Corals themselves are found throughout all the world's oceans, at all depths. Reef building corals, hermatypic corals, are almost entirely found in warm, shallow, clear waters between the latitudes of 30N and 30S. Coral reefs are fragile ecosystems made up of a variety of different coral species. Each individual coral is made up of tiny organisms called polyps. These polyps contain symbiotic zooanthellae that rely on clear warm water for photosynthesis and survival. The coral relies on food from both the zooanthellae and food caught from the ambient water to build skeletons of calcium carbonate. It is the skeletons of corals that are critical in coral reef formation.

The Yaebishi is an extensive coral table that appears above the surface of the sea for a few days a year around March 3 by the lunar calendar, known as Sanitsu. It is located near Miyako Island, Japan. Photo courtesy of Topham, UNEP

Coral reefs are, even in ideal conditions, very very slow growing. Some of the massive coral structures, like the one shown below, will only grow a few millimetres a year. Even the faster growing branching corals grow just 150 millimetres per year.

An elkhorn coral colony. Photographer: Paige Gill. Photo courtesy of: Florida Keys National Marine Sanctuary and NOAA.

Corals are vulnerable to any activity that effects the water they live in. The range of activities taking place around coral reefs covers the whole scope of marine activities. Careless scuba divers, shipping pollution, land based sources of pollution, natural disasters, and human initiated disasters alike, all effect the ability of corals to survive. The immense diversity of marine life that live on and around coral reefs will also be lost should the corals die.