|Communautés métazooplanctoniques de la zone épipélagique de deux environnements contrastés, le plateau des Kerguelen et la mer Méditerranée : caractérisation, distribution spatiale et rôle dans l’écosystème. |
Auteur(s): Nowaczyk A.
(Thèses) , 2011
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Mesozooplankton from the epipelagic layer (0-200 m) was studied in two contrasted ecosystems: the first one is located in the Austral Ocean, around the Southern part of the Kerguelen shelf and over the HNLC (High Nutrient Low Chlorophyll) area, at the end of summer bloom period supported by natural iron enrichment (KEOPS, January-February 2005). The second study focused on the whole Mediterranean Sea, along a 3 000 km transect characterized by an oligotrophy gradient decrease from West to East (BOUM, June-July 2008) with low phosphorus concentration. Mesozooplanktonic community was characterized by both its stock composition (abundance and biomass) and its structure (taxonomic composition and size spectrum). Spatial distribution at the regional scale was studied and linked to different environmental and trophic parameters. The community impact on primary production was also estimated from different physiological process analyses (ingestion, respiration and excretion). Mesozooplanktonic community showed higher abundance and biomass over the Kerguelen shelf than in HNLC area. The community was essentially composed by copepodite stages, large quantity of exuviae and high respiration rates suggesting active growth. However, phytoplankton based ingestion rates were low implying the use of other food source such as microzooplankton. In the Mediterranean, abundance showed an increasing westward gradient with a southward decreasing gradient in the Occidental Basin. This distribution was strongly linked to the chlorophyll concentration. Mesozooplankton grazing on primary producers was important. Biogeochemical flux associated with the metabolic activities supported in excess of 100 % of the primary production needs in term of carbon, nitrogen and phosphorus. Relationships between the specific diversity and the environmental variables (physical, chemical and biological) showed a high regionalization in the Mediterranean Sea whereas in the Kerguelen shelf these relations are weak.