IMPACT OF OFFSHORE OIL PRODUCTION INSTALLATIONS ON THE BENTHOS OF THE NORTH-SEA

Input of contaminants into the sea associated with offshore oil drilling and production include accidental spillage, discharge of cuttings and discharge of production water. Of these, oil discharged on drilling cuttings is by far the greatest source of oil pollution in the North Sea from these operations, having peaked in 1985 at 25 880 tonnes. The response to the seabed fauna to these inputs has been shown to follow established patterns in which there may be high individual abundance of a few species close to the source of contamination (organic enrichment effect) or a reduced number of individuals with few species close to the installation (smothering or toxic effect). Diversity shows a similar pattern to species richness, both are low in the immediate vicinity of the installation and, in most cases, attaining preoperational levels within 2000. High levels of hydrocarbon contamination have also been shown to be concentrated around installations. There are indications that a fall in diversity can be expected when total hydrocarbon concentrations in the sediment reach 50-60 ppm. There is also increasing evidence to suggest that for some areas where there has been intensive drilling/production activity (e.g. Shetland Basin), there has been a significant rise in hydrocarbon levels in the sediment at distances between 5 and 10 km from installations. © 1992 International Council for the Exploration of the Sea.