and dry weight may have been slightly affected 

 due to an unknown loss of chemical constituents. 

 Methods of preservation of animals before com- 

 busting or determining chemical composition and 

 weights have been a subject of debate. Omori 

 (1970) showed there was considerable variation 

 with no apparent trend of chemical composition 

 and weight ofCalanus cristatus that were frozen, 

 dried, or preserved in Formalin. Except for dry 

 weight, which was lowest in Formalin-preserved 

 specimens, he found no clear relationship between 

 percent ash, carbon, nitrogen, and hydrogen com- 

 position and the methods of preservation. Faustov 

 and Zotin ( 1965) determined that fixing by drying 

 or in 4% Formalin had no significant effect on the 

 caloric value of fish embryos and, consequently, 

 results obtained with fresh or fixed material could 

 be directly compared. In the present study, sam- 

 ples of fresh and preserved (5% Formalin) C. 

 finmarchicus were compared. Calories per gram 

 dry weight and percent ash were less for the pre- 

 served sample, however, the differences were min- 

 imal (274.8 cal/g dry weight and 3.78% ash which 

 corresponds to 275.0 cal/g ash-free dry weight) and 

 only slightly greater than one standard deviation 

 (Table 1). 



In view of the apparent lack of specific effects of 

 preservation method on chemical composition, 

 weights, and caloric values reported in the litera- 

 ture and the results with C finmarchicus in this 

 research, it may be concluded that the values pre- 

 sented in this paper are only slightly underesti- 

 mated, if at all. Also, since all samples in this 

 study were treated the same way, relative com- 

 parisons between them should be valid. 



Attempts to explain the differences in caloric 

 values on the basis of phylogeny proved in- 

 adequate. All species are calanoid copepods and, 

 although C. finmarchicus and P. minutus are 

 members of a different, more primitive taxonomic 

 subdivision under the Calanoida than the other 

 species (Sars 1903), the values for P. minutus 

 were statistically more similar to the lower values 

 for the other species than to C. finmarchicus. 



There is a lack of information on the specific 

 chemical composition of the species tested in this 

 research with the exception of C finmarchicus. 

 Calanus finmarchicus is known to have a reasona- 

 bly high fat content. Comita et al. (1966) noted 

 that, upon fixation, globules of fat were extruded 

 from living specimens and that a layer of oil 

 formed on the surface of the fixed sample. They 

 determined the caloric value of the fat of C. 



finmarchicus to be 9,500 cal/g. Fisher (1962) de- 

 termined the lipid content for a number of marine 

 Crustacea and found the concentrations in C 

 finmarchicus to be consistently among the higher 

 values recorded. Although there are no fat content 

 values for the six other species tested in this re- 

 search to compare with C. finmarchicus, the im- 

 plication is that the lipid content in C. finmarchi- 

 cus may be the cause of its higher caloric value. 

 The caloric determinations of C. finmarchicus 

 recorded in this research (Table 1) compare closely 

 with the results of other workers (Slobodkin 1962; 

 Comita and Schindler 1963; Comita et al. 1966). In 

 fact, the caloric values of C. finmarchicus have 

 been some of the highest recorded for copepods. 



Temora longicornis had lower caloric values 

 than the other species and the highest percentage 

 of ash (Table 1). This may be the result of its 

 morphology which is somewhat different com- 

 pared to the other species. It has a proportionately 

 rounder and deeper cephalothorax that may con- 

 tribute to a higher percentage of inorganic exo- 

 skeleton. 



The overall means for the caloric values of all 

 the species (5,251.9 cal/g dry weight and 5,626.3 

 cal/g ash-free dry weight) are similar to composite 

 sample caloric values recorded by other inves- 

 tigators. A calculation based on the data of Os- 

 tapenya et al. (1967) using their values of calories 

 per gram dry weight and percent organic matter 

 for Gulf of Mexico plankton samples, which were 

 predominantly copepods including Acartia sp., 

 Centropages sp., and Temora sp. (separate values 

 for each of these genera were not reported), pro- 

 duced a mean value of 5,187 cal/g ash-free dry 

 weight. A similar confirming value of 5,016 cal/g 

 dry weight was obtained using the percent organic 

 matter in the dry material in my research (calcu- 

 lated by subtracting the mean percent ash, 6.70%, 

 from 100) and the regression relationship between 

 that and ash-fi-ee dry weight devised by Piatt et al. 

 (1969). 



Seasonal changes in the caloric value of zoo- 

 plankton have been verified in several studies 

 (Comita et al. 1966; Conover 1968; Siefken and 

 Armitage 1968). The species in this study undoubt- 

 edly undergo seasonal variations also, and this is 

 a subject for future investigation. However, all the 

 species used in this research, with the exception of 

 P. minutus, were collected at approximately the 

 same time in the same general area and can be 

 used for a comparison of the potential energy avail- 

 able to predators at a particular time and place. 



219 



