Potential use of Cu2+, K+ and Na+ for the destruction of Caulerpa taxifolia: differential effects on photosynthetic parameters

Chemical techniques were investigated in order to eradicate Caulerpa taxifo lia, a green alga spreading at a remarkable rate in the Mediterranean Sea. The action of copper, potassium and sodium ions on survival rates and photo synthetic parameters was compared, in order to optimise the conditions of f urther in situ treatments. The lethal doses were determined and the impact of the studied cations on photosynthesis and respiration rates and PSII pho tochemistry was analysed from measurements of net oxygen exchanges and chlo rophyll fluorescence. The Cu2+ concentrations required to obtain 100% morta lity were 15 x 10(2) to 10(4) times lower than those of K+ and Na+. Respira tion was slightly affected whatever the salt concentration, while photosynt hesis could be totally inhibited depending on the applied treatment. Change s in the structure of the Ribulose-1,5-biphosphate carboxylase/oxygenase (R ubisCO, EC: 4.1.1.39) were also detected when C. taxifolia underwent cation treatments (10 mg L-1 Cu2+, 1 h; 20 g L-1 K+, 3 h; 20 g L-1 Na+, 1 h). Giv en the high concentration and long incubation periods required with K+ and Na+ ions, these cations are not suitable to be used in situ. Our results ma ke possible the utilisation of copper cations following technical approache s such as ion-exchange textile covers, which allows a controlled release of cupric ions without dissemination in the marine environment.