Benthos supported by the tunnel-valleys of the Southern North Sea

The tunnel-valleys of the southern North Sea are arcuate and linear seabed depressions. The origin of these features has been the subject of much discussion, but they are generally considered to have been formed by subglacial erosion and sediment backfill beneath the outer margins of a receding ice sheet. We present here a study of two tunnel-valleys, the Silver Pit and the Sole Pit. Extensive areas of Sabellaria spinulosa reefs have been identified on the western flanks of the Silver Pit that extend down to the valley floor, representing a resource of significant conservation interest. The eastern flanks were found to support a diverse faunal assemblage with widespread hydroid and bryozoans turfs and abundant ascidians. The seabed of the Sole Pit is characterized by much sandier deposits than that of the Silver Pit, and it supports an abundant bivalve community, dominated by Abra alba. This bivalve assemblage also contains Coarcuta obliquata, which has only been recorded once before in the UK.