Population-level responses to long-term cadmium exposure in two strains of the freshwater gastropod Biomphalaria glabrata: results from a life-table response experiment.

A life-table response experiment was conducted to ascertain the demographic effects of low-level cadmium exposure on two strains, BS90 and NMRI, of the freshwater gastropod Biomphalaria glabrata. Snails were exposed to cadmium continuously from the embryonic stage through adulthood. Results indicated that cadmium significantly affected a number of individual-based parameters, including %hatch, juvenile survival, and adult survival in both strains. Also, fecundity and time to maturity were significantly affected in the NMRI strain. A stage-based, deterministic, population model indicated that population growth rate (lambda) was significantly affected by cadmium. Elasticity analysis indicated that juvenile survival, in general, had the greatest contribution to lambda. Decomposition analysis indicated that the effects of cadmium on the juvenile stage in BS90 and the embryonic stage in NMRI contributed most to cadmium-induced changes in lambda. The BS90 strain was more sensitive to cadmium toxicity than NMRI. Moreover, the two strains differed in pattern of response with different aspects of their respective life histories contributing to cadmium-induced changes in lambda. Comparisons were also made between the main model, based on a Z transformation of the life-cycle graph, and more commonly used matrix models.