Reefs 'see' light without eyes, coral's secret unlocked in new study

A recent study from Osaka Metropolitan University has uncovered a novel light-sensing mechanism in reef-building corals, revealing that certain coral opsins use chloride ions from their environment instead of amino acids to switch light sensitivity between ultraviolet (UV) and visible light. This discovery challenges the conventional understanding of opsins—proteins responsible for vision in animals—where typically a negatively charged amino acid acts as a counterion. The coral opsins, specifically a newly identified group called ASO-II opsins found in Acropora tenuis, employ chloride ions to stabilize the Schiff base, enabling reversible switching of light sensitivity depending on environmental pH levels. This mechanism allows corals, despite lacking eyes, to adapt their light detection in response to changes in ocean acidity, which is influenced by their symbiotic algae’s photosynthesis. The study highlights the ecological significance of this adaptation, suggesting that corals’ ability to toggle between UV and visible light sensitivity helps maintain their symbiotic relationship with algae under varying pH conditions caused