Symbiodiniaceae is the family name used for the symbiotic algae living inside many Great Barrier Reef corals.
These microscopic algae live within coral tissues and use sunlight to produce energy through photosynthesis. In return, the coral host receives much of that energy, while the algae gain shelter and access to nutrients. This partnership helps reef-building corals grow their calcium-carbonate skeletons in well-lit shallow water.
The older term “zooxanthellae” is still widely used in general discussions, but it is a broad informal label rather than the precise modern family name. Symbiodiniaceae contains multiple genera and many distinct lineages, and different coral species can associate with different algal partners.
During prolonged heat stress, corals may expel or lose these algae. The resulting coral bleaching does not always mean immediate death, but severe or extended bleaching can cause starvation and mortality. This relationship is therefore central to understanding both reef growth and climate-related coral decline.