Lancaster SERPENT visit report

Abstract

The SERPENT project carried a collaborative research mission with Hurricane Exploration (HEX) at the
Lancaster exploration well in August 2009. The well was drilled from the Byford Dolphin, west of
Shetland. The study was designed to investigate benthic biological diversity with particular reference to the
effects of disturbance on the seabed resulting from the drilling activities. Photographic and quantitative
video methods were used to observe benthic megafauna and demersal fish using a Spartan workclass
industrial ROV, collecting digital stills images and close-up video when possible. Physical data were
collected throughout the mission. In addition bait was deployed to attract fish to the ROV cameras. The
observations are archived in the SERPENT database. An experiment was carried out to assess the effects of
physical disturbance on the asteroid Porania pulvillus.
Mean seabed temperature was 10.2oC and salinity was 35.4. Maximum water temperature was 13.9oC in the
surface waters (9m) and the thermocline was at 100m. Current data were collected for a 48 hour period
during the visit. The current was tidally reversing with a mean velocity of 10.52 cm s-1 with dominant water
movement from southwest to northeast.
Drill cuttings extended to at least 60m from the BOP and beyond 100m to the north and west. The cuttings
pile was a maximum of 2m in height around the BOP reducing to around 400mm at 7m from the BOP and
was between 50 and 150mm at 15m from the BOP.
This disturbance resulted in a reduction in megafaunal density within 30m of the well and an increase in the
scavenging hermit crab Pagurus prideaux in impacted areas of sediment, particularly between 30-50m from
the BOP and measures of species diversity (S and H’) increased with distance from the source of the
disturbance.

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