Bacterivory of a mudflat nematode community under different environmental conditions |
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Authors: | Pierre-Yves Pascal Christine Dupuy Pierre Richard Jadwiga Rzeznik-Orignac Nathalie Niquil |
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Institution: | (1) Littoral, Environnement et Sociétés (LIENSS) UMR 6250 CNRS-Université de La Rochelle, 2 Rue Olympe de Gouges, 17042 La Rochelle Cedex, France;(2) Biologie des organismes marins et écosystèmes (BOME) UMR-CNRS 5178–USM 0401–MNHN, 61 Rue Buffon, 75231 Paris, France |
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Abstract: | The fate of the benthic bacterial biomass is a topic of major importance in understanding how soft-bottom environments function.
Because of their high abundance, production and nutritional value, benthic bacteria may constitute an important food resource
for benthic fauna. The trophic role of bacteria for a nematode community on the Brouage mudflat (Marennes-Oléron-France),
dominated by three species: Chromadora macrolaima (64% of the abundance), Daptonema oxycerca (15%) and Ptycholaimellus jacobi (8%), was determined in grazing experiments using 15N pre-enriched bacteria. On intertidal flats, seasonal, tidal and circadian cycles induce strong variations in environmental
conditions. Grazing experiments were performed in order to measure the effects of abiotic (temperature, salinity and luminosity)
and biotic (bacterial and algal abundances) factors on assimilation rates of bacteria by nematodes. In order to assess simultaneously
bacteria and algal assimilation rates, algal abundances were modified adding 13C pre-enriched Navicula phyllepta. Assimilation rate was significantly lower at 5°C; moreover, general trend shows a prominent temperature effect with an optimum
around 30°C. Assimilation at salinity 18 was not significantly different from the assimilation at salinity 31. Assimilation
was higher under light conditions than in the dark. Above 109 bacteria ml−1, assimilation of bacteria remained unaffected by bacterial abundance. However, assimilation of algae increased with the algal
concentration. Nematode kept feeding under conditions of stress, which are typical of the surficial sediment habitat and they
appeared to be principally dependent on the algal resource. |
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