Publication Abstract

Linking backscatter, particle-size distributions and infaunal data – results from the Dogger Bank, North Sea

Linking acoustic backscatter with seabed sediment properties as well as faunal communities via ground-truthing is crucial in habitat mapping, yet such links are only partly understood and often rely on expert judgement. Correlating backscatter with grain-size previously employed average statistics, but these are often inappropriate and do not allow for investigations into links with fauna. We therefore explored correlations in multibeam backscatter, sediment particle size and infaunal species abundance data from the Dogger Bank using multivariate techniques. The acoustic data consisted of backscatter intensity extracted from a circle of multibeam data (40 m diameter) around sampling sites. These values were used to construct histograms according to backscatter intensity, detailing the percentage occurrence of each 1 dB class. Backscatter histograms were examined using the SIMPROF routine, PRIMER v6, which identified seven genuine clusters. The clusters broadly fell into a group of high backscatter characterised by peaks in the histogram between –13 dB and –19 dB and a low backscatter group peaking between –24 dB and –31 dB. Similar analyses were performed on particle size and infaunal species abundance. Sediment particle size comprised five genuine clusters. One cluster was largely characterised by coarse sediment fractions whilst the others were fine to medium sands with varying proportions of mud and gravel. Infaunal species abundance data comprised two genuine clusters, of which Group 1 was characterised by Bathyporeia elegans, Magelona filiformis and Echinocyamus pusillus. Species that mainly contributed to the similarity within Group 2 included Notomastus sp., Glycera lapidum and Protodorvillea kefersteini and Nemertea. Group 1 coincided with sediments characterised as fine to medium sands and low backscatter whilst Group 2 was associated with coarse sediments and high backscatter.

Similarities in multivariate patterns between the three data sets were further explored using the PRIMER routine RELATE which measures how closely related two sets of multivariate data are by calculating a rank correlation coefficient between each component of their respective similarity matrices. Results indicated a significant correlation occurred between the multibeam backscatter and the sediment particle size (ρ = 0.673, significance = 0.1%) and also between the sediment particle size and the infaunal species abundance (ρ = 0.64, significance = 0.1%). However, whilst correlations between the multibeam backscatter and infaunal species abundance were significant (ρ = 0.466, significance = 0.2%) they were less pronounced than in the other comparisons.

This work results from a survey undertaken by Cefas, BGS and Envision Mapping on behalf of the JNCC, as part of its Offshore Natura Seabed Survey Programme.

Reference

Suzanne Ware*, Markus Diesing* (2009) Linking backscatter, particle-size distributions and infaunal data – results from the Dogger Bank, North Sea. NGF Abstracts and Proceedings, 2: p. 84.