Contribution de la méiofaune aux transferts des métaux dans le réseau trophique de la baie de Gdańsk (Baltique) et de la baie de Marennes-Oléron (Atlantique)

Les nématodes (groupe principal de la méiofaune) sont étudiés sous deux aspects: l un, écologique, vise à déterminer la structure taxonomique/trophique du peuplement et évaluer sa contribution au flux de carbone au sein du système benthique dans les Baies de Marennes-Oléron et Gdańsk. Les résultats des expériences de traçage radioactif (14C) ont permis de quantifier le flux de carbone des diatomées benthiques vers les nématodes et confirment l importance des nématodes dans le transfert du C au sein du réseau trophique benthique. L autre, écotoxicologique, s intéresse au compartiment comme réacteur biologique potentiel susceptible d accumuler, biotransformer et transférer les métaux aux maillons supérieurs du réseau trophique. Le compartiment des nématodes aux concentrations de métaux supérieures à celles de la macrofaune constituerait une voie importante de transfert des métaux dans la chaîne alimentaire et jouerait un rôle majeur dans le recyclage des métaux fixés par les diatomées.LA ROCHELLE-BU (173002101) / SudocSudocFranceF

Co-occurring nematodes and bacteria in submarine canyon sediments

International audienceIn 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

Dynamic of organic matter and meiofaunal community on a river-dominated shelf (Rhône prodelta, NW Mediterranean Sea): responses to river regime

International audienceIn the oligotrophic context of the Mediterranean Sea, riverine inputs of particulate organic matter represent an important source of food for benthic communities. However, since most of these inputs are delivered during short, but intense flood events, communities living in the vicinity of river mouths are also exposed to strong and frequent physical disturbances. A very tight and complex relationship links river dynamic and macrofaunal communities in Mediterranean deltas, but less is known on the response of meiobenthic communities to river regime. In 2010, sediments cores were collected in the Rhône River prodelta in winter and spring before the flooding of the Rhône River tributaries in June, and then twice in the early and late summer. The hypothesis was that increased runoff and export of terrigenous material would induce major changes in the sediment biochemistry, which would in turn trigger modifications in abundances and vertical distribution of the meiofauna. The origin and quality (lability, degradation state) of the different pools of organic matter preserved in these recent sediments were determined using bulk geochemical and molecular analyses (fatty acids, amino acids). Vertical profiles of descriptors for organic matter origin and quality revealed major changes in the nature of the inputs occurring at monthly time scales. Inputs of plant detritus from autumnal and winter flood events were still visible in the cores collected in February and April. A few days after the June 2010 high-discharge event, a newly deposit (∼7 cm) containing soil organic matter has recovered the prodeltaic sediments and the resident meiofaunal community, but at the end of August only 2 cm of this deposit remained. Multivariate analyses furthermore highlighted that the meiofaunal community was driven by both the trophic conditions and deposition of a new sediment layer driven by the hydrological regime of the Rhône River. In April, increased abundances of meiofauna were observed in response to the sedimentation of labile organic matter after the spring bloom. The June high-discharge event affected the meiofauna with a reduction of its abundance and the burial of the resident meiobenthic community. However, the meiofauna recovered in less than two months after this disturbance, showing the strong resilience of this component of the benthic ecosystem in this high energy environment