The epiplankton community in the southern Adriatic: Multiple trophic levels along the south - north and inshore-offshore gradients

The epiplankton community was investigated during Meduza cruises along south north and offshore – inshore transects in the middle and southern Adriatic in spring 2002. The diel and vertical distribution of heterotrophic bacteria, phytoplankton pigment composition, microand mesozooplankton were assessed. At most stations we observed a thermocline at approximately 20 m and a prominent chlorophyll a peak at about 70 m depth. The integrated phytoplankton and bacterial biomass were lower at the station in the central part of the southern Adriatic, and increased gradually towards middle Adriatic and towards coastal stations. Vertical profiles of both bacterial abundance and production showed a distinct peak in the surface layer. Bacterial abundance was high also in the layer of the deep chlorophyll a maximum. Higher bacterial production was associated with elevated abundance of picoand nanoplankton feeding zooplankton indicating that bacterial populations were generally controlled by predation.