Mlle Lagaria Anna, doctorante au LOG à Wimereux, dans la discipline Géosciences, Ecologie, Paléontologie, Océanographie, soutiendra publiquement sa thèse intitulée :
" Variabilité de la production primaire, particulaire et dissoute en Méditerranée : implications écologiques et interactions avec les osmotrophes "
Discipline : GEPO (Géosciences, Ecologie, Paléontologie, Océanographie),
Spécialité : Océanographie biologique.
Date : 8 juillet 2011 à 9h00
Lieu : Salle de conférence de la MREN à Wimereux.
Directeur de thèse :
Urania CHRISTAKI, Prof ULCO
Stella PSARRA, CR1, HCMR , Grèce
France Van Wambeke : Dr CNRS, Université de la Mediterranée, Marseille
Frede Thingstad : Prof. Univ. Bergen, Norvège
Vangelis Papathanassiou – Dr. HCMR, Grèce
Sebastien Lefevre – Pr. Lille 1 - USTL
This work aimed at extending existing knowledge on primary production variability in the Mediterranean Sea by including concurrent investigation of phytoplankton exudation (dissolved primary production). The putative environmental factors that designate variability of percentage extracellular release (PER) were examined,
focusing on the underlying trophic conditions, and the importance of phytoplankton exudation in covering carbon requirements of heterotrophic prokaryotes was evaluated. The thesis was developed in two parts, involving field and experimental work. Field studies were performed along two longitudinal trophic gradients
in the Mediterranean. One covered the west-east Mediterranean oligotrophy gradient (BOUM cruise) and the other a pronounced trophic gradient formed along the Turkish Straits System and their opening into the Aegean Sea (SESAME cruises). Spatial variations of primary production and PER were linked to and elucidated by the
varying environmental features. The large range of trophic conditions encountered along these gradients and the different areas studied, permitted to discriminate potential dominant processes responsible for phytoplankton exudation. The experimental work involved studies with microcosms and mesocosms where the effect of inorganic nutrient additions on PER was assessed in pelagic and coastal oligotrophic surface waters of the Mediterranean, testing the hypothesis that phytoplankton exudation is mainly regulated by nutrient limitation. The experiments were performed within the framework of BOUM and NUTRITUNNEL projects, identifying
the primary nutrient limiting phytoplankton and heterotrophic prokaryotes’ growth. The bioassays permitted to delineate the N and P co-limited character of phytoplankton, during and at the end of the warm stratified period and its effect on particulate and dissolved primary production variations. The role of phytoplankton exudation as a link between phytoplankton and heterotrophic prokaryotes was evaluated in each case, through estimated carbon budgets and correlations of production rates. Finally, the role of irradiance in affecting the partitioning between particulate and dissolved primary production was experimentally tested in oligotrophic surface waters.