The Mystic World of Corals Corals are small, sedentary marine animals. They occur in dense colonies in warm waters of oceans. Corals remove and recycle carbon dioxide thus making their contribution to reduce global warming. Corals live in symbiosis with algae. When the corals lose their algae they loose their colour. This is known as coral bleaching. Scientists are not quite sure why this happens, but there is some evidence to suggest that a rise in water temperature may be involved. Coral reefs are formed by the skeleton remains of many generations of stony corals. They are known to attract millions of customers every year. They are also vital importance to the stabilization of coastlines, as fish habitats and for the protection of our biodiversity. The world inside the deep blue sea is indeed fascinating.