Angola Block 18WAD and Block 31 pre-operational environmental survey, October 2005: analysis of seabed images taken using WASP (Wide-Angle Seabed Photography)

This report details seabed observations carried out on behalf of BP Angola for an environmental survey of Angola Blocks 18 and 31 (bathyal SE Atlantic). Seabed photography (still and video) was undertaken with the NOC WASP vehicle. The WASP deployments spanned water depths of 1550-2050m over the Angolan Margin and included studies on the open continental slope and on and around seabed pockmarks and salt diapirs. The shallower sites (Block 18; 1550-1650m) were dominated by small elpidiid holothurians. At intermediate depths (Block 31; c. 1800m) the megabenthos was dominated by the holothurian Scotoplanes globosa. The deeper sites (Block 31 >1900m) were dominated by the spatangoid urchin Pourtalesia alcocki. Two ‘local variant’ faunas were recognized; one associated with the elevated topography of salt diapirs and dominated by ophiuroids. The other from a large seabed pockmark with a highly abundant population of Pourtalesia alcocki (mean abundance 39.56 10m-2; maximum 108.88 10m-2) and also notable for the presence of fragments of cemented sediment, large numbers of dead bivalve tests (including Vesicomyidae Calyptogena-type), squat lobsters (Munidopsis sp.), a bacterial mat and a possible tubeworm (? Siboglinidae). All the latter observations suggest the possibility of fluid flow / cold seep conditions in the vicinity of the pockmark. Should you wish to consult or cite this report please contact the author directly (Brian Bett, bjb@noc.soton.ac.uk, +44 (0)23 80596355).