Benthic bacterial communities in sandy surface sediments (Helgoland Roads, North Sea)@en

Coastal sands are biocatalytic filters for dissolved and particulate organic matter of marine and terrestrial origin. In this study, we accessed the variability of benthic bacterial communities over two annual cycles at Helgoland Roads (North Sea, German Bight) sediments, where primary production does not occur during winter. Sediment cores were obtained by scientific divers. Benthic community structure in surface sediments (0-2 cm depth) was studied by 16S rRNA-based taxonomy (16S rRNA gene sequencing using primers S-D-Bact-0341-b-S-17 and S-D-Bact-0785-a-A-21, Illumina sequencing platform HiSeq2500, 2x250 bases, paired-end). Total organic carbon content was determined using 25-50 mg of freeze-dried sediments. To determine organic carbon, inorganic carbon was removed with 1 M HCl before analysis. Samples were analyzed in an Euro EA-CNS elemental analyser (HEKAtech, column temperature 75°C; carrier gas helium at 80 ml min-1, reactor temperature 1000°C with oxygen flow 10 ml min-1, oxidation time 7.9 sec) with thermal conductivity detection. Calibration was done with sulfanilamide (0.2 to 2 mg) standards.