Which is the part of the coral that is built up over thousands of years into a reef?

Answer 1

The part of the coral that is built up over thousands of years into a reef is primarily the calcium carbonate skeleton produced by coral polyps. Coral polyps are small, soft-bodied organisms that live in colonies. They secrete calcium carbonate to form a hard exoskeleton, and as these colonies grow and die, their calcium carbonate structures contribute to the development of coral reefs over time. The accumulation of these skeletal materials creates the large, complex structures we recognize as coral reefs.