clearly not a reliable indicator of the total area affected. Within 

 this affected area (shown by oil analysis), benthic macrofauna community 

 responses varied from a slight and temporary decrease in abundance of 

 motile species, especially Pontoporeia femorata, to a drastic and last- 

 ing reduction in amphipods (Pontoporeia af finis and P. femorata ) . The 

 disappearance was possibly caused by emigration from the contaminated 

 area, since very few dead specimens were found. In laboratory experi- 

 ments, Pontoporeia af finis has been shown to actively avoid oil con- 

 taminated sediments. However, even at the most affected station, the 

 sedentary macrofauna species remained with no observed increases in 

 mortality. The few remaining gravid amphipods showed a statistically 

 significant increase in the number of abnormal eggs at the most affected 

 station. 



Of the meiofauna, all taxonomic groups except the nematodes showed 

 abnormally low abundance at the most affected station and there was 

 evidence of greatly increased mortality of ostracods following the 

 spill . 



As late as August and September the following year, 10 months after 

 the spill occurred, there was still no sign of recovery of the affected 

 groups of macro- and meiofauna. The oil content of Macoma balthica , 

 which had initially shown some decrease, increased again in August to 

 values even higher than the highest recorded earlier, one month after 

 the spill. Whether this increase is a real increase due to a new influx 

 of oil, presumably mobilized from shallower sediments, or just an expres- 

 sion of considerable patchiness in the oil distribution, is uncertain. 

 It supports the hypothesis that the breakdown of oil in such sediments 

 is very slow, and that a prolonged period may be needed for full recovery. 



Because of the long life-cycle (two years) and non-migrating be- 

 havior of ostracods, the effects of the oil on the soft bottoms will 

 remain for at least two years. Most other meiofauna groups have a much 

 shorter life-cycle and can recolonize the bottoms shortly after the oil 

 is degraded. The amphipods, P. af finis and P. femorata have a more 

 mobile lifestyle and are expected to invade the area very quickly after 

 the oil is degraded. 



48 



