Pulse amplitude modulated (PAM) fluorometry measures the photosynthetic efficiency within the endosymbiotic Symbiodinium spp. that may be used as a quantitative measure of photoinactivation during coral bleaching.

When a coral bleaches, it loses its zooxanthellae, which are microscopic algae that work like an internal symbiotic vegetable garden, carrying out photosynthesis and providing nutrients to the coral. When zooxanthellae are lost, corals appear white, or "bleached."