what is a coral reef? A coral reef is a huge sea organism that stretches for hundred and thousands of kilometres. coral reefs may be the most largest organism, but it is also the most valuable organism in the ocean. Apart from this, coral reefs live and grow like us. They expand with age, eat and feed on decomposed organisms and die when affected by abiotic factors either by itself or affecting bionic organisms. when a coral reef does die, it first loses its colour and shrinks in size. When humans damage the reefs, or a large abiotic or biotic damages it, chunks of the coral reefs will break off and drift through currents or float depending on the size and may wash up on a beach. the appearance of the coral on the beach will look grey-white but still has all of its detail over it.