The impact of the Braer oil spill on the macrobenthic infauna of the sediments off the Shetland Islands

Following the wreck of the oil tanker Braer, a study of the benthic fauna in areas of sea-bed contaminated by oil was carried out. The results showed that no significant changes in benthic community structure, as characterized by species richness, individual abundance and diversity could be related to the areas of sea-bed affected by the Braer oil spill. The major factors determining the distribution of species in the affected areas appeared to be primarily related to the nature of the sediments, and not the degree of oil contamination. However, the levels of petroleum hydrocarbons in the most heavily contaminated sediments were sufficiently high to have eliminated sensitive groups such as the Amphipoda and encourage species associated with oil pollution, but the overall numbers of species involved and their abundances were too small to significantly affect community structure. There is no evidence from the analysis of species abundance distributions that mass mortality of the benthos took place at any time after the Braer oil spill, although there are indications that a few species may have been eliminated and were recruiting at the time of the survey. The lack of evidence of major impact from the spill indicates that either the Braer oil was of such low toxicity as to not significantly disrupt benthic community structure, or that the sampling programme was carried out too soon after the spill to enable the full effects of its impact to be detected.