Patterns of Prokaryotic Activities and Abundance among the Epi-Meso and Bathypelagic Zones of the Southern-Central Tyrrhenian Sea

The southern- central Tyrrhenian Sea is a poorly studied area of the Mediterranean Sea, although its importance for the biological fluxes among the western and eastern basins is recognised. This note aimed at evaluating in the waters of the Southern Tyrrhenian Sea the efficiency of some steps of the organic matter processing (enzymatic hydrolysis, prokaryotic production and oxidation) and the role played by the prokaryotic community in this context. During the MEDBIO multidisciplinary cruise performed in July 2005, the distribution of prokaryotic abundance and activities (exo enzymatic activity, heterotrophic production and respiratory activity) was studied. The results showed the presence of high exo enzymatic activity rates (mostly leucine amino peptidase) in the deep sea, while heterotrophic production and respiratory activity rates were high at surface. Some speculations on the different behaviors of the Carbon fluxes occurring among the different epi, meso and bathypelagic layers are reported. At the epipelagic layer both the decomposition and biomass production processes were high. At the mesopelagic layer the organic matter was quickly mobilised but not efficiently incorporated into biomass, therefore the dissolved monomers remained available in the water column for export to other trophic levels or utilization in other chemical processes (lateral advection, oxidation). The bathypelagic layer was characterised by high levels of hydrolytic activity coupled with relatively high prokaryotic production; in this layer, exo enzymatic activity levels fall in an order of magnitude similar to that observed at the epipelagic one. This finding highlights the importance of microbially mediated processes in sustaining life in the marine depths.