Publication Abstract

Mapping of gravel biotopes: an integrated approach

C.J. Brown, A.J. Hewer, W.J. Meadows, D.S. Limpenny, K.M. Cooper, and H.L. Rees

Four sites were selected in the eastern English Channel to assess the utility of seabed mapping techniques for surveying gravelly habitats. Each site was intensively surveyed using a digital sidescan sonar system. A mosaic of the sidescan sonar data was produced to provide 100% spatial coverage maps at each location. Each mosaic was then divided into acoustically distinct regions. The regions were sampled using a suite of physical sampling and optical techniques. The main sampling tools were a 0.1m2 Hamon grab fitted with a video camera and light and a heavy duty 2m beam trawl which were used to characterise the benthic communities and sediment characteristics within each region. Relationships between acoustic regions, physical habitat characteristics and assemblages were then investigated using a range of statistical techniques. Results from these analyses were used to identify discrete biotopes at each site. In acoustic regions where there was a high degree of sediment homogeneity within discrete habitat boundaries, statistically distinct assemblages were identified. The situation was less clear where the seabed consisted of a complex arrangement of sediment types.

Further work is currently underway to evaluate these and other techniques in soft sediments and at different spatial scales.

Reference:

C.J. Brown, A.J. Hewer, W.J. Meadows, D.S. Limpenny, K.M. Cooper, and H.L. Rees, 2002. Mapping of gravel biotopes: an integrated approach. ICES Copenhagen, CM2002/K:01, 18pp.