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. Unfortunately these defenses are not enough to combat human impacts. Humans may damage the reef in a number of ways, often without realizing it. Standing on the reef to rest while snorkeling crushes the coral polyps.