Autoradiographs of nannoplankton show high photosynthetic fixation rates relative to
net plankton during early daylight hours. However, net plankton contribute increasingly to
community fixation during the afternoon and early evening. During darkness nannoplankton
show losses of fixed 14C greatly exceeding those from net plankton. This lack of uniformity
in [14C]C02 fixation and losses will affect the short term daylight ‘“C measurements
routinely used to assess long term trends in eutrophication.