Polysaccharide Characterisation of Marine Organic Matter in a Coastal Station of the Gulf of Trieste (Northern Adriatic Sea, Italy)

In the last two decades the presence and distribution of large aggregates in the Mediterranean Sea have encouraged to study the macromolecular features of dissolved organic matter and the implication of molecular characteristics of biopolymers on the aggregation processes. Monthly monitoring of marine carbohydrates in a coastal station of the Northern Adriatic sea during years 2001–2003 at 0.5, 10 and 15 m depth showed different pattern for dissolved and total carbohydrates in concurrence of the massive formation of aggregates. Since March to June 2004 marine water was collected for the partition experiment. The polysaccharide component was isolated by ultrafiltration. The monosaccharide compositions were very similar to those obtained from Adriatic pelagic mucilage. In June a significant reduction of the concentration of the low molecular weight polysaccharidic fraction was observed, in conjunction with the rapid increase of the high-molecular weight polysaccharides (HMW). In addition, the concentrations of deoxysugar (rhamnose and fucose) in the particulate matter decreased, and the fucose disappeared in June. These two monosaccharides and galactose may be considered bioindicators of the different degradation steps of marine polysaccharidic matter. This enrichment suggested that galactose-rich polysaccharides are able to undergo aggregate formation. Scanning electron microscopy and AFM imaging on extracted fractions showed the presence of fibrillar structures forming a highly branched tri-dimensional network similar to those found in Adriatic pelagic aggregates.