Atolls usually form on top of submerged volcanoes. They are mostly found in deep water in the Indian and Pacific Oceans. The patch reef is located in some shallow, tropical waters. They are small and isolated. There are two types of coral, soft and hard.
Soft coral has flexible skeletons that can sway in strong currents.
Sea whips and sea fans are examples of soft coral. Hard coral is just the opposite. The skeleton is hard and stony. Some examples of hard coral are pillar, cabbage, brain, plate, and bubble coral. Coral reef zones are home to one quarter of all marine plants and animals.