Tidal coupling between carbohydrate concentrations and bacterial activities in diatom-inhabited intertidal mudflats

Sediment bacterial production, abundance and P-glucosidase activity were studied in relation to carbohydrate concentrations in diatom-inhabited intertidal mudflats during the tidal cycle in the Ems-Dollard estuary in summer 1996. During the diurnally emerged period significant increases in water- and EDTA-extracted carbohydrates, bacterial production and abundance in the sediment surface layer (0 to 2 mm) were established. Exposure had no effect on algal biomass (chlorophyll a), doubling times of bacteria or beta-glucosidase activity in the surface layer. Net changes in water-extracted carbohydrates together with net changes in total and CTC (5-cyano-2,3-ditolyl tetrazolium chloride) stained bacteria accounted for 85 % of the variations in net increase in bacterial production during the emerged period. During the submerged period significant decreases of water-extracted carbohydrate concentrations occurred. The changes in beta-glucosidase activity and water-extracted carbohydrates could explain 93 % of the net changes in bacterial production during the submerged period. Water-extracted carbohydrates derived mainly from Live diatoms. The source of EDTA-extracted carbohydrates was less specific, but related to chlorophyll a and pheopigments. The results suggest that the net increases in water-extracted carbohydrates due to diatom activities are indirectly coupled to benthic heterotrophic bacterial production. Bacteria do respond to tidal variations in organic compounds, and water-extracted carbohydrates are an important indicator.