Sulfate-reducing bacteria in temporarily oxic sediments with bivalves

Under seasonally fluctuating redox conditions in sediment of Kiel Bay (eastern Baltic Sea), viable counts (MPN) of sulfate-reducing bacteria (SRB) ranged between 4 X 102 and 7 X 104 cm-3 These MPN appeared fairly independent of ambient redox potentials and followed peaks of phytoplankton productivity in the water column with a time lag of 2 to 3 wk. The relative proportions of SRB using acetate, lactate or succinate as their electron donors fluctuated widely. Shells of the clam Arctica islandfca, which can survive anoxia, were, even In oxlc sediments, colonized by eplzolc SRB Significant differences between the abundance of epizoic SRB and SRB from ambient sediment were not detected. In terms of enrichment kinetics, however, epizo~c SRB, and particularly those d e p e n d ~ n g on succinate as electron donor, showed quicker responses. It 1s hypothesized that SRB associated with benthic infauna represent the biogeochemically more reactive group.