Rising sea temperatures are causing coral reefs around the world to bleach. For the first time, a research team at the Research Neutron Source Heinz Maier-Leibnitz (FRM II) at the Technical University of Munich (TUM) has investigated the biological processes behind coral bleaching directly in living corals. With the help of neutrons, they were able to visualise structural changes during the bleaching process.

Coral reefs are important marine ecosystems, providing habitat, food, and shelter for countless species. Many coral species live in symbiosis with photosynthetic algae. The algae provide nutrients, while the corals offer protection and carbon dioxide in return. However, this symbiosis is extremely sensitive to rising sea temperatures.

Photosynthesis takes place in special membranes in algae, known as thylakoid membranes. When sea temperatures rise, this system becomes unbalanced because the excess energy can no longer be processed sufficiently. As a result, the corals reject the algae, losing both their colour and their most important source of energy: the corals bleach. They can survive short-term bleaching events, but if the loss of algae persists, the corals die.

Looking inside living corals with neutrons

Previous analytical methods often required complex sample preparation, which can damage or kill the cells. The researchers therefore turned to small-angle neutron scattering, a non-destructive method that allowed them to study the algae and, for the first time, analyse their structure within the living host. “Neutrons enable us to observe the membranes directly during active photosynthesis,” explains Dr Christopher Garvey, co-author of the study and instrument scientist at FRM II.

The experiments conducted at the KWS-2 small-angle scattering instrument from Forschungszentrum Jülich at FRM II in Garching revealed that changes in the distance between algae membranes provide important clues about their physiological stress. “On the one hand, this highlights the strength of neutron scattering for investigations on living cells and, on the other hand, it can make an important contribution to protecting coral reefs in a changing climate,” says Dr Christopher Garvey.

Publication

Robert W. Corkery, Christopher J. Garvey and Judith E. Houston: In hospite and ex hospite architecture of photosynthetic thylakoid membranes in Symbiodinium spp. using small-angle neutron scattering. Journal of Applied Crystallography, Volume 58, Part 5, 1516 (2025). DOI: 10.1107/S1600576725007332

Further information and links

In addition to scientists from TUM and FRM II, researchers from Jülich Centre for Neutron Science, Australian National University, European Spallation Source and Newcastle University have also contributed to this project.

The investigations at FRM II were conducted some time ago. However, the results have only now been published in a scientific study.

Contact for this article

Dr. Christopher Garvey
Technical University of Munich
Instrument scientist at FRM II
christopher.garvey@frm2.tum.de

Technical University of Munich
Corporate Communications Center

Laura Richter und Ulrich Meyer
presse@tum.de
Teamwebsite

Original article: https://www.tum.de/en/news-and-events/all-news/press-releases/details/why-corals-bleach