Mesocosm experiments on the effects of produced water discharges from offshore oil platforms in the northern North sea

Abstract

The effect of ‘produced water’ (an oily-water discharge from production platforms) on several pelagic trophic levels including fish larvae were investigated using 300 m³ columnar plastic enclosures. The produced water (at a concentration equivalent to a point 0.5-1 km downstream from the discharge point) caused an increase in bacterial biomass but only had a transient, slightly depressant, effect on the rate of primary production by phytoplankton. The most noticeable effect was on the copepod populations where considerable mortality occurred in the early naupliar stages in the treated enclosures. No increased mortality was observed in cod (Gadus morhua L.) and herring (Clupea harengus L.) larvae although in the latter an increase in the activity of the enzyme aryl hydrocarbon hydroxylase (AHH) was correlated with the addition of the pollutant. Indirect food-chain effects were noticed since the reduction in the copepod numbers resulted in increased phytoplankton standing stocks and in reduced growth of the larvae.