CHANNELING OF BACTERIOPLANKTONIC PRODUCTION TOWARD PHAGOTROPHIC FLAGELLATES AND CILIATES UNDER DIFFERENT SEASONAL CONDITIONS IN A RIVER

The objective of this study was to analyze the flux of biomass through the communities of bacteria and phagotrophic protists in the cold and warm conditions occurring seasonally in Butron River. Bacterial and h eterotrophic protistan (flagellate and ciliate) abundance was determin ed by epifluorescence direct counts; protistan grazing on planktonic b acteria was measured from fluorescently labeled bacteria uptake rates; and the estimate of bacterial secondary production was obtained from [H-3]thymidine incorporation rates. The abundance of bacterial, flagel late, and ciliate communities was similar during cold and warm situati ons. However, we observed that estimates of dynamic parameters, i.e., secondary bacterial production and protistan grazing, in both situatio ns were noticeably different. In the warm situation, grazing rates of flagellates and ciliates (bacteria per protist per hour) were, respect ively, 7 times and 18 times higher than those determined in the cold s ituation, and the grazing rates of the protistan communities (bacteria per protists present in 1 ml of water per hour) increased up to 5 tim es in the case of flagellates and 42 times in the case of ciliates. Es timates of bacterial secondary production were also higher during the warm situation, showing a ninefold increase. The percentage of bacteri al production preyed upon by flagellates or ciliates was not significa ntly different between the two conditions. These results showed that i n the different conditions of a system, the flux of biomass between th e trophic levels may be quite different although this process may not be reflected in the abundance of each community of bacteria, flagellat es, and ciliates.