Niels J. de Winter , Sterre van Sikkeleras, Barbara Goudsmit-Hazevoort, Wim Boer, Lennart de Nooijer, Gert-Jan Reichart, Philippe Claeys , Rob Witbaard

Growth experiments present a powerful tool for determining the effect of environmental parameters on growth and carbonate composition in biogenic calcifiers. For successful proxy calibration and biomineralization studies, it is vital to exactly identify volumes of carbonate precipitated at precise intervals during the experiment. Here, we investigate the use of strontium labelling in mollusk growth experiments. Three bivalve species (C. edule, M. edulis and O. edulis) were grown under monitored field conditions. The bivalves were regularly exposed to seawater with elevated concentrations of dissolved strontium. In addition, the size of the shells was determined at various stages during the experiment using calliper measurements and digital photography. Trace element profiles were measured in cross sections through the shells of these mollusks using laser ablation ICP-MS and XRF techniques. Our results show that doses of dissolved strontium equivalent to 7-8 times the background marine value are sufficient to produce reproducible peaks in shell incorporated strontium in C. edule and M. edulis shells. No negative effects were observed on shell calcification rates. Lower doses (3-5 times background values) resulted in less clearly identifiable peaks, especially in M. edulis. Strontium spiking labels in shells of O. edulis are more difficult to detect, likely due to their irregular growth. Nevertheless, strontium spiking seems a useful technique for creating time marks in cultured shells and a reproducible way to monitor shell height along the growing season while limiting physical disturbance of the animals. However, accurate reconstructions of growth rates at high time resolution require frequent spiking with high doses of strontium.