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Soutenance de thèse Sophie Chambord

jeudi 16 juin 2016

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Sophie Chambord (Doctorante du LOG) soutiendra sa thèse intitulé :

Rôle du mésozooplancton dans un estuaire restauré : l’Escaut

Date : 16 juin 2016 à 9h

Lieu : Amphithéatre Shannon, bat U4 TOULOUSE

Directeur/trice(s) de Thèse :

- Michèle TACKX, Professeur à l’université de Toulouse 3
- Patrick MEIRE, Professeur à l’université d’Anvers
- Sami SOUISSI, professeur à l’université de Lille 1

Jury :

- Gesche WINKLER, Professeur à l’université de Québec - Rapporteur
- Wim VYVERMAN,Professeur à l’université de Gant - Rapporteur
- Pascal CLAQUIN, Professeur à l’université de Caen - Examinateur
- Stefan VAN DAMME, Professeur à l’université d’Anvers - Examinateur
- Eric CHAUVET, Directeur de recherche au CNRS - Examinateur

Résumé :

The Scheldt is an estuary on way of recovery. The study concerns the ecology of
the zooplankton community in the freshwater reach of the estuary. In parallel to water quality improvement, the copepod Eurytemora affinis has become dominant since 2007 and abundance of cyclopoid copepods has decreased. We tried to find out which environmental factors had caused these changes in the zooplankton community composition. The results of RDA and GLM analysis between the abundance of zooplankton taxa and the environmental factors showed a strong link between E. affinis abundance and the increasing O2 concentration, but also the decreasing NH4-N concentration. The upstream Scheldt became permissive for E. affinis development as soon as oxygen concentration was above the threshold level of 4 mg L-1 and the NH4-N concentration remained below 2 mg L-1. The cause of the decrease in cyclopoid abundance remains unclear. The phytoplankton community of freshwater Scheldt is strongly dominated by diatoms, but the dissolved silica concentration could become limiting for their development. The question arises on which phytoplankton taxa the dominant zooplankton feeds. Grazing selectivity of E. affinis adults and CV was measured by incubation experiments using natural Scheldt water and by gut pigment content quantification. Phytoplankton taxa concentration was quantified by HPLC. E. affinis selects diatoms and sometimes cryptophytes. The impact of the E. affinis population on the phytoplankton standing stock is < 4.5% d-1, which means that the zooplankton community is not food limited and hence does
not present a limitation to the development of higher trophic levels. The grazing activity of the microzooplankton community has also been measured by incubation experiments. Its impact on the freshwater Scheldt phytoplankton community is variable in intensity and in selectivity, and clearly needs further investigation.