They attributed this reduction to an anaesthetic effect upon the gill cilia. 

 Preliminary investigations at the Environmental research Laboratory, 

 Narragansett, revealed that feeding rates of clams, Mercenaria mercenaria , and 

 scallops, Argopecten irradians, were notably diminished after exposure to No. 

 2 fuel oil (7). 



A reduced feeding rate has also been noted for My tilus edulis. For instance, 

 Abel (1) observed reduced filtration rates in mussels exposed to various 

 pollutants including copper, zinc, mercury, cyanide, thiocyanate, and sulfide. 

 Gonzalez and Yevich (5) reported that Mytilus shov^/ a significant decrease in 

 filtering rate when exposed to higli temperatures in the laboratory. Gilfillan 

 (4), investigating the response of Mytilus to seawater extracts of crude oil, 

 reported a decrease in both food consumption and assimilation, and an increase 

 in respiration. The combined effects resulted in a reduction in the net carbon 

 flux at oil concentration as low as 1 ppm. 



The Oil Pollution Research Branch at the Narragansett Environmental 

 Research Laboratory has been assigned the task of evaluating the effects of 

 very low levels of oil on ecologically and commercially important marine 

 species. Such levels may not immediately lead to death of the organisms, but 

 may ultimately jeapordize their long-term success at survival. Since Mytilus 

 edulis is an important species in the marine community, and since a change in 

 filtration rate appears to be a well-defined response to environmental 

 disruption, we conducted an investigation to elucidate the behavioral effects of 

 very low levels of oil, and to evaluate the recovery potential of the stressed 

 animals. 



METHODS 



Adult Mytilus edulis were collected from the southeastern shore of 

 Conanicut Island, Rhode Island, in April, 1976. In the laboratory, the animals 

 were measured and separated into four groups of 50 individuals each. Mean 

 shell length of the mussels was 4.63 cm. Each group of mussels was maintained 

 for a two -week acclimation period in a plastic coated wire cage that was 

 suspended in a one meter diameter fiberglass tank. The tanks were supplied 

 with continuously renewed unfiltered seawater, which allowed the mussels to 

 feed on natural plankton from the incoming water. 



After the acclimation period, the filtration rate was measured for each of the 

 four groups of mussels. Next, these animals were placed for two weeks in a 

 flow-through oil exposure system designed by Hyland et al. (6). One group was 

 placed in each of three nominal oil concentrations— 0.01 ppm, 0.1 ppm, and 1 

 ppm— and one group was held under control conditions. Filtration rates were 

 measured at various intervals during the two-week oil exposure period. All 



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