Ocean Acidification

Carbon Capture and Storage (CCS) provides a promising mitigation technology for reducing the anthropogenic emission of carbon dioxide (CO₂) to the atmosphere. Despite CO₂ having been stored safely below the seafloor and the likelihood of leakage is considered small, experimental studies addressing the environmental impacts of potential leaks still present important support to ecological risk assessment. This study investigated biological responses at the cellular level to seawater acidification in a range simulating pH reduction in the overlying bottom water due to potential CO₂ leakage from the CCS site in the Baltic Sea. In a series of 40-day laboratory experiments, the infaunal polychaete Hediste diversicolor was exposed in a hyperbaric TiTank to three pH levels (7.7, 7.0 and 6.3) at increased hydrostatic pressure (900 kPa) mimicking the actual situation at 80 m water depth. Hypercapnic conditions, particularly pH 7.0, induced oxidative stress in cells activating the defence mechanisms that included inhibition of GST and activation of CAT and GPx. The acidic environment did also cause damage to cellular membranes as indicated by an increase in the concentration of MDA. The activation of defence processes in the polychaetes did not interfere, however, with the energetic metabolism and aerobiosis remained the principal energy production pathway. Patterns of temporal variation of most cellular biomarkers revealed that after a 15–20 day initial response, the antioxidant and detoxification systems recovered their capabilities to cope with acidification highlighting the acclimatisation potential of the nereids to hypercapnia.

Sokołowski A., Świeżak J., Hallmann A., Ziółkowska M., Altin D., Øverjordet I. B. & Smolarz K., 2026. Impact of CO₂-induced seawater acidification at increased hydrostatic pressure on cellular-level responses of the infaunal nereid Hediste diversicolor. Marine Environmental Research 213: 107669. doi: 10.1016/j.marenvres.2025.107669. Article (restricted access).