Abstract
Biomineral production in marine organisms employs transient phases of amorphous calcium carbonate (ACC) in the construction of crystalline shells. Increasing seawater pCO2 leads to ocean acidification (OA) with a reduction in oceanic carbonate concentration which could have a negative impact on shell formation and therefore survival. We demonstrate significant changes in the hydrated and dehydrated forms of ACC in the aragonite and calcite layers of Mytilus edulis shells cultured under acidification conditions (1000 μatm pCO2) compared to present day conditions (380 μatm pCO2). In OA conditions, Mytilus edulis has more ACC at crystalisation sites. Here, we use the high-spatial resolution of synchrotron X-ray Photo Emission Electron Microscopy (XPEEM) combined with X-ray Absorption Spectroscopy (XAS) to investigate the influence of OA on the ACC formation in the shells of adult Mytilus edulis. Electron Backscatter Diffraction (EBSD) confirms that OA reduces crystallographic control of shell formation. The results demonstrate that OA induces more ACC formation and less crystallographic control in mussels suggesting that ACC is used as a repair mechanism to combat shell damage under OA. However, the resultant reduced crystallographic control in mussels raises concerns for shell protective function under predation and changing environments.
Highlights
Biomineral production in marine organisms employs transient phases of amorphous calcium carbonate (ACC) in the construction of crystalline shells
The changes in the peak intensities in these spectra are a reliable indicator of the relative abundance of aragonite, calcite and ACC in the shell structures under present day and ocean acidification (OA) conditions
The X-ray Absorption Spectroscopy (XAS) spectra reported in this study are the first Ca-L2,3 edges for biogenic aragonite and calcite comparison in the mussel M. edulis, both appearing as previously reported spectra for synthetic calcite[15]
Summary
Biomineral production in marine organisms employs transient phases of amorphous calcium carbonate (ACC) in the construction of crystalline shells. The resultant reduced crystallographic control in mussels raises concerns for shell protective function under predation and changing environments. Marine organisms, such as molluscs[1] and echinoderms[2,3], use amorphous calcium carbonate (ACC) as a transient phase in the formation of crystalline shell structures, moulding a solid crystalline shell from the inherent disorder of ACC4. High-resolution X-Ray Photo Emission Electron Microscopy (XPEEM) combined with X-ray Absorption Spectroscopy (XAS) is used to identify mineral phases throughout the Mytilus edulis shell structure cultured under current (380 μ atm pCO2) and OA scenarios (1000 μ atm pCO2). The results demonstrate that OA induces more ACC formation and less crystallographic control in mussels
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