Bacterial processes in the intermediate and deep layers of the Ionian Sea in winter 1999

Dissolved and particulated organic carbon, bacterial biomass (BB), microbial ectoenzymatic activities (EEA: leucine aminopeptidase, ß-glucosidase and alkaline phosphatase), bacterial production (BP), respiration rates (R) and bacterial growth efficiency (BGE) were determined in 10 station of the Ionian Sea with the aim of characterizing the recycling of biogenic carbon and phosphorus in different water masses. All the microbial activities decreased markedly with depth with a sharp increase in the benthic boundary layer, where potential remineralization rates of P up to 1.03µg P*dm-3d-1 and bacterial carbon production of 0.078µg C*dm-3d-1 were recorded.Those rates were close to the surface ones. The daily hydrolysis of organic carbon by EEA varied from 0.67% (Ionian Surface Water) to 0.02% (Cretan Deep Water). The BGE was also around 20% in BBL similar to the surface values sustaining microbial food chain at bottom.