Assessment of the ecological impact of an oil spill on shallow brackish-water benthic communities: a case study in the northeastern Baltic Sea

Abstract

The relationship between the abiotic environment and the structure of macrozoobenthos was studied in shallow bays of the southwestern Gulf of Finland, the Baltic Sea, that were impacted by a moderate oil spill in 2006. Seabed sediment characteristics, depth, and wave exposure best explained the structure of benthos. Statistical analyses did not show explicit effects of oil on benthos. The decrease in the abundance of Bathyporeia pilosa and Macoma balthica may be related to the oil, but it would be speculative to attribute this pattern solely to the spill without a proper before- after-control-impact (BACI) design with several control locations. Our study clearly showed that in the case of accidental environmental impacts like oil pollution it is impossible to apply a proper setup of the BACI design. This leads to difficulties in distinguishing between the effects of natural environmental factors and oil on the biota. The study also advocates for needs of alternative methodologies in order to effectively assess the impacts of accidental anthropogenic disturbances on benthic communities.