BACTERIAL CARBON FLUX THROUGH THE MICROBIAL LOOP IN KASTELA BAY (ADRIATIC SEA)

The role of bacteria and heterotrophic nanoflagellates (HNF) in the mi crobial food chain was studied in Kastela Bay (Adriatic Sea) during 19 92/93. The strong trophic coupling of bacteria with HNF, and HNF with ciliates was established. HNF accounted on average for 80%, and ciliat es for 20% of the total grazing of bacteria. The entire annual bacteri al (4.47 g C m(-3) year(-1)) and HNF (1.75 g C m(-3) year(-1)) product ion was consumed by their predators. About 32% (1.43 g C m(-3) year(-1 )) of the bacterial production was incorporated in HNF biomass (averag e gross growth efficiency was 40%). Ciliates incorporated about 8% (0. 36 g C m(-3) year(-1)) of bacterial production by direct grazing and a bout 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 ba cterial production about 21% (0.94 g C m(-3) year(-1)) is available to the metazoan food web. Flux of bacterial biomass through the microbia l loop showed marked seasonal oscillations with considerably higher va lues recorded during the warmer part of the year (June-November).