Whirlwind Recovery SERPENT report

Abstract

This document reports the results of SERPENT’s work at Hurricane’s Whirlwind site at 185 m depth in the north east Atlantic, west of Shetland, UK. The report focuses on the work carried out over two visits to the semisubmersible drilling rig Wilphoenix in 2011. These visits were the latest in a series of four visits to the Whirlwind location and part of a wider collaboration with Hurricane at Whirlwind and Lancaster involving six visits to Hurricane’s offshore operations in the area since 2009.

The Whirlwind project used work-class and observation-class remotely operated vehicles (ROV) launched directly from the drilling rig to explore marine biodiversity at the seabed in the vicinity of the drilling operations and monitor changes in biodiversity over time. Surveys took place immediately after drilling began, a month later and after a year of no further disturbance.

In total sixty one megafaunal species have been observed at Whirlwind and Lancaster since 2009. Most species have been recorded at both sites. Quantitative video surveys suggest the dominant species are the cnidarians Metridium sp. and hormathiid anemones, the crustaceans Pagurus sp. and Munida sp. and the echinoderm Porania pulvillus.

In 2011 there was evidence of a reduction in area of seabed visibly impacted by drill cuttings. The area of complete coverage of the seabed around the well reduced from 7054 m2 to 1433 m2. A relatively stable area of cuttings persisted close to the well, extending to approximately 20 m. Comparison of measurements from marker buoys deployed before drilling suggest that the vertical accumulation of cuttings had not reduced.

Megafaunal abundance and diversity were both higher in 2011 compared to 2010 suggesting evidence for recovery, although abundance remained low in the area closest to the well. There was photographic evidence for colonisation of the cuttings close to the well in the form of polychaete tube worms that were abundant on the soft sediment of the drill cuttings.

At Whirlwind a protective structure had been placed over the well for the period between the end of drilling in 2010 and when the operations began again in 2011. This had been colonised by numerous organisms including a coverage of hydroids which provided a habitat for many invertebrates and fish. Most notable were at least 10 large European Conger that were living within the structure.

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