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, micro- and 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 pico- and nanoplankton feeding zooplankton indicating that bacterial populations were generally controlled by predation.Original Abstract: Istrazivanje povrsinskih zajednica planktona obavljena su u proljece 2002. godine tijekom "Meduza" krstarenja srednjim i juznim Jadranom na transektima "jug-sjever" i "obala-otvoreno more". Utvrdena je dnevna vertikalna raspodjela heterotrofhih bakterija, sastava pigmenata fitoplanktona, te mikrozooplanktona i mezozooplanktona. Na glavnini postaja nadena je termoklina na oko 20 m i izrazeno visoke vrijednosti klorofila alpha na oko 70 m dubine. Intergrirana bakterijska i fitoplanktonska biomasa bila je manja na sredisnjoj postaji juznoga Jadrana, a postupno se povecavala prema postajama Palagruza i Jabucka kotlina kao i prema obalnim postajama. Vertikalna raspodjela bakterijske brojnosti i produkcije pokazala je izraziti maksimum u povrsinskom sloju. Bakterijska brojnost bila je velika u sloju dubokog maksimuma klorofila alpha . Veca bakterijska produkcija bila je u svezi s povisenom brojnocu zooplanktona koji se hrani piko i nanoplanktonom, sto ukazuje da su velicine bakterijskih populacija generalno kontrolirane predacijom.