Seasonal and inter-annual changes of microbial activities in the Central Mediterranean Sea

Knowledge of microbial metabolism in the Mediterranean Sea is still limited or absent. During 12 cruises carried out in the Ionian Sea and Central Mediterranean Sea from 1998 to 2012, different biochemical and microbial parameters involved in the Carbon cycle were measured, to check the changes in microbial transformation of organic matter in different seasons. It is assumed that the microbial community (both auto- and heterotrophic) plays a key role in oligotrophic environments, cycling the elements within the microbial loop. Bacterial Growth Efficiency was also calculated from prokaryotic production and respiration. The aim of our study is to identify the microbial key components which could explain the biogeochemical variability in the euphotic layer, following their evolution on seasonal and inter-annual scales. Inter-annual temperature were comprised between 14.96 °C (s.d. ±0.08) and 20.52 °C (±3.32) and showed greater differences between cold (winter -spring) and warm (summer -autumn) periods. Inter-annual differences were also found among all the summer periods. With respect to seasonal differences, only winter and summer groups differed significantly. During summer, prokaryotic abundance and T, as well as enzymatic activities, were important factors that contributed to the observed variability.