Living under natural conditions of ocean acidification entails energy expenditure and oxidative stress in a mussel species

We investigated the health conditions of the Mediterranean mussel Mytilus galloprovincialis recruited in the CO2
vents system of Castello Aragonese at Ischia Island (Mediterranean Sea). Individuals of M. galloprovincialis were
sampled in three sites along the pH gradient (8.10, 7.7 and up to <7.4). Untargeted metabolomics and
biochemical endpoints related to energetic metabolism, oxidative stress/damage, neurotoxicity and immune
defense were analyzed. Corrosion of the valves occurred at low pH. A separation of the metabolome was
observed along the pH gradient. Metabolites belonging to amino acids, nucleosides, lipids and organic osmolytes
were significantly reduced in the organisms from the most acidified sites. The content of reactive oxygen species
and the activity of glutathione peroxidase were reduced in organisms from the acidified sites compared to
ambient pH, and no oxidative damage was induced. Overall results suggested the presence of an energy cost
underpinning long-term survival in acidified conditions for this species.