GRAZING BEHAVIOR OF HETEROTROPHIC NANOFLAGELLATES OBSERVED WITH A HIGH-SPEED VTR SYSTEM

The grazing patterns of heterotrophic nanoflagellates (Cafeteria roenb ergensis and Actinomonas mirabilis) were recorded by high speed video micrography. Experiments were carried out at 10, 15 and 25 degrees C a t a salinity of 36 psu and at 20 degrees C when the salinity was eithe r 20 or 36 psu. Bacteria entrained in a stream of water generated by f lagellar beating were propelled toward the cell body (phase 1). Each b acterium destined for ingestion made contact with the anterior end of the flagellum of Cafeteria or was captured with an actinopod of Actino monas (phase 2). The captured bacterium was drawn close to the cell bo dy (phase 3) and ingested (phase 4). Cafeteria was observed during 38 razing events and appeared to have two different patterns of ingestion , ''enclosing'' and ''pocket phagocytosis.'' The mean time for food ca pture was 0.10 a and the subsequent ingestion was complete on average in 1.59 s. No further bacteria were captured until ingestion was compl ete. Actinomonas was observed during 27 grazing events in which captur e of particles on an actinopod was followed by transport to the cell b ody acid subsequent ''enclosing phagocytosis.'' The mean time to compl ete grazing was 39.16 a, which is about 25 times longer than for Cafet eria; the phase of transport to the cell body occupied most of this ti me. During the grazing cycle, Actinomonas captured other bacteria on t he actinopodia, bur sometimes released them. Grazing time in Cafeteria was positively correlated with temperature but not correlated with sa linity. Grazing behavior in Actinomonas was correlated with neither te mperature nor salinity.