Epi-benthic megafaunal zonation across an oxygen minimum zone at the Indian continental margin

Macrofauna regulate heterotrophic bacterial carbon and nitrogen incorporation in low-oxygen sediments

“…D/L-Ala ratios demonstrate that in the OMZ core, bacterial assimilation accounted for 30-90% of the phyto C and phyto N labelling of the HAAs. This occurs concomitantly with peaks in phyto C and phyto N retention in the bulk OM and HAA pools (Figures 3 and 4), and oxygen concentrations B0.2% of those outside the OMZ (Hunter et al, 2011). In the OMZ boundary, bacterial phyto C and phyto N incorporation were low after 4 days, despite oxygen levels between 6 and 42 times higher than those OMZ core.…”

“…Sediment geochemistry and microbial biomass Environmental conditions at each station are described by Hunter et al (2011) and summarised in Table 1. HAAs made up 1.3-3.0% of the sediment organic C content and 15-30% of the sediment N content, across all stations.…”

“…The Arabian Sea OMZ impinges upon the western Indian continental margin between 150 and 1500 m producing depth-dependent changes in oxygen availability, sediment geochemistry and the megaand macrofauna (Hunter et al, 2011(Hunter et al, , 2012. The present study was carried out between September and November 2008, during R/V Yokosuka (JAM-STEC, Japan) cruise YK08-11.…”

“…Before analysis, bulk sediment samples were lyophilised ( À 60 1C; À 0.0001 mbar; 24 h), acidified with excess 1 mol l À 1 hydrochloric acid (HCl aq ) to remove carbonates and dried to constant weight at 60 1C (following Hunter et al, 2011). 15 N and 13 C incorporation into the sediment HAAs and the bacterial biomarker D-alanine (D-Ala) were analysed using the method developed by Veuger et al ( , 2007b. Briefly, 0.2 g samples of lyophilised sediment were washed in 2 mol l À 1 HCl aq and Milli-Q to remove soluble material.…”

“…In future climate projections, OMZs are predicted to expand with far-reaching implications for global biogeochemical cycles (Stramma et al, 2010). Changes in oxygen availability and sediment geochemistry across an OMZ influence sediment community composition, producing changes in the faunal and bacterial assemblages that control the rates and pathways for OM recycling (Woulds et al, 2007;Andersson et al, 2008;Gooday et al, 2009;Hunter et al, 2011Hunter et al, , 2012Moodley et al, 2011). Therefore, an understanding of the effects of oxygen limitation upon OM availability, sediment community structure and ecosystem processes is required in order to predict the effects of climate change upon global biogeochemical cycles.…”