[BPT06-P07] Radio- and stable carbon isotopic responses in experimentally-cultured bivalves for the understanding of acidification effect on bivalve nutrient uptake and biomineralization
Keywords:Mollusca, Radio isotope, Stable carbon isotope
Specimens of the filter-feeding clam Scapharca broughtonii (Bivalvia: Arcidae) were cultured in aquaria for 8 weeks, with a novel high-precision pCO2 control system which maintained steady CO2 levels. Bivalve shells and soft tissues, as well as the relevant water and plankton feed samples, were then analysed for δ13C in an Isotope Ratio Mass Spectrometer (IRMS) and Δ14C in an Accelerator Mass Spectrometer (AMS) to examine variations in end-member contributions to the bivalve components.
Shell carbon was found to be principally derived from seawater DIC in all pCO2 conditions. Mantle and soft tissue isotopic signatures stayed constant across pCO2 concentrations and were primarily correlated with the organic carbon signal. A high degree of correlation between Δ14C values of bivalve shell and seawater DIC may point to S. broughtonii’s suitability as a geochemical proxy of DIC palaeo-concentrations. Using Δ14C in concert with δ13C allowed separation of isotopic fractionations deriving from effects other than those caused by actual changes in end-member contributions. Shell δ13C thus might indicate biologically-related fractionation due to physiological adaptations to cope with effects of changes in ambient pH as these dictated the magnitude of this species-specific effect.