As we learned in class, the reef has a daytime and a nighttime appearance. In the day time it looks like rocks and branches. In the night time, however, it comes to life and feeds on the plankton and small sea animals. The reef system is formed when marine invertebrates and algae secrete carbonate materials that build up over time. They are wave resistant and are found in shallow waters.
Most reefs are in warm, clear, tropical seas with a lot of sunlight.
Fossiliferous limestone made of carbonate material, and fossils of corals and marine shells are good indicators that a specimen may have come from an ancient reef system.