Page and Ricard: Food availability and M\4ilus edulis growth in California coastal waters 



681 



'N D 



MAM 



M A M J 

 1987 



Month 



Figure 3 



(a) Seston concentrations, (b) particulate organic matter 

 (POM) concentrations, and (c) %POM at Avila Beach 

 ( • ) and Platform Holly (O). 



in the slopes of these lines (P>0.1, ANCOVA; Fig. 5). 

 However, a significant difference in the location of the 

 ^/-intercepts (F = 13.46, df = 1, 34, P<0.001, ANCOVA) 

 indicated that a substantially higher concentration of 

 "background" POC existed at Avila (623 Mg C/L) than 

 at Holly (264 f^g C/L). 



Covariance among environmental parameters 



We found weak but significant positive correlations 

 between chlorophyll a concentration and both water 

 temperature and POC concentration at Avila (Table 2). 



Figure 4 



Particulate organic carbon (POC) concentrations at 

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



Figure 5 



Linear regressions of particulate organic carbon (POC) concentra- 

 tion on chlorophyll « concentrations at Avila Beach (•) and Plat- 

 form Holly (6). Avila; (/ = 69.8x -i- 623. >- = 0.51; Holly: 

 y = 184x + 264. /• = 0.60. 



In contrast, we found a weak negative correlation 

 between chlorophyll a concentration and water tem- 

 perature at Holly. Chlorophyll a concentration was 

 positively correlated with both POC and POM concen- 

 tration at Holly. There was no correlation between 

 chlorophyll a concentration and total seston or percent 

 POM, or between POM and POC concentration at 

 either site (Table 2). 



Growth rate 



Shell growth rates for a mussel of 20 mm shell length 

 over a period of 1 month at Avila and at Holly are given 

 in Figure 6. Growth rate was temporally variable at 

 both locations, with slowest growth rate December- 

 March 1987 (5-7 mm/mo) and most rapid growth 



