Variations in coral reef net community calcification and aragonite saturation state on local and global scales

Abstract

Predicting the response of net community calcification (NCC) to ocean acidification (OA) and declining aragonite saturation state (Ωa) requires a thorough understanding of controls on NCC. The diurnal control of light and net community production (NCP) on NCC confounds the underlying control of Ωa on NCC and must be averaged out in order to predict the general response of NCC to OA. I did this by generating a general NCC-Ωa correlation based on data from 15 field and mesocosm studies around the globe. The general relationship agrees well with results from mesocosm experiments. This general relationship implies that NCC will transition from net calcification to net dissolution at a Ωa of 1.0 ± 0.6 and predicts that NCC will decline by 50% from 1880 to 2100, for a reef of any percent calcifier cover and short reef water residence time. NCC will also decline if percent calcifier cover declines, as evidenced by estimates of NCC in two Caribbean reefs having declined by an estimated 50-90% since 1880. The general NCC-Ωa relationship determined here, along with changes in percent calcifier cover, will be useful in predicting changes in NCC in response to OA and for refining models of reef water Ωa.