Physiological studies of the deep-water coral Madrepora oculata incubated at different temperatures and hydrostatic pressures.

Metabolic features of the deep-water coral Madrepora oculata were investigated for specimens originating from approximately 800 m depth in the Bay of Biscay (Northeast Atlantic). Incubations of live specimens were carried out as a function of temperature (7°C, 10°C and 13°C), and for the first time as a function of hydrostatic pressure (atmospheric and natural pressures). An influence of temperature was observed, with an approximately 40% reduction of oxygen consumption at a temperature cooler than in situ, but no obvious increase in a warmer experimental environment. CO2 production increased upon warming from 7°C to 13°C. Hydrostatic pressure had a significant influence on ammonium excretion (and on O:N ratio), suggesting a stress response following exposure to atmospheric pressure. It is the first time that such a response to pressure variation has been observed, calling for increased attention towards pressure effects on live deep-water corals. According to the expected shoaling of the aragonite saturation horizon, studies of deeper-living samples, situated at the lower boundary of their natural depth distribution, appear necessary to better understand the impact of ocean acidification on reef-building scleractinian corals. The present work shows that some biological features are pressure-sensitive, and suggests that investigations on such corals should be undertaken at in situ pressure.