Coral ecosystems

Coral reefs are some of the most diverse ecosystems in the world; thousands of species and millions of people depend on reefs for food and protection.

Because of the diversity found in the habitats created by corals, reefs are often called the "rainforests of the sea." About 25% of the ocean's fish depend on healthy coral reefs. Fishes and other organisms hide, find food, reproduce, and have their young in the many nooks and crannies formed by corals. The Northwest Hawaiian Island coral reefs provide an example of the diversity of life associated with shallow-water reef ecosystems. This area supports more than 7,000 species of fishes, invertebrates, plants, sea turtles, birds, and marine mammals. Deep water reefs or mounds are less well known but also support a wide array of sea life in an otherwise barren world.

Compared to healthy coral, which appear in shades of purple and gold, bleached coral on the Great Barrier Reef appear bone white.
New study suggests coral reefs may be able to adapt to moderate climate change
Coral reefs may be able to adapt to moderate climate warming, improving their chance of surviving through the end of this century, if there are large reductions in carbon dioxide emissions...

Coral characteristics

One fascinating feature of shallow water, reef-building corals is their mutualistic relationship with photosynthetic algae called zooxanthellae, which live in their tissues. The coral provides the algae with a protected environment and the compounds they need for photosynthesis. In return, the algae produce oxygen and help the coral to remove wastes. Deep sea corals occur in much deeper or colder oceanic waters and lack zooxanthellae. Unlike their shallow water relatives, which rely heavily on photosynthesis to produce food, deep sea corals take in plankton and organic matter for much of their energy needs.

Benefits of coral reef ecosystems

People receive many benefits from coral reefs. These ecosystems protect coastlines from storms and erosion; provide jobs for local communities; offer opportunities for recreation; and are a source of food and new medicines. Over half a billion people depend on reefs for food, income, and protection. Fishing, diving, and snorkeling on and near reefs add hundreds of millions of dollars to local businesses. The net economic value of the world’s coral reefs is estimated to be nearly 29.8 billion U.S. dollars per year. These ecosystems are also of great cultural importance to indigenous people in many regions of the world.

Corals are popular as souvenirs, for home decor, and in costume jewelry, yet corals are living animals that eat, grow, and reproduce. It takes corals decades or longer to create reef structures, so leave corals and other marine life on the reef.
Does coral jewelry make a good gift?
Corals have long been popular as souvenirs, for home decor, and in jewelry, but many consumers are unaware that these beautiful structures are made by living creatures. Fewer still realize that corals are dying off at alarming rates...

Threats to coral reef ecosystems

Unfortunately, coral reef ecosystems are severely threatened. Scientists estimate that the world has lost 19% of its coral reefs with an additional 35% under the threat of being lost over the next 20-40 years. Some threatsoffsite link are natural, such as diseases, predators, and storms. Other threats are caused by people, including pollution, sedimentation, unsustainable fishing practices, and climate change which is raising ocean temperatures and causing ocean acidification. Many of these threats can stress corals, leading to coral bleaching and possible death, while others cause physical damage to this delicate ecosystem.

Coral reefs support one of the most diverse ecosystems in the world with thousands of species relying on the delicate reefs for survival.
Picture climate: How can we learn from corals?
To gather data and information about coral growth bands, scientists jump in their scuba gear and dive down among the reefs...


Educators can use the resources in this Collection to teach their students about the science and beauty of corals. They can use these organisms and ecosystems to teach many scientific concepts including symbiotic relationships, reproduction strategies, food webs, chemistry, biotic and abiotic interactions, human impacts, etc. Additionally, educators can use corals to teach about conservation and stewardship of the environment. Even if you don't live near a reef, students can learn that they can help protect coral reefs in the U.S. and around the world. There are many actions, small and large, that you and your students can take to help conserve coral reefs.