THAYER ET AL. : CALORIC MEASUREMENTS OF ORGANISMS 



(1966) stated that acid digestion would reduce 

 the ash content and the endothermal effect but 

 that the influence of this treatment on the cal- 

 oric content of the treated samples is not known. 

 Richards and Richards (1965) found small 

 amounts of organic carbon were lost from Nas- 

 sarius trivitattus during decalcification, and this 

 would cause some loss of energy from the sam- 

 ples. Since the majority of gastropods and some 

 of the pelecypods analyzed were decalcified prior 

 to analysis (Appendix Table 1) , we analyzed the 

 effect of decalcification on the caloric content of 

 eight sets of mollusc tissues, including three sets 

 of Modiolus demissus from Virginia, North Car- 

 olina, and Georgia (Table 1). 



To determine the maximum effect of decalci- 

 fication larger organisms were decalcified for a 

 longer period of time than in the routine anal- 

 ysis. Twelve organisms of each set were 



shucked and one-half of each group was placed 

 in 20 Sr HCl for 15 min (3-8 times longer than 

 for routine analysis of small molluscs). All 

 samples were then dried in a lyophilyzer, and the 

 ash content of the dried material was measured 

 after combustion for 36 hr in a muffle furnace 

 at 500°C. Although decalcification generallj'^ 

 tended to reduce the caloric values, in two cases, 

 Modiolus demissus (from Virginia) and Tagelus 

 jAebeius, differences between untreated and de- 

 calcified tissue caloric values were significantly 

 different at the 5% level (Table 1). These data 

 suggest that although the shorter decalcification 

 time employed in routine analysis may have low- 

 ered the caloric content of the molluscs through 

 protein hydrolysis and extraction of carbon, the 

 decrease probably was insignificant and would 

 not have appreciably affected the regression 

 equation. 



o 



20 40 60 80 



ORGANIC MATTER (PERCENT ASH-FREE DRY WEIGHT) 



100 



Figure 1. — Relation between the caloric and organic content of estuarine organisms. Solid 

 line is the linear regression line; dashed line represents the 95% confidence limits for the 

 prediction equation; dotted line represents th3 95% confidence limits for the regression line. 



291 



