Climate change is increasingly affecting marine ecosystems, and its impacts on coastal environments remain complex and difficult to disentangle. Natural CO₂ vents offer a valuable in situ model for investigating the ecological and physiological consequences of ocean acidification. The island of Vulcano, in the Aeolian archipelago, hosts submerged CO₂ emissions, particularly in Levante Bay, where pH ranges from 5.70 to 8.05.

In this study, we investigated the effects of low pH on the metabolism of the snakelocks anemone, Anemonia viridis, a photosymbiotic species widely distributed in the Mediterranean sublittoral zone. Previous studies show that high pCO₂ can affect the microbial community and trophic metabolism of A. viridis. We applied a metabolomics approach to characterize variation in metabolite levels under different pH conditions.

We designed an experiment involving four treatment groups. The first two included individuals naturally living at the control site (pH 8.05) and at the low pH site, respectively. The other two groups were part of a cross-transplanting setup, in which individuals from each site were transplanted to the opposite pH condition. With this design, we aimed not only to characterize the baseline metabolic profiles of individuals adapted to ambient or acidified conditions, but also to assess the metabolic plasticity of the species when exposed to environmental change. All individuals were maintained in experimental conditions for seven days, after which tentacle tissues were sampled and analyzed using proton Nuclear Magnetic Resonance (¹H-NMR)-based metabolomics.

The 1D ¹H-NMR spectrum of polar extracts identified over 30 metabolites, with altered levels of organic osmolytes such as betaine, taurine, and glycine in individuals from the low pH site. A decrease in energetic molecules like pyruvate also suggested adaptive responses to acidified conditions.

Our findings help clarify how natural pH variability may shape the physiology of coastal species under future ocean acidification.