Mineralogical and geochemical composition of CaCO3 skeletons secreted by benthic invertebrates from the brackish Baltic Sea

This study presents mineralogical and geochemical data on the skeletal composition of organisms inhabiting the unique, brackish Baltic Sea. Calcifying invertebrates in this region can build skeletons made of calcite, aragonite or a mixture of both. Their polymorphic skeleton formation is species-specific. However, variations in the calcite: aragonite ratio in the bimineralic skeletons are likely influenced by an effect of salinity on the CaCO3 saturation states and energetic costs of living in brackish conditions. The elemental composition (Ca, Na, Sr, Mg, Ba, Mn, Cu, Pb, V, Y, U, Cd) of skeletons is likewise highly species-specific, probably indicating biological control over calcification. Understanding the processes that enable organisms to function in low salinity environments has vital implications in biomineralization research and in estimating their survival under projected desalinated conditions.