For the energetic calculations it was a prerequisite to determine a series of biometric data. They are presented completely and coherently in this chapter, but they are barely discussed here because they serve as a basis for the next chapter and will be more extensively considered there.
For purposes of comparison the measurements were performed on the Antarctic, Euphausia superba, and also on the Nordic krill, Meganyctiphanes norvegica. These two pelagic species were contrasted with the predominantly benthic living Crangan crangon - Crangon becomes pelagic only at night. Euphausia superba were welded into plastic foil and shock-frozen directly after catching. Some control measurements were kindly performed by Mr. Buchholz in the Polish Antarctic Station "Arctowsky" with freshly killed krill. Meganyctiphanes norvegica and Crangon crangon from the North Atlantic were measured right after death (caused by 02 -lack). The length was measured between front edge of the eye to end of telson, rounded off to the nearest millimeter below. The wet weight was determined to 0.1 mg precision, after absorption of adhesive water (the fined cetae of the filtering basket can hold a considerable amount of water by capillary action) with absorbent paper. Dry weight determination after drying at 80 degree Celsius over 48 hours. The underwater weight was determined by an underwater balance to 0.1 mg precision. Density and volume determinations were conducted with a hydrostatic balance. All values relate to 4 degree Celsius and a salinity of 35.
Figures 27 to 30 show the length / wet weight relationships. For the Antarctic krill there are data available by SAHRHAGE (1978) plotted also in fig.28 as dashes, by CHEKUNOVA et al. (1974) and LOCKYER (1973). Adult Euphausia superba were discriminated according to sex; gravid females are heavier, as would be expected. The regression applies to all animals together. Fig. 30 shows a comparison of the three investigated species: the curve for Euphausia superba and Meganyctiphanes norvegica coincide so close together that they can be expressed by a common regression with a correlation coefficient of r = 0.987. Figures 31 to 34 show the same correlations for dry weight. The variances are larger compared to the wet weight regressions - a reason for this could be differing nutritional conditions of the individual animals, which to a certain extent could eventually be balanced by a taking in or giving off of water. Figures 35 to 38 show the same correlations for underwater weight of the animals.
With these regressions, the portion of the dry weight from the wet weight (in %) for increasing animal lengths was calculated and plotted in fig.39. Since the body length provides an unsatisfactory criterion for comparisons between euphausiids and Crangon crangon (a Crangon of the same length is broader and heavier, see fig.30), animals with an equivalent weight are joined by an arrow and correspondingly marked. Fig.40 shows how adult male and female Euphausia superba deviate from the general relation. The portion of the underwater weight from the wet weight is shown in figures 41 and 42, the portion of the underwater weight from the dry weight in figures 43 and 44, the volume of the animals in figures 45 and 46, and the density of the animals in figures 47 and 48. In the plots of the density, animals with equivalent volumes again were joined by an arrow for easier comparison and interpretation; also, the densities of North Sea water and Antarctic water are indicated. Density data of GREENLAW, 1977, show for Euphausia pacifica a d = 1.037 - 1.052 g per cm cube (at 7.4 degree Celsius). All regressions and correlation coefficients are printed in the graphs and also the tables in the appendix; numerical values for each 5 mm size group are calculated in the table in the appendix. It should be considered in regard to all information of this work that the summer aspect only is investigated and reported; whether substantial changes are to be expected during the Antarctic winter, must be shown by further expeditions.
Fig. 27. Wet weight of Meganyctiphanes norvegica at increasing length
W = .00000680 L 3.00
units in gram and millimeter n = 37 r = .994
W = .00000158 L 3.40
units in gram and millimeter n = 116 r = .976
broken line: replotted after data from SAHRHAGE 1978:
W = .00000180 L 3.34
Fig. 29. Wet weight of Crangon crangon at increasing length
W = .00000863 L 3.06
units in gram and
millimeter n = 44 r = .995
Fig. 35. Underwater weight of Meganyctiphanes norvegica at increasing length
W = .0000000103 L 3.82
units in gram and millimeter n = 112 r = .976
W = .0000000173 L 3.67
units in gram and millimeter n = 78 r = .975
Fig. 37. Underwater weight of Crangon crangon at increasing length
W = .000000109 L 3.48
units in gram and millimeter n = 57 r = .984
Fig. 45. Underwater weight of Euphausia superba and Crangon Crangon at increasing length - animals with equivalent volumes are linked with arrows
Euphausids: v = .00000367 L 3.16
Crangonids: v = .00000849 L 3.04
(units: centimeter cube, millimeter)
Euphausids: d = 1.028 (1 - 0.00338 L .590) -1
Crangonids: d = 1.028 (1 - 0.01260 L .422) -1
(units: gram per centimeter cube, length in millimeter)