Figure 9-5. Two-week Recovery: Comparison of Filtering 
Activity of Mytilus edulis after Two Weeks of Recovery from 
Two Weeks Exposure to W.A.F. No. 2 Fuel Oil. 
feeding over a long period of time as a result of continued oil exposure. A 
question confronted, for example, is whether mussels exposed for several 
months to chronic inputs of oil reveal reduced growth. 
The laboratory experiments reported herein were designed to investigate 
responses to chronic oil pollution, and not the acute phenomena which occur 
immediately after an oil spill. However, in November, 1976, a small spill of No. 
6 fuel oil occurred at Quonset Point, Rhode Island. The resulting slick drifted 
across the western passage of Narragansett Bay, and impacted approximately 
one mile of shoreline on Conanicut Island. This incident provided an 
opportunity to investigate the effects of spilled oil on filtering activity in 
mussels, and thus supports the laboratory results with field data. Accordingly, 
48 hours after the spill ,Mytilus were collected from the polluted site and from 
an unimpacted area nearby. Filtration rates were measured in the laboratory, 
and feeding curves were generated for both groups (Figure 9-6). Compared to 
controls, a small but statistically significant reduction in feeding activity was 
observed in oiled mussels. For example, over a period of 45 minutes, the 
controls had removed approximately 96 percent of the food particles, while 
the polluted mussels removed only 84 percent. Filtration rates were calculated 
as 7.2 ml/min (S.E. = 1.0) for the controls, and 4.9 ml/min (S.E. = 0.5) for the 
oiled group. The relatively low value obtained for the control group is most 
likely a reflection of low winter ambient water temperatures (5-6°C). One 
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