ANGER and DAWIRS: ELEMENTAL COMPOSITION OF HYAS ARANEUS 



Table 10.— Average daily energy loss in 

 starved larval stages of Hyas araneus 

 (estimated from carbon-hydrogen-nitro- 

 gen values). J = energy contents; DW = 

 dry weight. 



Stage J/d per ind J/d per mg DW 



Zoea I 

 Zoea II 

 Megalopa 



002 

 0.07 

 0.11 



0.35 

 032 

 028 



The b values of the fitted curves were ca. 2.5, the 

 m's were -0.20 (Z-2) to -0.23 (Z-l); and the r's 

 varied between -0.964 (P<0.002; Z-2) and 

 -0.992 (P<10 10 ; Z-l). 



Using the conversion factor 20.19 J/ml O2 

 given by Brody (1945), approximate figures for 

 oxygen consumption could be estimated from the 

 energy values in Tables 6 to 8. In all stages there 

 was apparently a drastic reduction in respira- 

 tion rate during the first few days of starvation 

 (Table 11). For comparison of the stages, again 

 average values were computed (from values in 

 Table 10). Corresponding to the weight-specific 

 energy values (see above), from which they were 

 derived, a weak decreasing trend became 

 apparent (Table 11). 



The C :N ratio (Fig. 5) did not follow a uniform 

 pattern in starved larvae. In the Z-l stage a long 

 period of gradual increase was followed by a 

 short period of rapid decrease. This suggests that 

 protein was catabolized at a higher rate than 

 other constituents during most of the starvation 

 period; only in the premortal phase, wereN-poor 

 substances (most probably lipids) apparently 

 used as the main energy source. In the Z-2 and in 

 the megalopa variation was too high to discern 

 clear trends. In the former instar the C:N ratio 

 also showed a drop at the end suggesting some 

 similarity with the Z-l, whereas in the latter 

 stage apparently it did not change at all. 



The C:H ratio was practically constant in all 

 larval instars. It was in most cases significantly 

 lower in fed than in starved larvae. The mean 

 values and 95% confidence intervals (by weight) 

 were 6.67±0.08 versus 7.07±0.012 in the Z-l 

 (P<10 5 ), 6.64±0.26 versus 6.98±0.30 in the Z-2 



Table 11.— Weight-specific respiration rates 

 {jx\ 2 /h per mg dry weight) in relation to the 

 time of starvation of Hyas araneus. 



'Computed from Table 10 data 



(not significant), and 6.49±0. 11 versus 6.80±0.28 

 in the megalopa (P = 0.014). There was a similar 

 statistically significant difference (P = 0.002) 

 between the C:H ratios found in Z-l larvae in 

 May 1979 (6.86±0.09) and in February 1980 

 (6.67±0.08). 



DISCUSSION 



Larval growth has been measured and de- 

 scribed in a number of different ways. Incre- 

 ments in zoeal body size obey the general rules 

 summarized by Rice (1968), who calculated an 

 average growth factor of 1.29 for brachyurans. 

 From the figures given by Christiansen (1973) for 

 H. araneus, factors of 1.26 to 1.30 can be derived, 

 depending on the distance measured. A factor of 

 1.3 is also obtained, if size is assumed to be pro- 

 portional to the cube root of DW. As pointed out 

 by Rice (1968), the megalopa can hardly be 

 included in those considerations because of its 

 different shape. 



It is generally accepted that FW is a poor 

 measure of actual biomass. Its determination is 

 inaccurate and thus yields highly variable re- 

 sults. Moreover, it does not change in an orderly 

 manner during the molt cycle and therefore, it 

 must be regarded as insensitive to changes in 

 organic matter. This is caused by changes in the 

 water content. It is difficult to understand why a 

 number of authors described biochemical and 

 physiological changes in developing crustacean 

 larvae on a wet weight basis, and so severely 

 reduced the value of their information. We 

 suggest that FW or Formalin wet weight never 

 be used as a reference base in such studies, but 

 only as a source of additional information (e.g., 

 for water content of tissues). 



D W is a far better measure of biomass, although 

 it is influenced by inorganic salts. Unfortunate- 

 ly, different drying methods (temperatures and 

 times) are used by different investigators. Ash- 

 free DW should improve the accuracy in physio- 

 logical studies, if used as a basic unit. However, 

 again drying and combustion temperatures and 

 times are not uniformly applied. 



Elemental composition, especially C content, 

 can be used as a reliable expression of living 

 organic substance. Inorganic C does not play a 

 signficant role in marine planktonic organisms 

 (Curl 1962) and therefore C is also a measure of 

 energy equivalents (Salonen et al. 1976). C-based 

 energy estimations apparently tend to be some- 

 what lower than those calculated from bio- 



429 



