Biochemical and microbial features of shallow marine sediments along the Terra Nova Bay (Ross Sea, Antarctica)

Shallow marine sediments were collected from seven stations (three of which located at Gerlache Inlet, two at Tethys Bay, one at Adelie Cove and one just beneath the Italian Research Base) along the Terra Nova Bay coast (Ross Sea, Antarctica). Their chemical, biochemical and microbiological properties were studied in order to provide further insights in the knowledge of this Antarctic benthic ecosystem. Overall, the organic carbon (OC) represented the major fraction of total carbon (TC) and displayed concentrations similar to or slightly lower than those previously measured in Antarctic bottom sediments. The biopolymeric carbon within OC ranged from 4.1% to 19.9% and showed a wide trophic range (65–834 μg g−1 d.w.). Proteins (PRT) represented on average the main biochemical class contributing to labile organic carbon, followed by lipids (LIP) and carbohydrates (CHO). The activity of aminopeptidase, β-d-glucosidase, alkaline phosphatase and esterase was checked, giving the highest values at Tethys Bay and at the deepest water sediments. The principal component analysis, which was computed considering physical, chemical (elemental and biochemical sedimentary composition) and microbiological parameters (including bacterial abundance, ectoenzymatic activities, T-RFs richness and diversity indices), allowed to obtain two main clusters (“Tethys Bay” and “other stations”). Based on data obtained, two representative 16S rRNA clone libraries using samples from Tethys Bay and Gerlache Inlet were constructed. The sequences of 171 clones were compared to those available in public databases to determine their approximate phylogenetic affiliations. Both aerobic and anaerobic bacteria were disclosed, with the majority of them affiliated with the Gamma- and Deltaproteobacteria, Bacteroidetes and Acidobacteria. The occurrence of strictly anaerobic bacteria suggests that sediments might also undergo anoxic conditions that, in turn, could favor the accumulation of PRT in respect to CHO, assuming that fermentation of amino acids is slower than that of sugars from decomposing polysaccharides.