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Proposition de Sujet de thèse 2012
Nom du laboratoire (et n° de l’unité) dans lequel se déroulera la thèse :
Division Océanographie Spatiale, CLS, Ramonville Saint Agne
Titre du sujet proposé : Operational modeling of oceanic pelagic lower and mid trophic
levels
Spécialités de l’école doctorale : (cocher une seule spécialité sans la modifier)
 Astrophysique, Sciences de l’Espace, Planétologie
X Climat, Océan, Atmosphère, Surfaces Continentales
 Ecologie Fonctionnelle
 Hydrologie, Hydrochimie, Sol, Environnement
 Sciences de la Terre et des Planètes solides
Nom et statut (PR, DR, MCf, CR, …) du (des) responsable(s) de thèse (préciser si HDR) :
Patrick Lehodey (Dr) et Philippe Gaspar (Dr, HDR)
Coordonnées (téléphone et e-mail) du (des) responsable(s) de thèse :
Patrick Lehodey (PLehodey@cls.fr), Tél. : 05 61 393 770
Philippe Gaspar (PGaspar@cls.fr)
Résumé du sujet de la thèse (le descriptif ne doit pas dépasser une page recto/verso)
Contexte scientifique général, Compétences souhaitables,…
The micronekton at the Mid-Trophic Level (MTL) of the pelagic food web is one of the less
known components of the ocean ecosystem, despite that they are a major driver of the spatial
dynamics of their predators, many of them being exploited species (e.g., tunas). One
modelling approach (SEAPODYM) has been developed to represent the spatial dynamics of
large oceanic predators (e.g., tunas) and their prey composed of a myriad of species
dominated by crustaceans, fish, and cephalopods. In addition to drive the spatial dynamics of
their predators, these organisms at the Mid-trophic Level (MTL) control the grazing of
zooplankton and the predation of all eggs and larvae released in the pelagic environment.
They also contribute to the release of Particular Organic Carbon (POC) that is either recycled
by the microbial loop or sink to the deep ocean. The knowledge on MTL species reflects their
economical interest, and thus very few is known about oceanic micronekton despite their
pivotal role in the functioning of the oceanic ecosystem.
The modelling approach developed to describe the basin-scale spatiotemporal dynamics of
MTL in SEAPODYM includes a representation of six functional groups of MTL. The
definition of these groups are based on the occurrence of diel migration between the surface
(epipelagic), subsurface (mesopelagic) and deep (bathypelagic) layers, or the lack of thereof.
Recruitment, ageing, mortality and passive transport with horizontal currents are modeled by
a system of ADR equations, taking into account the vertical behavior of organisms. The
temporal dynamics is based on a relationship linking temperature and time of development of
MTL organisms, suggesting a macroscale equilibrium in the energy transfer through the
biomass size spectrum. The same approach is followed to model an additional functional
ED 173 - SDU2E
group for mesozooplankton and further developments could consider also including a
representation of organisms strictly associated to the surface (neuston, including many jelly
fish species) or the bottom (benthos) of the ocean.
This representation requires a limited number of parameters and allowed preliminary
development of a parameter optimization approach through data assimilation techniques
based on acoustic data. The parameterization of the total energy transfer requires absolute
biomass estimates obtained using calibrated biomass estimates combining acoustic and
micronekton net sampling used to convert backscatter values in micronekton biomass, after
careful discrimination between various recorded patches of records. The matrix of energy
transfer coefficients for each functional group can be estimated simply using relative day and
night values of acoustic backscatter integrated in each of the three vertical layers of the
model. Such acoustic data are collected in various parts of the World Ocean and
collaborations developed with several national and international laboratories will be useful to
process a database for assimilation allowing both parameter optimization and validation of the
model.
Therefore, in this PhD study, we propose new developments and analyses to produce
consolidated and validated global simulations of the zooplankton and micronekton functional
groups, relying on rigorous mathematical techniques to develop an innovative approach for
assimilating acoustic data in an ocean ecosystem model. The final objective is to propose new
operational products based on multi-satellite data and modeling, that will open the way to
many new applications, including the operational management of marine resources and the
monitoring of protected species.
References:
Lehodey P., Murtugudde R., Senina I. (2010). Bridging the gap from ocean models to population
dynamics of large marine predators: a model of mid-trophic functional groups. Progress in
Oceanography, 84: 69–84
Handegard, N.O., Demer, D., Kloser, R.J., Lehodey, P., Maury, O., Simard, Y. (2010). "Toward a
Global Ocean Ecosystem Mid-trophic Automatic Acoustic Sampler (MAAS)" in Proceedings of
OceanObs’09: Sustained Ocean Observations and Information for Society (Vol. 2), Venice,
Italy, 21-25 September 2009, Hall, J., Harrison D.E. & Stammer, D., Eds., ESA Publication
WPP-306.
Lehodey, P., Senina, I., Calmettes, B., Royer, F., Gaspar, P., Abécassis, M., Polovina, J., Parker, D.,
Domokos, R., Hernandez, O., Dessert, M., Kloser, R., Young, J., Lutcavage, M., Handegard,
N.O., Hampton, J. (2010). Towards Operational Management of Pelagic Ecosystems. ICES CM
Documents 2010, 20-24 Sep., Nantes, France. 13 pp. ISBN 978-87-7482-085-7.
This thesis will be performed in an international collaboration framework including Rudy
Kloser (CSIRO, Australia); Reka Domokos (NMFS, USA) and C. Guinet (CNRS, France). It
will contribute to several major projects : FP7 EURO-BASIN, ANR Mycto3DMap and
GMMC Mercator Vert.
The candidate shall have a significant background in physical oceanography, marine biology
numerical modeling and scientific programming (preferably in C/C++).