FECAL PELLET FLUX IN DABOB BAY DURING A DIATOM BLOOM - CONTRIBUTION OF MICROZOOPLANKTON

During a spring bloom primarily composed of the centric diatom Thalassiosira pacifica in Dabob Bay, Washington, an unarmored dinoflagellate, Gyrodinium sp., phagocytized chains of Thalassiosira. The diatoms were egested in peritrophic membrane-bound fecal pellets that were collected in sediment traps. The dinoflagellate pellets accounted for an average of 29% (SD = 16%) of the volume of fecal pellet flux at 50 m. The diatoms in the pellets were intact but void of plasma content, thus reducing the flux of both POC and pigments per volume of fecal pellets, as was apparent in the sediment trap measurements. Grazing by these dinoflagellates on the large diatoms and the export of relatively carbon- and pigment-deplete pellets have much different implications for organic material cycling than if the diatoms were consumed by mesozooplankton or if they sank.