Bacterioplankton production and protozoan bacterivory in a mesotrophic reservoir

Abstract

Protozoan bacterivory [via uptake of fluorescently labelled bacteria (FLB)] and production of bacteria ([H]thymidine assay) were simultaneously measured in the mesotrophic Rimov Reservoir (Southern Bohemia) from April to November, 1988. Heterotrophic nanoflagellates (HNF) were mostly responsible for a greater fraction of protozoan bacterivory during the spring period. From 10 to 23% of bacterial production was grazed daily with the only exception of the spring peak of ciliate abundance (up to 60%). Protozoans decreased significantly during the clearwater phase (ciliates disappeared), and thus their role in bacterivory was negligible. Through the summer-fall period ciliates, not HNF, were the most important bacterial micrograzers. Protozoan community grazing balanced or even exceeded the daily bacterial production in August and September. Alternate fates of bacterial production besides protozoan grazing during the spring period are discussed.