There are three main types of reefs; fringing reefs, barrier reefs and atoll reefs. Fringing reefs are the most common of the three because they grow directly from the shore, surrounding islands like borders along the coastline. When a fringing reef continues to grow from a fully submerged volcanic island below sea level, an atoll forms. Atoll reefs are circular/oval in shape and have an open lagoon in the center. Barrier reefs are quite similar to fringing reefs in that they also border a coastline, but what differentiates them from a fringing reef is that they do not grow directly from the shore, but are separated from land by an expanse of land. deep water. This creates a deep water lagoon between the shore and the reefs. Hard corals or stony corals are primary hermatypic corals that have a rigid skeleton of calcium carbonate (CaCo3), which in crystalline form is known as aragonite. Hard coral colonies have many polyps cemented together by the calcium carbonate skeletons they create, and a layer of tissue covers the skeleton and connects the coral polyps for distribution....