BACTERIVORY BY HETEROTROPHIC NANOFLAGELLATES AND BACTERIAL PRODUCTIONIN SEDIMENTS OF A FRESH-WATER LITTORAL SYSTEM

We made simultaneous measurements of benthic bacterial production, usi ng [H-3]thymidine assays, and bacterivory by benthic heterotrophic nan oflagellates (HNAN), using fluorescently labeled bacteria. Sediment sa mples were collected at two stations in a eutrophic freshwater littora l in different seasons. Bacterial production ranged from 19.7 to 263.0 x 10(9) bacteria dm(-3) h(-1), with the highest values measured in su mmer. HNAN grazing rates (3.8-64.2 bacteria flagellate(-1) h(-1)) vari ed significantly with season and station, and rates were correlated wi th flagellate biovolume. At both stations, there were large discrepanc ies between bacterial production and HNAN grazing. The estimated bacte rivory ranged from 0.4 to 5.2% of bacterial production. The minor impa ct of HNAN as grazers on bacteria during summer months was caused by h igh bacterial production and low HNAN abundances. During winter, bacte rial production decreased, whereas HNAN abundance increased. However, due to the low grazing rate of these relatively small flagellates, the total HNAN community still consumed only an insignificant amount of t he bacterial production. The results of our measurements show that bac terivory by HNAN cannot account for the fate of bacterial production i n the littoral studied.