engleski

Distribution patterns of key components of microbial food web in meromictic saline lake

Interactions among heterotrophic bacteria, heterotrophic (HNF) and autotrophic (ANF) flagellates and nonloricate ciliates were studied in water column samples collected from small meromictic saline lake (Rogoznica Lake, Croatia). Special emphasis was paid on relationships between investigated parameters and water column oxygen saturation. Bacterial abundances did not exhibit considerable changes in respect to water column hypoxia retaining at the similar values during both periods. However bacterial biomass and cell specific volume were much higher in hypoxic environment compared to oxic conditions. Low-DNA bacteria dominated the bacterial community in hypoxic environment accounting from 76 to 80% of total number of bacteria. The abundances of HNF and ANF decreased 5-7 times in the presence of low O2 concentrations implying their strong relation to oxygen saturation. No relationship between bacteria and their predators could be observed during hypoxia. However in oxic environment HNF exerted strong influence on bacterial population (R=0.45 n=14, p0.05). Also the activity of bacterial populations shifted toward the domination of high-DNA cells in oxic environment. Ciliate assemblages were dominated by oligotrichs. The abundance and biomass of nonloricate ciliates maintained at low values through the whole period of hypoxia. One month after establishing oxic conditions the ciliate populations showed the first sign of regeneration by increasing the number of small size organisms (20-40mm). In that period a strong impact on HNF population could be observed. As the result of this cascade effect, the top down control of HNF on bacteria diminished.

heterotrophic bacteria; heterotrophic flagellates; autotrophic flagellates; nonloricate ciliates; Rogoznica Lake

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