CARBON ISOTOPIC DISEQUILIBRIUM IN THE SHELL OF THE FRESH-WATER MUSSELELLIPTIO-COMPLANATA

Isotopic analyses of shell material from the freshwater mussel Ellipti o complanata produced mean C concentrations that were depleted in C-14 and C-13 relative to the lake water DIG. Depleted C isotope values we re attributed to the incorporation of C-12-enriched metabolic C into t he shell. Microsampling of longitudinal sections of shell revealed a s easonal pattern in the delta(13)C values. The seasonal pattern matched predictions that DIC delta(13)C and metabolic rate determine the fina l shell delta(13)C concentration. The greatest depletion of delta(13)C occurred in the summer. Similar delta(13)C patterns in marine and fre shwater mollusks probably record not only temperature fluctuations, up welling events, and phytoplankton blooms as reported, but also the cha nges in metabolic activity brought on by such events. (C) 1988 Elsevie r Science Ltd. All rights reserved.