First data on microbial biomass and activities in the Tyhrrenian Sea (Mediterranean Sea)

First estimations of microbial biomass and activities in the water column of the Tyrrhenian basin in association with the main Mediterranean water masses, are reported. Exponential decrease with depth of biomass and activities was registered assessing the predominant weight of export production in the basin and the scarce advection of preformed organic matter within the water masses. Important seasonal changing patterns occurred for respiration and primary production more than for biomass. The evaluation of the carbon budget by microbial community showed PP/R ratios close to 1 in July, and a clear productive metabolism in December.