Fecal pellet flux in Dabob Bay during a diatom bloom: contribution of microzooplankton. Limnology and Oceanography

During a spring bloom primarily composed of the centric diatom Thalassiosira paczfca 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 dino-flagellate 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 dinoflag-ellates 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. Carbon sinking from continental margins and derived from the open oceans may contribute equal amounts to the global marine flux (Walsh 199 1). In many coastal areas, most of the flux is in the form of fecal pellets (Dunbar and Berger 198 1). The majority of these feca