The relationship between dissolved carbohydrates and carbohydrate-degrading enzymes in the salinity gradient of the Pomeranian Bight (Southern Baltic)

From 1994 to 1996 changes in the concentrations of dissolved mono- (MCHO) and total dissolved polysaccharides (TCHO) as well as the activities of carbohydratedegrading enzymes (α- and β-glucosidase, glucosaminidase) were investigated during mixing of water from the River Odra and the open Pomeranian Bight. This study addresses the question of whether their distribution was a result of physical dilution alone or if biological interactions were detectable. Within the salinity gradient, ranging from 1.9 to 7.8 PSU, TCHO declined from 13.2 μmol l−1 near the Świna mouth to 2.8 μmol l−1 after mixing. Concentrations of MCHO decreased from 3.4 μmol l−1 to 1.1 μmol l−1 but its distribution pattern varied more between summer and autumn than that of TCHO. The hydrolysis rate (Hr) by glucosidase and glucosaminidase activities was reduced from 13.9% h−1 to 0.3% h−1 and 9.9% h−1 to 0.2% h−1, respectively, and correlated with the uptake rate of glucose (To) by bacteria. In summer, the To/Hr ratio increased from about 1.2 to 29.4, mainly because of stronger decreases in Hr than in To. It was shown that the relationship between enzymatic release and uptake of carbohydrates influences the concentration of dissolved carbohydrates within the salinity gradient. Most probably, the decrease in carbohydrate-degrading enzymes is the result of reduced substrate stimulation and the lower number of particle-associated bacteria.