World map showing location of coral found in My Submarine Ocean Explorations off the west coast of the U.S.


Coral reefs are one of the most studied and most interesting parts of ocean life. Coral reefs are complex and diverse ecosystems. Many plants and animals can be part of a coral reef’s ecosystem. Corals have great value to sea life as well as humans. Millions of fish, plants, animals, and humans depend on them.

Corals have been on Earth for many millions of years. Most coral live in warmer water and in shallow water, as they depend on sunlight. The kind of corals that live in shallow, warmer waters can form coral reefs with their skeleton. But some can also live in cold water, even up to a few thousand feet deep! Some of these cold-water corals have been found off the coast of Washington (state), Alaska, and Scotland. Scientists have recently found deep-sea corals in the colder deep waters of our continental shelves, submarine canyons, seamounts, and mid-ocean ridges. Probably the most famous coral reef is the “Great Barrier Reef” in Australia, which is the world’s largest structure built by living things. It has over 900 islands and covers about 133,000 square miles! That is slightly bigger than New Mexico and slightly smaller than Montana.

Corals are made up of hundreds or thousands of individual animals called polyps. Each polyp has a stomach that opens at one end, which is surrounded by tentacles. Tentacles capture food through stinging it. Tentacles help the coral defend itself; they have stinging cells similar to those of a jellyfish. Some corals, such as soft corals and sea fans have 8 tentacles. Other coral have multiples of 6 (like 12, 18, etc.) and this includes the reef-building corals. Some corals use algae to get food; the coral gets food from the algae and in return gives the algae a home. This is called a “mutualistic symbiotic” relationship - two organisms living together and helping one another.

You may have heard of coral bleaching and wondered what that is. The coral polyp gets its color from the algae that live inside it. When the coral becomes stressed it kicks the algae out and loses its color. The coral is then white or bleached.
• Homes for others: Coral reefs provide habitats for more than one millions species of plants, animals, and fish.
• Protection of coasts: The structure of coral reefs helps protect the coastlines from waves, storms, and floods. This helps save people’s lives, slow erosion, and decrease damage to property.
• Billions of dollars for people: Fishing, medicine, tourism, and recreation.

Corals are always changing and growing and are very sensitive to any changes in the life or environment around them. People can have a big effect on coral reefs through pollution, trash, boats, scuba diving, and over-fishing. To protect corals, people have to be very aware of the things that can harm them. Corals are a very important part of the marine world.