Effects of water flow and drilling waste exposure on polyp behaviour in Lophelia pertusa

Abstract

Polyp expansion state in Lophelia pertusa was studied in situ close to an oil rig during the drilling of a well (Statoil) off mid-Norway, in order to study possible effects on behaviour. The expansion state was monitored visually during the discharge of drill cuttings at one reef exposed to discharges and one not exposed. The reef situated down-current from the discharge point was monitored during 5 days and 15 h with a benthic lander equipped with a stills camera and current meter. This reef was exposed to drill cuttings 11 times during the monitoring. The total exposure time was 13 h 37 min. A remotely operated vehicle was used to provide additional images from both reefs for comparison. The proportion of polyps in different expansion states did not differ significantly between exposed corals and unexposed corals. Rather, changes in polyp behaviour were related to changes in current direction and velocity. A higher proportion of the polyps was expanded during periods with prevailing northeasterly currents compared to northwesterly. This could be related to quantity and type of food particles or the polyps' local position in the colony relative to current direction. There was also a clear difference in the degree of polyp expansion between polyps situated high up in the colony compared to low. This may be related to local environmental differences representing different hydrodynamic conditions. Whether or not there are effects of exposure to drill cuttings over a longer timescale than the observed 5 days and 15 h cannot be concluded from this study.