Silicate depletion was observed during a bloom of netplankton diatoms. Netplankton chlorophyll a increased over the same salinity range and at the same rate that silicate decreased. Silicate depletion coincided with a decrease in the apparent Si:N uptake ratio as well as a change in the magnitude and diurnal phasing of light saturated photosynthesis (PmB) by netplankton diatoms. Nanoplankton PmBwas unaffected by silicate depletion and increased with temperature. Consequently, nanoplankton PmBeventually exceeded netplankton PmBwhile netplankton biomass was still increasing relative to nanoplankton biomass.