Transfer of bacterial production based on labile carbon to higher trophic levels in an oligotrophic pelagic system
(English)Manuscript (preprint) (Other academic)
It is debatable whether bacterial production (BP) based on labile carbon (C) is an important energy subsidy for higher trophic levels in the pelagic zone of lakes. Increased BP may reduce phytoplankton and basal production through competition for phosphorus. However, enhanced BP can also be regarded as an additional basal food resource used directly by unselective filter feeding (cladocerans) or indirectly through grazing on the microbial food web (cladocerans and copepods). In a mesocosm experiment we traced the contribution of BP to crustacean zooplankton and planktivorous fish using stable isotopes and labile glucose-C as a biomarker. BP increased with glucose-C addition and all zooplankton and fish incorporated some glucose-C. Although cladocerans incorporated the most glucose-C, increased BP did not affect cladoceran biomass. Instead, calanoid copepod biomass increased with glucose addition. This suggests that the ability to select high quality food such as bacterial grazing protists capable of trophic upgrading (i.e. de novo synthesis of fatty acids), had a stronger positive effect on calanoids, than unselective grazing on bacteria and protists had on cladoceran biomass. Higher BP was associated with increased survival and population growth of young-of-the-year perch when stocked at high densities, which suggested that BP had a density dependant effect on fish growth. Although the total amount of energy mobilized did not affect fish growth, energy mobilized through the microbial food chain increased calanoid copepod biomass; the favored prey species of planktivorous fish in this system.
IdentifiersURN: urn:nbn:se:umu:diva-43465OAI: oai:DiVA.org:umu-43465DiVA: diva2:414054