Sedimentary organic matter and micro-meiobenthos with relation to trophic conditions in the tropical northeast Atlantic

The biological and chemical characteristics of sediments sampled during the EUMELI cruise in the tropical northeast Atlantic are presented. These sediments are representative of three different trophic conditions prevailing in surface waters off the Mauritanian coast: EUtrophic, MEsotrophic and oLIgotrophic. The benthic response to surface primary production, considered as the main supply of biogenic material to the sea floor, was evaluated through the qualitative and quantitative analysis of: (i) the composition of the sedimentary organic matter; (ii) the biomass of the micro- and meiobenthos; and (iii) the benthic metabolic activity. The bacterial biomass (17.5 μg cm−2 at the oligotrophic site and 64.5 μg cm−2 at the mesotrophic site) the meiofauna biomass (1.12, 4.34 and 9.63 μg cm−2 at the oligo-, meso- and eutrophic sites, respectively), the respiratory potential (ETS) and the utilization of labeled amino acids by heterotrophic microbenthos are germane tracers of the benthic response. However, their relative variations between the three different sites are reduced in comparison to the carbon fluxes measured or estimated at the sediment-water interface. Sedimentary organic carbon and biopolymer analysis show still further reduced variations between the three environments. In order to better distinguish the three different oceanographic provinces, it is more suitable to integrate the various properties investigated over depth in sediment than to consider surficial characteristics. We conclude from our multi-parameter approach that micro-meiobenthos may be more efficient utilizers of the vertical carbon supply than their counterparts in rich shallower zones.