Bacterial production in the stratified karstic estuary of the Krka River
Abstract
Spatial bacterial abundance and production in the stratified Krka River estuary were analyzed in the fall of 1990. The bacterial abundance (0.3 - 2.6 x 109 cells l-1) within the estuary was several times higher than in the open central Adriatic waters, but was lower than in the mostly eutrophicated western part of the northern Adriatic. Meanwhile, the bacterial production (0.11 - 5.76 µg C l-1h-1) was of the same ranges as in the open northern Adriatic waters. A strong overall correlation between chlorophyll a content and bacterial numbers, production and growth rate, respectively, was recorded along the depth profile. The bacteria to phytoplankton biomass index lower than 1 at the brackish layer indicates that bacterial production is mostly supported by phytoplankton activity. Halved drop (35%) of bacterial number between the brackish and seawater layers compared to a 60% decrease of the flagellates number indicated a net bacterial production below the halocline which grazing was unable to match. A prevailing bacterial remineralization in the seawater layer is supposed.
