Bacterial carbon flux through the microbial loop in Katšela Bay (Adriatic Sea)

The role of bacteria and heterotrophic nanoflagellates (HNF) in the microbial food chain was studied in Kaštela Bay (Adriatic Sea) during 1992/93. The strong trophic coupling of bacteria with HNF, and HNF with ciliates was established. HNF accounted on average for 80%, and ciliates for 20% of the total grazing of bacteria. The entire annual bacterial (4.47 g C m-3 year-1) and HNF (1.75 g G m-3 year-1) production was consumed by their predators. About 32% (1.43 g G m-3 year-1) of the bacterial production was incorporated in HNF biomass (average gross growth efficiency was 40%). Ciliates incorporated about 8% (0.36 g C nr3 year1) of bacterial production by direct grazing and about 13% (0.58 g C m-3 year-1) indirectly through HNF, assuming a gross growth efficiency of 40%. This means that of the total annual bacterial production about 21% (0.94 g C m-3 year-1) is available to the metazoan food web. Flux of bacterial biomass through the microbial loop showed marked seasonal oscillations with considerably higher values recorded during the warmer part of the year (June-November).