Plankton respiration and bacterial production in the Celtic sea
The downward flux and ultimate storage of particulate and dissolved organic carbon in shelf seas is constrained by the respiration of bacteria, phytoplankton and zooplankton in the water column. The recent refinement of an indirect method to determine microplankton community and bacterial respiration, based on the cellular reduction of a tetrazolium salt, was therefore seen as a major step forward on our knowledge of plankton respiration. In order to quantify microplankton respiration and the bacterial efficiency (relevance of bacterial biomass synthesis over bacterial respiration), we undertook a seasonal study of plankton community respiration, bacterial production and bacterial respiration in the Celtic Sea (UK) as part of the NERC Shelf Sea Biogeochemistry programme. Here I will discuss the seasonal evolution of the different metabolic rates in surface and bottom mixing layers.