Animals from unpolluted localities were incubated in clean water, 

 while those from polluted localities were incubated in water collected 

 together with the mussels. 



The measurements were made on specimens with a mean shellfree 

 dry-weight of 31 mg (S.D. = 8 mg, shell length = 17-22 mm). Single 

 specimens were incubated for 50 to 150 minutes in syringes with a volume 

 of 10 ml and a diameter of about 15 mm. 



In order to study the acute effects of high oil concentrations, 

 fresh mussels were incubated in a laboratory prepared oil-in-water 

 mixture. This mixture was prepared from 10 ml of Tsesis oil and 900 ml 

 sea water which was mixed using a magnetic stirrer for 18 hours at 20 C. 

 The water phase served as an incubation medium and was used both undi- 

 luted and diluted (1:10) and was added fresh at the start of the incu- 

 bation. Mussels incubated in uncontaminated Baltic sea water were used 

 as a reference. 



The oxygen concentration was measured in control syringes with both 

 polluted and unpolluted water which had been incubated as long as the 

 syringes with animals present. These values were then subtracted from 

 measurements with animals present, before the oxygen consumption of the 

 mussels was calculated. Concentrations were determined with a Radiometer 

 oxygen electrode (D 616) connected to a Radiometer PHM 716 with a P0 -module, 

 PHA 930. 



10.2.2 Results 



Data from the respiration measurements are presented in Tables 

 10.2.1 and 10.2.2 and illustrated in Fig. 10.2.1. 



The respiration rates of M. edulis from different localities, and 

 those from the experiments with different incubation water, were examined 

 with Bartlett's test (Bailey 1976:189) and with analysis of variance 

 (Dixon and Massey, 1969 : 156-162)* in order to determine whether variances 

 or means were significantly different. When variances in the measure- 

 ments from all stations (polluted and unpolluted) were compared no 

 differences were found (x = 8.17, df = 6). However, in testing the 

 means by analysis of variance, a p-value between 0.005 and 0.001 

 (F., = 4.098) was obtained rejecting the hypothesis that all the 

 samples came from populations with the same respiration rates. 



206 



