Crustaceana 96 (2) 113-129

BODY LENGTH, DRY AND ASH-FREE DRY WEIGHTS, AND
DEVELOPMENTAL CHANGES AT EACH COPEPODID STAGE IN FIVESYMPATRIC MESOPELAGIC AETIDEID COPEPODS IN THE WESTERNARCTIC OCEAN
BY
YUNOSUKE KOGUCHI1,6 ), KOKI TOKUHIRO1,2 ), CARIN J. ASHJIAN3 ),ROBERT G. CAMPBELL4 ) and ATSUSHI YAMAGUCHI1,5,7 )1 ) Faculty / Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho,Hako-date, Hokkaido 041-8611, Japan2 ) Present address: Environmental Management Research Institute, National Institute of Advanced
Industrial Science and Technology, 16-1 Onogawa, Tsukuba, Ibaraki 305-0053, Japan3 ) Biology Department, Woods Hole Oceanographic Institution, 266 Woods Hole Road., Woods
Hole, MA 02543, U.S.A.
4 ) Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, U.S.A.
5 ) Arctic Research Center, Hokkaido University, Kita-21 Nishi-11 Kita-ku, Sapporo, Hokkaido
001-0021, Japan
ORCID iD: Koguchi: 0000-0002-1647-4804

ABSTRACT
Aetideid copepods dominate the mesopelagic layer of the Arctic Ocean and play an importantrole in the vertical material flux and biodiversity. However, little information about the lengths
and weights of their copepodids is available. In this study, we collected five sympatric aetideid
copepods, Chiridius obtusifrons Sars G.O., 1902, Gaetanus tenuispinus (Sars G.O., 1900), Gaetanus
brevispinus (Sars G.O., 1900), Aetideopsis multiserrata (Wolfenden, 1904), and Aetideopsis rostrata
Sars G.O., 1903, from the Arctic Ocean and examined their body lengths, dry and ash-free dryweights, and developmental growths at each copepodid stage. Highly significant length-weight
relationships were obtained among copepodids for all species. Within genera, individuals of the samelength were heavier at shallower depths. This may result from the greater nutritional availability to
species within genera inhabiting shallower depths. Common to all species, the organic content (ashfree dry weight per dry weight) was high for the early copepodid stages. This may be due to theresidual organic content of lipid-rich eggs retained in the non-feeding nauplii. The largest growth infemales occurred at C5/C6, whereas the largest growth in males occurred at C4/C5, as determined bymoult increment and proportion of growth in weight. These sex differences in weight growth could
be due to the degeneration of the feeding appendage and cessation of feeding in C6 males of aetideid
copepods.

6 ) Co-corresponding author; e-mail: makaroni1009@eis.hokudai.ac.jp
7 ) Co-corresponding author; e-mail: a-yama@fish.hokudai.ac.jp© KONINKLIJKE BRILL NV, LEIDEN, 2023

DOI
10.1163/15685403-bja10272
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Key words. — Aetideidae, mesopelagic copepods, moult increment, organic contents, prosome
lengthRÉSUMÉ
Les copépodes Aetideidae dominent la zone mésopélagique de l’Océan Arctique et jouent unrôle important dans le flux vertical de matière et dans la biodiversité. Cependant, peu d’informations
sur les longueurs et les poids de leurs copépodites sont disponibles. Dans cette étude, nous avons
collecté cinq espèces sympatriques d’Aetideidae, Chiridius obtusifrons Sars G.O., 1902, Gaetanus
tenuispinus (Sars G.O., 1900), Gaetanus brevispinus (Sars G.O., 1900), Aetideopsis multiserrata(Wolfenden, 1904), et Aetideopsis rostrata Sars G.O., 1903, dans l’Océan Arctique et nous avons
examiné leur longueurs du corps, leur poids sec et leur poids sec sans cendres ainsi que leurcroissance au cours du développement à chaque stade copépoditique. Des relations longueur-poids
hautement significatives ont été obtenues chez les copépodites pour toutes les espèces. Au sein desgenres, les individus de même longueur étaient plus lourds lorsque la profondeur était moindre.
Ceci peut résulter de la plus grande disponibilité nutritionnelle pour les espèces des genres vivant àde plus faibles profondeurs. Pour toutes les espèces, le contenu organique (poids sec sans cendres
par poids sec) était élevé chez les premiers stades copépoditiques. Ceci peut être dû au contenu
organique résiduel des œufs riches en lipides conservé par les nauplies qui ne s’alimentent pas. La
plus forte croissance chez les femelles a été observée aux stades C5/C6, tandis que la plus forte
croissance chez les mâles se situe aux stades C4/C5, tel que déterminé par l’accroissement de la mue
et le pourcentage de la croissance en poids. Ces différences de la croissance en poids entre sexes
pourraient être dues à la atrophie des appendices buccaux et l’arrêt de la nutrition chez les mâles C6
des copépodes Aetideidae.
Mots clés. — Aetideidae, copépodes mésopélagiques, accroissement de la mue, contenusorganiques, longueur du prosome

INTRODUCTION

In Arctic marine ecosystems, zooplankters are important secondary producers
and play important roles in energy transfer for higher trophic-level organisms andvertical material transport (Lowry et al., 2004; Wassmann et al., 2006). Copepods
are the most dominant zooplankton taxa in the Arctic Ocean (Thibault et al.,
1999; Ashjian et al., 2003). Ecological information on Arctic planktonic copepods
is generally available for the dominant surface-dwelling copepod species (e.g.,
Pseudocalanus spp.) and the interzonal, biomass-dominant copepods that havea diapause phase at deeper depths (e.g., Calanus spp.). However, the species
diversity of copepods is known to be high in the deep sea, especially in mesopelagiczones (Auel & Hagen, 2002; Kosobokova et al., 2011; Smoot & Hopcroft, 2017),
and these species have received much less attention.
In the mesopelagic zone of the Arctic Ocean, copepods belonging to Aetideidae
are dominant and characterized by high species diversity (Richter, 1995; Markhaseva, 1996; Auel, 1999). Aetideid copepods are omnivores or detritivores, opportunistic feeders, and carnivores (Richter, 1995; Auel, 1999; Sano et al., 2013,2015). The occurrence of species-specific food preferences (Laakmann et al.,Downloaded from Brill.com08/18/2023 11:48:24AM
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2009a, b; Sano et al., 2013, 2015) and species-specific vertical segregations within
the family (Kosobokova & Hirche, 2000; Auel & Hagen, 2002; Laakmann et al.,2009a; Smoot & Hopcroft, 2017) are well documented. Although the environmental conditions of the deep Arctic Ocean are homogeneous (cold and dark), thecoexistence of many aetideid species is thought to have been achieved by verticaldisplacement of species and food segregation (Laakmann et al., 2009a, b; Laakmann & Auel, 2010). Mesopelagic copepods have been reported to substantiallyaffect vertical material flux to the deep sea by feeding on sinking particles andegesting faecal pellets (Dilling et al., 1998; Wilson et al., 2010). Aetideid copepods in the Greenland Sea consume 40% of the particulate organic carbon fluxthat reaches their habitat depth (Auel, 1999). These facts suggest that Aetideidae
is an important copepod family in the Arctic Ocean because of their high species
diversity and ability to affect the vertical distribution of organic carbon.
For mesopelagic copepods, the body length and weight of each copepodid
stage and their moult increments reflect their growth rate and time spent at eachstage (Yamaguchi & Ikeda, 2000; Yamaguchi et al., 2019, 2020). However, owing
to difficulties in species identification, especially in the early copepodid stages,
information on the length and weight of each copepodid stage of Aetideidae in the
Arctic Ocean is scarce. In addition, developmental changes in length and weightremain unknown.
In this study, we examined a year-round time series of zooplankton samples
collected from the drifting ice station at the Surface Heat Budget of the Arctic
Ocean (SHEBA) project in the western Arctic Ocean. Using these samples, werecently presented species identification keys on five sympatric aetideid copepods(Koguchi et al., 2022). In this study, we determined the length and weight of five
sympatric aetideid species, including all copepodid stages except the C1 and C2stages of one species (Aetideopsis rostrata Sars G.O., 1903). Organic contents(ash-free dry weight fraction within the dry weight) were also determined, andthe moult increments and proportions of growth among the stages were calculated
and compared. Through inter-species comparisons of the five sympatric aetideid
species, we discuss the mechanisms underlying the coexistence of the five species
in the mesopelagic layer of the Arctic Ocean.

MATERIAL AND METHODS

Field sampling
Zooplankton sampling was conducted at Ice Station SHEBA at 10-14-day
intervals from 27 October 1997 to 29 September 1998. Vertically stratified samples
were collected using a closing net with a 1-m2 mouth area equipped with a 150-μm
or 53-μm mesh from two to seven depth layers over a depth range of 0-3500 m. Ice
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Station SHEBA drifted from the Canadian Basin to the Mendeleyev Basin during
the one-year sampling period (Ashjian et al., 2003). Because of this drift, the water
depth varied from 352 m to 3800 m during the sampling period. Consequently,
collection depths and numbers of layers sampled ranged from 0 to 100 m to 03500 m and from two to seven layers, respectively. All zooplankton samples were
preserved in seawater with 4% buffered formaldehyde.
Prosome length
Using a stereomicroscope, the five dominant aetideid copepods — Chiridius
obtusifrons Sars G.O., 1902, Gaetanus tenuispinus (Sars G.O., 1900), Gaetanus
brevispinus (Sars G.O., 1900), Aetideopsis multiserrata (Wolfenden, 1904), andA. rostrata — were sorted, identified, and each copepodid stage was enumerated.
While other aetideid species occurred in the samples, we concentrated on theabove-mentioned species because of the dominant numbers of individuals. We
have published elsewhere details of species identification methods of them down
to the C1 stage (Koguchi et al., 2022). Note that no C1 and C2 stages of A. rostrata
occurred in the samples, because of the deepest occurrence of this species (cf.
Koguchi et al., 2022). Based on the presence or absence of leg 5, we identified
males and females of C4 and C5. The specimens of each species/stage when
they were most abundant in the samples were used for the subsequent length andweight measurements. For details on the abundance of each species/stage in eachsample, see Koguchi et al. (2022). The prosome length (PL) was measured for 510 individuals at each copepodid stage under a stereomicroscope using an eyepiecemicrometre with a precision of 10 μm.
Dry and ash-free dry weightThe dry weight (DW) and ash-free dry weight (AFDW) of the five aetideid
species were measured at each copepodid stage using formaldehyde-preserved
samples. Each copepodid stage of each species was pooled into five duplicate
batches, including 2-15 individuals of each stage, selected depending on bodyweight, rinsed briefly in distilled water, blotted dry using filter paper, and placedin a pre-weighed, pre-combusted aluminium pan. The specimens were dried in anoven at 60°C for 5 h, and the DW was determined using an electronic balance(XP6 Micro Balance; Mettler Toledo, Greifensee, Switzerland) with a precisionof 1 μg. The ash weight was determined by reweighing the same samples after
combusting them at 480°C for 5 h. The AFDW was then determined based on
the difference between DW and ash weight (AFDW = DW − Ash weight). The
organic content, expressed as a percentage of AFDW in DW (% DW), was also
calculated. Based on the PL, DW, and AFDW data for each copepodid stage, aDownloaded from Brill.com08/18/2023 11:48:24AM
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LENGTHS AND WEIGHTS OF AETIDEID COPEPODS

length-weight relationship for each species was expressed by the power equation
W = a × Lb , where W is the DW or AFDW (μg), L is the PL (mm), and a andb are fitted constants. For organic content, differences among copepodid stages ofa species, and among the same copepodid stage of different species, were tested
using one-way ANOVA. For ANOVA, we confirmed that the normal distributionof each stage (n = 5) and the variances of the residuals were at the same levels.
We performed ANOVA by using the software StatView.
Based on the PL, DW, and AFDW data, the moult increment (MI; %) was
calculated using the following formula (Mauchline, 1998) for all three attributes:
MI(%) = 100 × (post-moult size − pre-moult size)/ pre-moult size

To evaluate the proportion of growth at each stage, the proportions of growth(PG; %) at Cn−1 /Cn for PL, DW, and AFDW were determined for females andmales, and the values of the adults were set as 100% (Yamaguchi et al., 2020).
PG(%) at Cn−1 /Cn =6
(Value of Cn − Value of Cn−1 )n=1Value of adult (C6)× 100

RESULTS

Length and weights
The length and weight data at each stage and length-weight relationships basedon the power equation for the five sympatric aetideid copepods in the Arctic Ocean
are summarized in tables I-X. Within the same genus, the PL varied with thespecies. For the genus Gaetanus, the PLs of G. brevispinus were larger than thoseof G. tenuispinus for all copepodid stages. For the genus Aetideopsis, A. rostrata
was larger than A. multiserrata for all stages. For all species, the length-weightequations (DW-PL and AFDW-PL) were highly significant (r 2 = 0.982 − 0.992,
p<0.0001). Inter-species comparison in terms of the weights at the same PL
revealed that Chiridius obtusifrons was the heaviest, followed by A. multiserrata,
A. rostrata, G. tenuispinus, and G. brevispinus (fig. 1).
Organic contents
The mean organic contents of the five aetideid copepods at each copepodid
stage are shown in fig. 2. Overall, the organic content ranged between 77.9%
and 96.3% of the DW. Within species, the organic content was higher in the early
copepodid stages than in the late copepodid stages (p<0.05, one-way ANOVA).
This ontogenetic pattern for organic content was found among all studied aetideid
copepod species studied here. Inter-species differences were detected in seven of
the nine stages examined (p<0.05, one-way ANOVA).
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TABLE I
Summary of prosome length (PL), dry weight (DW), and ash-free dry weight (AFDW) data of
Chiridius obtusifrons Sars G.O., 1902
Stage

PL (mm)DW (μg)

AFDW (μg)

C10.77 ± 0.01
(10)
1.04 ± 0.02
(10)
1.30 ± 0.02
(10)
1.75 ± 0.03
(10)1.71 ± 0.04
(10)
2.36 ± 0.03
(10)
2.27 ± 0.05
(10)
3.08 ± 0.06
(10)
2.30 ± .005
(10)

3.38 ± 0.38
(5)10.61 ± 0.66
(5)23.18 ± 1.81
(5)
63.83 ± 7.99
(5)50.3 ± 13.12(5)
161.48 ± 30.23(5)
216.38 ± 33.96(5)
514.48 ± 60.26(5)177.28 ± 12.11(5)

3.62 ± 0.35
(5)9.61 ± 0.71
(5)19.93 ± 1.78
(5)
52.97 ± 7.21
(5)43.23 ± 11.13(5)
142.28 ± 27.06(5)190.08 ± 31.11(5)446.48 ± 56.13(5)
151.48 ± 11.31
(5)

C2
C3
C4F
C4M
C5F
C5M
C6F
C6M

Values are represented as mean ± 1 SD. The numbers of replicates are in parentheses. To analyse
the body allometry, the power regression model was used Y = a · X b , where Y is DW or AFDW(μg) and X is PL (mm). F, female; M, male.

Moult increment
The MIs for length and weight of the five aetideid copepods are shown infig. 3. Throughout the stages and species, the MI ranged from −20.3% to 339.6%.
Common for all species, the MI at C5/C6 varied with sex; the MIs of C5/C6
females were much larger than those of males. For C5/C6 males, minus MI(negative growth) was observed for the DW and AFDW of C. obtusifrons, and
the PL of G. brevispinus.
TABLE II
Regression statistics for body allometry of Chiridius
obtusifrons Sars G.O., 1902

Constant (a)Power (b)
r2
p

DW-PL

AFDW-PL

9.11
3.55
0.99
<0.0001

8.15
3.50
0.99
<0.0001
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TABLE III
Summary of prosome length (PL), dry weight (DW), and ash-free dry weight (AFDW) data of
Gaetanus tenuispinus (Sars G.O., 1900)
Stage

PL (mm)DW (μg)

AFDW (μg)

C10.81 ± 0.02
(10)
1.11 ± 0.02
(10)
1.41 ± 0.03
(10)
1.95 ± 0.07
(10)
1.89 ± 0.05
(10)
2.52 ± 0.09
(10)
2.53 ± 0.04
(10)
3.20 ± 0.09
(10)
2.73 ± 0.07
(10)

4.12 ± 0.25
(5)7.53 ± 0.50
(5)15.50 ± 1.12
(5)59.73 ± 11.74(5)58.40 ± 3.04
(5)
144.30 ± 31.95(5)
153.80 ± 28.10(5)376.40 ± 57.24(5)
209.45 ± 34.92(5)

3.67 ± 0.33
(5)6.80 ± 0.48
(5)14.00 ± 0.42
(5)54.73 ± 10.40(5)52.88 ± 4.11
(5)126.12 ± 28.43(5)
135.72 ± 26.29(5)
317.52 ± 51.14(5)
185.10 ± 31.58
(5)

C2
C3
C4F
C4M
C5F
C5M
C6F
C6M

Values are represented as mean ± 1 SD. The numbers of replicates are in parentheses. To analyse
the body allometry, the power regression model was used Y = a · X b , where Y is DW or AFDW(μg) and X is PL (mm). F, female; M = male.

Proportion of growth
The results of the PG at each copepodid stage, treating the adult value as 100%,are shown in fig. 4. As previously mentioned, PG also showed sex differences inC5/C6. For all weights (DW and AFDW) and species, the PG was the largest infemales at C5/C6. Thus, more than half of the PGs were observed at C5/C6. In
contrast, in males, the PGs were small at C5; the PGs were the largest at C4/C5,
rather than those at C5/C6.
TABLE IV
Regression statistics for body allometry of Gaetanus
tenuispinus (Sars G.O., 1900)

Constant (a)Power (b)
r2
p

DW-PL

AFDW-PL

6.31
3.42
0.99
<0.0001

5.71
3.39
0.99
<0.0001
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TABLE V
Summary of prosome length (PL), dry weight (DW), and ash-free dry weight (AFDW) data of
Gaetanus brevispinus (Sars G.O., 1900)
Stage

PL (mm)DW (μg)

AFDW (μg)

C11.03 ± 0.02
(10)
1.35 ± 0.02
(10)
1.85 ± 0.03
(10)
2.47 ± 0.04
(10)
2.44 ± 0.03
(10)
3.12 ± 0.04
(10)
3.08 ± 0.06
(10)
3.83 ± 0.09
(10)
3.07 ± 0.06
(10)

9.27 ± 0.58
(5)14.51 ± 1.33
(5)
50.23 ± 3.83
(5)
108.63 ± 11.48(5)
113.17 ± 9.98
(5)
284.65 ± 26.07(5)
317.15 ± 56.60(5)
557.75 ± 39.01(5)
345.35 ± 54.89(5)

8.61 ± 0.73
(5)13.20 ± 1.38
(5)45.05 ± 3.37
(5)97.02 ± 11.79(5)
98.15 ± 9.57
(5)234.12 ± 27.37(5)247.83 ± 48.11(5)474.80 ± 38.01(5)304.10 ± 47.34
(5)

C2
C3
C4F
C4M
C5F
C5M
C6F
C6M

Values are represented as mean ± 1 SD. The numbers of replicates are in parentheses. To analyse
the body allometry, the power regression model was used Y = a · X ∗ b, where Y is DW or AFDW(μg) and X is PL (mm). F, female; M, male.
DISCUSSION

Length, weights, and organic contents
This study established length (PL)-weight (DW and AFDW) equations for fiveaetideid copepod species in the Arctic Ocean. In the inter-species comparison,
weights at the same PLs were the largest for Chiridius obtusifrons, followed by
the genus Aetideopsis spp., whereas Gaetanus spp. was the lightest (fig. 1). In
the Arctic Ocean, the vertical distribution of these aetideid copepods varied withspecies, from shallow to deep in the order of C. obtusifrons (shallowest) < G.
TABLE VI
Regression statistics for body allometry of Gaetanus
brevispinus (Sars G.O., 1900)

Constant (a)Power (b)
r2
p

DW-PL

AFDW-PL

6.66
3.31
0.99
<0.0001

6.24
3.22
0.99
<0.0001
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TABLE VII
Summary of prosome length (PL), dry weight (DW), and ash-free dry weight (AFDW) data of
Aetideopsis multiserrata (Wolfenden, 1904)Stage

PL (mm)DW (μg)

AFDW (μg)

C10.73 ± 0.02
(10)
0.98 ± 0.03
(10)
1.20 ± 0.03
(10)
1.58 ± 0.04
(10)
1.59 ± 0.03
(10)
2.08 ± 0.07
(10)
2.13 ± 0.07
(10)2.64 ± 0.10(10)
2.18 ± 0.04
(10)

2.78 ± 0.27
(5)5.81 ± 0.58
(5)
11.36 ± 1.73
(5)30.82 ± 6.78
(5)37.42 ± 4.13
(5)108.83 ± 15.02(5)98.68 ± 29.60(5)
273.77 ± 93.21(5)
109.67 ± 13.39(5)

2.68 ± 0.25
(4)5.60 ± 0.57
(5)
10.35 ± 1.66
(5)
27.67 ± 5.88
(5)33.07 ± 4.24
(5)89.00 ± 11.85(5)85.60 ± 27.74(5)232.90 ± 82.77(5)95.40 ± 12.31
(5)

C2
C3
C4F
C4M
C5F
C5M
C6F
C6M

Values are represented as mean ± 1 SD. The numbers of replicates are in parentheses. To analyse
the body allometry, the power regression model was used Y = a · X b , where Y is DW or AFDW(μg) and X is PL (mm). F, female; M, male.

tenuispinus < G. brevispinus < A. multiserrata < A. rostrata (deepest) (Richter,
1994; Laakmann et al., 2009a; Smoot & Hopcroft, 2017). This vertical distribution
order was also observed for the SHEBA samples treated in this study (Koguchi
et al., 2022). Notably, the weights were higher for shallower dwelling species
under the same PL conditions within the same genus. Within the same stages,
the organic content (% DW) was higher for the shallower dwelling species thanfor the deeper dwelling ones. This pattern was the most prominent, especiallyin the late copepodid stages (fig. 2). The weight per length and organic content
TABLE VIII
Regression statistics for body allometry data of
Aetideopsis multiserrata (Wolfenden, 1904)

Constant (a)Power (b)
r2
p

DW-PL

AFDW-PL

6.90
3.61
0.99
<0.0001

6.47
3.49
0.99
<0.0001
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TABLE IX
Summary of prosome length (PL), dry weight (DW), and ash-free dry weight (AFDW) data of
Aetideopsis rostrata Sars G.O., 1903
Stage

PL (mm)DW (μg)

AFDW (μg)

C31.50 ± 0.05
(10)
1.98 ± 0.07
(10)
2.21 ± 0.05
(10)2.64 ± 0.19
(10)
3.09 ± 0.06
(10)
3.34 ± 0.07
(10)
3.34 ± 0.11
(5)29.51 ± 4.50
(5)83.02 ± 5.54
(5)110.08 ± 13.33(5)
154.12 ± 33.73(5)335.83 ± 77.69(5)
402.58 ± 38.59(5)
481.75 ± 88.66(4)

26.20 ± 4.83
(5)69.92 ± 4.22
(5)93.12 ± 11.79(5)
126.38 ± 31.41(5)284.07 ± 68.50(5)323.20 ± 36.35(5)
409.50 ± 79.65
(4)

C4F
C4M
C5F
C5M
C6F
C6M

Values are represented as mean ± 1 SD. The numbers of replicates are in parentheses. To analyse
the body allometry, the power regression model was used Y = a · X b , where Y is DW or AFDW(μg) and X is PL (mm). F, female; M, male.

may reflect the nutritional conditions (Yamaguchi et al., 2019, 2020). Since foodresources are limited in the deep sea and are supplied from the upper layer, thenutritional supply within the same genus is expected to be higher for shallowerdwelling species than for deep-dwelling species (Yamaguchi et al., 2002, 2019).
Thus, the heavier weights per length and higher organic content observed in theshallow-dwelling species within the genera Gaetanus and Aetideopsis may reflect
a greater food availability to the shallower-dwelling species than to the deeperdistributed species.
Ontogenetic changes in the organic content within species were common for
Aetideidae, with high organic contents (90-95% DW) at early copepodid stages
and a diminution during development toward approximately 85% DW in adultfemales (fig. 2). This reflects the lipid-rich eggs of Aetideidae. In the Arctic
TABLE X
Regression statistics for body allometry of Aetideopsis
rostrata Sars G.O., 1903

Constant (a)Power (b)
r2
p

DW-PL

AFDW-PL

7.84
3.30
0.99
<0.0001

7.05
3.23
0.98
<0.0001
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Fig. 1. Relationships between dry weight (DW) and prosome length (PL) (upper) and ash-free dryweight (AFDW) and PL (lower) for the five dominant aetideid copepods in the western Arctic
Ocean: Chiridius obtusifrons Sars G.O., 1902, Gaetanus tenuispinus (Sars G.O., 1900), Gaetanus
brevispinus (Sars G.O., 1900), Aetideopsis multiserrata (Wolfenden, 1904), and Aetideopsis rostrata
Sars G.O., 1903. For details of the regressions, see tables II, IV, VI, VIII and X.

Ocean, the aetideid copepods spawn a small number of large eggs that are thought
to be able to develop without feeding during the naupliar stage (Kosobokova etal., 2007). Naupliar development without feeding has been reported during thelaboratory rearing of Gaetanus variabilis (Brodsky, 1950) (currently considered
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Fig. 2. Organic contents (% of DW) of the five dominant aetideid copepods in the western Arctic
Ocean: Chiridius obtusifrons Sars G.O., 1902, Gaetanus tenuispinus (Sars G.O., 1900), Gaetanus
brevispinus (Sars G.O., 1900), Aetideopsis multiserrata (Wolfenden, 1904), and Aetideopsis rostrata
Sars G.O., 1903, at each copepodid stage. Symbols and bars represent means and standard errors,
respectively. F, female; M, male. Inter-species differences were tested by one-way ANOVA for eachstage. * p<0.05, ** p<0.01, *** p<0.001.

a synonym and referred to as Gaetanus minutus (Sars G.O., 1907)), a dominant
aetideid copepod found in the mesopelagic zone of the western subarctic Pacific(Yamaguchi & Ikeda, 2000). As a reproduction characteristic of mesopelagic
copepods, spawning with a small number of large-sized eggs rich in lipids iswell documented (Mauchline, 1998). Hence, the high organic content in the early
copepodid stages observed in this study may result from the residual organic
content of lipid-rich eggs carried through the naupliar phase and into the early
copepodids.
Moult increment / proportion of growth
A common feature observed for the MI and PG of the five aetideid species wassexual differences at the C5/C6 stages. Thus, the MI was the greatest for females
between C5/C6 but almost non-existent for males at the same stage (fig. 3). For
PG, more than half of the growth of females occurred by C5/C6, especially ofbody weight, but showed extremely low proportions in males (fig. 4). These sex
differences in weight growth may result from the degeneration of the feeding
appendages and cessation of feeding in C6 male aetideid copepods (Ohtsuka &Huys, 2001; Yamaguchi et al., 2005, 2007). The longevity of the C6 males afterDownloaded from Brill.com08/18/2023 11:48:24AM
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Fig. 3. Moult increments (MI) in prosome length (PL) and body weights (DW: dry weight, AFDW:
ash-free dry weight) of the five dominant aetideid copepods in the western Arctic Ocean: Chiridius
obtusifrons Sars G.O., 1902, Gaetanus tenuispinus (Sars G.O., 1900), Gaetanus brevispinus (Sars
G.O., 1900), Aetideopsis multiserrata (Wolfenden, 1904), and Aetideopsis rostrata Sars G.O., 1903.
F, female; M, male.

cessation of feeding is expected to be short. This is confirmed by the extremely low
abundance of C6 males in the field populations (Yamaguchi & Ikeda, 2000). An
extremely low abundance of C6 males in the field was also observed in the western
Arctic Ocean in this study (Koguchi et al., 2022).
The PG in weight may depend on the time spent at each copepodid stage(Yamaguchi et al., 2020, 2022). Thus, females undergo more than half of the PG
in their lifetime at the C5/C6 stage and are considered to spend a longer time at
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Fig. 4. The proportion of growth (PG) in prosome length (PL) and weights (dry weight (DW) andash-free dry weight (AFDW)) at each stage, which is calculated by the C6 values as 100% for
the five dominant aetideid copepods in the western Arctic Ocean: Chiridius obtusifrons Sars G.O.,
1902, Gaetanus tenuispinus (Sars G.O., 1900), Gaetanus brevispinus (Sars G.O., 1900), Aetideopsis
multiserrata (Wolfenden, 1904), and Aetideopsis rostrata Sars G.O., 1903. Note that C1 and C2 were
not available for Aetideopsis rostrata; their C2/C3 stage is treated as <C3.

C6. In contrast, the highest PG was observed for males at C4/C5, suggesting thatmales spend a long time in the field at C5. These facts indicate that there are sex
differences in the stages with the longest residence time: C6 in females and C5 inmales. The longer time females spend at C6 may allow them to promptly adapt
to the initiation of reproduction and changes in food availability (Yamaguchi &Ikeda, 2000; Yamaguchi et al., 2020).
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ACKNOWLEDGEMENTS

The comments by Dr. Frank D. Ferrari were very valuable for improving themanuscript. We thank the crew members of the CCGS “Des Groseilliers” and the
SHEBA project members, most especially Harold “Buster” Welch, for assistancein collecting the samples and CTD data. The collection of samples was supported
in part by grants #OCE9707184 to C. J. Ashjian and #OCE9707182 to R. G.
Campbell from the U.S. National Science Foundation. This work was partially
supported by the Arctic Challenge for Sustainability II (ArCS II) Program Grant
Number JPMXD1420318865. This research was also supported by the Environment Research and Technology Development Fund (JPMEERF20214002) of theEnvironmental Restoration and Conservation Agency of Japan. In addition, thiswork was partly supported by a Grant-in-Aid for Challenging Research (Pioneering) JP20K20573 and Scientific Research grants JP22H00374 (A), JP21H02263(B), JP20H03054 (B), and JP19H03037 (B) from the Japanese Society for the Promotion of Science (JSPS).

REFERENCES
ASHJIAN, C. J., R. G. CAMPBELL, H. E. WELCH, M. BUTLER & D. V. KEUREN, 2003. Annual cycle
in abundance, distribution, and size in relation to hydrography of important copepod species in
the western Arctic Ocean. Deep-Sea Res. I, 50(10-11): 1235-1261.
AUEL, H., 1999. The ecology of Arctic deep-sea copepods (Euchaetidae and Aetideidae). Aspects of
their distribution, trophodynamics and effect on the carbon flux. Ber. Polarforsch., 319: 1-97.
AUEL, H. & W. HAGEN, 2002. Mesozooplankton community structure, abundance and biomass inthe central Arctic Ocean. Mar. Biol., 140(5): 1013-1021.
BROCK, T. D., 1981. Calculating solar radiation for ecological studies. Ecol. Model., 14(1-2): 1-19.
DILLING, L., J. WILSON, D. STEINBERG & A. ALLDREDGE, 1998. Feeding by the euphausiid
Euphausia pacifica and the copepod Calanus pacificus on marine snow. Mar. Ecol. Prog. Ser.,
170: 189-201.
KOGUCHI, Y., K. TOKUHIRO, C. J. ASHJIAN, R. G. CAMPBELL & A. YAMAGUCHI, 2022. Interspecies comparison of the copepodite stage morphology, vertical distribution, and seasonal
population structure of five sympatric mesopelagic aetideid copepods in the western Arctic
Ocean. Front. Mar. Sci., 9: 943100. DOI:10.3389/fmars.2022.943100.
KOSOBOKOVA, K. & H. J. HIRCHE, 2000. Zooplankton distribution across the Lomonosov Ridge,
Arctic Ocean: species inventory, biomass and vertical structure. Deep-Sea Res. I, 47(11): 20292060.
KOSOBOKOVA, K. N., H. J. HIRCHE & R. R. HOPCROFT, 2007. Reproductive biology of deep-watercalanoid copepods from the Arctic Ocean. Mar. Biol., 151: 919-934.
KOSOBOKOVA, K. N., R. R. HOPCROFT & H. J. HIRCHE, 2011. Patterns of zooplankton diversity
through the depths of the Arctic’s central basins. Mar. Biodiv., 41(1): 29-50.
LAAKMANN, S. & H. AUEL, 2010. Longitudinal and vertical trends in stable isotope signatures(δ 13 C and δ 15 N) of omnivorous and carnivorous copepods across the south Atlantic Ocean.
Mar. Biol., 157: 463-471.
Downloaded from Brill.com08/18/2023 11:48:24AM
via communal account128

YUNOSUKE KOGUCHI ET AL.

LAAKMANN, S., M. KOCHZIUS & H. AUEL, 2009a. Ecological niches of Arctic deep-sea copepods:
vertical partitioning, dietary preferences and different trophic levels minimize inter-specificcompetition. Deep-Sea Res. I, 56(5): 741-756.
LAAKMANN, S., M. STUMPP & M. AUEL, 2009b. Vertical distribution and dietary preferences ofdeep-sea copepods (Euchaetidae and Aetideidae; Calanoida) in the vicinity of the Antarctic
polar front. Polar Biol., 32: 679-689.
LOWRY, L. F., G. SHEFFIELD & C. GEORGE, 2004. Bowhead whale feeding in the Alaskan Beaufort
Sea, based on stomach contents analyses. J. Cetacean Res. Manage., 6(3): 215-223.
MAUCHLINE, J., 1998. The biology of calanoid copepods. Adv. Mar. Biol., 33: 1-710.
OHTSUKA, S. & R. HUYS, 2001. Sexual dimorphism in calanoid copepods: morphology andfunction. Hydrobiologia, 453: 441-466.
RICHTER, C., 1994. Regional and seasonal variability in the vertical distribution of mesozooplankton
in the Greenland Sea. Ber. Polarforsch., 154: 1-87.
RICHTER, C., 1995. Seasonal changes in the vertical distribution of mesozooplankton in theGreenland Sea Gyre (75°N): distribution strategies of calanoid copepods. ICES J. Mar. Sci.,
52(3-4): 533-539.
SANO, M., K. MAKI, Y. NISHIBE, T. NAGATA & S. NISHIDA, 2013. Feeding habits of mesopelagic
copepods in Sagami Bay: insights from integrative analysis. Prog. Oceanogr., 110: 11-26.
SANO, M., Y. NISHIBE, Y. TANAKA & S. NISHIDA, 2015. Temporally sustained dietary niche
partitioning in two mesopelagic copepod species and their mouthpart morphology. Mar. Ecol.
Prog. Ser., 518: 51-67.
SMOOT, C. A. & R. R. HOPCROFT, 2017. Depth-stratified community structure of Beaufort Sea
slope zooplankton and its relations to water masses. J. Plankton Res., 39(1): 79-91.
THIBAULT, D., E. J. H. HEAD & P. A. WHEELER, 1999. Mesozooplankton in the Arctic Ocean insummer. Deep-Sea Res. I, 46(8): 1391-1415.
WASSMANN, P., M. REIGSTAD, T. HAUG, B. RUDELS, M. L. CARROLL, H. HOP, G. W.
GABRIELSEN, S. FALK-PETERSEN, S. G. DENISENKO, E. ARASHKEVICH, D. SLAGSTAD &O. PAVLOVA, 2006. Food webs and carbon flux in the Barents Sea. Prog. Oceanogr., 71(2-4):
232-287.
WILSON, S. E., D. K. STEINBERG, F. L. E. CHU & J. K. B. BISHOP, 2010. Feeding ecology ofmesopelagic zooplankton of the subtropical and subarctic north Pacific Ocean determined withfatty acid biomarkers. Deep-Sea Res. I, 57(10): 1278-1294.
YAMAGUCHI, A., C. J. ASHJIAN & R. G. CAMPBELL, 2022. Comparison of population structure, vertical distribution and growth of sympatric, carnivorous, mesopelagic copepods,
Paraeuchaeta glacialis and Heterorhabdus norvegicus, in the western Arctic Ocean. J. Plankton Res., 44(3): 443-453.
YAMAGUCHI, A., C. J. ASHJIAN, R. G. CAMPBELL & Y. ABE, 2019. Ontogenetic vertical migrationof the mesopelagic carnivorous copepod Paraeuchaeta spp. is related to their increase in bodymass. J. Plankton Res., 41(5): 791-797.
YAMAGUCHI, A., C. J. ASHJIAN, R. G. CAMPBELL & Y. ABE, 2020. Vertical distribution, population structure and developmental characteristics of the less studied but globally distributed
mesopelagic copepod Scaphocalanus magnus in the western Arctic Ocean. J. Plankton Res.,
42(3): 368-377.
YAMAGUCHI, A. & T. IKEDA, 2000. Vertical distribution, life cycle, and developmental characteristics of the mesopelagic calanoid copepod Gaidius variabilis (Aetideidae) in the Oyashio
region, western north Pacific Ocean. Mar. Biol., 137: 99-109.
YAMAGUCHI, A., S. OHTSUKA, K. HIRAKAWA & T. IKEDA, 2007. Vertical distribution and feeding
ecology of a copepod Gaetanus variabilis in the southern Japan Sea during winter. La Mer, 45:
47-58.
Downloaded from Brill.com08/18/2023 11:48:24AM
via communal accountLENGTHS AND WEIGHTS OF AETIDEID COPEPODS129

YAMAGUCHI, A., S. TACHIBANA, K. HIRAKAWA & T. IKEDA, 2005. Descriptions of the copepodid
stages of the mesopelagic copepod, Gaetanus variabilis (Brodsky, 1950) (Calanoida, Aetideidae) from the Japan Sea. Crustaceana, 78(7): 819-837.
YAMAGUCHI, A., Y. WATANABE, H. ISHIDA, T. HARIMOTO, K. FURUSAWA, S. SUZUKI,
J. ISHIZAKA, T. IKEDA & M. TAKAHASHI, 2002. Community and trophic structures of pelagic
copepods down to the greater depths in the western subarctic Pacific (WEST-COSMIC). DeepSea Res. I, 49(6): 1007-1025.

First received 28 July 2022.
Final version accepted 13 January 2023.
Published online 22 February 2023.
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