N-remineralization of phyto- and bacterioplankton by the marine ciliate Euplotes vannus

Ammonia excretion by the marine ciliate Euplotes vannus was investigated with the aid of feeding experiments involving algal food organisms (Dunaliella tertiolecta) and a bacterial diet (Vibrio sp.). The ciliates displayed a typical growth curve with a generation time of 6.2 to 6.9 h at 25 °C. With increasing consumption of the preferred food organisms by ciliates a steady increase in ammonia content of the culture medium was observed. During the logarithmic growth phase Euplotes vannus excreted 0.22 × 10⁻⁵ and 0.41 × 10⁻⁵ μmol N ciliate⁻¹ h⁻¹, utilizing algal and bacterial nourishment, respectively. The role of ciliates in the regeneration of inorganic nutrients in water is discussed.