Heterotrophic bacteria in the pelagic realm of the Mediterranean Sea
Résumé
Heterotrophic bacteria contribute significantly to food web structure and biogeochemical cycling in the ocean. In oligotrophic regions such as the Mediterranean Sea, the functioning and productivity of the pelagic ecosystem largely depends on the activity of heterotrophic bacteria which are at the center of the balance between exported and mineralized carbon. As a result of pioneer studies developing techniques to assess bacterial production and abundance, these parameters have been measured in the Mediterranean Sea since the late 1980s. Much more recently, thanks to the advances in molecular methods for exploring microbial biodiversity, an understanding of the biogeochemical implications of the assemblage's taxonomic composition begins to emerge. Today, research efforts on the role of heterotrophic bacteria in the Mediterranean Sea face new challenges related to understanding and foreseeing the probable responses to changing natural and anthropogenic forcing. This chapter aims at reviewing the current state of knowledge on the variability of bacterial abundance, activity and community structure at both spatial and temporal scales in the pelagic waters of the Mediterranean Sea. In addition, the response of heterotrophic bacteria to major human driven changes is evoked. Finally, future directions dealing with key questions and new tools related to research on heterotrophic bacteria are proposed.