Hypoxia disrupts metabolism in coral and sea anemone larvae.

Anthropogenic pollution is driving an increase in the frequency and severity of seawater hypoxic events in coastal marine ecosystems. Although hypoxia decreases physiological performance in coral and sea anemone (phylum Cnidaria) larvae, the underlying cellular mechanisms remain unexplored. Here, larvae of the reef-building corals Galaxea fascicularis and Porites astreoides and the estuarine sea anemone Nematostella vectensis were exposed to normoxia or a simulated hypoxic event (6 h at <2 mg dissolved O2 l-1), and their metabolomic response was quantified at the end of the exposure period using targeted liquid chromatography-mass spectrometry. Baseline metabolite profiles (81 amino acids, acylcarnitines, organic acids and nucleotides) were broadly divergent between the three species, with the corals displaying a reliance on nitrogen cycling through amino acid metabolism, whereas N. vectensis relied on nucleotide metabolism. By contrast, several changes in metabolite abundances under hypoxia were shared (e.g. increases in lactate) and suggest the upregulation of glycolysis, lactic acid fermentation and fatty acid β-oxidation as conserved mechanisms for energy production under hypoxia. Changes in these pathways were correlated with adverse physiological outcomes, including conserved declines in swimming behavior and growth. Importantly, life history traits affecting metabolism influenced hypoxia responses. For example, P. astreoides larvae, which possess algal endosymbionts, displayed the least severe metabolic response to hypoxia among these species, possibly owing to symbiont resources. Overall, these findings demonstrate that hypoxia disrupts metabolic performance in coral and sea anemone larvae through conserved and divergent pathways, emphasizing the need to limit drivers of ocean deoxygenation.