What is a reef? 
Reefs are massive accumulations of limestone created by reef-building organisms with calcite skeletons. Mounds of these skeletons build up over thousands of years.
Caves and channels within these mounds are home to many other animals, the reef-dwellers. Some reef-dwellers bore, burrow or scrape away at the calcite framework, reducing it to loose sediment. They are known as reef-destroyers.
All these groups of animals and plants together form the reef community.
