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Picoplankton distribution and activity in the deep waters of the southern Adriatic Sea

This paper describes picoplankton distribution and activity in the Southern Adriatic Pit, in relation to environmental parameters and hydrographic conditions prevailing in the pre-winter and post- winter period. Picoplankton abundances were higher in the pre-winter period compared to the post- winter period. The changes in the observed community were mainly driven by nutrient availability, HNF abundance and consequently by water mass movements. In the pre-winter period, significant numbers of picoaoutotrophs were found in the meso- and bathypelagic layer, and Synechococcus dominated the group. Higher values of bacterial production and domination of HNA bacteria were found in deep waters in the post- winter period, suggesting that bacteria are an active part of the studied deep-sea environment. Our results suggest that autotrophic and heterotrophic members of the picoplankton community are an important source of essential nutrients in the food web below the epipelagic layer. In addition, viral lysis may affect the activity of the picoplankton community and enrich the deep sea with dissolved organic carbon.

picoplankton, MED, Adriatic Sea, South Pit, deep water, water masses

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