Ecophysiological responses of marine calcifiers to the acidification and bicarbonation of the oceans

Background/Question/Methods

Calcification is a critical process in marine biota and the Earth’s carbon cycle. A current concern is that anthropogenic carbon dioxide emissions are causing a decline in the concentration of carbonate ions in seawater, which may result in dissolution of marine calcareous shells and skeletons.  Although most studies show a decrease in calcification rates in response to decreasing carbonate ion concentrations, a significant number of reports show varying physiological responses to increasing carbon dioxide levels.

Results/Conclusions

Marine calcifiers seem to have evolved mechanisms to concentrate the most abundant inorganic carbon species in seawater, bicarbonate ions, which increase via CO2-induced ocean acidification or “ocean bicarbonation”. This strategy enables carbon transport through biological membranes, as these appear to be impermeable to carbonate ions. Many studies have proposed that calcification requires the uptake of bicarbonate ions into the calcification reservoir and its subsequent conversion into carbonate ions accompanied by the production of protons, which must be extruded from the calcification reservoir to prevent acidification. In this talk, I will review mechanisms underlying the diversity of marine calcification responses to the acidification and bicarbonation of seawater that accompanies rising atmospheric pCO₂.