ALBERT

Description: Subseabed CO 2 storage is considered a future climate change mitigation technology. We investigated the ecological consequences of CO 2 leakage for a marine benthic ecosystem. For the first time with a multidisciplinary integrated study, we tested hypotheses derived from a meta-analysis of previous experimental and in situ high-CO 2 impact studies. For this, we compared ecological functions of naturally CO 2 -vented seafloor off the Mediterranean island Panarea (Tyrrhenian Sea, Italy) to those of nonvented sands, with a focus on biogeochemical processes and microbial and faunal community composition. High CO 2 fluxes (up to 4 to 7 mol CO 2 m –2 hour –1 ) dissolved all sedimentary carbonate, and comigration of silicate and iron led to local increases of microphytobenthos productivity (+450%) and standing stocks (+300%). Despite the higher food availability, faunal biomass (–80%) and trophic diversity were substantially lower compared to those at the reference site. Bacterial communities were also structurally and functionally affected, most notably in the composition of heterotrophs and microbial sulfate reduction rates (–90%). The observed ecological effects of CO 2 leakage on submarine sands were reproduced with medium-term transplant experiments. This study assesses indicators of environmental impact by CO 2 leakage and finds that community compositions and important ecological functions are permanently altered under high CO 2 .