Coral bleaching is the most serious global disease threat to
corals (Harvell et al. 2007). Bleaching occurs when the
zooxanthellae algae vacate their places within the coral
structure. The coral animals themselves are transparent,so the loss of the brightly colored algae leaves the
“bleached” skeletal calcium carbonate structure visible.
The coral can survive for short periods without their
algae, but they will eventually die if they do not reestablish
their dinoflagellate flora. High water
temperatures can directly induce bleaching, and in other
instances it is caused a bacteria related to cholera.