zooxantellák

Zooxantellák, atau zooxanthellae, are photosynthetic dinoflagellates that live inside the tissues of many marine invertebrates, most notably scleractinian corals. They belong to the family Symbiodiniaceae and were formerly grouped under the genus Symbiodinium. Within corals they inhabit the endodermal cells in a mutualistic symbiosis.

Through photosynthesis they fix carbon and transfer organic compounds such as glycerol, glucose, and amino acids to their hosts, providing a significant fraction of the coral's energy needs. In return, the zooxanthellae receive inorganic nutrients, a protected environment, and access to light. This relationship also contributes to the vibrant colors of corals.

Zooxanthellae are common in shallow, sunlit tropical and subtropical reefs but occur in other cnidarians and some foraminifera. The symbionts are diverse; different lineages show varying thermal tolerance, nutrient requirements, and light optima, enabling some corals to host different clades.

Under stress such as elevated sea temperatures, intense light, or pollution, corals expel or lose their zooxanthellae, causing bleaching. Prolonged bleaching reduces energy supply and can lead to coral mortality. Ongoing climate change and nutrient enrichment threaten these symbioses by increasing stress and altering reef ecosystems.

Symbiont transmission can be vertical or horizontal, depending on species; some corals inherit symbionts from parent colonies, others acquire them from the environment during larval or juvenile stages.