Oil Spill Effects 403 

 Zooplankton 



The major effect of the oil spills on the ponds was the rapid kill of the 

 zooplankton. O'Brien (1978) studied the animals during the Pond Omega 

 experiment and showed the great sensitivity of the fairyshrimp and 

 Daphnia and the lesser sensitivity of the copepods (Table 9-5). In pond E, 

 which received 10 times more oil than Pond Omega, the copepods were 

 eliminated in 1970 but a few were found in 1971 (Table 9-6). Some animals 

 of each species were present at the beginning of every year, presumably 

 due to transfer of animals during the spring flooding of the tundra. These 

 were killed each year by the small amounts of the water-soluble fraction 

 (WSF) released each year from the oil in and near the pond (Figure 9-1). 

 Daphnia did not return to Pond E until 1977 (Butler and Keljo personal 

 communication); therefore, production of the zooplankton community 

 was extremely low even though some copepods were present (Table 9-7). 



The differential sensitivity of the zooplankton to oil was confirmed in 

 aquarium studies of O'Brien (1978). Daphnia were killed at all levels of 

 added oil including 0.2 ml oil liter "^ or about 15% of the Pond Omega 

 treatment level. Fairyshrimp were most sensitive, Daphnia next, 

 Heterocope next, and Cyclops least, exactly duplicating the field results of 

 Table 9-5. The toxicity could be eliminated by vigorous aeration. 



The results of the pond studies are similar to those from other marine 

 and freshwater studies. For example, Busdosh and Atlas (1977) found that 

 3.0 ml liter "' of Prudhoe crude oil killed marine amphipods and that it 

 was the WSF that was toxic. A tidepool copepod was killed by 1 ml diesel 

 oil liter ' within 3 days (Barnett and Kontogiannis 1975). Aeration of oil 

 and water dispersions resulted in a loss of 80 to 90% of the WSF within 24 

 hours (Anderson et al. 1974). Because the aeration did eliminate the toxic 

 effects of small amounts of oil, O'Brien (1978) suggests that aeration 

 might be used in an actual spill. 



Aquatic Insects 



Insects from the ponds are not killed by oil in aquarium studies. 

 Mozley (1978) added up to 8.4 ml liter"' in 13-liter aquaria and found no 

 change in survival of several kinds of chironomid larvae and eggs, of 

 trichopteran larvae, and of plecopteran nymphs. Unfortunately, up to 50% 

 of the animals in the controls of these experiments died during the 12-day 

 test so that a low level of toxicity would have been missed. 



Despite the lack of toxicity of oil in the laboratory, some insects and 

 other invertebrates were eliminated or drastically reduced in numbers In 

 the oiled ponds, at Barrow (Mozley and Butler 1978). The Agabus 

 (beetles), Asynarchus and Micrasema (caddisfiies), Nemoura (stoneflies) 

 and Physa (snails) were especially affected while Libertia (mites) remained 

 present in all ponds. Most of these animals live only in the plant beds and 



