Activity and distribution of bacterial populations in Middle Atlantic Bight shelf sands

Spatiotemporal variation and metabolic activity of the microbial community were studied in coarse-grained Middle Atlantic Bight shelf sediments in relation to pools of dissolved and particulate carbon. Algal cells were present 8→70 μm) fraction of the sediment held the major share (61-98%) of benthic bacteria. Bacterial and algal cell abundances, exoenzymatic activity, and [DOC] generally showed higher values in May/July 2001 than in August/December 2000. Carbohydrates and proteins were hydrolyzed at potential rates of 1-12 nmol cm^-3 h^-1 (β-glucosidase) and 3-70 nmol cm^-3 h^-1 (aminopeptidase), respectively. Fluorescence in situ hybridization analyses of the benthic microbes assigned 45-56% of DAPI-stained cells to Eubacteria and less than 2% to Eukarya. The prokaryotic community was dominated by planctomycetes and members of the Cytophaga/Flavobacterium cluster. Near the sediment surface, iodonitrotetrazolium violet reducing cells, that are considered actively respiring, amounted to 15-29% of total bacteria. Despite a low organic content (particulate organic carbon <0.03%) and relatively low bacterial abundances (<10⁹ cm^-3), the Middle Atlantic Bight shelf sediments showed organic matter turnover rates that are comparable to those found in organic-rich finer-grained deposits. Our findings suggest a high biocatalytic filtration activity in these coarse permeable sediments.