The European FOCE ([http://efoce.eu eFOCE]) comprises two open-top chambers (control and experimental) as well as a surface buoy housing the electronics and pumps to produce CO-enriched water. The system is powered by solar and wind energy. Data packets are wirelessly sent to the nearby laboratory and can be monitored on the internet. The eFOCE system is currently deployed in the bay of Villefranche-sur-mer (France) at about 12 m depth and 300 m offshore. The eFOCE project has been developed to investigate the long-term effects of acidification on benthic marine communities of the North West Mediterranean Sea, especially Posidonia seagrass beds. Over a 3-year period, the aim of the project is to develop relatively long (> 6 month) experiments.