Measuring changes in photosynthetic membranes of living coral symbionts to understand bleaching

What is it about?

Corals rely on tiny algae called Symbiodinium (often known as zooxanthellae) that live inside their tissues. These algae provide most of the coral’s energy through photosynthesis and give reefs their golden-brown colour. When seawater warms, the algae’s photosynthetic membranes (thylakoids) destabilize, their structure rearranging or breaking down, and the algae are lost — leaving corals pale or white, a process known as bleaching. In this study, we used small-angle neutron scattering (SANS), a non-destructive technique, to measure the detailed architecture of thylakoid membranes in living symbionts, both inside their coral hosts and after extraction. This is the first time such structural information has been obtained in vivo, opening the way to study bleaching at the level of the membranes that power the symbiosis.

Why is it important?

Coral bleaching has already stripped colour from vast stretches of the Great Barrier Reef and other reef systems worldwide. Our study is unique because it shows that SANS can measure how thylakoid membranes — the energetic heart of the symbiosis — rearrange or break down in living symbionts inside corals. This provides a robust baseline for future experiments to test how heat and light drive structural changes in these membranes. By directly linking membrane architecture to the loss of symbionts, our method offers insights that have never before been possible, at a time when reefs face unprecedented climate-driven bleaching.