Abstract

Euphausiids were identified, measured and then dried during a research cruise to sites in the north-eastern Atlantic Ocean and shelf waters of the Celtic Sea in late summer. The lengths of furcilia larvae and later stages were measured in three ways, and regressions relating each pair of measures were calculated for different developmental stages of each species. Four hundred and ninety-three dried specimens of nine species were weighed and length–weight regressions were calculated. A subset of 187 specimens was selected for analysis of carbon (C) and nitrogen (N) content soon after return to the laboratory. The C and N contents of a further 122 specimens were determined after the specimens had been stored for 9 years. No consistent differences in percentage C and N content were found between the two groups, indicating no systematic change during prolonged storage in desiccators. Calyptopes of Nyctiphanes couchi contained a lower percentage of both C (mean 36.2%) and N (mean 8.6%) than later stages (means: 40.6% C, 11.0% N). Carbon content and C:N ratios of a group of specimens of Thysanoessa longicaudata, including some juveniles, adult males and adult females, were distinctly higher (>46% and >5.0, respectively) than those of the majority of specimens of the same species.

Introduction

Euphausiacea, of which there are <90 species, constitute an important and, in some times and places, a dominant component of the zooplankton/micronekton of the world's oceans and deeper shelf waters. Preserved samples from towed plankton samplers or pumped water can provide data on the identity and numerical abundance of euphausiids, but the effects of preservation limits the value of such material for deriving estimates of dry weight biomass and carbon (C) and nitrogen (N) content (e.g. Williams and Robins, 1982). Lindley (1978, 1980, 1982a,b) calculated the biomass and production of euphausiids for near-surface water of the north Atlantic using length–weight regressions derived from formalin-preserved specimens. Data on the C and N content of euphausiids dried when freshly caught have been presented by numerous authors. Ikeda (1984) and Iguchi and Ikeda (1998) presented data on a full range of developmental stages and these were of the Antarctic krill, Euphausia superba, and the north Pacific species Euphausia pacifica. Both of these species are free spawners with three non-feeding nauplius and metanauplius stages before developing into the calyptopis stage which actively feeds.

The work presented here gives data on three measurements of length, dry weight and C and N content of nine species taken in the oceanic north Atlantic and in continental shelf waters to the south-west of the British Isles. Data are presented for developmental stages from calyptopis to adult males and adult females of Nyctiphanes couchi, from furcilia to adult male and female Thysanoessa longicaudata, and more than one development stage for some of the less abundant species. In contrast with Euphausia spp., N.couchi carries its eggs in a sac and these hatch as ‘pseudometanauplii’ which moult almost immediately to become metanauplii (one stage) (Mauchline and Fisher, 1969).

A subset of the C and N weight determinations was derived in analyses soon after collection of the samples and a further subset of analyses was carried out after the specimens had been stored in desiccators for 9 years. This provided an opportunity to determine whether dried specimens deteriorated during a prolonged period of storage.

Method

Plankton samples were taken during a research cruise by RRS ‘Challenger’ in late August and early September 1981. Samples were taken in oceanic waters at 59°N, 19°W between 28 August and 1 September, and over the continental shelf at 51°30′N, 5°20′W between 4 and 8 September. The specimens were sorted live from 0.5-m-diameter, 280-μm-mesh hand net samples deployed close to the surface (Williams and Robins, 1982; Conway and Robins, 1991) and a rectangular midwater trawl (RMT) net (Clarke, 1969) deployed at depths of >500 m at the oceanic station.

The plankton in the net hauls were sorted by eye or using stereomicroscopes at low magnification. Particular care was taken with the specimens from RMT net samples to select only undamaged specimens. The specific identity, developmental stage and sexual character of each specimen were recorded. Four hundred and ninety-eight euphausiids were identified and measured to the nearest 0.1 mm with an eyepiece graticule. Calyptopes were measured from the front margin of the carapace to the end of the telson (excluding spines). Furcilias and later stages were measured (La) from the posterior margin of the eye socket to the end of the last abdominal segment, (Lb) from the posterior margin of the eye socket to the end of the telson (excluding spines) and (Lc) from the tip of the rostrum to the end of the telson (excluding spines).

Each specimen was washed in deionized water, placed on absorbent paper to remove excess water, then placed individually in a compartment in a Sterilin™ Repli dish (25 compartments) or, in the case of larger specimens, individually on planchettes. These were dried for ~24 h in an oven at 60°C, then stored in desiccators. After loss and rejection of specimens damaged during handling, 493 euphausiids were weighed using a Cahn 25 Electrobalance. Analysis for C and N content was carried out using a Carlo-Erba MOD 1106 elemental analyser as described by Williams and Robins (1982). Within a few months of sampling, the C and N contents of 187 specimens, selected to give a representative coverage of the sizes and developmental stages of the dominant species, were determined. The remainder were kept in desiccators until 1990 when a similar analysis was carried out on a further 120 specimens representing all the species sorted from the plankton samples.

Linear regression equations and product moment correlation coefficients between the three different length measurements and between log of each length and log dry weight were calculated for each species/stage for which >8 specimens were present, and for totals within species and across species. The C and N contents as a percentage of dry weight were calculated for comparable development stages (calyptopis, furcilia, juvenile, adult female or adult male), where present, of each species. Juveniles include all post-larval specimens in which the sexual character could not be readily distinguished. The C and N contents determined within a few months of the sampling and those determined after 9 years of storage were compared by t-tests.

Results

The numbers of individuals of each developmental stage of the species taken are listed in Table I. All specimens of Meganyctiphanes norvegica and N.couchi were taken at the Celtic Sea station; the others were all taken at the oceanic site. The length (Lc) distributions of specimens of the calyptopis to adult stages of the five most abundant species that were weighed and analysed for C and N content are shown in Figure 1.

Regressions describing the relationships between the three measurements of length and the correlation coefficients (r) are listed in Table II. All the r values were >0.93 (P < 0.001 in all cases). Overall, the regressions of La on Lc had the lowest r values, while those of Lb on Lc had the highest. The equivalent data for regressions on dry weight on the length measures are given in Table III. The weakest correlations were those for adult males and females of T.longicaudata. In the case of the males, the r values were only significant at the 5% level, whereas all others were significant at the 0.1% level.

Results for C and N content as a percentage of the dry weight are presented in Table IV. The dry weight, N and C content of each calyptopis stage of N.couchi is given in Table V. The N and C contents of the last (third) calyptopis were higher than those of the earliest calyptopis stage. All four calyptopes stored for 9 years were stage III.

Comparisons of the results from the earlier analyses with those performed after prolonged storage show no clear patterns. The percentages of N and C in all specimens analysed before the prolonged storage were 10.7% (σ = 1.6) and 39.9% (σ = 4.0), and the equivalent values after storage were 10.5% (σ = 1.3) and 41.1% (σ = 5.0), respectively. The higher value after storage for C was significant (P = 0.02). However, excluding calyptopes, the values before storage became 11.1% (σ = 1.4) and 40.6% (σ = 3.5) with no change (at one decimal place) from the values including calyptopes after storage. The percentage N content before storage was significantly higher than the value derived after 9 years in the desiccator (P = 0.002). Nyctiphanes couchi and T.longicaudata were the only species for which sufficient numbers were analysed both before and after the prolonged storage period for detailed analysis. The values for all stages of N.couchi (Table IV) for both N and C after storage were significantly higher than before (P = 0.006 and P = 0.001, respectively). Again, excluding the calyptopes, the values were 10.7% (σ = 1.6) and 40.6% (σ = 4.6) before storage, and 10.9 (σ = 1.5) and 42.3 (σ = 6.1) afterwards; neither difference was significant. In the case of T.longicaudata, the values for mean C and N content before storage were higher, but not significantly so. The lack of a consistent pattern in the results indicates that the prolonged storage in desiccators did not result in any deterioration resulting in a systematic change in N and C content of the material.

The percentage of C and N for all specimens is plotted against dry weight in Figure 2. The significant positive correlation of %N against weight (r = 0.404, P < 0.001) can be attributed to the high N content of some large M.norvegica and low values for calyptopes. The scatter of points in Figure 2 shows greatest variability at the lower end of the weight range, but there is a cluster of high C values and low N values in the dry weight range between 1.5 and 3.1 mg. This is due to the data from a group of specimens of five juvenile and three adult male and one female T.longicaudata, of which one male and two females were analysed before prolonged storage, and the remainder afterwards. In Table IV, it is notable that the C:N values are higher for these stages of T.longicaudata than for other species. The distinctness of a group of specimens with high C and low N content, not only in the values but also the positive correlation between C:N ratios and dry weights, can be seen in Figure 3.

Discussion

The length distributions shown in Figure 1 demonstrate the differences in the annual cycles of the species in the sampling areas. Euphausia krohni breeds from spring to late autumn in the north-eastern Atlantic (Lindley, 1982b; Mauchline, 1985), the lengths of specimens measured here ranged from a furcilia of 4.8 mm to an immature specimen of 19.7 mm with a mode at 7.0–7.5 mm, probably due to a peak in recruitment in early summer. Lindley (1982b) found a similar situation, but with the mode less marked, in continuous plankton records in August 1967. In the same area, T.longicaudata produces two generations per year: one spawned in spring and the second in mid- to late summer in the area (Lindley, 1978; Mauchline, 1985). The bimodal size distribution in the present samples consists of the larger spring spawned generation, including adult males and females, and the more numerous mode of the second generation containing calyptopes, furcilias and juveniles. Thysanopoda acutifrons spawns in the spring to early summer and the individuals may live for 2 years (Einarsson, 1945; Mauchline, 1985). In the present samples, a single generation, which was spawned earlier in the same year, was present. Any older (1–2 years) specimens, which would have been ~30 mm long (Mauchline, 1985), may have been confined to deeper water than that sampled in this study.

In the waters adjacent to the Celtic Sea, M.norvegica breeds in the spring and lives for ~1 year, and N.couchi breeds through much of the year and few, if any, complete a full year of life (Lindley, 1982a). The specimens of the former species caught in early September 1981 were all post-larval and include some adults of both sexes. All stages from calyptopes to adults of N.couchi were found and the length distribution may well have been polymodal.

The measures of total length presented here can be related to measures such as carapace length (including or excluding the rostrum) or uropod length using regressions summarized by Mauchline (1980) for M.norvegica, Thysanoessa inermis and T.longicaudata. Gros and Cochard (1978) presented regressions relating carapace length to abdomen length for N.couchi. Many length measurements of euphausiids from the furcilia stage onward take the base of the eye or the posterior margin of the eye socket as the anterior limit to avoid including the rostrum, which varies in proportion to the carapace between species and even between sexes within species. However, in the calyptopis stage, the eyes are covered by the carapace but the rostrum is not developed, so the relationship between the lengths of calyptopes and those of later stages is not precise. The correlations do not show any clear advantage to any of the length measures for determining relationships with dry weights, but once the regressions have been calculated, La can be applied to specimens where the rostrum or telson has sustained damage. Within the length ranges for which data are available here, the differences between species and between stages within species in regressions of log weight on log length were not substantial except for the difference in regression coefficients between calytopes and the later stages.

The present results for C and N content are consistent with those published by other authors (Table VI). The lower values for calyptopes than for later stages in N.couchi are consistent with results from Ikeda (1984) for E.superba and Iguchi and Ikeda (1998) for E.pacifica, and the detailed studies of the early developmental stages of E.superba by Ikeda (1985) and Ross and Quetin (1989). This is perhaps unexpected, as the retention of eggs by the female and the abbreviated naupliar development in N.couchi would be expected to result in lower energy and material demand than is the case in free spawners with a full sequence of naupliar development and an ascent of several hundred metres at the first calyptopis stage. The implication of the present result is that either the eggs of N.couchi contain lower reserves than those of E.superba and E.pacifica, or that the strategy of retaining eggs and abbreviated early development has no energetic advantages for the early developmental stages. Data on C, N and energy content of eggs of N.couchi would contribute to resolving this. Further data on a wider range of species are needed to interpret the energy budget implications for the different spawning and developmental strategies as discussed by Lindley (1997).

The high C content and C:N ratios of some of the larger generation of T.longicaudata are probably a result of accumulation of lipids comparable with the rapid accumulation during growth periods in T.inermis by Falk-Petersen (1981) and Hopkins et al. (1984). Thysanoessa longicaudata appears to overwinter at depths of several hundred metres (Østvedt, 1955; Williams and Lindley, 1982), an overwintering strategy similar to that of the copepod Calanus finmarchicus (Gunnerus) in deep water areas. Calanus accumulates lipids, enhancing C content and C:N values prior to the winter (Hirche, 1983). It would appear that the lipid-rich specimens here are from the spring spawned generation which would be expected to die out before the winter; the generation represented by the smaller specimens in the present samples should be the source of the overwintering population. The accumulation of lipids by the larger specimens taken in late August would appear to be related to reproductive cycles rather than overwintering strategies.

Length/weight relationships and elemental and biochemical composition of euphausiids vary seasonally (e.g. Bämstedt, 1976; Falk-Petersen, 1981; Iguchi and Ikeda, 1998). Interpretation and application of the present data derived from sampling on a single cruise must be constrained by knowledge of the magnitude of seasonal variations.

Table I.

Numbers of specimens sorted and measured, categorized by species, developmental stage and sex

 Calyptopis Furcilia Juvenile Female Male 
Euphausia krohni (Brandt)  40   
Meganyctiphanes norvegica (M. Sars)   37 10 
Nematobrachion boopis (Calman)     
Nematoscelis megalops G.O. Sars    
Nyctiphanes couchi (Bell) 50 58 49 20 41 
Stylocheiron longicorne G.O. Sars     
Stylocheiron maximum Hansen    
Thysanoessa longicaudata (Kröyer) 87 20 17 
Thysanopoda acutifrons Holt and Tattersall   23   
 Calyptopis Furcilia Juvenile Female Male 
Euphausia krohni (Brandt)  40   
Meganyctiphanes norvegica (M. Sars)   37 10 
Nematobrachion boopis (Calman)     
Nematoscelis megalops G.O. Sars    
Nyctiphanes couchi (Bell) 50 58 49 20 41 
Stylocheiron longicorne G.O. Sars     
Stylocheiron maximum Hansen    
Thysanoessa longicaudata (Kröyer) 87 20 17 
Thysanopoda acutifrons Holt and Tattersall   23   
Table II.

Euphausiacea. Intercepts (a), regression coefficients (b) and product moment correlation coefficients (r) for relationships between lengths from the posterior margin of the eye socket to the end of the sixth abdominal segment (La), from the posterior margin of the eye socket to the tip of the telson excluding terminal spines (Lb), and from the tip of the rostrum to the tip of the telson excluding terminal spines (Lc)

 La = a + b Lb La = a + b Lc Lb = a + b Lc 
 a b r a b r a b r 
All = all stages of all species. 
Euphausia krohni 
Total 0.037 0.759 0.995 –0.190 0.755 0.993 0.076 0.950 0.999 
Meganyctiphanes 
norvegica 
Total –0.276 0.840 0.995 –0.248 0.807 0.993 0.024 0.961 0.999 
Nematoscelis megalops 
Total –0.193 0.823 0.999 –0.298 0.757 0.999 –0.126 0.919 1.000 
Nyctiphanes couchi 
Total –0.301 0.852 0.998 –0.511 0.828 0.999 –0.243 0.971 0.999 
Furcilias –0.081 0.874 0.995 –0.275 0.760 0.993 –0.238 0.967 0.995 
Juveniles –0.263 0.839 0.984 –0.535 0.826 0.986 –0.246 0.967 0.990 
Females –0.308 0.858 0.992 –0.411 0.825 0.991 –0.101 0.960 0.997 
Males –0.218 0.846 0.983 –0.349 0.812 0.981 –0.124 0.957 0.995 
Thysanoessa longicaudata 
Total –0.124 0.819 0.998 –0.168 0.750 0.997 –0.050 0.914 0.998 
Furcilias –0.035 0.787 0.971 –0.120 0.732 0.961 –0.088 0.924 0.983 
Juveniles 0.142 0.787 0.994 0.024 0.728 0.995 –0.136 0.924 0.997 
Females 0.661 0.744 0.983 0.861 0.660 0.933 0.191 0.895 0.957 
Males 0.890 0.709 0.954 2.200 0.517 0.962 2.280 0.687 0.950 
Thysanopoda acutifrons 
Total –1.460 0.927 0.985 –1.730 0.908 0.984 –0.272 0.978 0.997 
All excluding calyptopes –0.184 0.830 0.999 –0.361 0.798 0.997 –0.216 0.962 0.999 
 La = a + b Lb La = a + b Lc Lb = a + b Lc 
 a b r a b r a b r 
All = all stages of all species. 
Euphausia krohni 
Total 0.037 0.759 0.995 –0.190 0.755 0.993 0.076 0.950 0.999 
Meganyctiphanes 
norvegica 
Total –0.276 0.840 0.995 –0.248 0.807 0.993 0.024 0.961 0.999 
Nematoscelis megalops 
Total –0.193 0.823 0.999 –0.298 0.757 0.999 –0.126 0.919 1.000 
Nyctiphanes couchi 
Total –0.301 0.852 0.998 –0.511 0.828 0.999 –0.243 0.971 0.999 
Furcilias –0.081 0.874 0.995 –0.275 0.760 0.993 –0.238 0.967 0.995 
Juveniles –0.263 0.839 0.984 –0.535 0.826 0.986 –0.246 0.967 0.990 
Females –0.308 0.858 0.992 –0.411 0.825 0.991 –0.101 0.960 0.997 
Males –0.218 0.846 0.983 –0.349 0.812 0.981 –0.124 0.957 0.995 
Thysanoessa longicaudata 
Total –0.124 0.819 0.998 –0.168 0.750 0.997 –0.050 0.914 0.998 
Furcilias –0.035 0.787 0.971 –0.120 0.732 0.961 –0.088 0.924 0.983 
Juveniles 0.142 0.787 0.994 0.024 0.728 0.995 –0.136 0.924 0.997 
Females 0.661 0.744 0.983 0.861 0.660 0.933 0.191 0.895 0.957 
Males 0.890 0.709 0.954 2.200 0.517 0.962 2.280 0.687 0.950 
Thysanopoda acutifrons 
Total –1.460 0.927 0.985 –1.730 0.908 0.984 –0.272 0.978 0.997 
All excluding calyptopes –0.184 0.830 0.999 –0.361 0.798 0.997 –0.216 0.962 0.999 
Table III.

Euphausiacea. Intercepts (a), regression coefficients (b) and product moment correlation coefficients (r) for regressions of dry weight (DW) on three measures of length. Numbers of specimens were as listed in Table I except for four furcilias and one juvenile of N.couchi that were lost or damaged

 Log DW = a + b Log La Log DW = a + b Log Lb Log DW = a + b Log Lc 
 a b r a b r a b r 
All = all stages of all species. 
Euphausia krohni 
Total 0.916 2.638 0.971 0.587 2.714 0.971 0.508 2.723 0.973 
Meganyctiphanes 
norvegica  
Total 0.651 2.932 0.988 0.308 3.01 0.987 0.258 3.010 0.986 
Nematoscelis 
megalops  
Total 0.937 2.661 0.994 0.587 2.753 0.995 0.397 2.822 0.997 
Nyctiphanes couchi 
Furcilias 1.260 2.134 0.980 0.977 2.183 0.979 0.780 2.356 0.981 
Juveniles 0.988 2.516 0.940 0.615 2.672 0.932 0.415 2.822 0.937 
Females 0.820 2.721 0.958 0.475 2.840 0.959 0.368 2.885 0.956 
Males 0.758 2.783 0.971 0.396 2.911 0.964 0.272 2.964 0.963 
Total 1.199 2.266 0.994 0.853 2.420 0.993 0.665 2.556 0.994 
Thysanoessa longicaudata 
Furcilias 0.952 2.555 0.925 0.627 2.639 0.928 0.380 2.871 0.991 
Juveniles 0.749 2.928 0.987 0.476 2.924 0.986 0.283 2.998 0.989 
Females 0.316 3.367 0.856 0.143 3.238 0.877 0.281 2.974 0.785 
Males 1.180 2.360 0.647 0.631 2.695 0.788 1.455 1.772 0.637 
Total 0.881 2.734 0.992 0.523 2.834 0.993 0.380 2.871 0.991 
Thysanopoda 
acutifrons 
Total 0.485 3.056 0.953 –0.383 3.592 0.943 –0.573 3.701 0.949 
Calyptopes       1.194 1.402 0.810 
All excluding calyptopes 0.986 2.581 0.991 0.639 2.691 0.992 0.456 2.800 0.993 
 Log DW = a + b Log La Log DW = a + b Log Lb Log DW = a + b Log Lc 
 a b r a b r a b r 
All = all stages of all species. 
Euphausia krohni 
Total 0.916 2.638 0.971 0.587 2.714 0.971 0.508 2.723 0.973 
Meganyctiphanes 
norvegica  
Total 0.651 2.932 0.988 0.308 3.01 0.987 0.258 3.010 0.986 
Nematoscelis 
megalops  
Total 0.937 2.661 0.994 0.587 2.753 0.995 0.397 2.822 0.997 
Nyctiphanes couchi 
Furcilias 1.260 2.134 0.980 0.977 2.183 0.979 0.780 2.356 0.981 
Juveniles 0.988 2.516 0.940 0.615 2.672 0.932 0.415 2.822 0.937 
Females 0.820 2.721 0.958 0.475 2.840 0.959 0.368 2.885 0.956 
Males 0.758 2.783 0.971 0.396 2.911 0.964 0.272 2.964 0.963 
Total 1.199 2.266 0.994 0.853 2.420 0.993 0.665 2.556 0.994 
Thysanoessa longicaudata 
Furcilias 0.952 2.555 0.925 0.627 2.639 0.928 0.380 2.871 0.991 
Juveniles 0.749 2.928 0.987 0.476 2.924 0.986 0.283 2.998 0.989 
Females 0.316 3.367 0.856 0.143 3.238 0.877 0.281 2.974 0.785 
Males 1.180 2.360 0.647 0.631 2.695 0.788 1.455 1.772 0.637 
Total 0.881 2.734 0.992 0.523 2.834 0.993 0.380 2.871 0.991 
Thysanopoda 
acutifrons 
Total 0.485 3.056 0.953 –0.383 3.592 0.943 –0.573 3.701 0.949 
Calyptopes       1.194 1.402 0.810 
All excluding calyptopes 0.986 2.581 0.991 0.639 2.691 0.992 0.456 2.800 0.993 
Table IV.

Euphausiacea. Numbers of specimens used for elemental analysis (n), means and standard deviations of carbon (C) and nitrogen (N) content as a percentage of dry weight, and C:N ratios. Values are given for data derived from analyses conducted soon after the sampling cruise (1981) and after storage for 9 years (1990)

 n %N %C C:N 
Euphausia krohni 
Furcilia     
1981 11.2 ± 0.3 39.2 ± 0.3 3.5 ± 0.1 
Juvenile     
1981 25 11.5 ± 0.8 41.4 ± 1.5 3.6 ± 0.3 
1990 10.5 ± 0.4 40.6 ± 1.4 3.9 ± 0.1 
Total 28 11.4 ± 0.8 41.3 ± 1.6 3.7 ± 1.3 
All stages     
1981 27 11.5 ± 0.8 41.2 ± 1.5 3.6 ± 0.3 
Total 30 11.4 ± 0.8 41.2 ± 1.6 3.6 ± 0.3 
Meganyctiphanes norvegica 
Juvenile     
1981 26 12.0 ± 0.7 39.7 ± 2.0 3.3 ± 0.1 
1990 11.1 40.0 3.6 
Total 27 12.0 ± 0.7 39.7 ± 2.0 3.3 ± 0.1 
Female     
1981 12.4 ± 0.5 41.3 ± 0.7 3.3 ± 0.1 
Male     
1981 14.0 ± 0.6 43.3 ± 0.1 3.0 ± 0.1 
All stages     
1981 36 12.2 ± 0.8 40.2 ± 2.0 3.3 ± 0.1 
Total 37 12.2 ± 0.8 40.2 ± 2.0 3.3 ± 0.1 
Nematobrachion boopis 
Juvenile     
1990 11.3 ± 0.8 40.7 ± 1.8 3.6 ± 0.2 
Nematoscelis megalops 
Furcilia     
1990 10.8 ± 0.2 41.6 ± 2.7 3.9 ± 0.2 
Juvenile     
1990 10.6 ± 0.4 40.5 ± 1.4 3.8 ± 0.2 
All stages     
1990 10.7 ± 0.4 41.3 ± 2.4 3.8 ± 0.2 
Stylocheiron maximum 
Furcilia     
1990 10.3 ± 0.5 40.4 ± 0.7 3.9 ± 0.1 
Thysanopoda acutifrons 
Juvenile     
1990 10.5 38.0 3.6 
Nyctiphanes couchi 
Calyptopis     
1981 21 8.3 ± 0.7 35.0 ± 3.6 4.2 ± 0.4 
1990 10.3 ± 1.3 42.6 ± 5.0 4.1 ± 0.2 
Total 25 8.6 ± 1.1 36.2 ± 4.7 4.2 ± 0.4 
Furcilia     
1981 22 9.8 ± 1.6 40.5 ± 6.2 4.2 ± 0.5 
1990 21 10.8 ± 1.6 41.2 ± 5.8 3.8 ± 0.3 
Total 44 10.3 ± 1.6 40.8 ± 6.0 4.0 ± 0.4 
Juvenile     
1981 14 10.7 ± 0.6 39.6 ± 2.3 3.7 ± 0.1 
1990 14 11.2 ± 1.7 44.3 ± 6.8 4.0 ± 0.4 
Total 28 11.0 ± 1.3 42.0 ± 5.5 3.8 ± 0.3 
Female     
1981 11.5 ± 0.6 41.7 ± 1.4 3.6 ± 0.2 
1990 10.4 ± 0.8 39.9 ± 3.5 3.9 ± 0.1 
Total 13 11.1 ± 0.9 41.0 ± 2.4 3.7 ± 0.2 
Male     
1981 11 11.8 ± 0.5 41.0 ± 2.1 3.5 ± 0.2 
1990 11.7 ± 1.5 46.0 ± 9.0 3.93 ± 0.3 
Total 13 11.8 ± 0.6 41.8 ± 3.7 3.6 ± 0.2 
All stages     
1981 78 10.1 ± 1.6 39.1 ± 4.8 3.9 ± 0.5 
1990 47 10.8 ± 1.5 42.3 ± 6.0 3.9 ± 0.3 
Total 123 10.4 ± 1.6 40.3 ± 5.5 3.9 ± 0.4 
Thysanoessa longicaudata 
Furcilia     
1981 23 9.6 ± 1.3 37.9 ± 2.0 4.0 ± 0.4 
1990 41 10.4 ± 1.1 38.4 ± 2.5 3.7 ± 0.3 
Total 64 10.1 ± 1.2 38.2 ± 2.3 3.8 ± 0.4 
Juvenile     
1981 11.4 ± 1.0 41.1 ± 1.7 3.6 ± 0.2 
1990 9.0 ± 1.8 47.4 ± 5.5 5.5 ± 1.7 
Total 16 10.2 ± 1.9 44.3 ± 5.1 4.6 ± 1.5 
Female     
1981 10.9 ± 1.3 43.5 ± 3.5 4.1 ± 1.0 
1990 10.6 ± 0.2 41.7 ± 1.2 3.9 ± 0.1 
Total 16 10.7 ± 0.9 42.6 ± 2.7 4.0 ± 0.7 
Male     
1981 10.6 ± 2.1 45.1 ± 6.7 4.6 ± 1.9 
1990 7.4 51.2 6.9 
Total 10.2 ± 2.3 45.8 ± 6.5 4.8 ± 1.9 
All stages     
1981 46 10.3 ± 1.5 40.5 ± 4.3 4.0 ± 0.9 
1990 58 10.2 ± 1.3 40.3 ± 4.5 4.1 ± 1.0 
Total 101 10.2 ± 1.4 40.4 ± 4.4 4.0 ± 0.9 
 n %N %C C:N 
Euphausia krohni 
Furcilia     
1981 11.2 ± 0.3 39.2 ± 0.3 3.5 ± 0.1 
Juvenile     
1981 25 11.5 ± 0.8 41.4 ± 1.5 3.6 ± 0.3 
1990 10.5 ± 0.4 40.6 ± 1.4 3.9 ± 0.1 
Total 28 11.4 ± 0.8 41.3 ± 1.6 3.7 ± 1.3 
All stages     
1981 27 11.5 ± 0.8 41.2 ± 1.5 3.6 ± 0.3 
Total 30 11.4 ± 0.8 41.2 ± 1.6 3.6 ± 0.3 
Meganyctiphanes norvegica 
Juvenile     
1981 26 12.0 ± 0.7 39.7 ± 2.0 3.3 ± 0.1 
1990 11.1 40.0 3.6 
Total 27 12.0 ± 0.7 39.7 ± 2.0 3.3 ± 0.1 
Female     
1981 12.4 ± 0.5 41.3 ± 0.7 3.3 ± 0.1 
Male     
1981 14.0 ± 0.6 43.3 ± 0.1 3.0 ± 0.1 
All stages     
1981 36 12.2 ± 0.8 40.2 ± 2.0 3.3 ± 0.1 
Total 37 12.2 ± 0.8 40.2 ± 2.0 3.3 ± 0.1 
Nematobrachion boopis 
Juvenile     
1990 11.3 ± 0.8 40.7 ± 1.8 3.6 ± 0.2 
Nematoscelis megalops 
Furcilia     
1990 10.8 ± 0.2 41.6 ± 2.7 3.9 ± 0.2 
Juvenile     
1990 10.6 ± 0.4 40.5 ± 1.4 3.8 ± 0.2 
All stages     
1990 10.7 ± 0.4 41.3 ± 2.4 3.8 ± 0.2 
Stylocheiron maximum 
Furcilia     
1990 10.3 ± 0.5 40.4 ± 0.7 3.9 ± 0.1 
Thysanopoda acutifrons 
Juvenile     
1990 10.5 38.0 3.6 
Nyctiphanes couchi 
Calyptopis     
1981 21 8.3 ± 0.7 35.0 ± 3.6 4.2 ± 0.4 
1990 10.3 ± 1.3 42.6 ± 5.0 4.1 ± 0.2 
Total 25 8.6 ± 1.1 36.2 ± 4.7 4.2 ± 0.4 
Furcilia     
1981 22 9.8 ± 1.6 40.5 ± 6.2 4.2 ± 0.5 
1990 21 10.8 ± 1.6 41.2 ± 5.8 3.8 ± 0.3 
Total 44 10.3 ± 1.6 40.8 ± 6.0 4.0 ± 0.4 
Juvenile     
1981 14 10.7 ± 0.6 39.6 ± 2.3 3.7 ± 0.1 
1990 14 11.2 ± 1.7 44.3 ± 6.8 4.0 ± 0.4 
Total 28 11.0 ± 1.3 42.0 ± 5.5 3.8 ± 0.3 
Female     
1981 11.5 ± 0.6 41.7 ± 1.4 3.6 ± 0.2 
1990 10.4 ± 0.8 39.9 ± 3.5 3.9 ± 0.1 
Total 13 11.1 ± 0.9 41.0 ± 2.4 3.7 ± 0.2 
Male     
1981 11 11.8 ± 0.5 41.0 ± 2.1 3.5 ± 0.2 
1990 11.7 ± 1.5 46.0 ± 9.0 3.93 ± 0.3 
Total 13 11.8 ± 0.6 41.8 ± 3.7 3.6 ± 0.2 
All stages     
1981 78 10.1 ± 1.6 39.1 ± 4.8 3.9 ± 0.5 
1990 47 10.8 ± 1.5 42.3 ± 6.0 3.9 ± 0.3 
Total 123 10.4 ± 1.6 40.3 ± 5.5 3.9 ± 0.4 
Thysanoessa longicaudata 
Furcilia     
1981 23 9.6 ± 1.3 37.9 ± 2.0 4.0 ± 0.4 
1990 41 10.4 ± 1.1 38.4 ± 2.5 3.7 ± 0.3 
Total 64 10.1 ± 1.2 38.2 ± 2.3 3.8 ± 0.4 
Juvenile     
1981 11.4 ± 1.0 41.1 ± 1.7 3.6 ± 0.2 
1990 9.0 ± 1.8 47.4 ± 5.5 5.5 ± 1.7 
Total 16 10.2 ± 1.9 44.3 ± 5.1 4.6 ± 1.5 
Female     
1981 10.9 ± 1.3 43.5 ± 3.5 4.1 ± 1.0 
1990 10.6 ± 0.2 41.7 ± 1.2 3.9 ± 0.1 
Total 16 10.7 ± 0.9 42.6 ± 2.7 4.0 ± 0.7 
Male     
1981 10.6 ± 2.1 45.1 ± 6.7 4.6 ± 1.9 
1990 7.4 51.2 6.9 
Total 10.2 ± 2.3 45.8 ± 6.5 4.8 ± 1.9 
All stages     
1981 46 10.3 ± 1.5 40.5 ± 4.3 4.0 ± 0.9 
1990 58 10.2 ± 1.3 40.3 ± 4.5 4.1 ± 1.0 
Total 101 10.2 ± 1.4 40.4 ± 4.4 4.0 ± 0.9 
Table V.

Nyctiphanes couchi. Dry weights, N and C content of calyptopis stages

Stage Dry weight (mg) %N %C C:N 
CI 0.02 ± <0.01 8.34 ± 08 33.41 ± 4.2 4.01 ± 0.4 
CII 0.03 ± 0.01 8.24 ± 0.7 36.02 ± 3.3 4.36 ± 0.5 
CIII 0.04 ± 0.01 9.08 ± 1.3 37.60 ± 5.6 4.15 ± 0.2 
Stage Dry weight (mg) %N %C C:N 
CI 0.02 ± <0.01 8.34 ± 08 33.41 ± 4.2 4.01 ± 0.4 
CII 0.03 ± 0.01 8.24 ± 0.7 36.02 ± 3.3 4.36 ± 0.5 
CIII 0.04 ± 0.01 9.08 ± 1.3 37.60 ± 5.6 4.15 ± 0.2 
Table VI.

Euphausiacea. Carbon and nitrogen content from other authors

Species Reference C (%DW) N (%DW) 
Euphausia krohni Gorsky et al., 1988 31.1 11.0 
Euphausia krohni Mauchline and Fisher, 1969 35.8 6.8 
Euphausia mutica Nemoto et al., 1969 41.7 11.2 
Euphausia nana Nemoto et al., 1969 42.0 10.4 
Euphausia pacifica Lasker, 1966 42.0 11.5 
Euphausia pacifica Ross, 1982 <40.0 <11.7 
Euphausia pacifica Mauchline and Fisher, 1969 38.1–45.1 10.4–13.0 
Euphausia pacifica Omori, 1969 38.7 10.7 
Euphausia pacifica Childress and Nygaard, 1974 40.1 12.4 
Euphausia pacifica eggs Iguchi and Ikeda, 1998 47.2 ± 0.4 9.6 ± 0.7 
Euphausia pacifica calyptopis Iguchi and Ikeda, 1998 37.5 9.9 
Euphausia pacifica furcilia I–II Iguchi and Ikeda, 1998 42.4 11.2 
Euphausia pacifica furcilia III–VI Iguchi and Ikeda, 1998 42.7 11.9 
Euphausia pacifica juvenile Iguchi and Ikeda, 1998 42.4 ± 0.9 11.2 ± 0.4 
Euphausia pacifica adult <16 mm Iguchi and Ikeda, 1998 43.2 ± 1.5 11.1 ± 0.6 
Euphausia pacifica adult 16–19 mm Iguchi and Ikeda, 1998 42.9 ± 1.2 11.4 ± 0.4 
Euphausia pacifica adult >19 mm Iguchi and Ikeda, 1998 43.1 ± 0.7 11.5 ± 0.2 
Euphausia recurva Nemoto et al., 1969 39.5 10.6 
Euphausia similis Nemoto et al., 1969 43.2 11.0 
Euphausia superba Jawed, 1969  11.7 
Euphausia superba Yanase, 1974  10.8 
Euphausia superba egg Ikeda, 1984 55.1 ± 2.7 9.0 ± 1.8 
Euphausia superba calyptopis Ikeda, 1984 35.3 ± 2.6 9.2 ± 0.7 
Euphausia superba furcilia Ikeda, 1984 41.1 ± 1.0 10.1 ± 0.5 
E.superba juvenile 10–50 mg dry weight Ikeda, 1984 41.1 ± 4.7 11.0 ± 1.2 
E.superba juvenile 50–100 mg dry weight Ikeda, 1984 44.7 ± 2.1 10.2 ± 0.6 
E.superba adult 100–200 mg dry weight Ikeda, 1984 46.6 ± 1.7 9.9 ± 0.9 
E.superba adult 200–300 mg dry weight Ikeda, 1984 47.5 ± 2.2 10.2 ± 1.1 
E.superba adult >300 mg dry weight Ikeda, 1984 47.5 ± 2.5 10.3 ± 0.7 
Meganyctiphanes norvegica Gorsky et al., 1988 36.8 11.0 
Meganyctiphanes norvegica Mauchline and Fisher, 1969 33.4–37.0 5.2–7.1, 9.9–10.8 
Meganyctiphanes norvegica (winter) Mayzaud, 1973 39.4 ± 0.49 11.5 ± 0.2 
Meganyctiphanes norvegica (spring) Mayzaud, 1973 46.5 ± 0.3 9.6 ± 0.3 
Meganyctiphanes norvegica Hopkins et al., 1978 45.0 ± 2.6 8.5 ± 1.6 
Nematoscelis megalops Gorsky et al., 1988 35.6 9.7 
Nematoscelis difficilis Hopkins, 1968 40.3–44.0 9.7–11.9 
Nematoscelis difficilis Nemoto et al., 1969 41.8 10.2 
Nematoscelis difficilis Nemoto et al., 1972 40.7 10.7 
Nematoscelis megalops Boyd et al., 1978 32.5 10.7 
Nematoscelis microps Nemoto et al., 1972 43.7 10.6 
Stylocheiron abbreviatum Gorsky et al., 1988 34.5 8.5 
Tessarobrachion occulatum Omori, 1969 47.2 10.0 
Thysanoessa inermis Hopkins et al., 1978 43.9 ± 2.8 9.6 ± 1.8 
Thysanoessa inermis Dalpadado and Ikeda, 1989 42.5 ± 3.5 8.5 ± 1.1 
Thysanoessa raschi Hopkins et al., 1978 40.6 ± 4.4 10.2 ± 2.1 
Thysanopoda aequalis Nemoto et al., 1969 39.8 10.5 
Species Reference C (%DW) N (%DW) 
Euphausia krohni Gorsky et al., 1988 31.1 11.0 
Euphausia krohni Mauchline and Fisher, 1969 35.8 6.8 
Euphausia mutica Nemoto et al., 1969 41.7 11.2 
Euphausia nana Nemoto et al., 1969 42.0 10.4 
Euphausia pacifica Lasker, 1966 42.0 11.5 
Euphausia pacifica Ross, 1982 <40.0 <11.7 
Euphausia pacifica Mauchline and Fisher, 1969 38.1–45.1 10.4–13.0 
Euphausia pacifica Omori, 1969 38.7 10.7 
Euphausia pacifica Childress and Nygaard, 1974 40.1 12.4 
Euphausia pacifica eggs Iguchi and Ikeda, 1998 47.2 ± 0.4 9.6 ± 0.7 
Euphausia pacifica calyptopis Iguchi and Ikeda, 1998 37.5 9.9 
Euphausia pacifica furcilia I–II Iguchi and Ikeda, 1998 42.4 11.2 
Euphausia pacifica furcilia III–VI Iguchi and Ikeda, 1998 42.7 11.9 
Euphausia pacifica juvenile Iguchi and Ikeda, 1998 42.4 ± 0.9 11.2 ± 0.4 
Euphausia pacifica adult <16 mm Iguchi and Ikeda, 1998 43.2 ± 1.5 11.1 ± 0.6 
Euphausia pacifica adult 16–19 mm Iguchi and Ikeda, 1998 42.9 ± 1.2 11.4 ± 0.4 
Euphausia pacifica adult >19 mm Iguchi and Ikeda, 1998 43.1 ± 0.7 11.5 ± 0.2 
Euphausia recurva Nemoto et al., 1969 39.5 10.6 
Euphausia similis Nemoto et al., 1969 43.2 11.0 
Euphausia superba Jawed, 1969  11.7 
Euphausia superba Yanase, 1974  10.8 
Euphausia superba egg Ikeda, 1984 55.1 ± 2.7 9.0 ± 1.8 
Euphausia superba calyptopis Ikeda, 1984 35.3 ± 2.6 9.2 ± 0.7 
Euphausia superba furcilia Ikeda, 1984 41.1 ± 1.0 10.1 ± 0.5 
E.superba juvenile 10–50 mg dry weight Ikeda, 1984 41.1 ± 4.7 11.0 ± 1.2 
E.superba juvenile 50–100 mg dry weight Ikeda, 1984 44.7 ± 2.1 10.2 ± 0.6 
E.superba adult 100–200 mg dry weight Ikeda, 1984 46.6 ± 1.7 9.9 ± 0.9 
E.superba adult 200–300 mg dry weight Ikeda, 1984 47.5 ± 2.2 10.2 ± 1.1 
E.superba adult >300 mg dry weight Ikeda, 1984 47.5 ± 2.5 10.3 ± 0.7 
Meganyctiphanes norvegica Gorsky et al., 1988 36.8 11.0 
Meganyctiphanes norvegica Mauchline and Fisher, 1969 33.4–37.0 5.2–7.1, 9.9–10.8 
Meganyctiphanes norvegica (winter) Mayzaud, 1973 39.4 ± 0.49 11.5 ± 0.2 
Meganyctiphanes norvegica (spring) Mayzaud, 1973 46.5 ± 0.3 9.6 ± 0.3 
Meganyctiphanes norvegica Hopkins et al., 1978 45.0 ± 2.6 8.5 ± 1.6 
Nematoscelis megalops Gorsky et al., 1988 35.6 9.7 
Nematoscelis difficilis Hopkins, 1968 40.3–44.0 9.7–11.9 
Nematoscelis difficilis Nemoto et al., 1969 41.8 10.2 
Nematoscelis difficilis Nemoto et al., 1972 40.7 10.7 
Nematoscelis megalops Boyd et al., 1978 32.5 10.7 
Nematoscelis microps Nemoto et al., 1972 43.7 10.6 
Stylocheiron abbreviatum Gorsky et al., 1988 34.5 8.5 
Tessarobrachion occulatum Omori, 1969 47.2 10.0 
Thysanoessa inermis Hopkins et al., 1978 43.9 ± 2.8 9.6 ± 1.8 
Thysanoessa inermis Dalpadado and Ikeda, 1989 42.5 ± 3.5 8.5 ± 1.1 
Thysanoessa raschi Hopkins et al., 1978 40.6 ± 4.4 10.2 ± 2.1 
Thysanopoda aequalis Nemoto et al., 1969 39.8 10.5 
Fig. 1.

Euphausia krohni, Meganyctiphanes norvegica, Nyctiphanes couchi, Thysanoessa longicaudata and Thysanopoda acutifrons. Numbers of specimens in the 0.5 mm size ranges weighed only (black section of columns) and weighed and analysed for carbon and nitrogen content (open sections of columns).

Fig. 1.

Euphausia krohni, Meganyctiphanes norvegica, Nyctiphanes couchi, Thysanoessa longicaudata and Thysanopoda acutifrons. Numbers of specimens in the 0.5 mm size ranges weighed only (black section of columns) and weighed and analysed for carbon and nitrogen content (open sections of columns).

Fig. 2.

Euphausiacea. Carbon and nitrogen content (%) plotted against dry weight. The r values for the linear regression are shown, that for %N against dry weight is significant at the 0.1% level.

Fig. 2.

Euphausiacea. Carbon and nitrogen content (%) plotted against dry weight. The r values for the linear regression are shown, that for %N against dry weight is significant at the 0.1% level.

Fig. 3.

Thysanoessa longicaudata. C:N values plotted against dry weight. Separate regression lines are plotted and correlation coefficients are given for the group of high (>5.0) C:N values (open circles and broken line) and the majority of points (C:N < 5.0). The former is significant at the 5% level. For the group with high C:N values, the points are labelled as J (juvenile), F (female) or M (male).

Fig. 3.

Thysanoessa longicaudata. C:N values plotted against dry weight. Separate regression lines are plotted and correlation coefficients are given for the group of high (>5.0) C:N values (open circles and broken line) and the majority of points (C:N < 5.0). The former is significant at the 5% level. For the group with high C:N values, the points are labelled as J (juvenile), F (female) or M (male).

We thank the master and crew of RRS ‘Challenger’ and colleagues who participated in the cruise and contributed to the sampling programme. The work constituted part of the research programme of the Institute for Marine Environmental Research until 1989 and of the Plymouth Marine Laboratory thereafter.

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