The ?Tsesis? oil spill: Acute and long-term impact on the benthos

The Tsesis oil spill in October 1977 resulted in the release of over 1,000 tons of medium grade fuel oil in an archipelago in the brackish Baltic Sea. Considerable oil quantities reached the benthos by sedimentation. Within 16 d benthic amphipods of the genus Pontoporeia , as well as the polychaete Harmothoe sarsi Kinberg, showed reduction to less than 5% of pre-spill biomasses at the most impacted station. The showed little or no mortality, but was heavily contaminated by oil (about 2,000 mu g g super(-1) dry wt total hydrocarbons). The meiofauna was strongly affected, with ostracods, harpacticoids, Turbellaria and kinorhynchs showing clear reductions in abundance, while nematodes, as a group, were more resistant. In the winter following the spill gravid Pontoporeia affinis Lindstroem females showed a statistically significant increase in the frequency of abnormal or undifferentiated eggs. Food-chain transfer of oil to flounder (Platichthys flesus (L.)) was indicated. Full recovery is likely to require more than 5 yr and may take a decade or more.