Molecular mechanisms underlying the physiological responses of the cold-water coral Desmophyllum dianthus to ocean acidification

Cold-water corals (CWCs) are thought to be particularly vulnerable to ocean acidification (OA) due to increased atmospheric pCO(2), because they inhabit deep and cold waters where the aragonite saturation state is naturally low. Several recent studies have evaluated the impact of OA on organism-level physiological processes such as calcification and respiration. However, no studies to date have looked at the impact at the molecular level of gene expression. Here, we report results of a long-term, 8-month experiment to compare the physiological responses of the CWC Desmophyllum dianthus to OA at both the organismal and gene expression levels under two pCO(2)/pH treatments: ambient pCO(2) (460 mu atm, pH(T) = 8.01) and elevated pCO(2) (997 mu atm, pH(T) = 7.70). At the organismal level, no significant differences were detected in the calcification and respiration rates of D. dianthus. Conversely, significant differences were recorded in gene expression profiles, which showed an up-regulation of genes involved in cellular stress (HSP70) and immune defence (mannose-binding c-type lectin). Expression of alpha-carbonic anhydrase, a key enzyme involved in the synthesis of coral skeleton, was also significantly up-regulated in corals under elevated pCO(2), indicating that D. dianthus was under physiological reconditioning to calcify under these conditions. Thus, gene expression profiles revealed physiological impacts that were not evident at the organismal level. Consequently, understanding the molecular mechanisms behind the physiological processes involved in a coral's response to elevated pCO(2) is critical to assess the ability of CWCs to acclimate or adapt to future OA conditions.