Simulated leakage of high pCO2 water negatively impacts bivalve dominated infaunal communities from the Western Baltic Sea

Carbon capture and storage is promoted as a mitigation method counteracting the increase of atmospheric CO2 levels. However, at this stage, environmental consequences of potential CO2 leakage from sub-seabed storage sites are still largely unknown. In a 3-month-long mesocosm experiment, this study assessed the impact of elevated pCO(2) levels (1,500 to 24,400 mu atm) on Cerastoderma edule dominated benthic communities from the Baltic Sea. Mortality of C. edule was significantly increased in the highest treatment (24,400 mu atm) and exceeded 50%. Furthermore, mortality of small size classes (0-1 cm) was significantly increased in treatment levels >= 6,600 mu atm. First signs of external shell dissolution became visible at >= 1,500 mu atm, holes were observed at > 6,600 mu atm. C. edule body condition decreased significantly at all treatment levels (1,500-24,400 mu atm). Dominant meiofauna taxa remained unaffected in abundance. Densities of calcifying meiofauna taxa (i.e. Gastropoda and Ostracoda) decreased in high CO2 treatments (> 6,600 mu atm), while the non - calcifying Gastrotricha significantly increased in abundance at 24,400 mu atm. In addition, microbial community composition was altered at the highest pCO(2) level. We conclude that strong CO2 leakage can alter benthic infauna community composition at multiple trophic levels, likely due to high mortality of the dominant macrofauna species C. edule.