Dissolved organic matter and microbial food web interactions in the marine environment: the case of the Adriatic Sea

Focusing on the Adriatic Sea, the composition of dissolved organic matter (DOM) is described, and DOM autochtonous and allochtonous sources are identified. Also reviewed are the microbial food web and the DOM cycle, and factors affecting DOM uptake by microorganisms, such as diagenesis and molecular size, nutrient availability, marine water temperature, and abiotic alterations of DOM. Dissolved organic matter is particularly problematic in the Adriatic Sea, which is semi-enclosed. The DOM accumulation in the northern basin is attributed to an increase in the freshwater residence time, the setting up of strong vertical stratification, and eddy circulation in summer. The data suggest that the phenomenon of macroaggregate production in the Adriatic is due to two separate processes: the accumulation of DO and its transformation from dissolved and colloidal to gelatinous compounds. The DOM accumulation appears to be the result of an inefficient uptake by bacteria.