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Résumé :
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Although epibiotic protozoans are commonly observed on the chitinous exoskeleton of aquatic crustaceans, relatively little is known about their ecological significance. The significance of protozoan epibionts on benthic copepods has never been examined. Coullana sp., a meiobenthic harpacticoid copepod, is abundant in Louisiana salt marshes and has high incidence (similar to50%) of ciliate epibionts. Field and laboratory grazing experiments indicated that ciliate epibionts did not hinder Coullana feeding on benthic or planktonic algae. Contrary to expectations, Coullana with high levels of ciliate epibionts (> 8 ind(-1)) grazed at a significantly higher rate on (14)C-labeled benthic diatoms added to intact sediment cores than did Coullana with no epibionts. Coullana neutral lipids (examined using Nile Red, a hydrophobic fluorophore) were not significantly influenced by the presence of ciliate epibionts, suggesting that copepods are able to compensate for any additional energetic demands imposed by epibionts. Epibiont effects on Coullana susceptibility to hydrocarbon contaminants were measured by examining survivorship in diesel-spiked sediments. The presence of ciliate epibionts significantly decreased survivorship, at relatively low PAH concentrations (12.8 ppm). While ciliate epibionts on Coullana do not dramatically alter total food acquisition or energy storage, they may cause stress, which in turn makes Coullana more susceptible to contaminants and possibly other natural stressors such as food limitation.
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