Coral reef conservation fact file

What is a coral?

Corals are actually tiny, soft-bodied animals that belong to the same group as jellyfish and sea anemones, the Cnidarians. An individual coral animal is called a polyp. Coral polyps can live alone, but typically polyps live in colonies that may consist of hundreds to hundreds of thousands of individuals.
Corals are split into two main groups: soft corals and hard corals. Hard corals, also known as reef building corals, are the best-known type of coral, forming the large, colourful reefs found in clear, tropical seas. There are over 800 known species of reef-building coral.

How do coral reefs form?

The polyps of reef-building corals have a hard, protective calcium carbonate (limestone) skeleton, which attaches to a rock on the sea floor. Coral polyps can divide, or bud, into thousands of clones which are genetically identical to each other. Reefs begin to form as the hard skeletons of the living and dead polyps in a coral colony cement together.
As the coral colony grows over hundreds and thousands of years, it joins with other colonies and become a reef. Tropical reefs can grow at rates of 1 to 100 centimetres per year and can form huge structures over incredibly long periods of time, making them the largest and oldest living systems on Earth. Some of the coral reefs that exist today began growing over 50 million years ago.

How do corals get their food?

The polyps of reef-building corals have a special symbiotic relationship with single-celled algae, called zooxanthellae, which benefits both the algae and the coral. The zooxanthellae live inside the tissues of the coral and capture energy from the sun through photosynthesis, providing the coral with food. Up to 90% of a coral’s nutrients are obtained from the algae. In return, the coral provides the algae with protection, access to sunlight, and nutrients from plankton that is captured by the polyp.
Like jellyfish and sea anemones, coral polyps also have stinging tentacles that can they use to catch food. Corals mainly feed at night, extending the tentacles into the water current to catch plankton, small food particles and sometimes even small fish.

Where are coral reefs found?

Corals need salt water to survive and are found throughout the oceans, from deep, cold waters to shallow, tropical seas.
The most familiar and well-known corals, the reef-building corals, come from tropical regions. They grow best in warm, clear, shallow waters where lots of sunlight is able to filter through the water column to reach the symbiotic algae that live within their tissues.

Why are coral reefs important for biodiversity?

Coral reefs are among the most valuable ecosystems on Earth, forming massive, complex habitats for thousands of other species. Although coral reefs cover less than 1% of the ocean floor, the numbers of species living in, on and around coral reefs rivals even the most diverse tropical forests, including the Amazon rainforest in Brazil. Home to an estimated 2 million species, coral reefs are sometimes nicknamed the ‘rainforests of the oceans' because of their staggeringly rich biodiversity.
As well as supporting an enormous variety of species, tropical coral reef ecosystems are also important to human health and well-being. Coral reefs are vital to the world’s fisheries, forming nurseries for about a quarter of the ocean's fish and providing a source of income for local communities, as well as national and international fishing companies.
In coastal areas, coral reefs provide an important natural barrier against waves, hurricanes, typhoons and even tsunamis, helping to prevent coastal erosion and flooding. The beauty and diversity of coral reefs make them important tourist attractions which help to generate income and create jobs for local communities. Coral reefs are also becoming increasingly important in medicine, and coral reef organisms are already being used in treatments for diseases like cancer and HIV.