The effects of zooplankton grazing and phosphorus recycling on stoichiometry of mixotrophic nanoflagellates: an experimental and modeling approach

SCHENONE, L.; MODENUTTI, B.; MARTYNIUK, N.; BASTIDAS NAVARRO, M.; LASPOUMADERES, C.; BALSEIRO, E.

Congreso; ASLO Aquatic Science Meeting; 2021

SOCIETY FOR FRESHWATER SCIENCE y ASSOCIATION FOR THE SCIENCES OF LIMNOLOGY AND OCEANOGRAPHY

Pelagic microbial food webs are structured by zooplankton through grazing and nutrient recycling. Cladocerans and copepods are assumed to display different effects on the microbial loop by grazing on different prey sizes and releasing phosphorus (P) differentially. Here, we assessed these differential effects on the dynamics of microbial loop using both experimental and modelling approaches combined. We performed field incubation experiments in an oligotrophic mountain lake (North-Patagonian Andes) using the natural microbial community and the two dominant zooplankton taxa: a cladoceran (Diaphanosoma chilense) and a copepod (Boeckella gibbosa). We built a mechanistic model to estimate zooplankton grazing and P recycling and prey P quotas parameterized with our field experiment results. We found that D. chilense grazed mainly on picoplankton while B. gibbosa on mixotrophic nanoflagelates and algae. D. chilense reduced the biomass and increased P quota of picoplankton, and reduced the P quota of nanoflagellates. On the contrary, B. gibbosa released more P, increasing the picoplankton biomass and reducing the biomass of nanoflagellates, but increasing its P quota. Based on our experimental and model results, copepods would favour higher P acquisition rates for cladocerans by releasing more P for picoplankton. On the other hand, cladocerans would have a mixed effect on the main food items of copepods by increasing P quotas of the strict osmotrophic algae but decreasing P quotas of mixotrophic nanoflagellates.