Plankton- And cold-water COral ecology in the Comau fjord (PACOC)

PACOC investigates the growth of cold-water corals (CWC) in a naturally acidified Patagonian fjord and the role of zooplankton in sustaining their nutritional supply.

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 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 migration and seasonality. The project is carried out by AWI, UACh and Huinay Field Station and is funded by BMBF and CONICYT.

Cold-water coral Desmophyllum dianthus installed on holder (Photo: Jürgen Laudien (AWI))