Post-doctoral opportunity in FRANCE (BORDEAUX)


The Cemagref, Agricultural and Environmental Engineering Research, invites 
applications for the following Post-Doctoral position: “Taking seasonal and 
interannual dynamics into account in the trophic modelling of the Gironde 
estuary ecosystem.”

Topic: this project aims at modelling and analyzing trophic network of 
estuarine ecosystem.

Context: In order to fully understand the structure of an ecosystem and to 
analyse its functioning , models have been developed which enable us to 
gather together all available knowledge and give a better understanding of 
the role of exchanges between compartments and changes that occur under the 
effect of natural or anthropogenic constraints. Using ecotrophic models in 
particular to describe interspecies relations within biological edifices 
(Shin 2000, Gascuel 2001, 2005), energy transfers can be identified from 
the first levels in the food web to the higher levels.
For this purpose, a first model of the trophic network of the Gironde 
estuary (France) was produced using the Ecopath programme (Lobry 2004). 
There were several reasons for selecting ECOPATH (Polovina 1984, 
Christensen & Pauly 1992), among which, the fact that this well-documented 
model has already been applied to the Bay of Biscay (Ainsworth et al. 
2001), to a section of the Garonne at Toulouse (Palomares et al. 1993), and 
more recently to the Seine estuary (Rybarczyk & Elkaim 2003) and the Bay of 
the Somme (Rybarczyk et al. 2003), all these studies providing points of 
comparison with the Gironde estuary.

Current knowledge and description of the project: Despite the 
methodological limitations associated with applying our hypotheses to an 
environment where there is so much fluctuation at the interface between the 
upstream river and the downstream marine environment, a stable state model 
was established on an annual basis, and only in a small area of the Gironde 
estuary. The justification for this initial choice is based on the relative 
stability of the trophic structure from year to year, with relatively well-
balanced results when looking at an annual cycle.
Parameterization of the model is based on available data from bibliography, 
combined with the knowledge and experience of research teams specialized in 
the different levels of the food web and evaluation of human withdrawal. 
Results from this first application of the Ecopath model to the downstream 
area of the Gironde highlight a certain number of features that dominate 
this system, among which, a good overall productivity, especially of the 
fish component, and despite a very low primary productivity because of the 
very high level of turbidity; a large proportion of flux derives from the 
degradation of the detritic matter coming from upstream, while a 
significant proportion of which is exported downstream in the form of 
detritus or through the food web, towards the ocean.
Combined with the survey of the dynamics of fish assemblages (Lobry et al. 
2003), these results suggest that the trophic dynamic in the estuary is 
still strongly dominated by seasonal variations in the hydrodynamics and 
river-born material.
These elements therefore justify the development of an annual model, based 
on the existing stable state and producing it on a seasonal level.
Moreover, work have been finalised on a doctoral thesis (Pasquaud et al. in 
press, Pasquaud 2006) which sheds essential light on the reality of trophic 
relations within fish populations, whereas the first model was necessarily 
limited to general data from bibliography related to the species. Thus it 
is now possible to bring information relating to prey-predator interactions 
in the fish compartment right up to date. In the same way, these new data 
will also be complemented by information from a thesis on zooplankton 
populations (David 2006), dealing with prey-predator relations among these 
organisms.
Objectives of the study: The work to be carried out during the post-
doctoral placement will be to develop and perfect the existing model by 
integrating newly available data concerning exchanges between compartments. 
With these developments we will be able to use the Ecopath model to work on 
equilibrium, and the Ecosim module to study transitions between the 
different seasonal stable states; other models should also be explored to 
take into account the seasonal dynamic of the biological edifice and the 
fluxes between the upstream and downstream environments, and to resolve any 
problems of exchanges and variability that may be encountered. It is 
expected that the various aspects of this study will give rise to 
suggestions for perfecting ecosystem indicators of the ecological quality 
of the environment and for managing it in a sustainable way.
The key question of this research project, via the example of the Gironde 
estuary ecosystem, concerns the flexibility and resilience of estuary 
ecosystems in response to the combined effects of natural and anthropogenic 
constraints over several time scales: seasonal variability of the 
hydrodynamic environment.

Qualifications: Candidates should ideally already possess a strong 
backgrounds in fisheries and marine ecosystems modelling. Communication 
skills and team spirit, ability to work independently, high motivation, are 
also required. 

Position: The position is open until filled. It is limited to 18 months, 
and will be paid according to the Cemagref clauses (e.g. monthly gross 
salary: 2150 €).
The appointee will join the Estuarine ecosystems and diadromous fish 
research unit, based in Bordeaux, which comprise 6 PhD students, 2 Post-
doctoral fellows, and 15 research engineers and scientists staff, working 
on a broad range of topics from conservation biology and fisheries science 
to community ecology and estuarine ecosystem management. For more details 
visit: http://www.bordeaux.cemagref.fr/rabx/index.html 
<http://www.bordeaux.cemagref.fr/rabx/index.html> 



Application procedure: Please send your application, preferably by email, 
with the usual material (expression of interest, CV, copies of certificates 
if available, representative reprints of published work) including a short 
statement of personal research aims and interests, and a summary of the PhD 
thesis, ideally not later than March 5th 2007 to: Paul Gonthier 
([log in to unmask] <mailto:[log in to unmask]> ), Philippe 
Boët ([log in to unmask] <mailto:[log in to unmask]> ), Mario 
Lepage ([log in to unmask] <mailto:[log in to unmask]> ). Feel 
free to contact us for any further information about the project and 
related issues.