REEVE and BAKER: PRODUCTION OF A CHAETOGNATH AND CTENOPHORE 



Conversion of Raw Data to Other Units 



The shrinkage in length of S. hispida with For- 

 mahn' preservation was estimated by measuring 

 over 100 live animals from a freshly caught 200-ju.m 

 mesh sample, and repeating this 10 and 420 days 

 following preservation of that collection in a 5% 

 formaldehyde solution buffered with meth- 

 enamine, which was the standard preservative for 

 all plankton samples. The degree of shrinkage was 

 judged by the extent of the downward shift in the 

 peak of the length/frequency histogram. Half the 

 total shrinkage (12.5% of the original length) oc- 

 curred within the first 10 days. Assuming a linear 

 rate of shrinkage after day 10, and preservation 

 time of the samples before analysis varying from 1 

 to 9 mo, the degree of shrinkage was computed to 

 be 20% with a range of + 3.5%. This mean estimate 

 was used to adjust size classes from preserved to 

 live length. 



Live length was converted to dry weight using 

 the relationship obtained from a linear regression 

 analysis of more than 40 separate weight deter- 

 minations of animals over their entire size range. 

 Animals to be weighed were rinsed in isotonic 

 ammonium formate and dried at 60°C. The ash- 

 free (i.e., organic) dry weight was previously de- 

 termined to be 90.7% of the dry weight (Reeve et 

 al. 1970). The mean carbon and nitrogen content of 

 S. hispida was determined by a Perkin-Elmer 

 elemental analyzer to be 44.9% with a standard 

 error of ± 1.0% and 11.9% + 0.2% of the ash-free 

 dry weight from 23 separate estimations over its 

 entire size range. The raw biomass units for 

 ctenophores were obtained in terms of live volume. 

 Over 100 separate determinations of animals over 

 their entire size range were made for wet 

 (drained), dry (at 60°C), and ash (at 500°C) 

 weights. Live volume was approximately 

 numerically equal to wet weight (1.000 ml = 0.958 

 +. 0.002 g standard error). Dry weight was 4.43% 

 + 0.40% of wet weight and ash-free dry weight 

 was 21.90% ± 0.15% of dry weight. 



Eighteen separate determinations of carbon 

 and nitrogen content of Mnemiopsis mccradyi 

 Mayer were made which yielded unusually low 

 values 8.72% + 0.06% and 2.32% + 0.07% of the 

 ash-free dry weight of carbon and nitrogen re- 

 spectively. A value of 44.9% carbon was reported 

 for Sagitta (above), and Curl (1962) quoted values 

 for various planktonic crustaceans between 44 and 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



52%. Even his value for Mnemiopsis sp. was con- 

 siderably higher at 20.6%. Hirota (1974) assumed a 

 50% carbon content of organic weight for 

 Pleurobrachia bachei in his calculations, because 

 analysis by wet combustion with acid dichromate 

 was unsuccessful due to problems with chloride ion 

 interference (J. Hirota, pers. commun.). 



We considered the possibility that our analyses 

 were also yielding incorrect results and tested 

 three possible sources of error: a) interference in 

 the analysis by the unusually large amount of 

 inorganic salts present in the ctenophore tissue, b) 

 errors of dry weight determination, and c) errors 

 of ash weight determination. Mixtures of bovine 

 serum albumin (5-15%) and sodium chloride did not 

 reduce the theoretical yield of carbon when com- 

 busted in the elemental analyzer. Since, however, 

 the dried ctenophore material was a more intima- 

 tely bound complex of organic and inorganic sub- 

 stances, which might be more resistant to 

 complete combustion, potassium persulfate was 

 added to promote complete oxidization (see 

 Strickland and Parsons 1968). No increase in car- 

 bon yield was achieved by this method. The 

 reliability of dry and ash weight determinations 

 affects the reliability of the carbon value since the 

 numbers so obtained are used in its computation. 

 The possibility of any significant loss of organic 

 matter during drying at 60°C was checked by 

 performing carbon analyses on freeze-dried 

 material. The previously derived mean value 

 remained unchanged. Finally, ash weights were 

 determined at a temperature 100°C lower than 

 previously. Slightly higher ash weights resulted, 

 which in turn slightly increased the computed 

 carbon level to 10.3% of the ash-free dry weight. 

 Since any significant source of error in this deter- 

 mination has so far eluded us, we report produc- 

 tion values below for ctenophores and chaetog- 

 naths in terms of ash-free dry weight for direct 

 comparison and in terms of the analyzed carbon. 

 Mullin (pers. commun.), on the basis of un- 

 published observations, suggested that the weight 

 lost on ashing may be largely "bound" water, and 

 that in Pleurobrachia bachei, at least, only about 

 12% of the ash-free dry weight is organic matter. 

 This suggests that comparisons based on carbon 

 content are more valid than those based on "or- 

 ganic" or ash free-dry weight. 



Growth Rates 



Growth rates of populations of the ctenophore 



241 



