Potential for protozoan grazing of bacteria in streambed sediments

350 210 Stroud Water Research Center

Bott, T.L., and L.A. Kaplan. 1990. Journal of the North American Benthological Society 9:336–345.

doi: 10.2307/1467901


Consumption of bacteria by ciliates and microflagellates in streambed sediments was estimated from changes in bacterial densities in feeding experiments. Sediments were sterilized and recolonized with bacteria and then inoculated with cultured ciliates or microflagellates to approximate natural densities. In experiments conducted at 20°C, bacterial densities declined rapidly during the first 4 hr and were relatively stable thereafter. Ingestion rates determined from changes occurring within the first 4 hr were regressed against bacterial densities. Predicted ingestion rates at the average streambed bacterial density when streamwater temperature was 20°C were 2113 and 12 bacteria per protozoan/hr for ciliates and microflagellates, respectively. Ingestion rates of 414 and 9 bacteria per protozoan/hr were predicted for ciliates and microflagellates, respectively, at the average streambed bacterial density when the stream was 10°C. Depending on whether the cell size of bacteria used in experiments or the cell size of streambed bacteria are used in calculations, protozoa could potentially ingest from 21 to 48 g bacterial C/m<sup>2</sup> annually, an estimate based on bacterial and protozoan densities in White Clay Creek at 20°C and 10°C, ingestion rates measured in the laboratory at those temperatures, and the proportion of the year the stream was at those temperatures. These values range from 80% to 183% of our present estimate of annual streambed bacterial productivity.