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Chemical techniques were investigated in order to eradicate Caulerpa taxifolia, a green alga spreading at a remarkable rate in the Mediterranean Sea. The action of copper, potassium and sodium ions on survival rates and photosynthetic parameters was compared, in order to optimise the conditions of further in situ treatments. The lethal doses were determined and the impact of the studied cations on photosynthesis and respiration rates and PSII photochemistry was analysed from measurements of net oxygen exchanges and chlorophyll fluorescence. The Cu 2+ concentrations required to obtain 100% mortality were 15 x 10 to the second to 10 to the fourth times lower than those of K+ and Na+. Respiration was slightly affected whatever the salt concentration, while photosynthesis could be totally inhibited depending on the applied treatment. Changes in the structure of the Ribulose-1,5-biphosphate carboxylase/oxygenase (RubisCO, EC: 4.1.1.39) were also detected when C. taxifolia underwent cation treatments (10 mg/L CU 2+, 1 h; 20 g/L K+, 3 h; 20 g/L Na+, 1 h). Given 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 make possible the utilisation of copper cations following technical approaches such as ion-exchange textile covers, which allows a controlled release of cupric ions without dissemination in the marine environment.

Ce document de synthèse était originellement accompagné des annexes suivantes : I-A. Évaluation des apports en azote et en phosphore des bassins versants (données statistiques et bibliographiques). Application aux etangs du departement de l'Hérault. I-B. Évaluation des apports en azote et en phosphore des bassins versants (approche préliminaire des mesures de flux). Application au bassin versant du Salaison. II. Cartographie et estimation des stocks de nutriments dans les sediments. Application aux étangs du complexe palavasien. III-A. Le fractionnement du phosphore en milieu saumâtre (etude bibliographique et comparaison de methodes). Application aux sediments de l'etang de l'Or. III-B. Échanges de phosphore eau-sediment en milieu saumatre (mesures du flux diffusif par peepers). Application aux etangs de l'Or et du Prevost. IV. Recherche de la limitation de Ia croissance des ulves par les nitrates et les phosphates (étude de terrain et de laboratoire). Application a l'etang du Prevost. V. Interventions pour reduire Ia masse de nutriments. Actions sur les bassins versants, les sédiments et les algues (analyse bibliographique et enquêtes). Application technique et économique aux lagunes palavasiennes. Le document numérisé joint ne comprend que les annexes, I-A, II, III-A, III-B