Hyporheic biofilms ― a potential food source for interstitial animals

Glass-beads (diam. = 250 mu m) were buried 10 cm deep in the sediment of a stream. After an exposure of eight weeks, bacterial densities on the beads varied between 2.7 x 10 super(5) and 2.4 x 10 super(7)/cm super(2), and the length of the fungal mycelium between 0.2 and 5.3 mm/cm super(2). Bacterial densities did not show any correlation with the DOC content of the water, but were positively correlated with respiration on the beads. Fungal mycelium was negatively correlated with water temperature. Acid hydrolysis of stream-exposed beads released sugars and amino acids, whose combined carbon content exceeded that of the microbial cells by a factor of at least 4. Gut extracts of Gammarus tigrinus) and Tipula caloptera released amino acids and sugars from stream-exposed beads.