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© CI/Photo by Sterling Zumbrun
IUCN Red List: Undergoing Assessment

Coral reefs are among the most beautiful, yet often misunderstood, marine ecosystems on our planet.

Coral reefs are actually made up of hundreds of types of reef-building corals and thousands and thousands of individual coral polyps. Reef-building corals have a hard skeleton made from calcium carbonate under a soft body of tissues. It is these skeletons that, over thousands of years, build up and form the foundation of coral reefs.

Reef-building corals thrive in clear, shallow waters in tropical and sub-tropical regions. Their skeletal shapes provide abundant hiding places and homes for nearly one-third of marine species such as snails, anemones, sponges and fish, to name just a few.

But while coral reefs support amazing diversity, around the world they are under intense threat from over-fishing, pollution, increased levels of carbon dioxide in the oceans and even irresponsible tourism. What scientists have learned is that corals and the coral reefs they make up are bellwethers for ocean health and are highly vulnerable to the effects of climate change.

Why Are Healthy Coral Reefs Important?

Corals are quickly affected by changes in the environment. Pollution or subtle changes in water temperature – due to climate change or industrial runoff, for example — can affect their structure and, therefore, the life that lives within and around the reef.

Because coral reefs are composed largely of corals' hard skeletons, changing water acidity from increasing carbon dioxide levels and pollution can quickly undermine the structure of a coral reef and its ability to grow. As changes to their environment take place reefs become less able to support the organisms that depend on them.

Healthy coral reefs sustain important marine food supplies for human communities as well. Millions of people in coastal communities around the world rely on the ocean for their livelihood. An entire ecosystem benefits from thriving coral populations.

Where Are Corals Found?

Coral reefs are found all over the world. About nine percent of the world's coral reefs are found in the Caribbean Sea and Atlantic Ocean, sprinkled beyond the coasts of the Caribbean islands and the countries of North and South America. Nearly 15 percent of the world's reefs are found in the Indian Ocean and eight percent are found in the ocean and seas surrounding the Saudi Peninsula.

IN PHOTOS: Check out a gallery of coral reefs and the threats they face.

Southeast Asia, together with islands cast throughout the Pacific Ocean, has the greatest number of coral reefs – some of the most diverse in the world. The Great Barrier Reef is the largest reef on Earth, located off the northeast coast of Australia. And the Coral Triangle — a vast area surrounding Indonesia, the Philippines, Papua New Guinea and their neighboring countries — has the greatest diversity of corals on the planet.

What Is CI Doing to Keep Corals Healthy?

CI has identified and currently works in three marine seascapes where planned and coordinated actions can make a world of difference, but our efforts extend even beyond these large-scale management initiatives.

Short expeditions like the recent one to the Halmahera Island provide our scientists the opportunity to collect data and assess the health of corals and other marine life. With this information we create action plans and develop local and global partnerships that work toward a common goal: improving and protecting marine health.

And long-term scientific research can produce in-depth research reports and publications that give us a regional or global picture. By pursuing both long-term and rapid assessment research, CI scientists are ensuring the world's coral reefs have strong advocates.

FROM THE BLOG: CI's Elizabeth Selig is Working to Protect Reefs at Risk

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