Publication Abstract

The South Coast Regional Environmental Characterisation

The South Coast Regional Environmental Characterisation

J.C.W. James, B. Pearce, R.A. Coggan*, S.H.L. Arnott, R. Clark, J.F. Plim, J. Pinnion, C. Barrio Frójan*, J.P. Gardiner, A. Morando, P.A. Baggaley, G. Scott and N. Bigourdan

http://www.alsf-mepf.org.uk/projects/2008/rec-0802/final-report.aspx

This is an ALSF funded study of an area to the east, south and west of the Isle of Wight, English Channel, from 2°W (Poole) to 0°W (just beyond Brighton). 

Executive summary

The South Coast Regional Environmental Characterisation (REC) is a multidisciplinary marine study encompassing the geology, biology and archaeology of an extensive area – 5600 km2 — of the English Channel which has been funded by the Marine Aggregate Levy Sustainability Fund (MALSF).

The South Coast Region is an important source of marine aggregates with a long-standing history of extraction. The industry is actively looking for new extraction areas and these have to be assessed in the light of increasing pressure on sea bed use. The South Coast REC provides a context for these assessments.

Eleven principal objectives for the interpretation were set by the MALSF and these included the characterisation of rock, sediments and biological communities across the region. The biological and geological character of the region was also integrated in order to map the occurrence of biotopes as well as areas of potential conservation interest. Archaeological objectives were also set to distinguish, characterise and map wrecks and objects on the sea bed, and also characterise the potential of the area to contain submerged sites of prehistoric occupation. Finally the study was to identify any gaps in data, analysis and interpretation prior to and remaining after completion of the study.

The study was hampered initially by a relative lack of survey geophysical data but the partners actively procured further survey data and this with sample coverage has mitigated the issue to a reasonable, if not complete, extent. These datasets have provided the basis for an adequate perspective of the regional character of the geology, biology and archaeology of the study area.

The South Coast REC area is characterised by large expanses of rock and thin sediment, with approximately 75% of the sea bed dominated by habitats resting on a rock based foundation. Thick (>1 m) sediment is confined to channel systems, banks and sand sheets with about 14% of the study area covered by sandy sediment and 11% covered by coarse sediment. Marine aggregate extraction and prospecting is confined to these areas of thicker sediment, particularly coarse sediment, rather than across the REC area as a whole.

Extensive areas of sand are limited to sand banks within the inner parts of Poole Bay and Christchurch Bay and the Northern Palaeovalley and sand sheets and wave fields on the coastal platform off West Sussex.

The sea bed south of the Isle of Wight is an area of relatively strong tidal currents with a winnowed sea bed comprising mostly immobile coarse sediment with cobbles and rock.

The complexity of the sediment filled channel systems which have been identified have not been adequately characterised during the study. A greater density of seismic lines would add greatly to our understanding of these channel systems which are the principal aggregate resource in the study area.

Analysis of the benthic macrofauna revealed 13 discrete assemblages. This is a relatively large number and a reflection of the geological and morphological diversity which exists in this area. The predominance of rock and coarse substrate, across much of the area, also plays an important role in shaping the benthic macrofauna.

A number of benthic assemblages were associated with sand deposits, and characterised by interstitial polychaetes and the pea urchin Echinocyamus pusillus.

Six discrete epibenthic assemblages were identified and are a reflection of the diverse environmental conditions within the study area. The influence of the rock and coarse sediments was also evident in the epibenthic trawl samples.

A few new biotopes were discovered in the South Coast REC area and a number of issues were encountered in regional biotope modelling using the EUNIS habitat classification system particularly in areas of rock and thin sediment. It may be appropriate to modify the EUNIS classification system to take account of this type of rock and thin sediment substrate which is very common in the English Channel and elsewhere in UK waters.

A number of rare species were identified from the grab and trawl samples collected from the study area, the most notable being the sea squirt, Microcosmos claudicans and the colonial bryozoan, Hincksina fulstroides.

The invasive American slipper limpet, Crepidula fornicata, was found to be very well established across the South Coast REC study area forming an important component of the benthic and epibenthic assemblages. Other alien species identified include the leathery sea squirt, Styela clava and the barnacle Elminius modestus.

Surveys conducted for the South Coast REC have highlighted two features of conservation interest within the area, namely rocky reefs and black bream Spondyliosoma cantharus (L.) nests. The reefs are listed under Annex I of the EU Habitats Directive. The black bream is a commercially important species whose nesting sites occur where bedrock is covered by a thin layer of gravel. As the nests are vulner­able, they are being considered within local management plans.

The tubiculous amphipod, Ampelisca spp. and the sand mason, Lanice conchilega, were both found to form bed features in this area, together and individually. Whilst these biogenic features would not be classified as biogenic reef under the current Annex I definition, they are certainly unusual and their influence on environment and associ­ated fauna is not yet fully understood. A more detailed study on these small-scale biogenic features would be of value to both the scientific community and the conservation agencies.

The South Coast REC area is a region rich in archaeology, with finds ranging from the Lower Palaeolithic to the Second World War. Archaeological material found on or beneath the sea bed can be broadly divided into prehistoric, maritime and aviation and all categories are present in abundance.

The precise location of prehistoric archaeological material offshore is unknown at present but areas have been highlighted where there is a higher potential for the resource to survive. The characterisation indicates that, under the appropriate preservation conditions, there is potentially a very large resource of prehistoric archaeology present.

The maritime archaeological resource has been successfully characterised in respect of the late 19th century and more recently. However, no evidence from earlier periods was found and no conclusion can be drawn about the volume, distribution or character of the pre-19th century maritime activity.

The area has been a major focus for aviation throughout the 20th century. The vast majority of aircraft sites date from the Second World War and as most aircraft commonly break up on impact with the sea, wreckage is generally not intact on the sea bed. Therefore the distribution and location of aircraft crash sites are likely to be seriously underestimated.

http://www.alsf-mepf.org.uk/projects/2008/rec-0802/final-report.aspx

J.C.W. James, B. Pearce, R.A. Coggan*, S.H.L. Arnott, R. Clark, J.F. Plim, J. Pinnion, C. Barrio Frójan*, J.P. Gardiner, A. Morando, P.A. Baggaley, G. Scott and N. Bigourdan

British Geological Survey Open Report OR/09/51. 249 pp.