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Soutenance de thèse en Biologie Marine par Daniel GRADOS

Cette soutenance de thèse aura lieu le mardi 16 décembre 2014 à 15h à l'IUEM, amphi A.

Sujet : "Caractérisation multi-échelle des dynamiques des composantes de l'éco-système dans le système Nord du courant de Humboldt."


Identifying relevant spatial and temporal scales is a necessary step to understand ecological structuring and processes. Marine ecosystems are heterogeneous at a variety of spatiotemporal scales. In these systems, there is evidence of a bottom-up transfer of spatial structuring and behaviours. Whereas the physical forcing itself involves multiscale spatiotemporal patterns, it initiates the space-time structuring of the water masses and the distribution of planktonic organisms. Since predators are required to locate their prey, their behaviour tends to reflect the patchy distribution of their prey. Due to the lack of observation data, the extent to which this bottom-up transfer operates for the finest scales (< 1 km) is a scientific challenge.


Throughout this work, we address the characterization of the multiscale space-time structuring of abiotic and biotic ocean processes from the fine-scale (~100 m) to the mesoscale (~100 km) scales. Considering the Northern Humboldt Current system (NHCS) as case study, we rely on the analysis of high-resolution acoustic survey data. More specifically, three acoustics-derived proxies were considered: the oxycline depth, macrozoopankton biovolume and fish biomass. We first provide general information on the NHCS for the interpretation of our results (Chapter 2). From a methodological point of view, we explore different statistical methodologies to reveal multiscale patterns and significant associations (Chapter 3). In this context, we demonstrate the relevance of wavelet methods and propose a novel wavelet-based approach, which resorts to an event-based characterization of the significant scale-space patterns exhibited by the observed processes (Chapter 4). The application of this methodology to the NCHS acoustics-derived data provides new insights on the importance of the fine-scale processes in the observed bottom-up transfer. Our results strongly support the co-existence of two different processes: a submesoscale-to-mesoscale direct cascade and a fine-scale-specific process (i.e. horizontal scales from ~100 m up to ~1 km) (Chapters 4 and 5). The latter is interpreted as being associated with internal wave processes, which result from the interactions between bathymetry, current flows and stratification conditions. We show these fine-scale processes along with organisms’ behavior play a critical role in shaping the seascape of the ecological components (Chapters 4 and 6). Given the expect impact of the global change on the fine-scale range, this work strongly advocates for future work to further investigate the of the fine-scale physical processes onto trophic interactions and the dynamics of marine populations.

Photo du mois


(C) Pascale Lherminier / Ifremer