BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-10-6161-2013 Effect of increased <i>p</i>CO<sub>2</sub> level on early shell development in great scallop (<i>Pecten maximus</i> Lamarck) larvae Andersen S. 1 Grefsrud E. S. 2 Harboe T. 1 Institute of Marine Research, Austevoll Research Station, 5392 Storebø, Norway Institute of Marine Research, Postbox 1870 Nordnes, 5817 Bergen, Norway 01 10 2013 10 10 6161 6184 Copyright: © 2013 S. Andersen et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/10/6161/2013/bg-10-6161-2013.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/10/6161/2013/bg-10-6161-2013.pdf

As a result of high anthropogenic CO<sub>2</sub> emissions, the concentration of CO<sub>2</sub> in the oceans has increased, causing a decrease in pH, known as ocean acidification (OA). Numerous studies have shown negative effects on marine invertebrates, and also that the early life stages are the most sensitive to OA. We studied the effects of OA on embryos and unfed larvae of the great scallop (<i>Pecten maximus</i> Lamarck), at <i>p</i>CO<sub>2</sub> levels of 469 (ambient), 807, 1164, and 1599 μatm until seven days after fertilization. To our knowledge, this is the first study on OA effects on larvae of this species. A drop in <i>p</i>CO<sub>2</sub> level the first 12 h was observed in the elevated <i>p</i>CO<sub>2</sub> groups due to a discontinuation in water flow to avoid escape of embryos. When the flow was restarted, <i>p</i>CO<sub>2</sub> level stabilized and was significantly different between all groups. OA affected both survival and shell growth negatively after seven days. Survival was reduced from 45% in the ambient group to 12% in the highest <i>p</i>CO<sub>2</sub> group. Shell length and height were reduced by 8 and 15%, respectively, when <i>p</i>CO<sub>2</sub> increased from ambient to 1599 μatm. Development of normal hinges was negatively affected by elevated <i>p</i>CO<sub>2</sub> levels in both trochophore larvae after two days and veliger larvae after seven days. After seven days, deformities in the shell hinge were more connected to elevated <i>p</i>CO<sub>2</sub> levels than deformities in the shell edge. Embryos stained with calcein showed fluorescence in the newly formed shell area, indicating calcification of the shell at the early trochophore stage between one and two days after fertilization. Our results show that <i>P. maximus</i> embryos and early larvae may be negatively affected by elevated <i>p</i>CO<sub>2</sub> levels within the range of what is projected towards year 2250, although the initial drop in <i>p</i>CO<sub>2</sub> level may have overestimated the effect of the highest <i>p</i>CO<sub>2</sub> levels. Future work should focus on long-term effects on this species from hatching, throughout the larval stages, and further into the juvenile and adult stages.

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