| Summary: | The rapid acidification of seawater poses a significant threat to the persistence of coral reefs. However, taxa‐specific, mechanistic understandings of holobiont responses to ocean acidification (OA) stress remain largely unknown. Understanding these mechanisms is crucial to uncovering predictive markers of OA stress. This could subsequently be used to assist field‐based conservation efforts. We hypothesized that exposure to elevated pCO 2 levels would decrease the abundance of primary metabolites such as amino acids and carbohydrates and increase the production of secondary metabolites, specifically those involved in cnidarian‐symbiodinium cell signaling. In this study, we applied untargeted capillary electrophoresis time‐of‐flight mass spectrometry (CE‐TOFMS) to profile changes in the intracellular polar and semi‐polar metabolite composition of the coral holobiont after exposure to elevated pCO 2 concentrations. Nubbins of Acropora millepora were exposed to ambient (410 µatm) or elevated (805 µatm) pCO 2 levels under controlled conditions over a period of 10 days. Measurement of treatment‐induced bleaching was performed by quantification of symbiodinium cell density and chlorophyll a concentration. We hope to identify molecules in the metabolite profiles associated with the individual cellular responses of holobiont members to osmotic stress. Additionally, we hope to provide further insight into unknown roles of secondary and tertiary metabolite pools in cellular homeostasis and acclimation to thermal stress in the coral holobiont, and specifically the cnidarian‐symbiodinium symbiosis. Our goal is for these findings to assist conservation efforts, specifically in the development of rapid tests for field‐based conservation efforts.
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