How do coral reefs form?
Hard coral colonies, like brain and staghorn coral, secrete and deposit a solid skeleton of calcium carbonate, also known as limestone. Layer on layer, generation on generation, these protective skeletons can grow to become massive stony reefs that stretch for thousands of miles and last for millions of years. The Great Barrier Reef in Australia is over 1,200 miles long, the largest in the world. Soft corals don’t form massive limestone skeletons, and usually live among the hard corals on a reef.
