In this extreme close up of a coral head, the amazing color and pattern produced is clearly evident.

Actually a colony of animals which have negotiated an unusual alliance with single-celled plants called zooxanthellae, each minute critter secrets calcium carbonate to erect the various limestone boulders that make up the most diverse ecosystem in the sea.

Inside each of the coral polyps this tiny plant receives carbon dioxide, protection and nutrition from its landlord and, in return, the polyp gets energy, nutrients and even its color from this lone photosynthesizing cell.

When feeding some coral polyps use tiny stinging tentacles to stun prey and guide food to the mouth. Others use mucus to trap tiny food particles, moving it to the mouth with little arms called cilia.

This fortunate relationship is also a delicate one. Very small changes in temperature, salinity or even water clarity can cause the plant cell to abandon its host, leaving the coral vulnerable and, oftentimes, without color.

Since coral grows so slowly and so many other animals rely on it for food and lodging, even these minor setbacks can create enormous troubles for the system.