Cette thèse porte sur l’étude de la dynamique du zooplancton de deux écosystèmes Méditerranéens, la Baie de Marseille (France) et le Canal de Bizerte (Tunisie). Le mésozooplancton de la Baie de Marseille a été prélevé à la station SOMLIT de mars 2009 à juillet 2011 et étudié à l’aide de deux méthodes d’analyse (la loupe binoculaire et le ZooScan). Les résultats obtenus nous ont permis de caractériser à la fois le stock (abondance et biomasse) et la structure (composition taxonomique et spectre de taille) de la communauté zooplanctonique. Une succession saisonnière de la structure de la communauté zooplanctonique a été observée, et qui est principalement commandée par la température et les blooms phytoplanctoniques. Les organismes de petites tailles ont dominé en abondance et en biomasse la communauté zooplanctonique. Une étude in situ de la dynamique de population et de la reproduction des copépodes Centropages typicus et Temora stylifera a été réalisée à cette même station SOMLIT. Une saisonnalité des taux de ponte des deux copépodes a été enregistrée, avec des minima au printemps et des maxima de la fin d’automne au début d’hiver.L’activité de reproduction des copépodes Centropages ponticus et Temora stylifera prélevés in situ à la station Canal de Bizerte, a été étudiée en automne, en 2006 et en 2010. Les taux de ponte et de viabilité des œufs ont été assez stables pour C. ponticus, alors qu'ils variaient fortement pour T. stylifera. Les variations des paramètres de reproduction des deux copépodes ont été associées à des variations de paramètres environnementaux, en particulier la turbidité et la composition phytoplanctonique. / This thesis focuses on the study of zooplankton dynamics in two Mediterranean ecosystems, the Bay of Marseille (France) and the Channel of Bizerte (Tunisia). The mesozooplankton of Marseille’s Bay was collected from SOMLIT station, from March 2009 to July 2011, and studied using two analytical methods (microscope and ZooScan). The results led us to a precise characterization of both stock (abundance and biomass) and structure (taxonomic composition and size spectrum) of the zooplankton community. A seasonal succession of the zooplankton community structure was observed, mainly controlled by the temperature and phytoplankton blooms. Planktons of small sizes have dominated in abundance and biomass the zooplankton community. An in situ study of population dynamics and reproduction of copepods Centropages typicus and Temora stylifera was made at the same station SOMLIT. A seasonal egg production of both copepods was recorded, with minima in spring and maxima from the late autumn to early winter.An in situ reproduction activity of the copepods Centropages ponticus and Temora stylifera was investigated in autumn 2006 and 2010 in the Bizerte Channel. Egg production and hatching success remained fairly stable for C. ponticus throughout the study period compared with T. stylifera in which reproductive traits fluctuated considerably. Changes in reproductive traits for both species resulted from environmental parameter variations, in particular the turbidity and the phytoplankton composition.

In the northeastern Gulf of Mexico, relating changes in zooplankton communities to environmental factors is crucial to understanding the marine ecosystem and impacts of perturbations such as oil spills on marine ecosystems. Zooplankton samples were collected each year between 2005–2014 in spring and summer in the vicinity of the oil spill (Deepwater Horizon) that occurred in spring 2010. Zooplankton assemblages and environmental conditions significantly differed seasonally, driven by strong variations in zooplankton at continental shelf stations, and by environmental factors including Mississippi River discharge, wind direction, temperature, and chlorophyll concentrations. Total zooplankton abundances were greatest at shelf stations, intermediate at slope stations, and lowest at offshore stations. Seasonal separation was driven by greater abundances of crab zoea, cladocerans, ostracods, and the copepod, Eucalanus spp. during summer. Copepods, Centropages spp., were significant indicators of summer conditions both before and after the oil spill. Sub-regional comparisons in percent composition and abundances of six major non-copepod and seven copepod taxa revealed that most taxa either remained the same or significantly increased in abundance following the spill. A significant decrease in post oil spill taxa was observed only during spring for total copepods, Eucalanaus spp., and for salps at continental slope stations, however varying processing techniques used for zooplankton before and after the spill were employed and should be considered. . Based on our sampling periods, these results indicate that the 2010 oil spill did not significantly impact zooplankton communities in the northeastern Gulf of Mexico.