title: Protist herbivory: a key pathway in the pelagic food web of Lake Tanganyika.
abstract: Herbivory and bacterivory by phagotrophic protists were estimated in the southern basin of the oligotrophic Lake Tanganyika at different seasons (in the rainy season in February-March 2007 and in the dry season in July-August 2006 and September 2007), using two independent methods: the selective inhibitor technique for assessing community grazing on picocyanobacteria (PCya) and fluorescently labelled bacteria (FLB) and Synechococcus (FLA) to estimate bacterivory and herbivory by phagotrophic nanoflagellates (NF) and ciliates. Protistan grazing impact on both heterotrophic bacteria and PCya was mainly due to NF, which contributed up to 96% of the microbial grazing. There was a clear selection of FLA by protists. PCya represented the main carbon source for both flagellates and ciliates in the mixolimnion, accounting for an average of 83% of the total carbon obtained from the ingestion of picoplanktonic organisms. Protists were the main consumers of particulate primary production (46-74% depending on season). Significant seasonal variation of grazing rates (0.011-0.041 h(-1)) was found, chiefly following variation of PCya production and biomass. Assuming a growth efficiency of 0.4, total protozoan production varied seasonally (189-313 g C m(-2) day(-1)) and was roughly half of particulate phytoplankton production. This study provides evidence that NF and PCya were tightly coupled in Lake Tanganyika and that herbivory by protists may be one of the reasons why this great lake has high productivity. Our results bring support to the idea that microbial herbivory is a major process in oligotrophic freshwater systems.
authors.affiliation: Laboratory of Freshwater Ecology, Department of Biology, University of Namur, rue de Bruxelles 61, 5000, Namur, Belgium.
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Tarbe
authors.forename: Fernando
authors.initials: F
authors.lastname: Unrein
authors.forename: Stephane
authors.initials: S
authors.lastname: Stenuite
authors.forename: Samuel
authors.initials: S
authors.lastname: Pirlot
authors.forename: Hugo
authors.initials: H
authors.lastname: Sarmento
authors.forename: Danny
authors.initials: D
authors.lastname: Sinyinza
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Descy
mesh_terms: D000349:Africa; D058491:Bacterial Load; D002244:Carbon / Q000378:metabolism; D000458:Cyanobacteria / Q000254:growth & development; D056890:Eukaryota / Q000254:growth & development / Q000502:physiology*; D020387:Food Chain; D060434:Herbivory / Q000502:physiology*; D060106:Lakes; D008856:Microscopy, Fluorescence; D010839:Phytoplankton / Q000254:growth & development; D012621:Seasons; D046940:Synechococcus / Q000254:growth & development; D014871:Water Microbiology
chemical_list: D002244:Carbon