1CNRS-INSU, Laboratoire d'Océanographie de Villefranche (UMR7093), BP 28, 06234 Villefranche-sur-Mer Cedex, France
2Univ. Pierre et Marie Curie-Paris 6, Observatoire Océanologique de Villefranche, 06230 Villefranche-sur-Mer Cedex, France
3Univ. of Cambridge, Department of Earth Sciences, Cambridge CB2 3EQ, UK
4Roem van Yerseke BV, Gr. van Zoelenstraat 35, Postbus 25, 4400AA Yerseke, The Netherlands
5Netherlands Institute of Ecology (NIOO-KNAW), Centre for Estuarine and Marine Ecology, Postbus 140, 4400 AC Yerseke, The Netherlands
6NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Organic Biogeochemistry, P.O. Box 59, 1790 AB Den Burg (Texel), The Netherlands
7Faculty of Geosciences, Utrecht Univ., P.O. Box 80021, 3508 TA Utrecht, The Netherlands
Abstract. 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 pHNBS~7.8 (pCO2~1100–1200 μatm) than at a control pHNBS 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 pHNBS 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 pHNBS~7.6 (pCO2~1900 μatm) than at a control pHNBS 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.