#wall diving

The main difference between soft and hard corals is that hard corals produce and leave behind a rock-like skeleton as they grow, made of calcium carbonate - CaCO3 (the same substance that chalk and Tums is made out of).

It is these calcified skeletons that together make up the primary structure of a coral reef, which can eventually grow to the size of a mountain range. A good example is the Great Barrier Reef, which despite recent mass bleaching is still presently the largest living thing on Earth and is visible from space - photo taken at Foammulah Atoll, Indian Ocean