Insights into the response of coral biomineralisation to environmental change from aragonite precipitations in vitro

Precipitation of marine biogenic CaCO3 minerals occurs at specialist sites, typically with 19 elevated pH and dissolved inorganic carbon, and in the presence of biomolecules which 20 control the nucleation, growth, and morphology of the calcium carbonate structure. Here we 21 explore aragonite precipitation in vitro under conditions inferred to occur in tropical coral 22 calcification media under present and future atmospheric CO2 scenarios. We vary pH, ΩAr and pCO2 between experiments to explore how both HCO3 - and CO3 2- 23 influence precipitation 24 rate and we identify the effects of the three most common amino acids in coral skeletons 25 (aspartic acid, glutamic acid and glycine) on precipitation rate and aragonite morphology. We find that fluid ΩAr or [CO3 2- 26 ] is the main control on precipitation rate at 25°C, with no significant contribution from HCO3 - 27 or pH. All amino acids inhibit aragonite precipitation at 28 0.2-5 mM and the degree of inhibition is inversely correlated with ΩAr and, in the case of 29 aspartic acid, also inversely correlated with seawater temperature. Aspartic acid inhibits 30 precipitation the most, of the tested amino acids (and generates changes in aragonite 31 morphology) and glycine inhibits precipitation the least. Previous work shows that ocean 32 acidification increases the amino acid content of coral skeletons and probably reduces 33 calcification media ΩAr, both of which can inhibit aragonite precipitation. This study and 34 previous work shows aragonite precipitation rate is exponentially related to temperature from 35 10-30°C and small anthropogenic increases in seawater temperature will likely offset the 36 inhibition in precipitation rate predicted to occur due to increased skeletal aspartic acid and 37 reduced calcification media ΩAr under ocean acidification.