PLANT E NTRAINMENT OF ESTUARINE P HYTOPLANKTON

Productivities of natural phytoplankton assemblages were significantly altered in passage through a cooling system of an electrical power station in mid-Chesapeake Bay, U.S.A. Carbon fixation in assemblages collected at the intake structure was significantly lower than rates noted at the discharge in June but significantly higher than rates observed at discharge in July through September. Productivity of a representative of the microflageUates, C1yptomonas acuta, was significantly reduced after passage through the plant (AT = 6 ° C) in July through September. Photosynthetic C incorporation rates for the dinoflagellate Prorocentrum mariae-lebouriae, the centric diatom Cyclotella caspia and the pennate diatom Thalassionema nitzschioides were not altered during entrainment. These data support previous observations of lower fixation rates and cell lysis in microflagellates than in more rigid diatoms following power plant entrainment.