REPLACEMENT OF ZINC BY CADMIUM IN MARINE-PHYTOPLANKTON

The concentration of cadmium varies like that of a nutrient in the open ocean. Detailed studies of the marine diatom Thalassiosira weissflogii have shown that cadmium can act as an algal nutrient under conditions of zinc Limitation. We show here that cadmium can also enhance the growth of a variety of species, including a chlorophyte and some prymnesiophytes, when they are zinc limited. The replacement of zinc by cadmium occurs at environmentally relevant inorganic cadmium and zinc concentrations. Very low concentrations of inorganic cadmium that are beneficial under conditions of moderate zinc-limitation become toxic in cultures severely limited by zinc. The role of cadmium as an algal nutrient is thus observable in a narrow, species-specific range of inorganic zinc and cadmium concentrations.