Energy metabolism and cellular homeostasis trade-offs provide the basis for a new type of sensitivity to ocean acidification in a marine polychaete at a high CO2 vent: adenylate and phosphagen energy pools vs. carbonic anhydrase.

Species distributions and ecology can often be explained by their physiological sensitivity to environmental conditions. Whilst we have a relatively good understanding of how these are shaped by temperature, for other emerging drivers, such as P-CO2 we know relatively little. The marine polychaete Sabella spallanzanii increases its metabolic rate when exposed to high P-CO2 conditions and remains absent from the CO2 vent of Ischia. To understand new possible pathways of sensitivity to CO2 in marine ectotherms, we examined the metabolic plasticity of S. spallanzanii exposed in situ to elevated P-CO2 by measuring fundamental metabolite and carbonic anhydrase concentrations. We show that whilst this species can survive elevated P-CO2 conditions in the short term, and exhibits an increase in energy metabolism, this is accompanied by a significant decrease in carbonic anhydrase concentration. These homeostatic changes are unlikely to be sustainable in the longer term, indicating S. spallanzanii may struggle with future high P-CO2 conditions.