Zooxanthellae
Symbiotic algae living inside coral cells that give corals their color and produce energy through photosynthesis.
Single-celled algae (dinoflagellates) that live symbiotically within the tissues of corals and other marine organisms. They photosynthesize and transfer nutrients to their host, while receiving shelter and access to sunlight. When stressed by heat or pollution, corals expel these algae, causing the white appearance known as coral bleaching.
What this means in real life
When ocean temperatures spike during an El Niño event, corals become stressed and expel their zooxanthellae, turning white and losing their primary food source—like a plant losing its leaves during drought.
What it isn’t
These are not parasites that harm corals; they are essential partners in a mutually beneficial relationship. Corals cannot survive long without them.
Commonly misused online
Often described as 'coral food' when they are actually energy-producing partners; some posts conflate bleaching with death, though bleached corals can recover if conditions improve quickly.