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Marine Pollution Bulletin 62 (2011) 2753-2760
Sampling epifauna, a necessity for a better assessment of benthic ecosystem functioning: An example of the epibenthic aggregated species Ophiothrix fragilis from the Bay of Seine
Sophie Lozach 1, 2, Jean Claude Dauvin 1, Yann Méar 3, Anne Murat 3, Dominique Davoult 4, Aline Migné 4

Sampling the sea bottom surface remains difficult because of the surface hydraulic shock due to water flowing through the gear (i.e., the bow wave effect) and the loss of epifauna organisms due to the gear's closing mechanism. Slow-moving mobile epifauna, such as the ophiuroid Ophiothrix fragilis, form highdensity patches in the English Channel, not only on pebbles like in the Dover Strait or offshore Brittany but also on gravel in the Bay of Seine (>5000 ind m 2 ). Such populations form high biomasses and control the water transfer from the water column to the sediment. Estimating their real density and biomass is essential for the assessment of benthic ecosystem functioning using trophic web modelling. In this paper, we present and discuss the patch patterns and sampling efficiency of the different methods for collecting in the dense beds of O. fragilis in the Bay of Seine. The large Hamon grab (0.25 m 2 ) highly under-estimated the ophiuroid density, while the Smith McIntyre appeared adequate among the tested sampling grabs. Nowadays, diving sampling, underwater photography and videos with remote operated vehicle appear to be the recommended alternatives to estimate the real density of such dense slow-moving mobile epifauna.
1 :  Morphodynamique continentale et côtière (MCC)
CNRS : UMR6143 – INSU – Université de Caen Basse-Normandie – Université de Rouen
2 :  Laboratoire d'Océanologie et de Géosciences (LOG)
CNRS : UMR8187 – Université Lille I - Sciences et technologies – Université du Littoral Côte d'Opale
3 :  Institut des Sciences et Techniques de la Mer (INTECHMER)
Conservatoire National des Arts et Métiers (CNAM)
4 :  Station biologique de Roscoff [Roscoff] (SBR)
CNRS : FR2424 – Université Pierre et Marie Curie (UPMC) - Paris VI
Planète et Univers/Interfaces continentales, environnement

Sciences de l'environnement/Milieux et Changements globaux
Ophiothrix fragilis Epifauna Benthic sampling English Channel Grabs Video