Sunlight is the main energy source used by the symbiotic algae living in Great Barrier Reef corals.
These microscopic algae, commonly called zooxanthellae, live inside coral tissues and photosynthesise. Using sunlight, they convert carbon dioxide and water into organic compounds that provide much of the energy required by their coral hosts.
The partnership helps corals build and maintain reef structures in clear, shallow tropical waters. In return, the algae receive shelter and access to carbon dioxide and nutrients produced by the coral’s metabolism.
When corals experience prolonged heat stress, they may expel or lose their algae, producing coral bleaching. A bleached coral is not necessarily immediately dead, but it has lost a major energy source and becomes more vulnerable if stressful conditions continue.