Uptake patterns of the hydrocarbon material indicate that rapid 

 depuration of fresh oil characterized the Mytilus samples during the 

 early months of the spill and throughout the following year degraded 

 Tsesis petroleum was present in Mytilus tissues. One year after the 

 spill, much of the petroleum was gone from mussel tissue except at 

 station C from which samples continued to exhibit aliphatic and aromatic 

 petroleum hydrocarbons in their tissues. This was presumably due to the 

 greater initial exposure of the Mytilus population to oil at this station. 

 Macoma, on the other hand, received a sizeable petroleum impact during 

 the early stages of the spill probably due to direct sedimentation of 

 the oil. After apparent depuration occurred during the winter, a secon- 

 dary impact was observed, especially at station 20. The transport path 

 of this secondary oil might include (1) landfall, (2) sinking at the 

 shoreline with age, and (3) transport and redistribution throughout the 

 30-meter-depth basin of which station 20 is at the bottom. It is possi- 

 ble that as the water temperature increased and pumping rates of both 

 Mytilus and Macoma increased, the increased activity aided in the depura- 

 tion of the former and recontamination of the latter. 



The station 20 location appears to be at the focus of the benthic 

 impact of the spill which is observed at all benthic stations (station 2 

 west of Fifong Island included) except for station 15, the control 

 station south of the island of Askb*. Macoma balthica appears to be an 

 excellent indicator of pollutant input to the benthos. As was previous- 

 ly suggested by Shaw et al. (1976), Macoma apparently receives material 

 identical in composition to that captured in the sediment traps. It is 

 puzzling why, even with careful sampling of surface sediment, the direct 

 confirmation of the presence of oil in sediment is ambiguous at best. 

 Bieri and Stamoudis (1977) were also unable to directly confirm the 

 presence of fuel oil in sediment in their experimental oil spill in 

 spite of its obvious presence in benthic organisms. The hydrocarbon 

 material present in the fine floe at the sediment/water interface is 

 difficult to sample even with careful grab or core sampling. Thus, the 

 sedimented hydrocarbons from the Tsesis spill may reside at this diffi- 

 cultly sampled, highly mobile pseudo-surface from which Macoma obtains 



270 



