The carbon fluxes between phytoplankton and heterotrophic bacterioplankton were studied in two coastal oligotrophic sites in the NW Mediterranean. Phytoplankton and bacterial production rates were measured under natural conditions using different methods. In the Bay of Villefranche, the temporal variability revealed net heterotrophy in July-October and net autotrophy in December-March. The spatial variability was studied in the Bay of Palma, showing net autotrophic areas in the west and heterotrophic areas in the east. On average bacterial respiration, represented 62% of the total community respiration. Bacterial growth efficiency (BGE) values were significantly higher in autotrophic conditions than in heterotrophic ones. During autotrophic periods, dissolved primary production (DPP) was enough to sustained bacterial metabolism, although it showed a positive correlation with organic carbon stock (DOC). Under heterotrophic conditions, DPP did not sustain bacterial metabolism but bacterial respiration correlated with DPP and bacterial production with DOC. Temperature affected positively, DOC, BGE, bacterial respiration and production when the trophic status was autotrophic. To summarize, the response of bacterial metabolism to temperature and carbon sources depends on the trophic status within these oligotrophic coastal systems.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: Many individuals contributed to the successful completion of the field work, in particular the skippers and crew of the research boats. The CTD data were provided by C. Heyndrickx and the SOMLIT program. The two sampled regions maps were kindly provided by P. Vandromme and F. Gazeau. This research was supported by the European Union in the framework of the EUROTROPH project (contract # EVK3-CT-2000-00040) and N. González-Benítez was supported by a Marie Curie individual fellowship (MCFI-2001-01425). Additional support was provided by The Netherlands Organisation for Scientific Research (Dutch-French co-operation on sea research programme). L.S. García-Corral was supported by a Juan de la Cierva fellowship from the Spanish Ministry of Science, Innovation and Universities.