Calcification , a physiological process to be considered in the context of the whole organism

Abstract

Marine organisms that produce calcium carbonate structures are predicted to be most vulnerable to a decline in oceanic pH (ocean acidification) based on the understanding that calcification rates will decrease as a result of changes in the seawater carbon- 5 ate chemistry thereby reducing carbonate ion concentration (and associated satura- tion states). Coastal seas are critical components of the global carbon cycle yet little research has been conducted on acidification impacts on coastal benthic organisms. Here, a critical appraisal of calcification in six benthic species showed, contrary to pop- ular predictions, calcification can increase, and not decrease, in acidified seawater. 10 Measuring the changes in calcium in isolated calcium carbonate structure as well as structures from live animals exposed to acidified seawater allowed a comparison be- tween a species’ ability to calcify and the dissolution affects across decreasing levels of pH. Calcium carbonate production is dependant on the ability to increase calcification thus counteracting an increase in dissolution. Comparison with paleoecological studies of past high carbon dioxide (CO2) events presents a similar picture. This conclusion implies that calcification may not be the critical process impacted by ocean acidifica- tion; particularly as all species investigated displayed physiological trade offs including reduced metabolism, health, and behavioural responses, in association with this cal- cification upregulation, which possess as great a threat to survival as an inability to calcify.