Limitation of marine phytoplankton reproductive rates by zinc, manganese, and iron1

The reproductive rates of 21 species of marine phytoplankton were measured in media in which free zinc, manganese, and iron ion activities were controlled at different levels using EDTA‐trace metal ion buffer systems. In general, the reproductive rates of neritic species were limited by zinc activities below 10 ‒11.5 M, while those of oceanic species were either not limited or only slightly limited at the lowest zinc activity attained in the experiment, ca. 10 ‒13 M. The reproductive rates of oceanic coccolithophores were either not limited or only slightly limited by the lowest manganese ion activity attained, ca. 10 ‒11 M, but those of a neritic coccolithophore and all diatoms, both neritic and oceanic, were limited below a manganese activity of 10 ‒10 M. Neritic species had reduced reproductive rates in media containing <10 ‒7 M iron while oceanic species reproduced at maximal or close to maximal rates in the media with the lowest iron concentrations, ca. 10 ‒9 M. The habitat‐related patterns in zinc, manganese, and iron requirements of oceanic and neritic species are consistent with the oceanic‐neritic distributions of concentrations of these metals. This similarity in requirement and distributional patterns provides evidence that Zn, Mn, and Fe availability have been important selective forces on marine phytoplankton populations and communities.