached corals in the Gulf of Mexico are the result of increased water temperatures.

With so many threats, much of the news about coral reefs is grim. How can they be saved? One promising solution is the creation of marine protected areas (MPAs). Like national parks on land, MPAs protect natural and historical treasures underwater–including coral reefs.

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Human Connections

A scuba diver explores elkhorn corals growing on a tropical reef.

Coral reefs give so much to people, what can people give back? Some practical guidelines: Never feed or handle animals, and never touch a coral reef! Choose souvenirs that don’t jeopardize reef organisms, and stock your home aquarium with animals that were obtained in a sustainable manner.

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