This word describes the microorganisms that dwell in the tissue of some ocean animals, including many corals. Zooxanthellae are single-celled algae. They have a symbiotic relationship with coral. That means the algae and coral each help the other out. The algae photosynthesize, turning light and carbon dioxide into food that they share with the coral. The algae help corals get enough energy to build reefs. The algae also provide oxygen and remove some of the coral’s wastes. In return, the coral shelters the algae and shares some nutrients with them.
But global warming and rising sea temperatures could spell trouble for these partnerships. When the algae are stressed by too-hot conditions, corals sometimes kick the algae out. This is called bleaching. The corals now look bone white because they lack the zooxanthellae that have given them their vivid hues. If a bleached coral doesn’t find new algae to live move in, the corals will eventually die.