Symbiodiniaceae

Symbiodiniaceae is a family of unicellular, marine dinoflagellates that form endosymbiotic associations with tropical corals and other cnidarians, as well as some protists and tunicates. In healthy coral reefs they inhabit the host gastrodermal cells as intracellular symbionts, widely distributed in tropical and subtropical seas. They are photosynthetic, using light to fix carbon that is translocated to the host, providing a major portion of the host's energy budget, while the host supplies inorganic nutrients and a protected intracellular environment. This mutualism underpins reef-building corals and their productivity.

The relationship is sensitive to environmental conditions. Temperature, light, and nutrient balance influence symbiont density and pigment content. When stressed by heat or other stressors, many corals expel their symbionts or lose photosynthetic pigments, causing bleaching and potentially mortality. Different lineages within Symbiodiniaceae vary in thermal tolerance, and shifts in symbiont community composition can alter coral resilience.

Taxonomy: Historically grouped under the single genus Symbiodinium, the group was reorganized in 2017 into a family, Symbiodiniaceae, comprising several genera such as Symbiodinium, Cladocopium, Durusdinium, and Breviolum, among others. The taxonomy remains under active revision due to molecular data.