Microzooplankton Stoichiometric Plasticity Inferred from Modeling Mesocosm Experiments in the Peruvian Upwelling Region

Alexandra Marki,Markus Pahlow

doi:10.3389/fmars.2016.00258

Alexandra Marki, Markus Pahlow

Open Access

https://doi.org/10.3389/fmars.2016.00258

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Abstract

Abstract Oxygen minimum zones (OMZs) are often characterised by nitrogen-to-phosphorus (N:P) ratios far lower than the canonical Redfield ratio. Whereas the importance of variable stoichiometry in phytoplankton has long been recognised, variations in zooplankton stoichiometry have received much less attention. Here we combine observations from two shipboard mesocosm nutrient enrichment experiments with an optimality-based plankton ecosystem model, designed to elucidate the roles of different trophic levels and elemental stoichiometry. Pre-calibrated microzooplankton parameter sets represent foraging strategies of dinoflagellates and ciliates in our model. Our results suggest that remineralisation is largely driven by omnivorous ciliates and dinoflagellates, and highlight the importance of intraguild predation. We hypothesize that microzooplankton respond to changes in food quality in terms of nitrogen-to-carbon (N:C) ratios, rather than nitrogen-to-phosphorus (N:P) ratios, by allowing variations in their phosphorus-to-carbon (P:C) ratio. Our results point towards an important biogeochemical role of flexible microzooplankton stoichiometry.

Highlights

Cell quotas (N:C and P:C ratios) in phytoplankton are flexible and vary in response to the availability and stoichiometry of ambient inorganic nutrients (Quigg et al, 2003; Klausmeier et al, 2008; Finkel et al, 2010)
We develop an optimality-based nutrient-phytoplanktonzooplankton (NPZ) ecosystem model and analyse time-series observations of two shipboard mesocosm experiments in the Peruvian Upwelling (PU) region (PU1 and PU2; Franz et al, 2012b, 2013a,b; Hauss et al, 2012)
We investigate the effects of top-down control with the (OCF) for zooplankton (Pahlow and Prowe, 2010) where we progressively increase the number of trophic levels by representing nutrients, (NN), phytoplankton (P) and up to two microzooplankton types, Z1 and Z2 (Figure 2, Figure S1)

Summary

Introduction

Cell quotas (N:C and P:C ratios) in phytoplankton are flexible and vary in response to the availability and stoichiometry of ambient inorganic nutrients (Quigg et al, 2003; Klausmeier et al, 2008; Finkel et al, 2010). The OCM simulates dynamic phytoplankton stoichiometry and the OCF represents different feeding strategies in higher trophic levels (zooplankton).

Results

Conclusion