Calcification and growth of CWC depends on seawater chemistry, particularly the saturation state of aragonite, the mineral composing the skeleton. The rising CO2 levels in the atmosphere are predicted to change seawater chemistry and lower the aragonite saturation state, with negative consequences particularly for the deep biota. Because many CWC live at or near aragonite saturation, already slight changes in saturation state may have dire consequences for the calcification and survival of these corals. Comau Fjord (Chile) offers a unique window into the future, where the stratified fjord allows to time-travel from aragonite-supersaturated waters near the surface to undersaturated waters at depth. Recent research has shown that the CWC Desmophyllum dianthus abounds below the aragonite saturation horizon, suggesting adaptation to ocean acidification. Because coral calcification is energetically costly, we postulate that a high supply of zooplankton food provides the metabolic energy for the coral to maintain calcification in acidified waters. The project involves observational and experimental studies on the ecology of the corals and their regulation of internal pH, their ability to cope with global CO2 and temperature rise, and the ecology of the plankton, its distribution in space and time, vertical migrations and seasonality.