Effects of a former discharge of drill cuttings on the macrofauna community

As part of the ICES/IOC Bremerhaven Workshop, the macrofauna near a former drilling site for gas in the southern North Sea was investigated. Three years prior to the present investigation oil-contaminated drill cuttings had been discharged at the locality. Shortly after this operation had stopped, a macrofauna survey was carried out which showed effects at the drilling site and revealed a gradient of increase in species abundances and richness in the residual current direction from the discharge point. During the present study 9 stations along the same transect were sampled, up to a distance of 15 000 m from the drilling site. In order to assess whether the initial gradient still existed, several univariate and multivariate methods were applied to the data set. Univariate methods showed decreasing trends in species number, biomass and total abundance within 1000 m (Stn E) of the drilling site. The abundances of some deep-burrowing species were low, particularly near the drilling site. However, differences between the stations were in many cases not highly significant. Cluster analysis and ordination with DECORANA and Multidimensional Scaling produced station patterns which point to a dependence between distance from the discharge site and the composition of the macrofauna. ABC curves of the stations did not show any major changes along the transect. Photographic evidence that conditions in the upper sediment layer improved after 1988 is discussed together with the results of the meiofauna and bioassay work.