The Red Sea is an underwater paradise mainly because of one thing: the Coral Reefs.
Coral Reefs form via colonies of a stationary animal with a calcified skeleton. The coral animals feed by filtering plankton from the water, driven its way by sea currents. As the animals die off, their skeletons form the basis of the reef, and other animals adhere to the mass, and the cycle continues.
Corals also have algae living within its tissue. These algaes use photosynthesis to build up nutrients from sea minerals and dissolved carbon dioxide. It is the algae that give the corals their varying colors.