The formation of highly consolidated reefs only occur where the temperature does not fall below 18°C for extended periods of time. This specific temperature restriction -18°C- does not, however, apply to the corals themselves. In Japan, where this has been studied in detail, approximately half of all coral species occur where the sea temperature regularly falls to 14°C an approximately 25% occur where it falls to 11°C (Veron 2000). Many grow optimally in water temperatures between 23° and 29°C, but some can tolerate temperatures as high as 40°C for limited periods of time.

Most importantly, they supply the coral with organic products of photosynthesis