Interaction between specific hydrological and microbial activity leading to extensive mucilage formation in the northern Adriatic Sea

The massive formation of marine snow and the senescent stage of it, the mucilage, is a phenomenon largely restricted to the Adriatic Sea. In this contribution the major environmental factors potentially leading to the formation of this mucilage are discussed. It is proposed that the specific hydrological conditions in combination with severe phosphorus depletion lead to excessive formation of colloidal organic matter by phytoplankton. This colloidal organic matter coagulates to marine snow due to the low-turbulence regimes prevailing in the water column. Subsequently, this marine snow is colonized by bacteria which, in turn, produce and release copious amounts of capsular polymers into the matrix of marine snow. It is speculated that a significant fraction of the later stages of marine snow (mucilage) consists of bacterial-derived organic matter which has been shown to be semi-labile to refractory for further bacterial utilization. The marine snow matrix acts as efficient adsorption site and allows the bacteria to utilize scavenged molecules from the ambient water. Thus it is proposed that the matrix ages without significant biotic degradation.