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ICES Journal of Marine Science: Journal du Conseil 2006 63(9):1604-1615; doi:10.1016/j.icesjms.2006.06.010
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© 2006 International Council for the Exploration of the Sea

The REBENT monitoring network, a spatially integrated, acoustic approach to surveying nearshore macrobenthic habitats: application to the Bay of Concarneau (South Brittany, France)

Axel Ehrhold*, Dominique Hamon and Brigitte Guillaumont

Ifremer, Département Dynamiques de l'environnement côtier, Technopole de Brest-Iroise BP 70, 29280 Plouzané, France

*Correspondence to A. Ehrhold: tel: +33 298 224319; fax: +33 298 224548. e-mail: axel.ehrhold{at}ifremer.fr.

A 200-km2 area in the Bay of Concarneau on the South Brittany coast was surveyed acoustically using different sidescan sonars (a 100-kHz EdgeTech DF1000, and a 240-kHz Reson SeaBat 8101). The area corresponds to a sector of the REBENT network. It was selected for its physical and biological characteristics, reflecting the sedimentary heterogeneity and biological diversity of Brittany's coastal seafloors. The work presented here illustrates the methodology for mapping subtidal seabed habitats in the context of the network. Backscatter mosaics were produced covering 100% of the survey area. Extensive ground-truthing was carried out involving 93 Shipek grab samples and 25 drop-down video profiles. From interpretation of the acoustic facies, 40 biological soft-bottom stations were sampled using a Hamon grab to characterize macrobenthic communities (>2 mm). The results indicated considerable variation in backscatter responses in relation to high densities of macrobenthic species (Lithothamnion, Asterias, Haploops, Maldane, Ophiocomina), and a wide variety of substratum types present within a relatively small area. Dense biocenoses of maerl were accurately surveyed from 20-m to <5-m depth (Lower Astronomical Tide; LAT). Boundaries of Haploops communities are associated with dense small pockmarks in the centre of the bay. The relationships between sediment sometimes colonized by macrobenthic species and backscatter responses are discussed.

Keywords: benthic habitats, grab sampling, maerl, ortho-rectified aerial photography, pockmark, sediment, sidescan sonar, submarine video

Received 3 June 2005; accepted 28 June 2006.


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