Zeno Karl Schindler Award 2024 for Nils Rädecker

For revealing the metabolic interactions leading to the breakdown of the coral-algal symbiosis, helping us to understand and mitigate coral bleaching.

The evolutionary success of the cnidarian-algal symbiosis has given rise to the formation of coral reef ecosystems. Yet, climate change and other anthropogenic impacts are disrupting this symbiosis at increasing frequencies and scales. Understanding the collapse of this symbiosis will not be possible without understanding the processes that maintain it in the first place. Combining physiological, OMICS, and NanoSIMS imaging approaches, my research investigates the role of metabolic interactions in the stable and stressed cnidarian-algal symbiosis. My work shows that, in a stable state, mutualistic interactions in the symbiosis are maintained by competition for inorganic nutrients between the host and its symbionts. A breakdown of this resource competition during heat stress, in turn, destabilizes nutrient cycling and, thus, the symbiosis itself. While this passive regulation has underpinned the evolutionary success of coral holobionts for millions of years, it also renders these organisms highly vulnerable to the rapid environmental change of the Anthropocene. This ecological understanding of the symbiosis could hold the key to developing novel conservation approaches, e.g., using probiotics to mitigate heat stress effects on nutrient cycling in corals.