The effect of electrostatic charge of food particles on capture efficiencyby Oxyrrhis marina dujardin (dinoflagellate)

Laboratory experiments were carried out to investigate the effect of food q uality, measured as surface charge of the particles, on capture efficiency and ingestion rate by the heterotrophic dinoflagellate Oxyrrhis marina. Flu orescent particles in two size classes of around 1 and 4 mu m and of 7 diff erent qualities were offered to the flagellate: carbohydrate and albumin pa rticles, the algae Synechocystis spec. and Chlorella spec., carboxylated mi crospheres, silicate particles and bacteria. Rates of particle uptake showe d significant differences depending on particle size and quality, and range d from 0 to 4 particles cell(-1) h(-1). Ingestion rates were up to 4 times higher for 4 pm particles than for 1 mu m particles, which indicates strong size-selective feeding. Our main result is that the surface charge or zeta potential, of artificial particles, i.e. carboxylated microspheres (greate r than or equal to -107 my) and silicate particles, strongly differ from mo re natural and natural food (less than or equal to -17 mV). For both size c lasses Oxyrrhis had ingestion rates up to 4 times higher for particles with less negative charge, such as albumin particles or algae. Thus, the zeta p otential of the model food should be considered in experimental design. Par ticles with a zeta potential similar to that of natural food, e.g. albumin, seem to be the preferred model food.