Effects of Varying Copper Concentrations on Photosynthesis of Gracilaria salicornia and Padina sanctae-crusis

Two tropical macroalgae, Gracilaria salicornia and Padina sanctae-crusis, were exposed to varying concentrations of total Cu and subsequently subjected to photosynthesis-irradiance (P-I) response experiments. The study aimed to determine the effects of total Cu toxicity on the P-I model parameters and growth rate of the macroalgae. The photosynthetic efficiency (α) showed a decreasing pattern with increasing total Cu concentration. Light saturation (Ik) for both algae increased at lower concentration and showed transient shift at 12.5 μg total Cu L-1. The maximum photosynthesis (Pmax) of P. sanctae-crusis was higher in specimens exposed to 12.5-25 μg total Cu L-1 compared to the controls. Unlike P. sanctae-crusis, G. salicornia exposed total Cu-free medium as well as those at 12.5-25 μg total Cu L-1 were comparable. But, both algae showed decreasing Pmax values from 50-500 μg total Cu L-1. Respiration (R) showed nonlinear pattern due to some delay of the effect of copper on the respiratory system. Growth data proved to be more sensitive to total Cu with the reductions of mean daily growth rate starting at 12.5 μg total Cu L-1 for G. salicornia and negative growth rate at 500 μg total Cu L-1 for P. sanctae-crusis. After 7 days of exposure the EC20 for G. salicornia and P. sanctae-crusis were 100 and 50 μg total Cu L-1, respectively. The results suggested severe impact of total Cu+ at high concentrations on P-I parameters and growth rate of G. salicornia and P. sanctae-crusis.