(2008), may result in damage to L. pertusa colonies. Still, evidence of extensive growth of L. pertusa on offshore platform

legs even after many years of discharge of OBM cuttings ( Bell and Smith, 1999) suggest that the corals must be rather tolerant to drilling waste. Video monitoring carried out during WBM cuttings discharge episodes at the Norwegian Morvin field in 2009 and 2010 revealed no significant behavioural differences between exposed and unexposed L. pertusa ( Buhl-Mortensen et al., 2010). Polyp retraction responded more systematically to changes in current velocity and direction than to cuttings plumes. Adriamycin mouse In conclusion, it is evident that discharged WBM cuttings may cause biological effects

both during suspension in the water masses and after sedimentation. The studies indicate that the effect mechanism is mainly physical stress, but chemical toxicity cannot be ruled out. The levels of suspended WBM and WBM cuttings causing effects have been above 0.5 mg L−1. Such levels are typically restricted to a radius of less than 1–2 km in the water masses (Neff, 1987). WBM cuttings deposits found to affect EX 527 the benthos have a thickness of at least 3 mm or more. Such layer thicknesses will normally be confined to a distance of 100–500 m (Carr et al., 1996, Currie and Isaacs, 2005, Daan and Mulder, 1996, Ellis et al., 1996, Montagna and Harper, 1996, Neff, 1987 and Trannum, 2011). Still, the

WBM cuttings discharges are large and frequent, and the material widely dispersed and one cannot rule out that they in the long run may cause subtle changes to the benthic community structure on a wider geographical scale than this. One must assume that it will be extremely difficult to distinguish such effects from the temporal shift in the benthic community one sees on the NCS (Brattegard, 2011). It has not yet been feasible to document effects of PW discharges on the population and community levels. Most of the laboratory and field studies described above support the conclusion Methisazone that significant biological effects on pelagic organisms will be limited to a distance of less than one km due to rapid effluent dilution and very short exposure time. Knowledge on individual sensitivity is a prerequisite, but not sufficient, for assessing effects on populations and communities. Phyto- and zooplankton populations and most fish species have a much wider distribution than the documented PW impact zones. Hence, for a significant impact to occur either harmful exposure to PW has to be sufficiently wide scale or the population influence from locally affected individuals has to be large enough. None of these are likely. It is also inherently difficult to make reliable extrapolation to the population level since effects on individuals may be masked by other factors acting on populations e.g.