Coral reefs what is

Coral reefs are made up of colonies of hundreds to thousands of tiny individual corals, called polyps. These marine invertebrate animals have hard exoskeletons made of calcium carbonate, and are sessile, meaning permanently fixed in one place. Polyps grow slowly, forming different shapes and sizes depending on their species.

Assisted by other animals with calcium carbonate skeletons and also coralline algae, corals form complex, three-dimensional reefs. Because photosynthesis requires sunlight, most reef-building corals live in clear, shallow waters that are penetrated by sunlight.

The algae also give a coral its color; coral polyps are actually transparent, so the color of the algae inside the polyps show through. Coral reefs provide habitat for a large variety of marine life, including various sponges, oysters, clams, crabs, sea stars, sea urchins, and many species of fish.

Coral reefs are also linked ecologically to nearby seagrass, mangrove, and mudflat communities. One of the reasons that coral reefs are so highly valued is because they serve as a center of activity for marine life. Some soft corals have zooxanthellae to acquire food and energy, but others, such as black corals, exist without this symbiotic relationship. However, the reef-building corals that rely on a symbiotic relationship with algae need shallow, clear water allowing light penetration for photosynthesis.

As the centuries pass, the coral reef gradually grows, one tiny exoskeleton at a time, until they become massive features of the marine environment. Corals are found all over the world's oceans, from the Aleutian Islands off the coast of Alaska to the warm tropical waters of the Caribbean Sea. The biggest coral reefs are found in the clear, shallow waters of the tropics and subtropics. The largest of these coral reef systems, the Great Barrier Reef in Australia, is more than 1, miles long 2, kilometers.

As such, ocean explorers continue to discover previously unknown coral reefs that have likely existed for hundreds of years. Coral have a dazzling array of shapes and colors, from round, folded brain corals named for their resemblance to a human brain to tall, elegant sea whips and sea fans that look like intricate, vibrantly colored trees or plants.

Corals belong to the phylum cnidaria pronounced ni-DAR-ee-uh , a group that includes jellyfish , anemones, Portuguese man o' war and several other gelatinous and stinging marine invertebrates.

Corals feed by one of two ways. Some species catch small marine life, like fish and plankton, by using the stinging tentacles on the outer edges of their bodies. Most corals, however, depend on algae called zooxanthellae to provide energy via photosynthesis. The corals have a symbiotic, or mutually beneficial, relationship with the zooxanthellae, according to the U.

These algae live inside the coral polyp's body where they photosynthesize to produce energy for themselves and the polyps. The polyps, in turn, provide a home and carbon dioxide for the algae. Additionally, the zooxanthellae provide the coral with their lively colors — most coral polyp bodies are clear and colorless without zooxanthellae. If corals are bombarded by stressors like poor water quality, a marine heatwave, or overfishing, their energy will be directed at survival instead of reproduction.

To ensure the future of coral reefs, we must keep corals healthy so they continue to reproduce—and we have to do this in strategic areas around the world. Because ocean currents tend to follow the same course, one coral reef can be genetically connected to another coral reef hundreds of miles away—one coral reef will provide the baby corals, and the other coral reef will provide the home upon which the larvae settle.