Skeletal properties of the coral Desmophyllum dianthus are related to the aragonite saturation state along a depth gradient in the Mediterranean Sea

Ocean biogeochemistry is now being strongly influenced by the oceanic uptake of anthropogenic carbon dioxide from the atmosphere, leading to an increase in hydrogen ion concentration (i.e., decreases pH) and to a decrease in the carbonate ion concentration, in a process commonly referred to as ocean acidification. Ocean acidification is likely to exhibit its most immediate effects on cold‐water corals in deep waters with the shoaling of the aragonite saturation horizon, leading to dramatic declines in rates of calcification. It is now clear that the Mediterranean area will be a hotspot for climate change effects, making it a miniature model of global patterns to occur in the world’s marine biota, and a natural focus of interest for research. This study aimed to investigate the effects of decreasing aragonite saturation state (Ωarag) on the biometric and skeletal parameters of Desmophyllum dianthus along a depth gradient (400 - 1200 m) in the Mediterranean Sea. The results indicate that as Ωarag decreases, bulk density decreased while skeletal porosity and micro-density increase. This trend could be explained through the inhibition of calcification as Ωarag decreased, leading to a more porous and likely fragile skeletal phenotype. This is one of the few in situ studies conducted on a cold-water coral species in the Mediterranean Sea, providing evidence on their susceptibility to increased ocean acidity.