title: 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.
abstract: 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 high-density 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.
authors.affiliation: Université de Lille 1, Station Marine de Wimereux, UMR CNRS 8187 LOG, 28 Avenue Foch, BP 80, 62930 Wimereux, France. sophie.lozach@unicaen.fr
authors.forename: Sophie
authors.initials: S
authors.lastname: Lozach
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Dauvin
authors.forename: Yann
authors.initials: Y
authors.lastname: Méar
authors.forename: Anne
authors.initials: A
authors.lastname: Murat
authors.forename: Dominique
authors.initials: D
authors.lastname: Davoult
authors.forename: Aline
authors.initials: A
authors.lastname: Migné
mesh_terms: D000818:Animals; D059001:Aquatic Organisms / Q000145:classification / Q000254:growth & development / Q000502:physiology; D001267:Atlantic Ocean; D044822:Biodiversity; D004242:Diving; D004447:Echinodermata / Q000254:growth & development* / Q000502:physiology; D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods*; D005602:France; D010781:Photography / Q000379:methods; D011156:Population Density; D014743:Videotape Recording / Q000379:methods