Why do corals bleach white?

Answer: Stress expels symbiotic algae

Stress expels symbiotic algae ✓ — Correct! Corals get color and food from zooxanthellae algae living in their tissues. When stressed (high temperature, pollution, acidity), corals expel the algae and turn white (bleach). Without algae, corals starve and may die. Climate change is causing mass bleaching events worldwide!

Absorbing too much sunlight — Wrong. Excess sunlight combined with high temperatures does stress corals, but bleaching specifically means losing the colorful algae, not just color fading.

Disease from bacteria — Wrong. While disease can affect corals, bleaching is specifically the expulsion of symbiotic algae due to environmental stress, not bacterial infection.