Copper sensitivity of Gonyaulax tamarensis 1

The copper sensitivity of the dinoflagellate Gonyaulax tamarensis was examined in artificial seawater medium. Two short term responses of the organism to copper toxicity are rapid loss of motility and reduced photosynthetic carbon fixation. The chelators tris(hydroxymethylamino)methane (Tris) and ethylenedinitrilotetraacetic acid (EDTA) were used to demonstrate that copper toxicity is a unique function of cupric ion activity. Copper additions to medium containing EDTA equilibrated with the chelator relatively slowly, resulting in misleading short term data. This kinetic effect was not seen when the major copper chelator was Tris or when the copper was added in a chelated form with EDTA. Variations in manganese concentrations over two orders of magnitude did not alter the results. Cells of G. tamarensis are 100% nonmotile at a calculated cupric ion activity of 10 −9.7 M with 50% of the cells nonmotile at 10 −10.4 M. Nonmotile cells do not divide or grow larger. Gonyaulax tamarensis growth is totally inhibited at cupric ion activities that only partially inhibit the growth of four other species that have been studied extensively. Furthermore, this toxicity occurs at the calculated copper activity of natural waters, assuming only inorganic copper complexation. Thus organic chelation may be necessary before G. tamarensis can successfully compete with other algal species in coastal waters.