bio

Coral bleaching

The loss of a coral's symbiotic algae from its tissues, exposing the white limestone skeleton beneath the now-transparent flesh. It is not death but the breakdown of a partnership. When seawater runs one or two degrees above the normal summer maximum for weeks, the algae's photosynthetic machinery is damaged and leaks toxic reactive-oxygen species; the coral responds by expelling or digesting the very algae that feed it. Cut off from that food, the animal starves. If the water cools in time the algae can return; if not, the colony dies. It is the clearest demonstration that even a powerful symbiosis can be fragile.