RESUMEN
A large acclimation experiment was performed with Daphnia magna in which two different copper bioavailability (as Cu2+) groups (N and M) were used. In the N group the cupric ion activity increased with increasing dissolved copper-acclimation concentration, while in the M group the ion activity decreased with increasing dissolved copper concentration. The activity of copper carbonates and hydroxides was up to an order of magnitude lower than the cupric ion activity. After five generations of acclimation, the acute copper sensitivity (mean +/- SD) of the N group ranged from 193 /- 24 to 296 +/- 50 microg Cu L(-1) and for the M group from 198 +/- 27 to 315 +/- 38 microg Cu L(-1) for daphnids acclimated to 1 and 100 microg Cu L(-1), respectively. The internal copper concentration of the acclimated daphnids also resulted in similar results between the two groups. Acclimation of the two daphnid groups for five consecutive generations to the three dissolved copper concentrations resulted in a shift in the optimal concentration range toward 1 microg Cu L(-1), using energy reserves as an endpoint. Our results suggest that copper acclimation and accumulation are related to the dissolved copper concentration of the culture medium, but not to the copper activity.
