Abstract
In submarine canyon sediments, bacteria and nematodes dominate the benthic biomass and play a key role in nutrient cycling and energy transfer. The diversity of these communities remains, however, poorly studied. This work aims at describing the composition of bacteria and nematode communities in the Lacaze-Duthiers submarine canyon in the north-western Mediterranean Sea. We targeted three sediment depths for two consecutive years and investigated the communities using nuclear markers (18S rRNA and 16S rRNA genes). High throughput sequencing combined to maximal information coefficient (MIC) statistical analysis allowed us to identify, for the first time, at the same small scale, the community structures and the co-occurrence of nematodes and bacteria Operational Taxonomic Units across the sediment cores. The associations detected by MIC revealed marked patterns of co-occurrences between the bacteria and nematodes in the sediment of the canyon and could be linked to the ecological requirements of individual bacteria and nematodes. For the bacterial community, Delta- and Gammaproteobacteria sequences were the most abundant, as seen in some canyons earlier, although Acidobacteria, Actinobacteria and Planctomycetes have been prevalent in other canyon sediments. The 20 identified nematode genera included bacteria feeders as Terschellingia, Eubostrichus, Geomonhystera, Desmoscolex and Leptolaimus. The present study provides new data on the diversity of bacterial and nematodes communities in the Lacaze-Duthiers canyon and further highlights the importance of small-scale sampling for an accurate vision of deep-sea communities.
Highlights
Submarine canyons represent deep incisions in the continental slope, that enlarge the heterogeneity of deep-sea habitats on the shelf break and generate biodiversity (Levin et al, 2010)
We present the first detailed description of the bacterial and nematodes diversity in a submarine canyon based on high throughput sequencing analysis
Earlier studies have shown a higher biomass of meiofauna and bacteria along the axes of canyon sediments compared to other seafloor areas at similar depth (Danovaro et al, 1999) but the detailed composition of the communities has never been reported and possible associations between nematodes and bacteria are not known
Summary
Submarine canyons represent deep incisions in the continental slope, that enlarge the heterogeneity of deep-sea habitats on the shelf break and generate biodiversity (Levin et al, 2010). In the Gulf of Lion (the north-western Mediterranean Sea), water transport driven by density contrast between surface and deeper waters occurs in winter through the formation of dense surface shelf waters by cold winds (Canals et al, 2006). This cascading phenomenon, and more generally the hydrodynamic features (including storm downwelling and eddies) promoting a fast and episodic transfer of organic material from the shelf to the deep sea, convert canyons into hotspots of benthic biomass (De Leo et al, 2010). A study of the structure of bacterial community by fingerprinting techniques showed differences in composition in sediment surface layers between canyons in the north-eastern Atlantic Ocean but the identity of the bacteria was not reported (Amaro et al, 2009)
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