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National Aquarium - Coral Reef

Coral Reefs

Often thought of as rocks or plants, corals are actually animals that create the structure—both living and dead—of reefs. The living component of the reef is the outer veneer that deposits calcium carbonate to slowly add to an underlying limestone structure. Corals are colonial animals made up of thousands of tiny, individual polyps, each secreting limestone to create a small protective cup. Corals form when a single polyp attaches to a hard surface and starts replicating and spreading to grow into a much larger organism. Every inch of a reef is occupied by coral species, sponges and other organisms attempting to grow and competing for space.

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Bright, beautiful and overflowing with life, coral reefs are among the most incredible natural wonders in the world.

Generally, corals are classified as either hard or soft corals. Hard corals continuously add to the non-living, hard support structure of the reef. Soft corals are soft and bendable, and look more like plants. Together, these organisms form a visually stunning and biologically important habitat for many ocean inhabitants, from tiny fish to large apex predators like sharks.

The Value of Coral Reefs

The loss of thriving coral reefs has real consequences, and not just to their many inhabitants. In addition to being essential habitats for fish, coral reefs have a measurable value to those who live on land. Because they essentially serve as mountain ranges for the ocean's coastlines, they deflect the energy of brutal storms that might otherwise decimate coastal communities. In fact, in areas that have been affected by tsunamis, the areas with coral reefs fared much better than those without.

Though coral reefs constitute less than one percent of the ocean floor, they support an estimated 25 percent of ocean life, serving as critical spawning, nursery, breeding and feeding grounds for thousands of species.
- Jack Cover, General Curator, National Aquarium

Chemical compounds unique to coral reefs are especially useful for medicinal purposes. Researchers have used coral amalgams to treat ailments including ulcers, skin cancers and heart disorders. Once the correct formula is identified, the medicines can be synthetically mass-produced.

And of course, the natural beauty of coral reefs makes them attractive for tourists, too. Visitors from all over the world flock to the Florida Keys, Barbados, Indonesia, Australia and other destinations to get a closer look. Most of these areas rely heavily on tourism for economic growth and sustainability, and preserving coral reefs is vital to their economies. All told, the economic value of coral reefs is an estimated $375 billion per year.

Reef in Danger

Coral reefs face many threats, including storm damage, invasive species, climate change, coastal development, commercial use, poor sewage treatment, agricultural runoff, excessive fertilizer use in coastal communities and increasing carbon dioxide levels. Corals are extremely sensitive, so even small shifts in light, temperature and water chemistry can be detrimental. Many of the everyday choices we make contribute to the devastation of coral reefs. Coral is able to grow and repair itself, but needs precisely the right environment to do so.

In order for many coral species to thrive, they must have exposure to bright sunlight. Many of these species have algae living in their tissues that produce food for the coral. Clear-water environments are necessary for corals to receive the maximum amount of direct light to keep this symbiotic algae alive. Deforestation and development on land can send tons of suspended sediments into the ocean that cloud the water and block essential sunlight. Pollution from stormwater runoff sends harmful chemicals and excessive nutrients into the ocean. These nutrients often cause algal blooms at the water’s surface that also block sunlight from reaching the corals below.

According to a report by the World Research Institute, 75 percent of the world's reefs are considered threatened.

In addition to chemical pollutants, coral reefs are also threatened by ocean acidification caused by the burning of fossil fuels. This process sends a deluge of carbon dioxide into the air, forming carbonic acid.

While the future of coral reefs may appear bleak, there's still a lot we can do to protect these aquatic treasures! The individual choices that we make each day can make a difference in the health of our ocean.

Meet Our Coral Reef Inhabitants

  • Anemones

    Sea anemones are polyps that attach to surfaces with an adhesive foot, called a basal disc. Their column-shaped bodies end in an oral disc, and they can have anywhere from a dozen to a few hundred tentacles.

  • Banggai Cardinalfish

    This small, disc-shaped fish is easily recognized by its tasseled first dorsal fin; long, tapering second dorsal fin; and deeply forked tail, or caudal fin.

    Banggai cardinalfish
  • Bonnethead Shark

    While many of our visitors point and declare “hammerhead!” when they see this shark cruising through the exhibit, the bonnethead shark is easily distinguished from its much larger cousin.

    Bonnethead shark
  • Green Moray Eel

    The green moray is actually brown! The yellow tint of the mucus that covers its body, in combination with the drab background color, gives the fish its namesake green appearance.

    Green Moray Eel
  • Percula Clownfish

    The percula clownfish is the most well known of the 29 species of clownfish.

  • Sea Stars

    There are nearly 2,000 species of sea stars in the world’s oceans.

    National Aquarium – Sea Stars
  • Spotfin Porcupinefish

    Like most pufferfish, the spotfin porcupinefish can draw in water to inflate itself. When it does, sharp spines on its body stick out, which is how it got its name.

    National Aquarium – Porcupine Fish
  • Yellow Sea Cucumber

    As a defense, yellow sea cucumbers can expel their internal organs—then quickly regenerate them.

    National Aquarium - Yellow Sea Cucumber
  • Yellow Tang

    This reef-dwelling fish is known for its bright yellow body.

    National Aquarium - Yellow Tang

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What Can You Do to Help?

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Do a home energy audit. Reduce your use of fossil fuels by using public transportation, riding a bike and carpooling when possible.

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Participate in a tree planting, beach cleanup or marsh restoration event. Reduce harmful stormwater runoff in your backyard. Dispose of trash properly, and recycle everything you can.

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Plan a family vacation to visit a reef. Support marine sanctuaries. Never buy coral skeletons. Support reef restoration programs. Use coral-safe sunscreen—avoid brands that use oxybenzone, which has been show to harm corals.

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Visit, volunteer, become a member—by connecting with the National Aquarium, you support our work to inspire conservation of the world’s aquatic treasures.