Coral and algae form a fascinating symbiotic relationship that is crucial for the health and vibrant appearance of coral reefs. While corals have some pigments of their own, much of their vibrant coloration comes from microscopic algae. The algae attached to the coral perform photosynthesis, using sunlight to produce energy, while the coral's own pigments often act as a "sunscreen," protecting the algae from excessive light. When corals are stressed (usually by increased water temperature or pollution), they expel the algae. This process is called coral bleaching because without the algae, the coral's white limestone skeleton becomes visible through its transparent tissue.