Attributing reductions in coral calcification to the saturation state of aragonite, comments on the effects of persistent natural acidification

The correct attribution of reductions in coral calcification rates to environmental parameters is key to predicting how coral reefs could respond under future climate change scenarios (1). Crook et al. (2) report a 35% reduction in the calcification rates of the coral Porites astreoides growing near submarine freshwater springs relative to specimens growing in the surrounding lagoon. Submarine springs in the area release intermittently ground water with low conductivity, low pH, low aragonite saturation (Ωarag), and for most of the year, low temperature (3, 4). Although Crook et al. (2) acknowledge the challenges of attributing to one single environmental variable the observed results when multiple parameters may covary, their main conclusion identifying low Ωarag as the sole driver for the observed reductions in coral calcification …