The Role of Circulation and Stability in Controlling the Relative Abundance of Dinoflagellates and Diatoms Over the Peru Shelf

During a six-week study, the dinoflagellate abundance at C-3, a mid-shelf station off the Peruvian coast, fluctuated widely. At times of maximum cell density (400 cells/ml) dinoflagellates comprised up to 80% of the combined dinoflagellate-diatom population. Our data suggest that after their initial advection into the study site, the dinoflagellates persisted because of stability in the euphotic zone and reseeding by the subsurface poleward undercurrent. The increased stability that favored dinoflagellates did not exclude diatoms at C-3. Diatoms could utilize the available silica and regenerated nitrogen to maintain growth rates adequate to counteract losses from sinking and grazing