Influence of subantarctic Macrocystis bed metabolism in diel changes of marine bacterioplankton and CO2 fluxes

The significance of bacterial communities in the fluxes of carbon and energy in giant kelp beds (Macrocystis pyrifera) in Kerguelen Archipelago, subantarctica, was estimated by measuring bacterioplankton biomass and production over diel cycles in surface seawaters located inside and outside of Macrocystis beds. Several physicochemical parameters [temperature, solar radiation, tide level, dissolved oxygen, total inorganic carbon (TCO2), partial pressure of CO2 (pCO(2)) and dissolved organic carbon (DOC)] were simultaneously recorded in order to establish possible relationships with observed changes in bacterial parameters. Bacterial biomass and production were significantly higher inside the kelp bed than in the surrounding area. Furthermore, the results showed large and clear diel variations of all parameters measured inside the kelp bed. Changes in dissolved oxygen, TCO2 and pCO(2) paralleled those of solar radiation, and were obviously related to the metabolic activity of the kelp. Mean cell volumes and saprophytic bacterial abundance varied over the diel cycles in the same way as photosynthetic activity, while DOC, bacterioplankton production and the frequency of dividing cells varied in an opposite way with maximal values at night-time.