Coral reefs have the greatest known ocean life diversity of any ocean ecosystem. Although, deep ocean floor comes close in terms of ocean life diversity. Despite coral reef's familiarity to scientists, tourists, and any observers, it is estimated that only 10% or less of the species in coral reef ecosystem have been described. There are many more ocean life around coral reefs than we know. And, we know even less ocean life in the deep ocean.

Coral reefs are warm, clear, shallow ocean habitats that are rich in ocean life. Coral prefers temperature of 20 - 30 degrees centigrade. A coral reef area is an area very high in deposition of calcium carbonate, not only from the corals themselves but also from many of the seaweeds and the shellfish associated with the coral reef. The calcium carbonate structure of coral reef is composed primarily of the skeletons of coral. Individual coral polyps secrete calcium carbonate to form chambers with one side open to the water. The coral reef's massive structure is formed from coral polyps or tiny ocean life that live in colonies. When coral polyps die, they leave behind a hard, stony, branching structure made of limestone.

The coral reef provides shelter for many ocean life including sponges, nudibranchs, fish, jellyfish, anemones, starfish (including Crown of Thorns), crabs, shrimp, and lobsters, turtles, sea snakes, snails, octopus, nautilus, and clams. Birds also feed on coral reef animals. They protect the ocean coast from wave erosion.

Coral reefs are found in about 100 countries. They are found in all oceans of the world, except the Arctic Ocean. Sadly, they are among the world's most fragile and endangered ecosystems. In the last few decades over 35 million acres of coral reefs have been obliterated. Coral Reefs off of 93 countries have been damaged . When corals are exposed to high temperature, ultraviolet light or other environmental changes, they lose their symbiotic algal cells, and appear white. Depending on the intensity and duration of the stress, the corals may recover or they may die.