Carbon isotopic disequilibrium in the shell of the freshwater mussel Elliptio complanata

Isotopic analyses of shell material from the freshwater mussel Elliptio complanata produced mean C concentrations that were depleted in 14C and 13C relative to the lake water DIC. Depleted C isotope values were attributed to the incorporation of 12C-enriched metabolic C into the shell. Microsampling of longitudinal sections of shell revealed a seasonal pattern in the δ13C values. The seasonal pattern matched predictions that DIC δ13C and metabolic rate determine the final shell δ13C concentration. The greatest depletion of δ13C occurred in the summer. Similar δ13C patterns in marine and freshwater mollusks probably record not only temperature fluctuations, upwelling events, and phytoplankton blooms as reported, but also the changes in metabolic activity brought on by such events.