Bleaching happens when rising water temperatures cause coral to expel the symbiotic algae living in its tissue, draining it of both color and a major food source. It looks like death, but it is closer to a fever.
Recovery is possible
If temperatures drop back within a few weeks, coral can reabsorb algae and regain its color. Reefs that have survived repeated bleaching events are now a major focus for scientists studying heat tolerance.
None of this makes bleaching harmless u2014 repeated events leave coral weaker and slower to recover each time u2014 but it does mean a bleached reef is not automatically a lost one.