Enzymatic activities and carbon flux through the microbial compartment in the Adriatic Sea

Carbon flux through the microbial community by the determination of biomass, heterotrophic bacteria, aminopeptidase and respiratory activities has been studied in two areas of the Adriatic sea with different trophic characteristics during four oceanographic surveys, carried out in June 96,97 and february 97,98. in front of the Po delta (area A), the average rates of the carbon released by aminopeptidase activity ranged from 4.9 to 9.9 mug Cl-1 h(-1) and near the Ancona coast (area B) from 3.1 to 7.6 mug Cl-1 h(-1),whereas the microbial respiration as metabolic carbon production (CO2) ranged from 0.19 to 2.29 and from 0.24 to 1.40 mug Cl-1 h(-1) in the two areas, respectively. In area A, both the microbial activities showed a seasonal trend with higher values in summer than in winter. In area B, respiration increased during years whilst aminopeptidase activity decreased; bacterioplankton abundance increased on average in the second year of the research (June 97 and February 98). However, all these differences were not statistically significant. The biovolume resulted always significantly higher during summer. Relationships between bacterial carbon production and organic carbon content were discussed. Bacterial growth efficiency ranged from 17 to 38% and from 13 to 44% in areas A and B, respectively. The relationship between hydrolysis of peptides and bacterial carbon production indicated a good coupling of processes during June 97. Various ratios between bacterial activities were reckoned with the aim to define the role of bacteria in the biogeochemical flux of C in the Northern Adriatic Sea. The C transfer from the biotic versus the abiotic compartment seems to flow better in summer, particularly in area A.