Journal of Plankton Research Vol.21 no.12 pp.2341-2360, 1999
© Oxford University Press 1999
Contribution of Picocyanobacteria to total primary production and community respiratory losses in a backwater system
Institut für Medizinische Biologie, Arbeitsgruppe Mikrobiologie, Universität Wien, Währingerstraße 10, A-1090 Vienna, Austria
1 To whom correspondence should be addressed
The contribution of autotrophic picoplankton (APP) to phytoplanktonic primary production, investigated during the phytoplankton growing season (March–September) in a macrophyte-dominated backwater system near Vienna, showed that APP mainly consisted of rod-shaped and coccoid cyanobacteria. Two stations were examined, exhibiting similar seasonal patterns in the development of picocyanobacteria, although the two sites differed in picocyanobacterial cell numbers and biomass by a factor of 1.5. Cell numbers determined by epifluorescence microscopy varied between 0.29 x 104 and 34.5 x 104 cells ml–1 at Station 1, and between 0.23 x 104 and 19.1 x 104 cells ml–1 at Station 2. At both sites, the mean cell volume of picocyanobacteria was 0.5 µm3. Carbon fixation in the planktonic community of the Kühwörter Wasser was dominated primarily by larger phytoplankton, although the picoplankton community sometimes supplied up to 74% (mean: 35%) of total primary production. Distinct differences in chlorophyll a concentrations and primary production between the two sites refer to a greater competition between phytoplankton and macrophytes at Station 2. Community respiration deviated greatly in time and in level at the two stations, showing a higher dynamic in community metabolism at Station 1. At this site, community respiration losses ranged between 12 and 100% of gross production. Hence, community metabolism comprised net autotrophic, balanced, and net heterotrophic situations over the investigation period, whereas at Station 2, only net autotrophic situations could be determined.