Calcifying Response and Recovery Potential of the Brown Alga Padina pavonica under Ocean Acidification

Anthropogenic carbon dioxide (CO2) emissions are causing ocean acidification (OA), which affects calcifying organisms. Recent studies have shown that Padina pavonica investigated along a natural pCO2 gradient seems to acclimate to OA by reducing calcified structures and changing mineralogy from aragonite to calcium sulfate salts. The aim of the present study was to study the potential for acclimation of P. pavonica to OA along the same gradient and in aquaria under controlled conditions. P. pavonica was cross-transplanted for 1 week from a normal pH site (mean values of pHTS 8.1 and pCO2 = 391 μatm) to a low pH site (mean values of pHTS 7.4 and pCO2 = 1044 μatm) and vice versa. Results showed that this calcifying alga did survive under acute environmental pHTS changes but its calcification was significantly reduced. P. pavonica decalcified and changed mineralogy at pHTS 7.4, but once brought back at pHTS 8.1, it partially recovered the aragonite loss while preserving the calcium sulfate phases that formed under low pHTS. These results suggest that P. pavonica could be used as a bioindicator for monitoring OA as well as localized anthropogenic acidity fluctuations.