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Several experiments have shown a decrease of growth and calcification of organisms at decreased pH levels but relatively few studies have focused on early life stages which are believed to be more sensitive to environmental disturbances such as hypercapnia. Here, we present experimental data demonstrating that the growth of planktonic mussel (Mytilus edulis) larvae is significantly affected by a decrease of pH to a level expected for the end of the century. Even though there was no significant effect of a 0.25–0.34 pH unit decrease on hatching and mortality rates during the first 2 days of development nor during the following 13-day period prior to settlement, final shells were, respectively, 4.5±1.3 and 6.0±2.3% smaller at pH_NBS~7.8 than at a control pH_NBS of ~8.1. Moreover, a decrease of 12.0±5.4% of shell thickness was observed. More severe impacts were found with a decrease of ~0.5 pH_NBS unit during the first 2 days of development which could be attributed to a decrease of calcification due toslight undersaturation of seawater with respect to aragonite. Indeed, important effects on both hatching and D-veliger shell growth were found. Hatching rates were 24±4% lower while D-veliger shells were 12.7±0.9% smaller at pH_NBS~7.6 than at a control pH_NBS of ~8.1. Although these results show that blue mussel larvae are still able to develop a shell in seawater undersaturated with respect to aragonite, decreases of hatching rates and shell growth suggest a negative impact of ocean acidification on the future survival of bivalve populations potentially leading to significant ecological and economical losses

Several experiments have shown a decrease of growth and calcification of organisms at decreased pH levels. There is a growing interest to focus on early life stages that are believed to be more sensitive to environmental disturbances such as hypercapnia. Here, we present experimental data, acquired in a commercial hatchery, demonstrating that the growth of planktonic mussel (Mytilus edulis) larvae is significantly affected by a decrease of pH to a level expected for the end of the century. Even though there was no significant effect of a 0.25–0.34 pH unit decrease on hatching and mortality rates during the first 2 days of development nor during the following 13-day period prior to settlement, final shells were respectively 4.5±1.3 and 6.0±2.3% smaller at pH_NBS~7.8 (pCO₂~1100–1200 μatm) than at a control pH_NBS of ~8.1 (pCO₂~460–640 μatm). Moreover, a decrease of 12.0±5.4% of shell thickness was observed after 15d of development. More severe impacts were found with a decrease of ~0.5 pH_NBS unit during the first 2 days of development which could be attributed to a decrease of calcification due to a slight undersaturation of seawater with respect to aragonite. Indeed, important effects on both hatching and D-veliger shell growth were found. Hatching rates were 24±4% lower while D-veliger shells were 12.7±0.9% smaller at pH_NBS~7.6 (pCO₂~1900 μatm) than at a control pH_NBS of ~8.1 (pCO₂~540 μatm). Although these results show that blue mussel larvae are still able to develop a shell in seawater undersaturated with respect to aragonite, the observed decreases of hatching rates and shell growth could lead to a significant decrease of the settlement success. As the environmental conditions considered in this study do not necessarily reflect the natural conditions experienced by this species at the time of spawning, future studies will need to consider the whole larval cycle (from fertilization to settlement) under environmentally relevant conditions in order to investigate the potential ecological and economical losses of a decrease of this species fitness in the field

Abstract. Elemental ratios in benthic foraminifera have been used to reconstruct bottom water temperature and carbonate saturation ). We present elemental data for the long-ranging benthic foraminifera Oridorsalis umbonatus from sediment core tops that span a narrow range of temperatures and a wide range of saturation states. B/Ca, Li/Ca, Sr/Ca and Mg/Ca ratios exhibit positive correlations with bottom water carbonate saturation. The sensitivity of individual element/calcium ratios to bottom water [CO To assess the fidelity of these relationships and the possibility of applying these relationships to earlier periods of Earth history, we examine the mechanisms governing elemental incorporation into foraminiferal calcite. Empirical partition coefficients for Li and Sr are consistent with Rayleigh fractionation from an internal pool used for calcification. For O. umbonatus and other benthic species, we show that the fraction of Ca remaining in the pool is a function of bottom water [CO 2− 3 ], and can be explained by either a growth rate effect and/or the energetic cost of raising vesicle pH at the site of calcification. Empirical partition coefficients for Mg and B may also be controlled by Rayleigh fractionation, but require that either the fractionation factor from the internal pool is smaller than the inorganic partition coefficient and/or additional fractionation mechanisms. O. umbonatus element ratio data may also be consistent with fractionation according to the surface entrapment model and/or the presence of discrete high-and low-Mg calcite phases. However, at present we are limited in our ability to assess these mechanisms. The new X/Ca data for O. umbonatus provide constraints to test the role of these mechanisms in the future.

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