Abstract
The integrated iodate and total-iodine concentrations accompanying accelerated growth of natural phytoplankton in eight 14-m deep mesocosm experiments did not vary significantly. Growth was induced by the addition of nutrients, while light irradiance was controlled by neutral density screens. These measures resulted in a range of particulate organic carbon concentrations of between 13 and 220 μmol L-1, that is, covering some that are well in excess of blooms generally found in the natural environment. This, together with most earlier results obtained from phytoplankton culturing and much hydrographic survey, is used as an opportunity to question whether phytoplankton growth can be the cause of iodate reduction in seawater.