Corals come in many shapes and sizes. Corals get their common name from how they look. The shape of a coral is determined both by how they build their skeleton and the environmental factors with which they must cope. In shallow areas with high surf you find corals with low, sturdy forms like lobe, rice, blue, and cauliflower coral. Branching, delicate corals such as shelf and finger coral are found in calmer or deeper waters.
Coral reefs face a number of threats, both natural and human made.
Natural factors affecting reefs include hurricanes and storms that can quickly destroy large areas of the reef. Predators such as fish, snails, worms, and starfish eat the coral polyps and bore into the coral. Corals also compete with each other for space and light. To protect themselves corals have evolved a variety of defenses. Large numbers of polyps, chemical defenses, and large numbers of offspring all help corals to survive.