Uptake of dissolved organic matter (DOM) and its importance to metabolic requirements of the zebra mussel, Dreissena polymorpha

We determined the rates at which Dreissena polymorpha assimilated radiolabeled acetate, monosaccharides, amino acids, and fatty acids at environmental concentration levels. The mussels incorporated all of the substances presented to them. Much of the C-14-labeled substrate that was taken up was respired to (CO2,)-C-14 indicating that the substrates were used for metabolic purposes. Nonacidic amino acids and fatty acids were taken up fastest, with absorption efficiencies (AE, percentage of filtered substrate removed) of 13% and 85%, respectively. The AEs for monosaccharides (1.5%), acetate (0.2%), and the acidic amino acid glutamic acid (0.79%) were much lower. Among the nonacidic amino acids, nonpolar forms (AE = 19.5%) were preferred over basic and polar neutral forms (AE = 9.3%). On the basis of direct measurements of free amino acid concentrations and literature estimates of free sugars, acetate, and short-chain fatty acids in surface waters, we estimated that direct uptake of these monomers amounts to similar to10-25% of the zebra mussel maintenance ration. Direct uptake of dissolved organic matter might be metabolically significant to zebra mussels.