The bleaching of reef corals — in which the symbiotic algae are lost from the reef-building invertebrates — is usually assumed to be a severe response to an adverse change in environmental conditions. In June 15 Nature Andrew Baker of the Wildlife Conservation Society, New York Aquarium suggests that in fact the process of bleaching enables the coral to jettison subopitmal symbiotic algae and acquire new partners better adapted to survival in the changed environment.

Reef corals are formed as a result of the symbiosis between scleractinian (stony) corals and photosynthetic dinoflagellate algae. Different types of algal symbiont are present depending upon the depth of the coral and are referred to as shallow, 'high-light' algae or deep, 'low-light' algae. In order to identify the effect of bleaching on the stability of these depth distributions Baker reciprocally transplanted 8 species of Caribbean coral between 'shallow' (2-4 m) and 'deep' (20-30...