Metaproteome analysis of the coral holobiont demonstrates algal symbiont quiescence under thermal stress

The accelerating loss of coral reefs worldwide due to anthropogenic climate change has led to a myriad of studies aimed at understanding the basis of coral resilience to support reef conservation. Central to this effort is elucidating metabolic interactions between the cnidarian host and dinoflagellate algal symbionts, which has traditionally been challenging to do in hospite. Here, using data from four divergent coral species, we develop the first metaproteome model of thermal stress-based coral-algal dysbiosis. Our results demonstrate that thermal stress induces quiescence of algal-symbiont metabolic pathways causing the host to shift its metabolism from symbiont maintenance to energy conservation. This degrades symbiosome function, further degrading the symbiotic partnership. Although each coral host species we studied shows a distinct response to the stress regime, reflecting divergent evolutionary histories, symbiont quiescence is consistently observed and comprises a major outcome of coral-algal dysbiosis. Our resultsalso provide novel biomarkers for holobiont conservation.