IDENTIFICATION OF ANNUALLY PRODUCED OPAQUE BANDS IN THE SHELL OF THE FRESH-WATER MUSSEL ELLIPTIO-COMPLANATA USING THE SEASONAL CYCLE OF DELTA-O-18

Three methods of aging Elliptio complanata were compared: (i) counting the number of opaque bands seen on the exterior of the shell using tr ansmitted Light, (ii) counting the number of opaque bands observed in polished longitudinal sections of shell, and (iii) counting the number of opaque bands identified as annual on the basis of their delta(18)O concentration. On average, the number of opaque bands counted in the shell interior was greater than the number of opaque bands counted on the shell exterior. The number of annually produced opaque bands, dist inguished from disturbance bands by their position within the seasonal cycle of delta(18)O in the shell, agreed with the number of bands cou nted in polished interior sections. Opaque bands caused by nonannual e vents were either not continuous from the growing edge to the umbo, or not continuous until they merged into and with other bands near the p allial line. The counting of the internal opaque bands, using the proc edures described in this study, provided the best estimate of the true age of Elliptio complanata.