Article révisé par les pairs
Résumé : In July 2005, the article ‘Abundance and biomass of heterotrophic micro-organisms in Lake Tanganyika was published in Freshwater Biology (Pirlot et al., 2005). Epifluorescence microscopy coupled with image analysis was used to estimate bacterial and protozoan biovolumes and then to calculate biomass adopting C:cell volume conversion factors found in the literature (Børsheim & Bratbak, 1987; Putt & Stoecker, 1989; Simon & Azam, 1989). Unfortunately, we discovered after publication that an error had been made programming the macro used to estimate the biovolume of heterotrophic micro-organisms by image analysis. This error produced globally small underestimations of bacterial biomass but more importantly, a systematic overestimation of protozoan biomasses. Recalculated values show that bacterial biomasses varied, in the mixed layer of Lake Tanganyika in 2002, between 17.6 and 48.7 mg C m)3, with an average of 26.8 mg C m)3. Fig. 1 presents the corrected biomass integrated on the 100 m water column. Averaged bacterial carbon content was 12.2 fg per cell in 2002. Flagellates biomass ranged between 5.1 and 10.8 mg C m)3, and ciliates biomass ranged between 0.7 and 3.0 mg C m)3. Averaged protozoan biomass was 9.0 mg C m)3 with 1.0 mg C m)3 attributed to the symbiotic green algae in Strombidium. The corrections presented above do not modify substantially our previous figures on bacterial biomass in Lake Tanganyika (Fig. 1) but, as flagellate and ciliate biomass was overestimated, bacteria were actually the most important heterotrophic compartment. Even if protozoan biomass is much lower than previously presented in Pirlot et al. (2005), these results confirm that heterotrophic micro-organisms are an important part of total planktonic biomass.