Calcification in hermatypic and ahermatypic corals

The evolutionary development of tropical coral reefs is presently ascribed to the association of corals with symbiotic algae (zooxanthellae) and to the enhancement of calcification by light. Contrary to this idea, the calcification rate in a non-reef-building tropical coral (Tubastrea faulkneri) without symbiotic algae was the same as the light-enhanced rate in a zooxanthellate reef-building coral (Galaxea fascicularis). The mechanisms of calcification, however, differed between the two species. Instead of being ''light-enhanced,'' calcification in corals with algae was ''dark-repressed.'' The evolutionary development of coral reefs may therefore not be related to light-enhanced calcification resulting from the association of corals with symbiotic algae.