Ref ID : 2163
Jaap Bloem and Marie-Jose B. Bar-Gilissen; Bacterial activity and protozoan grazing potential in a stratified lake. Limnol.Oceanogr. 34(2):297-309, 1989
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During summer stratification in Lake Vechten, heterotrophic nanoflagellates (HNAN) showed peak densities at very low oxygen concentrations in the lower metalimnion at a depth of 6-7 m. In this stratum, high HNAN numbers (>30x10E6 HNAN liter-1) coincided with high bacterial activity. Assuming a conversion factor of 2x10E18 bacteria mol-1 thymidine, we estimated a maximal bacterial production of about 4x10E9 bacteria liter-1 day-1 from thymidine incorporation. In the upper metalimnion (5-6 m depth) we found a low bacterial activity (estimated production 1x10E8 bacteria liter-1 day-1) and low HNAN numbers (3x10E6 HNAN liter-1). HNAN seem to be a link in the food web between bacteria and cyanobacteria on the one hand and ciliates on the other. Grazing experiments with selectively filtered lake water indicated ingestion rates of about 7 bacteria HNAN-1 hr-1. We calculated that the metalimnetic HNAN are able to consume the entire bacterial production even at high bacterial growth rates.