Publication Abstract

A new habitat map of the British part of the English Channel

Diesing*, M., Stephens*, D., Coggan*, R.

Worldwide, the oceans and marginal seas are under increasing pressure from human activities and there is an ever greater need for good habitat maps, both to underpin environmental and socio-economic impact assessments and to help in the development of effective management measures that will contribute to our responsible stewardship of the marine environment and the sustainable use of its resources. The development of habitat mapping is now driven more by specific policy needs than our innate desire to explore our world. For example, the European Union’s Marine Strategy Framework Directive requires better habitat maps than exist at present to support assessments of the status of the seabed and the proportion of each habitat significantly affected by human activities. We report on methodological developments that can be applied to provide better predictive habitat maps.

We present a case study to develop an improved habitat map for the British part of the English Channel. At its heart is a more realistic representation of seabed substrate types than has been available in standard seabed sediment maps. We have used geostatistical predictions and terrain modelling techniques, validated against observational data sets, to map seabed substrates and used this to model the distribution of rock and sediment habitats according to the EUNIS (European Union Nature Information System) classification.

We applied a hybrid spatial prediction model to map sediment composition using both spatial autocorrelation and correlation with auxiliary predictors (bathymetry and derivatives thereof, wave and tidal shear stress, etc.). The proportion of sand, mud and gravel were then analysed to classify the sediments according to Folk textural classes and the EUNIS habitat schema.

Morphologically distinct bedrock outcrops were extracted from a detailed bathymetric data set (30 m by 30 m bins). Several measures of rugosity were tested using a training data set for their ability to discriminate between rock and non-rock. The Vector Ruggedness Measure was selected for use, applying a cut-off value to discriminate flat from rugged terrain. The latter class included subaqueous dunes and sandbanks which were subsequently separated from rock outcrops.

The sediment predictions and the bedrock layer were unified to yield a substrate map. This layer was finally intersected with modelled biological zones (infralittoral, circalittoral and deep circalittoral) and hydrodynamic energy at the seabed to derive the EUNIS habitat model.

Reference:

M. Diesing*, D. Stephens* and R. Coggan* (2011) A new habitat map of the British part of the English Channel. Bulletin of the Geological Society of Finland, Vol 83, Special Issue 1: p. 32.