Hysteresis between coral reef calcification and the seawater aragonite saturation state

• Published in: Geophysical Research Letters
• Main Authors: McMahon, Ashly, Santos, Isaac R, Cyronak, Tyler, Eyre, Bradley D
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: ePublications@SCU 2013
• Subjects: Environmental Sciences; Ocean acidification
• Online Access: https://epubs.scu.edu.au/esm_pubs/2028; https://doi.org/10.1002/grl.50802

[1] Some predictions of how ocean acidification (OA) will affect coral reefs assume a linear functional relationship between the ambient seawater aragonite saturation state (Ωa) and net ecosystem calcification (NEC). We quantified NEC in a healthy coral reef lagoon in the Great Barrier Reef during different times of the day. Our observations revealed a diel hysteresis pattern in the NEC versus Ωa relationship, with peak NEC rates occurring before the Ωa peak and relatively steady nighttime NEC in spite of variable Ωa. Net ecosystem production had stronger correlations with NEC than light, temperature, nutrients, pH, and Ωa. The observed hysteresis may represent an overlooked challenge for predicting the effects of OA on coral reefs. If widespread, the hysteresis could prevent the use of a linear extrapolation to determine critical Ωa threshold levels required to shift coral reefs from a net calcifying to a net dissolving state.