682 



Fishery Bulletin 88(4). 1990 



N D 

 1986 



F M 



Month 



A M J 

 1987 



Figure 6 



Length-specific growtli rate nf a 20-mni length Mytilun 

 edulis at Avila Beach ( • ) and Platform Holly (O). Mean 

 values ±95% CI. 



Figure 7 



Relationship between Mytilus edulis growth rate and 

 chlorophyll a concentration with a time lag of 3 weeks 

 at Avila Beach (•) and Platform Holly (O). 



October-November 1986 and May- July 1987 (8-9 mm/ 

 mo). There was no effect of mussel stock on growth 

 rate (F = 0.901. P>0.1, 1-way ANOVA; Table 3). Mor- 

 tality of caged mussels was <5.0%. 



no correlation between growth rate and water tem- 

 perature (P>0.05). 



Relationship between growth rate and 

 chlorophyll a concentration 



We calculated correlation coefficients relating the 

 growth rate of M. edulis to chlorophyll a concentra- 

 tion and water temperature for grouped Avila and 

 Holly data integi'ated over the 4-week period of mussel 

 exposure and at time lags of 0-4 weeks. There was no 

 correlation between growth rate and chlorophyll a 

 concentration (/'>0.05, n = 14). However, growth rate 

 correlated v«th chlorophyll a concentration with a time 

 lag of 3 weeks, if the fall and winter values from Avila 

 (when seston concentrations exceeded 5 mg/L) were 

 excluded (r = 0.67, P<0.05, n = 11; Fig. 7). There was 



Scope for growth 



A summary of our theoretical scope-for-growth calcu- 

 lations, averaged by irionth, is given in Table 4. Our 

 analysis indicates that, overall, the estimated amount 

 of seston filtered from suspension liy mussels was 

 higher at Avila than at Holly (4.00 vs. 1.91 mg/h, t = 

 4.03, df = 46, P<0.001). However, mussels at Avila had 

 a significantly higher estimated percent pseudofeces 

 production (48.6% vs. 13.7%, ^ = 6.34, df=46, P< 

 0.001) than mussels at Hully. Thus despite the higher 

 seston concentrations at Avila, the actual amount of 

 estimated POM assimilated by mussels at each local- 

 ity should have been similar (0.43 mg/h at Holly vs. 0.36 

 mg/h at Avila, P>0.01). 



