Publication Abstract

Mapping sediment biotopes as continuous distributions rather than discrete entities with hard boundaries

P.D. Eastwood, S. Souissi, S.I. Rogers, R.A. Coggan and C.J. Brown

Seabed biotopes can be mapped and classified using a combination of acoustic systems and biological sampling. Biotopes classified in this way are described in terms of their key physical and biological characteristics and are visually presented as defined regions with distinct boundaries. This approach to seabed mapping is most suited to epi-benthic environments where relatively clear demarcations between biotopes are encountered, such as between reefs, seagrass beds, and mobile sediments. Where the benthic environment consists largely of sediment populated mostly by infaunal communities, changes in the physical structure of the seabed will be more gradual and result in a progressive shift in the structure of the biological assemblages. We present an approach to habitat mapping for sediment communities where boundaries between biotopes are indistinct. The approach combines multivariate classification, Bayesian statistics, and geostatistics to arrive at a series of continuous representations of the distribution of each biological community. Acoustic data (100% sidescan coverage) and biological data (from ground-truth sampling) collected from an area of seabed in the coastal waters of south-east England were used to assess the validity of the approach and demonstrate its application. A biotope map for the study area was produced showing the maximum likelihood of encountering a particular assemblage at each geographic location. We also compared output maps developed using a purely objective classification of the biological data with one developed from a supervised classification where the grab samples were assigned to one of eight acoustically distinct regions of the seabed. The latter approach arrived at a set of biotopes that were more clearly defined in terms of their spatial distribution and characterising species.

Reference:

P.D. Eastwood, S. Souissi, S.I. Rogers, R.A. Coggan and C.J. Brown. 2004.Mapping sediment biotopes as continuous distributions rather than discrete entities with hard boundaries . ICES ASC Vigo, Spain, 2004