Dissolved organic carbon released by zooplankton grazing activity-a high-quality substrate pool for bacteria

Abstract

Experiments were designed to investigate whether processes related to zooplankton feeding have a positive effect on bacterial growth. Bacterial abundance and [3H]thymidine incorporation rates were followed in grazer-free batch cultures originally containing either Scenedesmus quadricauda or Rhodomonas lacustris as food sources, and Daphnia cucullata or Eudiaptomus graciloides as grazers. Compared with controls lacking either animals or algae, a significantly higher bacterial abundance and productivity occurred in cultures which contained both phyto- and zoo-plankton. The same experimental methodology was tested during the decline of a diatom spring bloom in a eutrophic, temperate lake. A significant increase in bacterial biomass was observed due to the grazing activity of in situ mesozooplankters during the clear-water phase. Our results demonstrated that the dissolved carbon pathway from mesozooplankton to bacteria averaged 57% (26–78%) of the algal carbon filtered from suspension.