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This study examined the occurrence of Lophelia pertusa on North Sea oil infrastructure and its environmental sensitivity to oil and gas activities. Underwater videos from industry platform surveys were examined to identify L. pertusa, detail its occurrence at two sites (Heather and North Alwyn A (NAA)), and to look for evidence of exposure to drilling muds and cuttings (discharges). In addition, live corals were exposed to 4-h sedimentation events of increasing rates and polyp behaviour analysed. Sediment removal mechanisms were also examined. Finally, skeletal characteristics and trace metal concentrations were measured in skeletons sampled from platform sites exposed to drilling discharges and control sites. The results showed a newly established sub-population of L. pertusa in the northern North Sea. L. pertusa was identified on 14 platforms and 947 colonies were recorded on Heather and NAA between 59 to 132 m depth coinciding with the presence of year round Atlantic water. Original recruits were likely from the northeast Atlantic and are now annually self-recruiting to the platforms. Additional video from Tern in 1993, 1994, 1998, and 2002 provided the first in situ colony growth rate (26 ± 5 mm yr-1) for L. pertusa. Visual evidence of contamination from drilling discharges was limited to colonies close to drilling discharge points where partial and complete colonies were dead. Polyp behaviour was negatively affected only at the highest sedimentation rates (12-19 mg cm-2 min-1), which are likely to be significantly higher than in situ rates, and polyps cleared sediment with ciliary currents and ingestion, which may be an indiscriminate feeding response. Corals exposed to discharges had shorter and narrower corallites compared to controls but other causal factors merit consideration such as genetics and hydrography. Further results showed that polyps bud annually and reach their maximum height in their first year, while the theca thickens at a constant rate, thus implying that the innermost growth band likely represents the first year of growth. Relatively depleted δ13C and δ18O along the inner growth band, which indicates fast calcification, supported this result. Copper and barium in coral skeletons including visible detrital inclusions were significantly higher in exposed versus control colonies. Chromium and barium along the growth axis, avoiding detrital inclusions, showed one exposed polyp from a colony living two meters above the cuttings pile on North West Hutton (NWH) with higher barium compared to control colonies. Short-lived barium spikes were observed in two polyps from a control colony sampled from North Cormorant. It is hypothesised that the NWH coral may have been exposed to dissolved barium released during cuttings resuspension, while barium spikes in the control colony may result from natural fluctuations in seawater barium, thus advocating that L. pertusa can act as an archive of the marine environment. |
