CORAL reefs are one of the wonders of nature, because of their enchanting beauty and unusual biology. In addition, many consider them to be second only to tropical rain forests as incubators and protectors of biodiversity.

The reefs, which grow in shallow, warm waters, consist largely of the skeletons of small, sedentary animals called polyps, which are relatives of jellyfish and sea anemones. The remains of dead polyps — in the form of calcium carbonate — constitute the main body of the reef.

Living polyps form a kind of skin over the surface of the coral reef.

As they move through their life cycle, coral polyps secrete a hard skeleton or shell of calcium carbonate, into which they contract to protect themselves. When they die, their calcium carbonate remains add to the structure of the reef. For this reason, coral reefs enlarge themselves and become complex structures over the years.

Coral polyps begin their lives as larvae floating free. As mature adults, they are sessile animals, that is, they are fixed to one place. They range in size from the diametre of a teacup saucer to a pinhead.

Corals feed by reaching out from their perches with tentacles to sting plankton. Their most unusual biological property, however, is a symbiotic relationship they form with a species of algae named zooanthellae. The algae infiltrate the bodies of the coral polyps and use photosynthesis to produce nutrients they share with the polyps.

Zooanthellae can provide up to 90 per cent of the nutrition the coral needs to survive. By living in a polyp, the algae receive some protection and are moved closer upwards through the ocean towards the light as the coral structure grows — making it easier for them to perform their photosynthesis. It is the algae that give coral reefs their hues, dramatically reflected by many of the fish and plants and other animals that dwell in and around them. The colour pigment given to the polyp by the algae may even work as a kind of sunblock, protecting the polyp from solar radiation.

Coral polyps from various kinds of reef structures that have been given names like “brain”, “star”, and “elkhorn”. A non-reef-building coral, “octoral,” can look like trees and shrubs and forms “sea fans” and “sea whips.”

Coral reefs have been around for about 200 million years, and have survived eons of storm-induced damage and sea animal predation.

Unfortunately, their survival in this century is less certain. The year 2000 report from the Global Coral Reef Monitoring Network says that approximately 25 per cent of coral reefs worldwide have been effectively lost and another 40 per cent “may be lost” by 2010 unless urgent action is taken.

Warming oceans, pollution from human activities, damage from careless tourists and fishermen — even increased ultraviolet radiation from the sun due to the depletion of ozone in the upper atmosphere — have been blamed for extensive illness and death in the coral population. Corals are uniquely vulnerable because they are near coastlines and near the surface of the ocean. There are fewer healthy colonies on the planet than even a few decades ago, according to marine scientists. One of the most frequently studied pathologies is known as “coral bleaching”.