Copper regulation and homeostasis of Daphnia magna and Pseudokirchneriella subcapitata: influence of acclimation

This study aimed to evaluate (1) the capacity of the green alga Pseudokirchneriella subcapitata and the waterflea Daphnia magna to regulate copper when exposed to environmentally realistic copper concentrations and (2) the influence of multi-generation acclimation to these copper concentrations on copper bioaccumulation and homeostasis. Based on bioconcentration factors, active copper regulation was observed in algae up to 5 μg Cu L−1 and in daphnids up to 35 μg Cu L−1. Constant body copper concentrations (13 ± 4 μg Cu g DW−1) were observed in algae exposed to 1 through 5 μg Cu L−1 and in daphnids exposed to 1 through 12 μg Cu L−1. At higher exposure concentrations, there was an increase in internal body copper concentration, while no increase was observed in bioconcentration factors, suggesting the presence of a storage mechanism. At copper concentrations of 100 μg Cu L−1 (P. subcapitata) and 150 μg Cu L−1 (D. magna), the significant increases observed in body copper concentrations and in bioconcentration factors may be related to a failure of this regulation mechanism. For both organisms, internal body copper concentrations lower than 13 μg Cu g DW−1 may result in copper deficiency. For P. subcapitata acclimated to 0.5 and 100 μg Cu L−1, body copper concentrations ranged (mean ± standard deviation) between 5 ± 2 μg Cu g DW−1 and 1300 ± 197 μg Cu g DW−1, respectively. For D. magna, this value ranged between 9 ± 2 μg Cu g DW−1 and 175 ± 17 μg Cu g DW−1 for daphnids acclimated to 0.5 and 150 μg Cu L−1. Multi-generation acclimation to copper concentrations ≥12 μg Cu L−1 resulted in a decrease (up to 40%) in body copper concentrations for both organisms compared to the body copper concentration of the first generation. It can be concluded that there is an indication that P. subcapitata and D. magna can regulate their whole body copper concentration to maintain copper homeostasis within their optimal copper range and acclimation enhances these mechanisms.