what are corals made of
A coral reef is made of thin layers of calcium carbonate. Coral polyps form a living mat over a calcium carbonate skeleton. Stony corals (or scleractinians) are the corals primarily responsible for laying the foundations of, and building up, reef structures.Massive reef structures are formed when each individual stony coral organismâor polypâsecretes a skeleton of calcium carbonate.Most stony corals have very small polyps, averaging one to three millimeters (0.04 to 0.12 inches) in diameter, but entire colonies can grow very large and weigh several tons.assive reef structures are formed when each individual stony coral organismâor polypâsecretes a skeleton of calcium carbonate. Most stony corals have very small polyps, averaging one to three millimeters (0.04 to 0.12 inches) in diameter, but entire colonies can grow very large and weigh several tons.