Habitat point records from 1990 OPRU Sullom Voe sublittoral monitoring

The report describes the results of a macrobenthic survey carried out in Sullom Voe by the Oil Pollution Research Unit (OPRU) for the Shetland Oil Terminal Environmental Advisory Group (SOETAG). This survey was completed in conjunction with a chemical monitoring programme carried out by the Scottish Marine Biological Association (SMBA). Hydrocarbon samples from three stations were obtained and analysed for correlation with biological data by OPRU. In 1984 nine stations in Sullom Voe and a transect in Garth's Voe were sampled to provide a quantitative description of the benthic macrofauna. The particle size composition of the sediments was investigated at all stations. Sediment analysis gave similar results to previous years. The sediments in Garth's Voe had a high proportion of mud and were relatively uniform with the exception of station 6 which was very different from the other sites and from recorded values at this station from previous years. Glc analysis of sediments for hydrocarbons content at stations 9, 10 and 12 indicated heavily degraded residues derived from petrogenic inputs, probably due to oil industry activity. The bulk of undegraded hydrocarbons, i.e. resolved peaks, were atributable to biogenic sources such as Sphagnum moss. Sediment parameters , particularly percentage mud, were the most important factors correlating with the distribution of hydrocarbons. Qualitatively, the fauna found in 1984 was similar to that described in previous years. Quantitatively, numbers of taxa in 1984 had increased slightly since 1983, as had the diversity index values which were calculated. Weathered oil was observed during sorting of samples from stations 10 and 12 in the previous years, but not in 1984. However, a small amount of oil was found in one sample at station 11. Diversity and numbers of taxa had increased at stations 11 and 12, reversing the two-year downward trend. In the absence of hydrocarbon data there is no corroborative evidence to link the absence of weathered oil in the 1984 biological samples to the reversal of the trend. The number of amphipod taxa had increased throughout the Voe, to levels more comparable with recent years, but numbers of individuals were still reduced. It is not generally considered feasible to use amphipods as pollution indicators, due to the problems in sampling and natural population fluctuations, however, such a large decline is worth noting. SMBA reports to SOTEAG 1979-1983 (Stanley and Pearson, 1980, 1981, 1982, 1983; Stanley et al., 1984) showed a gradual increase in the numbers of stations in the Voe becoming 'mildly polluted'. Amphipod densities and distributions showed no similar pattern, and amphipod numbers have not followed patterns associated with pollution incidents in other areas. It is concluded that the large decrease in numbers of individuals were caused by natural fluctuations. Biological data in 1984 showed the presence of a distinct gradient away from the Port Authority jetty, which does not correlate with sediment composition or percentage organic matter. In addition Garth's Voe may be acting as a sink for contamination from other areas of the Voe to some extent, as a result of its high mud content (Woodman, 1984).

Organization: Joint Nature Conservation Committee