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. Coral polyps, the animals primarily responsible for reef building, can take many forms: large reef building colonies, graceful flowing fans, and even small, solitary organisms. More than 6,000 species of coral are known, some live in warm, shallow, tropical seas and others in the cold, dark depths of the ocean.
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.
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 US dollars per year. These ecosystems are also of great cultural importance to indigenous people in many regions of the world.
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 threats 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.
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.