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

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Abstract
NH3 excretion by the marine ciliate E. 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 6.2-6.9 h at 25.degree. C. With increasing consumption of the preferred food organisms by ciliates a steady increase in NH3 content of the culture medium was observed. During the logarithmic growth phase E. vannus excreted 0.22 .times. 10-5 and 0.41 .times. 10-5 .mu.mol 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.