Monitoring the prokaryotic and viral abundances and the microbial activities in two coastal sites of Terra Nova Bay (Antarctica)

Studies in coastal areas of Terra Nova Bay (TNB) highlighted the sudden variability of planktonic biomass with ecological implications on the heterotrophic microbial community and the fate of the organic substance on a seasonal scale. With the aim to monitoring the evolution of the prokaryotic and viral abundance and the hydrolysis of organic matter, in the frame of the CEFA project (Italian PNRA) two fixed stations (Faranda Field - FF; Michaud Pier - MP), were repeatedly sampled. In FF, a sea ice covered station, the prokaryotic and viral abundances were monitored from the 9th of November 2015 to the 19th of January 2016 with Image Analysis (IA) and Cytofluorimetry (FC). Starting from the 4th of January 2016 the potential enzymatic activities on proteins, carbohydrates and organic phosphates were determined. Moreover, the MP station was monitored from the 12th of January to the 8th of February 2016. The prokaryotic abundance in FF station varied in the ranges 0.73-3.38 and 0.26-1.85cellsx105ml-1 by IA and FC, respectively. Cells with high nucleic acid content (HNA) accounted from 32 to 84% of the total FC cells. Virus like particles by FC ranged between 8.08 and 22.3VPLx105ml-1 and V1 group accounted for the 64-94% of the total. The main activity in all samples taken from FF station (under ice) was the phosphatase with the highest values at the beginning of the sampling and showing a decreasing trend when the station was defrosted. This enzyme can be produced in surface water by both bacteria and phytoplankton. The glucosidase activity, showed lower values than phosphatase with a similar trend. The peptidase activities instead increased in the sampling at the end of January in correspondence of the ice absence. In the MP station, the prokaryotic abundance varied in the ranges 1.00-12.3 and 1.03-4.07cellsx105ml-1 by IA and FC, respectively. Cells with high nucleic acid content (HNA) accounted from 47 to 84% of the total FC cells. Virus like particles by FC resulted to be below the detection limits. High variability of enzymatic activities was observed with time in this station. Generally phosphatase prevailed on other activities with the maximum values on the 13rd and 22nd of January; thereafter it decreased with the ice melting. ?-glucosidase, showed peaks on January 16th and from 24th to 29th of January (bay covered by ice), then it decreased. The amino-peptidase showed variable values with peaks on the 12th and 17th of January.