WHAT IS A CORAL REEF?

Coral reefs are massive limestone structures, built by hard (or "stony") corals. Hard corals are the animals that provide the solid framework of the reef. In and around this framework live a complex array of other plants and animals. Some of them - like calcareous algae - help to build the reef up, some of them - such as boring sponges - bore into it and break it down. Others find shelter on the reef and make their homes there. This multitude of life is what we know as the coral reef.

Scientists studying 7 hectares of reef in the Caribbean estimated that whilst the reef was producing 206 tons of calcium carbonate a year, approximately 123 tons of calcium carbonate were being lost, primarily due to boring sponges, grazing fish and urchins.

The animals and plants of the reef depend upon one another for life and are linked in numerous ways, many of which are not yet fully understood. If one of these links is removed (for example through overfishing or reef destruction), the whole balance of the system can be dramatically changed, often with dire consequences. If herbivorous (plant eating) reef fish such as parrotfish and tangs are selectively removed from a reef, algae (marine plants) can quickly overgrow surrounding corals smothering and killing them.