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 mereenaria , 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 show a significant decrease in 
filtering rate when exposed to high 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 Elyland etal. (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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