Phagotrophy and fecal pellet production by an athecate dinoflagellate in Antarctic sea ice

A phagotrophic athecate dinoflagellate was found in sea ice and the underlying watercolumn of the Weddell Sea ice edge during the austral autumn of 1986. This organism lacked a sulcus, a cingulum and flagella but possessed a dinokont nucleus, a cytostome and ainphiesmal vesicles. Abundances exceeded 105 1-' in the ice. The single large food vacuole contained a variety of protistan prey but was predominantly composed of the pennate diatom N~tzschia cyljndrus. The fecal pellet produced upon the egestion of this vacuole was membrane bound. Of the fecal pellet volume 15 % was identifiable protoplasm, mostly N. cylindrus. Carbon per pellet averaged 97 pg, and abundances of the fecal pellet in the ice also exceeded 105 I-'. Release of the fecal pellet into the underlying water column upon melting of the ice may account for a significant proportion of the particulate organic carbon available to metazoan grazers at the ice edge. Flux of material out of the euphotlc zone via this fecal pellet may be significant.