The release of copper-complexing ligands by the brown alga Fucus vesiculosus (Phaeophyceae) in response to increasing total copper levels

The growth of Fucus vesiculosus L. germlings in chemically defined culture media containing a range of Cu concentrations (20-1000 nM) was monitored simultaneously with measurement of the Cu speciation in the media by competitive equilibrium-adsorptive cathodic stripping voltammetry. Fucus vesiculosus germlings were found to exude Cu-complexing ligands with conditional stability constants of the order of 1.6 x 1011. Ligand concentrations increased with increasing total dissolved Cu concentrations (CU(T)) until a concentration of 500-800 neq Cu·L-1 was reached. Concentrations of the ligand exceeded CUT in treatments containing 20 and 100 nM Cu, were similar to CU(T) in the 500-nM Cu treatment, but were less than CU(T) in the 1000-nM treatment. Therefore, [Cu2+] were calculated to be at concentrations of 10-11 - 10-10 M in the 20- and 100-nM treatments, 10-9 M in the 500-nM treatment, and 10-7 M in the 1000-nM treatment. Growth rates were lowest at Cu2+ concentration > 10-9. These results are discussed within the context of the potential roles for exuded copper-complexing ligands.