The toxic effect of copper on Oscillatoria (Trichodesmium) theibautii1

[ 14 C]CO 2 fixation in Oscillatoria theibautii decreased in response to copper at low cupric ion activities (10 −10 M) in test media containing Tris as a copper chelator and to low concentrations (10 −8 M) of total added copper in filtered seawater. This sensitivity could be important to natural systems as well as laboratory and shipboard cultures.