A coral display with descriptions of different types of coral found in Cook Islands. Photo by Cook Islands National Environment Service.

• What are corals?
• What are coral reefs?
• What are the different types of coral reefs?
• Why are coral reefs important?
• What damages coral reefs?

The myriad of colours we witness on a reef are actually living invertebrate animals called corals with each colony of coral composed of hundreds or thousands of individual animals called polyps. A coral polyp is a simple jelly fish-like animal with a simple stomach with a single mouth opening surrounded by stinging tentacles which it uses to protect and feed itself.

Corals are generally classified as either ‘hard coral’ or ‘soft coral’. There are around 800 known species of hard or 'reef building' corals. Soft corals, which include seas fans, sea feathers, and sea whips, don't have the rock-like calcareous skeletons of hard corals but instead grow wood-like cores for support and fleshy rinds for protection. Soft corals often resemble brightly coloured plants or trees, and are easy to distinguish from hard corals as their polyps have tentacles that occur in multiples of eight, and they have distinctive feathery appearances. Soft corals are generally found in caves or ledges throughout the world's oceans where they hang to capture food floating by on currents that are typical of such places.

Perhaps the most unique feature of corals is the highly evolved form of symbiosis they have with algae. Coral polyps have developed this relationship with tiny single-celled plants called zooxanthellae. Inside tissues of each coral polyp live these microscopic, single-celled algae, sharing space, gas exchanges, and nutrients to survive. This symbiotic relationship between plant and animal also contributes to the brilliant colors of coral in a reef.

The need for light for photosynthesis drives corals to compete for space on the sea floor, and so constantly pushes the limits of their physiological tolerances in a competitive environment among so many different species. This also makes corals highly susceptible to environmental stresses.

Massive corals, like this brain coral on the top, form the bulk of coral reefs while those of the genus Acropora, shown here on the bottom, grow between larger coral colonies. Photos courtesy of the GCRMN team.

Coral reefs are created by millions of tiny polyps forming large carbonate structures by extracting calcium from surrounding seawater. This is used to create a hardened framework for protection and growth as well as the foundations for homes of hundreds of thousands, if not millions, of other species. These living structures are the largest on Earth and have evolved over the past 200 to 300 million years to be the only living structures visible from space.

Coral reefs contain more life than most other natural areas in the world and are often called rainforests of the sea due to the large numbers of species they feed and shelter, many of which are too small to be seen with the naked eye. The total mass of plant material on reefs is very high, rivalling that of rainforests, as all life on reefs depend on plants. Plants are sometimes brown or red but contain green chlorophyll as well which enables them to manufacture carbohydrates by photosynthesis.

Based on current estimates, shallow water coral reefs occupy somewhere between 284,000 and 512,000 square kilometres of the Earth (cold-water/deep coral reefs occupy even more area). If all the world's shallow water coral reefs were crammed together, the space that structure would occupy would range from areas the size of Ecuador (the low estimate) to that of Spain (the higher estimate). That area represents less than 0.015 percent of the ocean, yet coral reefs harbour more than one quarter of the ocean's biodiversity. In the Pacific, some coral reefs hold up to 3,000 different species!

Coral reefs are parts of larger ecosystems that also include mangroves and seagrass beds. Mangroves are salt tolerant trees with submerged roots that provide nursery and breeding grounds for marine life that then migrate to reefs. Mangroves also trap and produce nutrients for food, stabilise shorelines, protect coastal zones from storms, and help filter land based pollutants from run off. Seagrasses are flowering marine plants that are a key primary producer in food webs. They provide food and habitats for turtles, seahorses, manatees, fish, and foraging sea life such as urchins and sea cucumbers. Seagrasses are also nurseries for many juvenile species of sea animals and are like fields that sit in shallow waters off the beach, filtering sediments from water, releasing oxygen, and stabilising the bottom.


Photo courtesy of the GCRMN team.

Why are coral reefs important?

Providing Pacific island biodiversity

Covering less than one percent of the ocean floor, reefs support an estimated twenty-five percent of all marine life including over 4,000 species of fish. Reefs provide spawning, nursery, refuge and feeding areas for large varieties of organisms, including sponges, worms, crustaceans (including shrimp, spiny lobsters, and crabs), molluscs (including cephalopods), echinoderms (including starfish, sea urchins, and sea cucumbers), sea squirts, sea turtles and sea snakes.

Healthy reefs sustain the lives of many Pacific islanders. More than 80% of Pacific islanders live in or near coastal areas and draw from coral reefs for their livelihoods. The medicinal and pharmaceutical potential of coral reefs is being explored for treatments for many of the world's most prevalent and dangerous illnesses and diseases.

Reef structures also play vital roles as natural breakwaters, minimizing wave impacts during storms and cyclones. The stronger our reefs, the greater the protection of our island homes.

Coral reefs contribute to local economies by sheltering sea life, attracting millions of tourists who visit our region to view our vibrant and diverse coral reefs, and protect our land-based activities. Benefits from coral reefs can be categorized into two types: "direct use values" which are derived from fisheries and tourism industries; and "indirect use values" which include coastline protection. Several attempts have been made to estimate the monetary values of coral reefs and an estimate by the United Nations puts the total economic value of coral reefs between US$100,000 to US$600,000 per square kilometre per year.

SPREP has conducted community workshops as part of coastal resource management strategies. These photos show proceedings from one in Tokelau. Photos courtesy of Caroline Vieux.

For more information on 2008 Pacific Year of the Reef, contact Caroline Vieux, SPREP Coral Reef Management Officer at [email protected] or Sereima Savu, SPREP Pacific Year of the Reef Campaign Coordinator, at [email protected].