Coral

What it means

A coral is in fact a colony of tiny polyps; reef-building corals secrete a skeleton of calcium carbonate which, accumulated over centuries, raises structures capable of sheltering an enormous variety of marine life. Most tropical-water corals live in symbiosis with microscopic algae, zooxanthellae, which supply them with food through photosynthesis and give them their colour. When the water gets too warm, the coral expels those algae and bleaches, and if the situation persists it can die.