!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> João Rodrigues

Y. (Yoan) Eynaud

Address: Oceanology Centre of Marseille (COM) Laboratory of Microbiology Geochemistry and Marine Ecology (LMGEM) Campus de Luminy Case 901 13288 MARSEILLE Cedex 09
Phone: 0033-0491829126
Email: eynaud@univmed.fr
Specialization: Theoretical ecology
Project: Physiological microbial activity models

Modelling the marine microbial network: the impact of physiological details

In the last ten years, some biogeochemical models have explicitly included the microbial compartment, which contributes to the remineralization of the organic matter among the water column in the marine environment (e.g. Anderson and Williams, 1999). Initially, the description of the processes describing the remineralization was really poor. Recent work has proposed numerical studies on the impact of more precise description of processes on the global behavior of marine ecosystems (Fultons et al.,2004, Baklouti et al.,2006). This works has ended up to contradictory results and it now appears essential to focus deeper on that matter.

Also, the integration of more and more precise mechanistic details inevitably leads to complex models production. Mathematical analysis of such models is impossible and even numerical study and information extraction given by simulations are hard. Recent works propose some approaches in order to analyse such outputs (Raick et al., 2006a, Clarck et Gelfand, 2006) or simplify it (Cox et al., 2006, Raick et al., 2006b, Auger et al., 2008).

Meanwhile, the fundamental influence of precise choices of mathematical formulations for processes on the dynamic of models has been shown in simple cases (Blasius and Fussman, 2005). This work demonstrates that different formulations describing the same process surprisingly leads to quantitatively and qualitatively different results. It shows that in certain case, taking account of mechanisms is essential in the choice of the right formulation.

LMGEM is specialized in the study of biotic and abiotic biodegradation, thus as in modeling (Tolla et al., 2006, Eichinger et al., 2006), for instance by using the DEB theory. At the same time, we also develop methods for simplification of in order to add mechanistic formulation in ecosystem models (Eichinger et al., in prep). Our original simplifying approach (Auger et al., 2008) was founded on the hierarchical structure of ecosystem. It allows keeping relationships between the detailed and the simplified model, including the ways mechanisms interact. The LOPB is specialized in studying and modeling the marine biogeochemical processes and coupling with physics.

The goals of this thesis are:

Those objectives are included in the study of the effect of the global change on ecosystem functioning. They also permit to outline the effect of those changes on the organism response (physiology, function).

More in particular I will focus on the dynamics of the microbial loop in the water column, and the interaction with phyto- and zooplankton dynamics on the context of the ECO3M model. I will focus on the processes of co-limitation, co-metabolism, competition, exudation, grazing and mineralisation.

Bibliography :

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