Table 9-1. Filtration Rates for Control and Oil-Exposed Mussels. 



NOTE: Mean and standard error (in parentheses) are both given. 



After 48 hours of exposure (Figure 9-2), the filtration curves for the three 

 experimental groups began to diverge, while the control curve retained 

 pre-exposure characteristics. Mussel feeding activity in all three oU 

 concentrations was significantly reduced from that of the control, wdth the 

 highest concentration producing the most severe reduction. Filtration rates for 

 the 0.01 ppm, 0.1 ppm, and 1 ppm polluted mussels, decreased to 10.5, 5.2 

 and 2.2 ml/min, respectively, wliile the control group filtered at an average rate 

 of 19.3 ml/min. Figure 9-3 illustrates that continued oil exposure produces 

 progressively lower filtration rates. Mussels exposed for two weeks to 0.01 ppm 

 required two hours to filter what the controls filtered in 30 minutes. Similarly, 

 after three hours, animals exposed to 1 ppm had only consumed approximately 

 35 percent of the algae; while the controls far surpassed this in less than 10 

 minutes. After two weeks of exposure, filtration rates for the three exposed 

 groups decreased to 5.3, 1.8, and 0.3 ml/min, while the control group filtered 

 at an average rate of 17.8 ml/min. 



Following the two-week exposure period, the animals were returned to clean 

 water. Some evidence of recovery was noted after 24 hours in clean water 

 (Figure 9-4); however, the filtration curves for all tliree exposure groups were 

 still significantly different from the control. Filtration rates increased to 9.9 

 ml/min for the 0.01 ppm group, 3.9 ml/min for the 0.1 ppm group, and 0.76 

 ml/min for the 1 .0 ppm group. 



116 



