the.com/coral bleaching

means The process by which heat-stressed coral expels the algae living in its tissue, losing its color and its main food source — and, if conditions don't improve, slowly starving.

from 'Coral' traces back through French and Latin to Greek 'korallion,' a word old enough that its deeper roots are lost to us. 'Bleach' comes from Old English 'blæc'-related words tied to whitening and burning brightness — the same family that gives us 'bleak' and 'black,' oddly enough, since both descend from ideas of burning and pallor. The phrase itself is modern marine-biology shorthand, coined once scientists understood what was actually happening: the coral polyp, stressed by warm water, ejects the symbiotic algae (zooxanthellae) that give it both color and nourishment, leaving behind the pale calcium skeleton beneath — the 'bleached' white you see.