Journal of

Plankton Research

academic.oup.com/plankt

J. Plankton Res. (2023) 45(4): 661–676. First published online June 13, 2023 https://doi.org/10.1093/plankt/fbad023

Diel, seasonal and vertical changes in theabundance, biomass and community
structure of pelagic polychaetes at thesubtropical station S1 in the western
North Paciﬁc: comparison with theresults from the subarctic station K2
KANAKO AMEI

1,†, *, RYO DOBASHI2 , MINORU KITAMURA3 AND ATSUSHI YAMAGUCHI

1,41

faculty/graduate school of fisheries sciences, hokkaido university, 3-1-1 minato-cho, hakodate, hokkaido 041−8611, japan, 2 departmentof oceanography, university of hawai‘i at mānoa, 1000 pope road, honolulu, hi, usa, 3 research institute for global change, japan agency
for marine-earth science and technology, 2−15 natsushima-cho, yokosuka, kanagawa 237−0061, japan and 4 arctic research center,hokkaido university, kita-21 nishi-11 kita-ku, sapporo, hokkaido 001−0021, japan*corresponding author: kanakoamei@gmail.com† present address: kanako amei, graduate school of agricultural and life sciences, the university of tokyo, kashiwa-shi, chiba 277-8564,
japan
Received September 25, 2022; editorial decision May 7, 2023; accepted May 7, 2023
Corresponding editor: Xabier Irigoien

Information on pelagic polychaete community structure in the western North Paciﬁc is available for the subarctic
region (Station K2) but not for the subtropical region. Hence, we analyzed day–night vertically stratiﬁed samples
collected in eight layers within the ﬁrst 1000 m of the water column during four seasons in 1 year, using the same
sampling method as St. K2, at the subtropical region (Station S1). At St. S1, 27 species of pelagic polychaetes
belonging to 13 genera and six families were identiﬁed. The annual mean abundance was 35.0 ind. 1000 m−3 and thebiomass was 17.3 mg WW 1000 m−3 . At St. S1, the numbers of genera and species were higher and the annual meanabundance and biomasses were much lower than St. K2. The pelagic polychaetes often peaked in the mesopelagic
layer at St. K2, with the carnivores and particle feeders peaking in the epipelagic and mesopelagic layers, respectively.

available online at academic.oup.com/plankt© The Author(s) 2023. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

ORIGINAL ARTICLE

JOURNAL OF PLANKTON RESEARCH

VOLUME 45

NUMBER 4

PAGES 661–676

2023

At St.S1, the carnivorous species predominated throughout the entire water column, and were most abundant in theepipelagic layer. Thus, In the western Paciﬁc Ocean, the subarctic pelagic polychaete community structure changed
vertically with feeding ecology. On the other hand, the subtropical community may be adapted to conditions of highirradiance and light transmission.
KEYWORDS: annelida; K2S1 project; species diversity; vertical distribution; water mass

Pelagic polychaetes are widely distributed from thesurface to the deep layers of oceans worldwide (Halanych
et al., 2007; Ushakov, 1974). Pelagic polychaete diets
differs widely among species: herbivorous (Day, 1967;
Hopkins and Torres, 1989), carnivorous (Feigenbaum,
1979; Lebour, 1922; Rakusa-Suszczewski, 1968) and
detritivorous (Christiansen et al., 2018; Robison et al.,2010; Uttal and Buck, 1996). Thus, understanding
accurately the role of pelagic polychaete in food webs andvertical material ﬂux of marine ecosystems worldwide
requires information at the species level. However,
our knowledge of the ecology of pelagic polychaetes,
especially their community structure, is scarce comparedto their importance.
The western North Paciﬁc has two large current systems: cold Oyashio (subarctic) and warm Kuroshio (subtropical). The subarctic and subtropical regions of thewestern North Paciﬁc have distinct physical, chemicaland biological characteristics. Two time-series observation stations, subarctic St. K2 and subtropical St. S1,
were set by the Japan Agency for Marine-Earth Scienceand Technology (JAMSTEC) as representative stations
for each area (Honda et al., 2017). Various projects havebeen conducted in subarctic and subtropical regions, suchas VERTIGO (Buesseler et al., 2007; Steinberg et al.,2008) and K2S1 (Honda et al., 2016, 2017). Throughthese projects, various biological aspects such as primary
production (Elskens et al., 2008; Matsumoto et al., 2014,2016), phytoplankton standing stock (Boyd et al., 2008;
Fujiki et al., 2014), bacterial communities (Kaneko et al.,2016) and zooplankton communities (Kitamura et al.,2016; Kobari et al., 2016; Steinberg et al., 2008) have been
evaluated.
Regarding pelagic polychaetes in the Paciﬁc Ocean,regionally different distributions of genera and species
have been reported, especially between the subarctic
and subtropical regions (Tebble, 1962). The subarctic–
subtropical comparisons have been carried out by
analyzing zooplankton swimmer samples, known toswim actively (not just sink), collected by sediment traps
moored at a depth of 200 m (Amei et al., 2020), reporting
seasonal abundances (ﬂuxes) and population structuresof the dominant species. Time-series surveys are essential
to reveal the effect of environmental factors on thecommunity structure of pelagic polychaete; however,no study has compared the time-series changes in thevertical structure between subarctic and subtropicalregions. Regarding the community structure of pelagic
polychaetes at St. K2 located in the western subarctic
Paciﬁc, diel, vertical and seasonal changes in community
structure have been reported based on the analysis of
day–night vertical stratiﬁed samples collected from the
0–1000 m water column in four seasons covering 1 year
(Amei et al., 2021). These ﬁndings are important forcomprehensively evaluating diel, vertical and seasonalchanges in pelagic polychaete communities from thesurface to the deep sea. However, there are few comparable studies from other regions. At St. S1, JAMSTEC’s
subtropical time-series station, zooplankton samples werecollected using the same methods as at St. K2 (Kitamura
et al., 2016). However, the polychaete abundance, biomass
and community structure at St. S1 have not yet been
analyzed.
Hence, in this study, we analyzed pelagic polychaetes
in the samples collected by day–night vertically stratiﬁedsampling to a depth of 1000 m during four seasonsin 1 year at St. S1 in the western Paciﬁc Ocean. We
compared the results of this study with those reported in
the study by Amei et al. at St. K2 in the western Paciﬁc
Ocean (Amei et al., 2021), who applied the same methods as those applied in this study. This comparison may
reveal the regional differences in polychaete communities
between the subarctic and subtropical regions of the western North Paciﬁc Ocean and the factors affecting them.

METHODS
Zooplankton samples were collected from eight layers of a
0–1000-m water column (0–50, 50–100, 100–150, 150–
200, 200–300, 300–500, 500–750 and 750–1000 m) by
oblique tows of the Intelligent Operative Net Sampling
System (IONESS, SEA Corporation) (mesh size, 335 μm;
mouth area, 1.5 m2 ) at St. S1 (30◦ 00’N, 145◦ 00 E; bottom
depth, 5 800 m; Fig. 1) in the western Paciﬁc Ocean
during the days and nights of November 2010 and February, May and July 2011 (Table I). Temperature, salinity,
dissolved oxygen (DO) and ﬂuorescence of each sample
were measured using a Conductivity, Temperature andDepth proﬁler (SBE 911 plus; Sea-Bird Electronics Inc.).

662

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

INTRODUCTION

K. AMEI ET AL.

DIEL, SEASONAL AND VERTICAL CHANGES

Table I: Zooplankton sampling data (eight vertical stratiﬁcation samplings between 0 and1000 m) at St. S1 in subtropical western North
Paciﬁc from November 2010 to July 2011. D:
day, N: night
Sampling date

Local time

D/N

10 November 2010
12 November 201015 February 201117 February 201119 February 2011
1 May 2011
2 May 201129 July 201129 July 2011

22:01–0:04
12:09–14:10
22:15–23:51
0:00–0:05
11:52–13:58
21:58–23:51
11:59–13:53
12:49–14:46
21:43–23:47

N
D
N
N
D
N
D
D
N

H = −The zooplankton samples were preserved in 4% (v/v)
borax-buffered formaldehyde. See Kitamura et al. (2016)
for detailed information on sampling.
Based on temperature and salinity, the water masses
were identiﬁed at each depth and sampling date.
Throughout the year, we classiﬁed ﬁve water masses at
St. S1: seasonal pycnocline water (SPW), subtropicalmode water (STMW), transition water (TW), upper
North Paciﬁc intermediate water (upper NPIW) andlower North Paciﬁc intermediate water (lower NPIW),
based on the T–S characteristics at each sampling layer(Masuzawa, 1969; Yasuda, 2003; Yasuda et al., 2001).
SPW is the water above the pycnocline and is thus
susceptible to solar radiation. STMW corresponds toS

i=1 pi × lnpi

(1)

Where S is the number of species, and pi is the relative
dominance of species i (Shannon and Weaver, 1949).
To determine the community structure of pelagic
polychaetes, we calculated the similarity of samples basedon abundance using the Bray–Curtis method (Bray andCurtis, 1957). The abundance data of pelagic polychaete
species (X : ind.1000 m−3 ) were log-transformed (log
[X + 1]) before analysis. A cluster analysis connected
to complete linkage methods was performed for sample
grouping. Nonmetric multidimensional scaling (NMDS;Minchin, 1987) and Pearson’s multidimensional coefﬁcient analysis analyzed the relationships between
environmental variables (depth, temperature, salinity, DO
and ﬂuorescence) and polychaete sample ordinations.
To evaluate the effects of the seasons, day–night cycles
and depth on the similarities between the samples, thepermutational multivariate analysis of variance (PERMANOVA), a non-parametric multivariate statisticalpermutation test, was performed; these analyses were
performed using PRIMER v7 (PRIMER-E, Ltd). Intercommunity and water mass differences in the abundanceof each species were tested using one-way ANOVA and663

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

Fig. 1. Location of the sampling stations: St. S1 (30◦ N, 145◦ E) in thesubtropical western North Paciﬁc Ocean. For comparison, the locationof the subarctic station (St. K2) is also shown. Approximate positions of
the currents are superimposed (cf. Yasuda, 2003).

the water of the remnant winter mixed layer in thesubtropical North Paciﬁc and has a temperature of 16–
18◦ C ∼100–300 m depth (Masuzawa, 1969). The water
between STMW and NPIW was deﬁned as TW in thisstudy. A salinity minimum near 26.8 σ θ characterizes
NPIW. This water originates from the Okhotsk Sea andthe western subarctic gyre (WSG) and ﬂows toward theKuroshio extension region (Yasuda, 2003). The upper
NPIW (density centered at 26.6 σ θ –26.9 σ θ ) and lower
NPIW (density centered at 27.0 σ θ –27.4 σ θ ) were morestrongly affected by the water in the Okhotsk Sea and
WSG, respectively (Yasuda et al., 2001).
We sorted pelagic polychaetes from 1/4th of the bottle
samples collected at each depth layer in the land laboratory. The specimens were identiﬁed to species andcounted under a stereomicroscope. Species identiﬁcation
was performed to the lowest level possible, following Dales(1957) and Tebble (1962). For each genus or species, abatch of specimens in each sample was placed on a preweighed mesh, and the water was removed with the aid of
wiping paper. Then, the wet weight (WW) was measured
using an electronic balance (Mettler Toledo AT261) witha precision of 0.01 mg. The vertical distributions of
the total abundance (ind. 1000 m−3 ) and total WW (mg1000 WW m−3 ) were then quantiﬁed. For each sample,
the Shannon-Weaver diversity index (H ) was calculated
according to abundance and biomass using the following
equation:

JOURNAL OF PLANKTON RESEARCH

VOLUME 45

NUMBER 4

PAGES 661–676

2023

the Tukey–Kramer test; these analyses were performed
using STAT-View.

RESULTS
Hydrography
The vertical changes in temperature, salinity, DO andﬂuorescence for each sampling date at St. S1 are shownin Fig. 2. Throughout the study period, the temperature,salinity, DO and ﬂuorescence ranged from 3.5–26.8◦ C,
34.0–34.9, 0.8–5.4 mL L−1 and 0.02–0.91 mg m−3 ,respectively. Regarding the temperature, the seasonal
thermocline developed at ∼50 m in November andJuly. In February and April, the temperature was almost
uniform at 200–300 m, decreased gradually at 100–
300 m and rapidly since 300–600 m and then smoothly
decreased by 2–5◦ C at depths below 600 m. The salinity
reached a maximum at ∼50 m in November and July.
Throughout the year, the salinity decreased graduallywith depth between 100 and 300 m, reaching theminimum (ca. 34.0) level at ∼600–700 m, and showed
an increase with increasing depths beyond 700 m.
The DO decreased with increasing depth. The rate ofdecrease in the DO was high at depths below 600 m.
An oxygen minimum layer (OML) of < 2 mL L−1 ) was
observed below 800 m. The ﬂuorescence was high at
depths of 0–200 m throughout the year. In February, theﬂuorescence was high at depths of 0–100 m. In otherFig. 3. T–S diagram for the 0–1000 m water column at St. S1 during
November 2010, February, April and July 2011. Five water masses wereidentiﬁed: SPW, STMW, TW, Upper NPIW and Lower NPIW. Solidlines on the background are isopycnals. Differences in the colors of thesymbols denote differences in the zooplankton sampling layers.

seasons, maximum subsurface ﬂuorescence was observed
near 100 m.
The T–S diagrams for each sampling date are shownin Fig. 3. In all seasons, water masses characteristic of thewestern North Paciﬁc subtropical region were observed.
Four water masses were identiﬁed vertically: the shallowest SPW, STMW, NPIW including upper and lower
NPIW, and TW present between the STMW and NPIW.
The seasonal differences were obscured except for theseasonal thermocline at above ∼ 100 m.

664

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

Fig. 2. Vertical changes in temperature (T), salinity (S), DO (O2 ), and ﬂuorescence (F) at St. S1 during the sampling period from November 2010
to July 2011. The dotted guidelines show the mean value of all data for each parameter (T:11.00◦ C, F: 0.097, DO: 3.34 mL L−1 , S: 34.4). Circled
numbers in the right column indicate the depth strata of the zooplankton sampling in this study.

K. AMEI ET AL.

DIEL, SEASONAL AND VERTICAL CHANGES

Table II: List of the pelagic polychaete species identiﬁed in the 0–1000 m water column at St. S1 in
the western subtropical North Paciﬁc from November 2010 to July 2011. Annual mean abundance andbiomass (mean ± 1 SE: ind. 1000 m−3 or mg WW 1000 m−3 at 0–1000 m water column), species
composition (%) and depth ranges (m) of occurrence are shown
FamilyAbundance
SpeciesPelagic polychaete abundance and biomass
We found 27 pelagic polychaete species belonging to 13
genera and six families at St. S1 (Table II). The polychaetegroup with large eyes, previously categorized as tribe
Alciopini (Phyllodocidae), was highly diverse (14 species).
The most abundant species was the Tomopteris spp. without
tails (annual mean: 21 ind. 1000 m−3 ), which accounted
for 59% of the total abundance. For species identiﬁcationof Tomopteris spp. (Tomopteridae), the following threecharacteristics were the most important: (i) the presenceor absence of ﬁrst tentacular cirri between the horn-like
antenna and cirri-like appendages, (ii) the presence orabsence and position of glands in the rami and (iii) the
presence or absence of a tail on the pygidium. Because
the rami condition was not good in this study and we
could not observe glands in the rami (chromophile glands,

Occurrence
depth (m)(ind.
1000 m−3 )(%)(mg WW
1000 m−3 )(%)

0.38 ± 0.06

1.08

1.33 ± 0.13

0.51

300–750

1.48 ± 00.54 ± 0.28
0.85 ± 0.30
0.71 ± 0.04

4.24
1.54
2.42
2.02

12.93 ± 01.76 ± 0.37
1.73 ± 0.87
2.66 ± 2.59

4.94
0.67
0.66
1.01

50–750100–750
200–1000
50–1000

0.34 ± 00.42 ± 0.18
0.33 ± 00.48 ± 0.23
0.24 ± 0.04
0.25 ± 00.32 ± 00.74 ± 0.15
0.26 ± 00.32 ± 00.31 ± 00.29 ± 0.01
0.58 ± 0.18
0.56 ± 0.15

0.98
1.21
0.95
1.37
0.68
0.71
0.91
2.11
0.74
0.91
0.90
0.90
1.67
1.60

16.56 ± 020.55 ± 18.26
0.80 ± 013.22 ± 8.82
1.44 ± 1.03
1.40 ± 04.55 ± 012.47 ± 4.11
18.32 ± 014.05 ± 0
1.05 ± 00.826 ± 0.826
7.74 ± 5.68
4.74 ± 2.67

6.32
7.85
0.31
5.05
0.55
0.53
1.74
4.76
7.00
5.36
0.40
0.32
2.96
1.81

0–50
0–100
150–200
0–100
50–200
150–200
50–100
0–150
50–100
100–150
100–150
0–100
0–200
0–150

0.45 ± 0.11

1.29

3.67 ± 0.89

1.40

50–1000

20.56 ± 2.56
0.33 ± 00.67 ± 0.19

58.7
0.95
1.91

46.10 ± 7.99
14.27 ± 032.15 ± 11.64

17.60
5.45
12.27

0–1000100–200
0–10000.85 ± 0.26
0.29 ± 0.01
1.42 ± 0.61
1.04 ± 0.36

2.43
0.84
4.05
2.98

9.38 ± 1.51
3.77 ± 0.14
9.05 ± 3.12
5.41 ± 1.15

3.58
1.44
3.45
2.07

0–300
50–3000–500
0–1000hyaline glands and rosette glands), we described Tomopteris
species as Tomopteris spp. (without tail), Tomopteris sp.1
(without tail) and Tomopteris spp. (with tail).
The abundance of pelagic polychaetes in the watercolumn ranged from 1 to 260 ind. 1000 m−3 (Fig. 4).
Throughout the days and nights of all seasons, the highest
abundance was observed at depths of 0–200 m, with the
maximum reported in November.
In terms of biomass, the Tomopteris spp. without a tailwere also dominant, but to a limited extent (18% of thetotal pelagic polychaete biomass) (Table II). The biomass
composition of the large Tomopteris spp. with a tail washigh (12%), while their abundance was low (1.9%).
The WW biomass ranged between 0.1 and 83.2 mg
WW 1000 m−3 (Fig. 5). Increased biomass in the daytime was observed at 0–200 m for all three seasons,665

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

Amphinomidae
Amphinomidae spp.
Lopadorrhynchidae
Lopadorrhynchus brevis Grube, 1855
Lopadorrhynchus uncinatus Fauvel,1915
Pelagobia longicirrata Greeff, 1879
Lopadorrhynchidae spp.
Phyllodocidae
Alciopa reynaudii Audouin & H Milne Edwards, 1833
Naiades cantrainii Delle Chiaje, 1830
Plotohelmis tenuis (Apstein, 1900)
Rhynchonereella fulgens Greeff, 1885
Rhynchonereella gracilis Costa, 1864
Rhynchonereella möbii (Apstein, 1893)
Torrea candida (Delle Chiaje, 1841)
Vanadis formosa Claparéde, 1870
Vanadis longissima (Levinsen, 1885)
Vanadis spp.
Alciopini sp.1
Alciopini sp.2
Alciopini sp.3
Alciopini spp.
Polynoidae
Lepidasthenia grimaldii (Marenzeller, 1892)
Tomopteridae
Tomopteris spp. (without tail)Tomopteris sp.1 (without tail)Tomopteris spp. (with tail)Typhloscolecidae
Sagitella kowalewskii Wagner, 1872
Travisiopsis levinseni Southern, 1910
Travisiopsis lobifera Levinsen, 1885
Typhloscolex muelleri Busch, 1851

Biomass

JOURNAL OF PLANKTON RESEARCH

VOLUME 45

NUMBER 4

PAGES 661–676

2023

except for July. During the daytime in July, the highest
biomass was observed at 750–1000 m because of the
distribution of large Tomopteris spp. (with tail). At night,
the highest biomass was observed at 0–200 m, especiallyin the shallowest layer of 0–50 m in November, February
and May.
The species diversity (H ) of the pelagic polychaetes
in the layers was 0–1.5 (based on abundance) and 0–1.6(based on biomass), and the maximum H was usuallyobserved in the surface layer with no evident seasonalpatterns (Figs 4 and 5). The H was 0.47–1.01, based on
the abundance in the samples.
A comparison of species abundance in each watermass showed that there was no signiﬁcant differencein the abundances of species between different water
masses, except for Vanadis formosa and Sagitella kowalewskii(Table III) that were abundant in the surface water mass,
SPW and STMW (P < 0.05). Fifteen species (12 species
belonging to Alciopini [tribe]) were distributed only at
SPW or STMW, although not at a signiﬁcant level.

Pelagic polychaete community structure
Based on abundance, the pelagic polychaete community
was clustered into six community groups (A–F) with a
45% dissimilarity (Fig. 6a). Each group contained 2–22
samples. NMDS separated the groups, and various environmental factors (depth, salinity, DO and ﬂuorescence)
were found to have signiﬁcant directions according toPearson’s multidimensional coefficient. From the plotted directions, depth and DO were related to pelagic
polychaete clustering. Depth and environmental factors
depending on the depth (salinity, temperature and ﬂuorescence) affect horizontally, and the clustering groups areplotted separately in the horizontal direction. DO had asigniﬁcant effect on the grouping of groups A (high DO),B (moderate DO) and C (low DO) (Fig. 6b). The meanabundance of group A (43.9 ind. 1000 m−3 ) was higher
than that of groups B (18.3 ind. 1000 m−3 ) and C (9.1 ind.
1000 m−3 ), with Tomopteris spp. (without tail) accountingfor 56%. Tomopteris spp. (without tail) was dominant ingroup B, while Sagitella spp. was dominant in group C

666

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

Fig. 4. Vertical changes in polychaete abundance (ind. 1000 m−3 ), species composition, and species diversity (H ) in the 0–1000 m water column
at St. S1 from November 2010 to July 2011. The composition of each genus is shown with a different color.

K. AMEI ET AL.

DIEL, SEASONAL AND VERTICAL CHANGES(Fig. 6c). Low abundances were observed in groups D, E
and F. Different species compositions were observed inthese groups. Typhloscolex muelleri was dominant in group
D, Pelagobia longicirrata, in group E and Travisiopsis spp.,
only in group F. The numbers of genera differed within
the groups (3–11 genera), and some genera occurredin speciﬁc groups (Alciopina spp.: A–C, Plotohelmis spp.:
B, Rhynchonereella spp.: A and B, Sagitella spp.: A–C, andTorrea spp.: A) (Fig. 6c). Most of them (except Sagitella spp.)
belonged to the Alciopini (tribe). Inter-group differencesin abundance were detected only for V . formosa, which wasabundant in group B (P < 0.05, Table IV).
The diel, vertical and seasonal distributions of pelagic
polychaete community groups at St. S1 are shown in
Fig. 7. The occurrence of each group was governedby depth. The high-abundance groups (A and B) wereobserved at depths of 0–300 m. Group C was mainly
observed at depths of 200–750 m. The occurrenceof low-abundance groups (D, E and F) was restricted
to depths below 300 m. Thus, the distribution of thepelagic polychaete community primarily varied verticallyand did not show diel or seasonal patterns. The resultsof the PERMANOVA also indicated that depth was
the most prominent environmental factor in polychaete grouping (P < 0.001) (Table V). The interaction
between season×day/night also had a signiﬁcant effect(P < 0.05).

DISCUSSION
Fauna and species diversity
In the western North Paciﬁc, the number of pelagic
polychaete species at subtropical St. S1 (27 species)(Table II) was much higher than that at subarctic St. K2(10 species) (Amei et al., 2021). Four common families were
present in both regions: Lopadorrhynchidae, Phyllodocidae, Typhloscolecidae and Tomopteridae. Iospilidae andFlabelligeridae occurred only in the subarctic region,
whereas Amphinomidae and Polynoidae were present
only in the subtropical region. Fernández-Álamo et al.
(2003) reported a clear latitudinal pattern reported forthe 0–200 m water column between 21◦ N and 40◦ N

667

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

Fig. 5. Vertical changes in polychaete biomass (wet weight: mg WW 1000 m−3 ), species composition and species diversity (H ) in the 0–1000 m
water column at St. S1 from November 2010 to July 2011. The composition of each genus is shown with a different color.

JOURNAL OF PLANKTON RESEARCH

VOLUME 45

NUMBER 4

PAGES 661–676

2023

Table III: Comparison of polychaete abundances for the ﬁve water masses (SPW, STMW, TW, Upper
NPIW, Lower NPIW) at St. S1. Mean abundances for each water mass are shown. Differences between
water masses were tested by one-way ANOVA and Tukey–Kramer test. For the results of the Tukey–Kramer
test, differences in superscript letters indicate signiﬁcant differences (P < 0.05). Numbers in the parentheses
indicate the number of samples included in each water mass
Species

one-way ANOVASPW (8)STMW (34)TW (16)Upper NPIW (10)Lower NPIW (8)

0.79
0
0
0.86
0.56
0.00
0.65
0
0
0.79
6.17a
0.65
0
0.75
0.75
0
0
4.95
0
6.63
3.87

0.46
0.49
0.29
0
0.87
0.20
0.69
0.15
0.28
0
0.72b
0
0.18
0.16
0.85
0.21
0.31
2.14
0.26
2.10
1.44

0.10
0.22
0.23
0
0
0
0
0
0
0
0b
0
0
0
0
0.22
0
0
0
0.14
0.91

0.15
0.13
0
0
0
0
0
0
0
0
0b
0
0
0
0
0.46
0
0
0
0
0.75

0
0
1.20
0
0
0
0
0
0
0
0b
0
0
0
0
0.39
0
0
0
0
0.77

NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
∗∗∗
NS
NS
NS
NS
NS
NS
∗
NS
NS
NS

∗ P < 0.05; ∗∗∗ P < 0.001; NS: not signiﬁcant; Alphabets on values show group.

latitudes off California, eastern North Paciﬁc, based on
CalCOFI samples. According to Fernández-Álamo et al.
(2003), the pelagic polychaete community can be divided
into the north, south and transition groups. The northgroup is characterized by high abundance and relative
diversity (11 species), the south group is characterized by
low abundance but the most diverse (16 species), and thetransition group has the lowest abundance and species
diversity (nine species). St. S1 is in 30◦ 00’N, which isincluded in the transition group of Fernández-Álamo
et al. (2003). However, the transition group showed asimilar pelagic polychaete community with the northgroup and different with St. S1. It suggests that thepelagic polychaete distribution pattern strongly depends
on water ﬂow rather than latitude. Cold California
Current ﬂows from north to south along California, andwarm Surface Equatorial Water (temperature > 20◦ C,
salinity < 35 in their study) existed only in the southern
region (∼21–25◦ N corresponding to St.32–35) (Fig. 2,
Fernández-Álamo et al., 2003). Among the three groups, asouth group characterized by the presence of subtropicalpelagic polychaete genera such as Vanadis, Rhynchonerella
and Plotohelmis had the most similar community withthat of St. S1 reported in this study. The high diversity
shown in St. S1 suggests the presence of a differencein pelagic polychaete community structure between thewest and east region of the subtropical gyre in the Paciﬁc
Ocean.
Tebble (1962) reported seven tomopterid species
from a wide region of the Paciﬁc Ocean, including
the sampling region of this study. He also mentioned
the important morphologic traits for Paciﬁc tomopterid
identiﬁcation. According to him, [Tomopteris spp. withtail] includes Tomopteris nisseni, Tomopteris krampi, Tomopteris
apsteini, Tomopteris paciﬁca, and [Tomopteris spp. withouttail] includes Tomopteris planktonis, Tomopteris elegans,
Tomopteris ligulata and Tomopteris septentrionalis. In subtropical S1, Tomopteris spp. (with and without tail),with high proportions throughout the water column,
were concentrated at the surface layer. Tomopteridae,
a common family worldwide, is reported to dominate the Paciﬁc Ocean, especially in subtropical andsubarctic regions (e.g. Tebble, 1962). In the present
study, subtropical Tomopteris spp. (without tail) were
too small to preserve the rami. In both regions, thisfamily was distributed widely at 0–1000 m, and peaks
in its abundance were observed at depths shallower
than 300 m. Tomopteris spp. (without tail) at S1 showedno seasonal changes in vertical distribution (Fig. 8), in
contrast to T. septentrionalis at K2. Unfortunately, in

668

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

Lopadorrhynchus brevis
Lopadorrhynchus uncinatus
Pelagobia longicirrata
Alciopa reynaudii
Naides cantraini
Plotohelmis tenuis
Rhynchonereella fulgens
Rhynchonereella möebii
Rynchonereella gracilis
Torrea candida
Vanadis formosa
Vanadis longissima
Alciopa sp.1
Alciopa sp.2
Alciopa sp.3
Lepidasthenia grimaldii
Tomopteris sp.1
Sagitella kowalewskii
Travisiopsis levinseni
Travisiopsis lobifera
Typhloscolex muelleri

Abundance (ind. 1000 m−3 )K. AMEI ET AL.

DIEL, SEASONAL AND VERTICAL CHANGES

this study, we cannot treat Tomopteris spp. (without tail)as one species. However, the difference in the vertical
distribution between these subtropical and subarctic
dominant Tomopteris species suggests that Tomopteris
species have different dynamics depending on marine
environmental factors, such as the concentration ofchlorophyll a in each region.
Within the four families commonly occurring in bothregions, the Alciopini (tribe), belonging to Phyllodocidae,
showed substantial diversity in the subtropical region.

Thus, while only two species were observed in thesubarctic region, 14 were in the subtropical region.
Phyllodocidae, including Alciopini, was the second mostdominant family in the subtropical region (Table II).
Alciopid polychaetes are abundant and adapted totropical/subtropical regions with eyes equipped withmorphologically specialized lenses (Dales, 1957; Ushakov,
1974). The eyes of alciopid polychaetes have accessory
retinas beside the lens that can even detect ultraviolet
light (Wald and Rayport, 1977). These facts suggest that

669

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

Fig. 6. (a) Results of cluster analysis based on pelagic polychaete abundance at St. S1. Six groups (A–F) were identiﬁed at 45% Bray–Curtis
dissimilarity connected with the complete linkage method. Numbers in parentheses indicate the number of samples each group contained. (b)NMDS plots of each group. Arrows indicate directions of signiﬁcant environmental parameters. Dep.: depth, Temp.: temperature, Sal.: salinity,
DO: dissolved oxygen, Fluo.: ﬂuorescence. Stress is a value used to evaluate the quality of NMDS, which is low for relevant NMDS. (c) Meanabundance (white circle) and genus composition of each group.

JOURNAL OF PLANKTON RESEARCH

VOLUME 45

NUMBER 4

PAGES 661–676

2023

Table IV: Comparison of the polychaete abundances in the six groups (A–F) identiﬁed by Bray–Curtis
dissimilarity (cf. Fig. 6a). Mean abundances for each group are shown. Differences between groups were
tested by one-way ANOVA and Tukey–Kramer test. For the results of the Tukey–Kramer test, differences insuperscript letters indicate signiﬁcant differences (P < 0.05). Numbers in the parentheses indicate numberof samples included in each group
Abundance (ind. 1 000 m−3 )SpeciesA (13)B (22)C (13)

D (2)

E (3)

F (11)

11.02
0
0
6.84
9.34
0
0
0
5.60
6.34
7.50b
0
0
5.60
9.23
0
3.92
7.43
5.60
33.06
9.33

0
8.36
4.95
0
5.09
6.69
9.57
4.94
3.98
0
15.43a
5.18
6.29
0
6.59
5.06
6.69
5.66
0
6.01
5.93

0
1.29
0
0
0
0
0
0
0
0
5.99b,c
0
0
5.99
5.99
1.97
0
29.96
3.09
20.12
3.30

0
0
0
0
0
0
0
0
0
0
0b,c
0
0
0
0
1.53
0
0
0
0
3.07

0
0
3.90
0
0
0
0
0
0
0
0b,c
0
0
0
0
0
0
0
0
0
1.39

0
2.29
2.84
0
0
0
0
0
0
0
0c
0
0
0
0
1.56
0
0
0
2.18
2.18

NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
∗
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS

∗∗∗ P < 0.001; ∗ P < 0.05; NS: not signiﬁcant; Alphabets show group.

Table V: PERMANOVA results based on Bray–Curtis dissimilarities using the polychaete abundance
data in relation to the environmental factors at St. S1 (season, day/night and depth). D: day, N: night
Factorsdf

Pseudo FP

SeasonD/N
Depth
Season×D/N
Season×Depth
D/N × Depth

3
1
7
3
21
7

1.37570.72803
4.277
1.534
1.10580.98467

ns
ns<0.001<0.05
ns
ns

alciopids are well adapted to high light conditions under
low light attenuation in the oligotrophic tropical/subtropical region. Thus, active visual-predator alciopids may
have more opportunities to prey under sufficient light withhigh light radiation and transmission in the subtropicalregion than in the subarctic region. These characteristics
of alciopids (high swimming ability and specializedeyes) may allow for their high diversity and numericaldominance in the pelagic polychaete community in thesubtropical region.
Pelagobia longicirrata was a common species in bothregions. Pelagobia longicirrata has been treated as acosmopolitan species; however, Kolbasova and Neretina(2021) reported that P. longicirrata has some geographicallydifferent clades in a phylogenetic tree based 28S and 18S.

There is no phylogenetic information on P. longicirrata in
the Paciﬁc Ocean. In the subtropical region, P. longicirrata
accounted for only 2% of the abundance and wasvertically concentrated at depths greater than 750 m(Table II). This species is the most abundant in thesubarctic region, accounting for 74% of the pelagic
polychaete abundance (Amei et al., 2021). In both regions,P. longicirrata was distributed at depths greater than 150 m.
They showed distribution at a wide depth range (150–1000 m) at subarctic St. K2 and were concentrated tothe deepest layer (750–1000 m) at subtropical St. S1.
Thus, the distribution of P. longiciratta ranged from thesubarctic region (below 150 m) to the subtropical region(in the NPIW layer). The abundance and biomass of
P. longicirrata in the subtropical region were much lower

670

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

Lopadorrhynchus brevis
Lopadorrhynchus uncinatus
Pelagobia longicirrata
Alciopa reynaudii
Naides cantraini
Plotohelmis tenuis
Rhynchonereella fulgens
Rhynchonereella möebii
Rynchonereella gracilis
Torrea candida
Vanadis formosa
Vanadis longissima
Alciopa sp.1
Alciopa sp.2
Alciopa sp.3
Lepidasthenia grimaldii
Tomopteris sp.1
Sagitella kowalewskii
Travisiopsis levinseni
Travisiopsis lobifera
Typhloscolex muelleri

one-wayANOVA

K. AMEI ET AL.

DIEL, SEASONAL AND VERTICAL CHANGES

Table VI: Diel-mean abundances of pelagic polychaetes for 0–1000 m depth reported by this study andcomparable previous studies conducting vertically stratiﬁed sampling into ≥1000 m depth in the subtropicaland subarctic Paciﬁc Ocean
Subtropic region in the western
Paciﬁc Ocean (St. S1)

Subarctic region in the western
Paciﬁc Ocean (St. K2)

Kuril Kamchatka Trench

St. K2St.
ALOHA

Study No.
Season

1
Nov.

4
July

6
Oct.

7
Feb.

8
April

9
July

10
1. Aug.

12
22. July–11. Aug.

5
22. Jun.
–9. July

Sampling layers
0–50 m50–100 m

Abundance (ind. 1000 m−3 )
134
103
128
124
182
138
143
107

11
29–30.
Aug.

114
66

202
131

375
43

345
151

380
380

450
325

950
75

100–150 m
150–200 m
200–300 m
300–500 m
500–750 m
750–1 000 m
Net

153
37
92
38
96
34
46
34
34
10
17
14
4
2
14
7
3
5
IONESS net (335 μm)

275
151
12
202
38
54
284
172
305
317
140
386
164
129
428
216
128
145
IONESS net (335 μm)

121
301
512
694
195
85

36
139
Incomplete
513

206

625

370

Reference

This study

2
Feb.

3
May

84
33
41
10
6
7

Amei et al., 2021

Fig. 7. Seasonal, vertical, and diel changes in the occurrence of
the ﬁve polychaete community groups (A–F) identiﬁed by Bray–Curtis
dissimilarity based on their abundance at St. S1 from November 2010
to July 2011 (cf. Fig. 6a). D: day, N: night.

2 580

460
509.5
2 129
688
603
Juday (DZhOM 80/113)
netof No. 38 mesh
Mileykovskiy, 1969

225
500
450
200
IONESS(335 μm)

175
5
0.5
0.25
MOCNESS(335 μm)
Steinberg et al., 2008

K2, while peaks formed at the surface layer at St. S1(Fig. 9). These results reﬂect regional differences in pelagic
polychaete communities. At St. K2, T. septentrionalis andT. muelleri dominated at 0–100 m, P. longicirrata dominatedat the deeper layers below 300 m, and the H peaked at
100–300 m depth where all the species occurred (Fig. 9).
At St. S1, the vertical distribution of pelagic polychaetes
was concentrated in the surface layer. The H  values also
peaked near the surface layer (Fig. 9). At both stations,vertical patterns of H were similar to that of pelagic
polychaete abundance. It suggests that the diversity ofrare taxa pelagic polychaetes strongly depends on theirabundance.

Abundance and biomass
than those in the subarctic region. It may be related to
the lower primary production in the subtropical region
than in the subarctic region.
For various zooplankton taxa, higher species diversity
has been reported in the subtropical regions than in
the subarctic areas (e.g. Tittensor et al., 2010; Sun andWang, 2017). Sun and Wang (2017) showed the change ofdiversity H on the transect of 160◦ E from 4◦ S to 46◦ N
based on zooplanktons sampled by 200 μm-mesh twoparalleled WP2 net from 200 m depth. They reported a
rapid decrease of H between 30◦ N and 40◦ N. However,the H values of the pelagic polychaetes throughout eachlayer were similar (0.82–1.17) at K2 and (0.47–1.01) at
S1. While the H values were similar for both regions, it
should be noted that the vertical distribution of H variedwith the region. Thus, H peaked at 100–300 m at St.

Annual mean abundance and biomass of the pelagic
polychaetes in the subtropical region were 35.0 ind.
1000 m−3 and 17.3 mg WW 1000 m−3 , respectively(Table II). These values are much lower than those in
the subarctic region (239.2 ind. 1000 m−3 and 517.5 mg
WW 1000 m−3 ; Amei et al., 2021) (Fig. 9). The differences
between the regions (S1:K2) were expressed as a factorof 0.146 (abundance) or 0.033 (biomass). The vertical
distributions of abundance also varied with the region.
The vertical patterns of pelagic polychaete abundance at
St. K2 resembled a gradual arch-shape with peaks from
200 to 500 m depth (Amei et al., 2021). On the other hand,that at St. S1 decreased increasing depth. For comparisonof the vertical pattern of pelagic polychaete community
structures between the subtropical and subarctic Paciﬁc
Ocean, we listed a diel-mean abundance of pelagic

671

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

Location

JOURNAL OF PLANKTON RESEARCH

VOLUME 45

NUMBER 4

PAGES 661–676

2023

Fig. 9. Vertical changes in the polychaete abundance, biomass, species diversity (H ) and genus composition in annual mean abundance (%) for
the 0–1000 m water column in the subarctic (St. K2) and the subtropical (St. S1) regions in western North Paciﬁc. Lines represent values for days
and nights during the four seasons from 2010 to 2011.

polychaetes for each depth layer shown by this study andcomparable previous studies (Table VI). Steinberg et al.
(2008) reported vertical patterns of some zooplankton
taxa at subtropical St. ALOHA and subarctic St. K2, andMileykovskiy (1969) reported the on pelagic polychaetes
at Kuril Kamchatka Trench. Excluding Mileykovskiy(1969), all studies used IONESS or MOCKNESS with
335 μm for sampling. The percentages of distributing

672

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

Fig. 8. Seasonal changes in the vertical distribution for the mean abundance of Tomopteris species in the subarctic and subtropical regions (K2: T.
septentrionalis, S1: Tomopteris spp.).

K. AMEI ET AL.

DIEL, SEASONAL AND VERTICAL CHANGES

depth of pelagic polychaetes are similar between thisstudy and the previous studies (Fig. 10).
Kitamura et al. (2016), reporting biomass data of mesozooplankton in the same samples as this study, suggested
the occurrence of diel vertical migration (DVM) andseasonality at St. S1 related to the primary production.
However, pelagic polychaetes at St. S1 did not show
signiﬁcant DVM and seasonality. A pelagic polychaete
DVM cannot be detected because of the surface layer
limited distribution of pelagic polychaetes in the subtropical Paciﬁc Ocean, especially Alciopini. It is also possiblethat pelagic polychaete DVM was too small to detect by
the resolution of sampling layers in this study. Besides,
the seasonality of this study’s pelagic polychaetes of St.
S1 can be related to their reproduction and ecology.
However, almost all of them remain unknown, especiallyfor subtropical species.
Given the regional differences in mesozooplankton
stocks in the western North Paciﬁc, the annual mean
biomass of the whole zooplankton population at St. K2(5.8 mg C m−2 ) has been reported to be ten times higher
than that at St. S1 (0.52 mg C m−2 ) (Kitamura et al.,2016). Further, the zooplankton biomass at 0–1 000 m
depths was greater at St. K2 than at the subtropical
St. ALOHA station (Steinberg et al., 2008). Based on
the contents of the sediment trap moored at 200 m
depth at St. K2 and S1, zooplankton ﬂuxes in number
and mass have also been reported to be 2.3–6.5 times
higher at St. K2 than at St. S1 (Yokoi et al., 2018).
The ﬂux of pelagic polychaetes was also analyzed forthese sediment trap samples, and their annual meanvalues were 5.37 ind. m−2 day−1 at St. K2 and 1.36
ind. m−2 day−1 at St. S1 (Amei et al., 2020). Thus, theabundance and biomass were several times greater in the

Factors affecting community structure
According to the results of multiple regression analysis
and PERMANOVA, the most important factor affecting
the clustering of the pelagic polychaete community inthe subtropical region was depth (P < 0.001, Table V). In
the subarctic region, the season was also found to affectthe pelagic polychaete community in addition to season(P < 0.05; Amei et al., 2021). This may be related tothe seasonal occurrence of the community in which P.
meseres was the dominant species, which feeds on sinking
particles (detritus) and is abundant in the 100–300 m
depths during spring and summer when a large amountof sinking particle detritus is available (Amei et al., 2021).
For both regions, interactions related to day or night(×D/N) had a signiﬁcant effect on the polychaete community (Table V), possibly owing to the effect of DVM of673

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

Fig. 10. Percentage composition of sampling layers in pelagic polychaete distribution within 0–1 000 m water column reported by thisstudy and previous studies. Study No. corresponds to Table VI. No. 1–5
research in the subtropical region and the rest in the subarctic region of
the Paciﬁc Ocean.

subarctic region than in the subtropical area, which arecommon phenomena for pelagic polychaetes and wholezooplankton.
In the K2S1 project, which focused on regional comparisons of carbon cycles, the standing stocks (mg C m−2 )and ﬂuxes (mg C m−2 day−1 ) of various biogeochemicalcomponents have been quantiﬁed (Honda et al., 2016,2017). While the standing stocks and ﬂuxes of most components were at similar levels in both regions, the standing
stocks of metazooplankton were reported to be ten times
greater in the subarctic region than in the subtropicalregion (Honda et al., 2016, 2017; Matsumoto et al., 2016;
Wakita et al., 2016). To explain the high mesozooplankton
standing stocks, Kitamura et al. (2016) proposed threefactors: (i) The respiratory and excretory carbon losses perunit biomass due to large organisms were lower than thosedue to small organisms (mesozooplankton at the K2 werelarger than those at the S1), (ii) the lower temperature at
St. K2 allowed the mesozooplankton to decrease respiratory carbon loss and (iii) the higher turnover rates ofsmall organisms at St. S1 may have helped maintain theirbiomass to low levels. The energy loss from primary producers to the mesozooplankton community at St. K2, in
which primary consumers were probably dominant, wasconsidered to be lower than the community at St. S1. The
regional patterns of the standing stocks of pelagic polychaetes ﬁt well with the mesozooplankton stocks in eachregion. The difference in the body lengths of dominant
Tomopteris species (without tail) was detected between thesubarctic and subtropical regions, and this may have led tovariations in the standing stocks between St. S1 and K2(Kitamura et al., 2016). To mention pelagic polychaetes
for other discussions (2) and (3) in Kitamura et al. (2016),
we need more information on their life cycle, metabolic
rate and food.

JOURNAL OF PLANKTON RESEARCH

VOLUME 45

PAGES 661–676

2023

of the subarctic region, a unique, specialized communityof pelagic polychaetes adapted to low oxygen conditions
is supported by the abundant nutrient ﬂux via sinking particles and zooplankton fecal pellets. Thus, the two regions
differed in the pelagic polychaete community structures
and the vertical patterns.

CONCLUSIONSThis study was conducted for latitudinal comparison withthe results of Amei et al. (2021), which revealed diel,seasonal, and vertical changes in the pelagic polychaete
community at St. K2 in the western subarctic Paciﬁc.
By applying the same sampling and analytical methods
as Amei et al. (2021) at St. S1 in the western subtropicalPaciﬁc, we evaluated several latitudinal differences in the
pelagic polychaete community. First, the numbers of genera and species were higher at St. S1 than at St. K2. The
annual mean abundance and biomass were much higher
at St. K2. These regional patterns were attributed toregional differences in productivity, temperature-induced
metabolism and community structure at each region. At
St. S1, carnivorous pelagic polychaetes were dominant
throughout the sampling layers and concentrated in thesurface layer, and their abundance rapidly decreased withincreasing depth. On the other hand, at St. K2, numerous particle-feeding species were present in the pelagic
polychaete community, and their abundance peaked at
a depth of 300 m, with the predominance of particle
feeders at the deep layer of the station; this ﬁnding can be
attributed to the passive ﬂux of sinking particulate matter,such as fecal pellets, at St. K2. The pelagic polychaete
community structures varied depending on depth, andthey differed between the two regions.

ACKNOWLEDGEMENTS
The zooplankton samples used in this study were collected from theR/V Mirai of the JAMSTEC. We highly appreciate Dr M. C. Honda,
the chief scientist on the cruises. We are grateful to Prof. H. Ueno
of Hokkaido University for valuable advice on the hydrography ofthe study area and Prof. N. Jimi of Nagoya University for signiﬁcantcomments on the identiﬁcation of polychaetes. RD appreciate ﬁnancial
support from the Crown Prince Akihito Scholarship Foundation.

FUNDING
Part of this study was supported by Grant-in-Aid for Scientiﬁc Research[22H00374 (A), 20H03054 (B) and 19H03037 (B) from the Japan Society
for the Promotion of Science (JSPS)]. This work was partially conductedin the Arctic Challenge for Sustainability II (ArCS II) Project (Program
Grant Number JPMXD1420318865). This work was also supported by
JSPS KAKENHI (grant number JP22J21880).

674

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

surface-dwelling carnivorous species (e.g. Tomopteris spp.)
in each region.
The abundance and biomass of pelagic polychaetes insubtropical S1 were concentrated at 200–300 m occupied
with STMW and decreased rapidly at deeper layer occupied with TW and NPIW (Figs. 3 and 4). SPW was only
observed in November and July. However, no differencesin pelagic polychaete abundance and composition on thesurface layer between the seasonal thermocline season(November, July) and non-seasonal thermocline season(February, April) were detected. This suggests that theseasonal thermocline cannot be a barrier to pelagic polychaete distribution at St. S1. The limited distribution ofvisual carnivore feeders, Alciopini (tribe) (cluster groupsA–C) in surface water (SPW and STMW), is related to
the vertical changes in the light transmission rate. Amongthe three groups, the group with the highest DO level had
the highest mean abundance (group A > B > C) (Fig. 6c).
Carnivores such as Tomopteris and Alciopini (tribe) dominate the surface group and have high metabolic rates for
DVM, positive swimming and seeks prey (Childress andThuesen, 1993; Thuesen and Childress, 1993). Besides,
Joost et al. (2021) suggested that Tomopteridae need to
stroke their parapodium when they swim actively. Thus,
they can need high concentrations of DO to feed on theirprey actively.
Poeobius meseres has unique feeding modes wherein it
secretes mucus nets to capture the sinking food particles(detritus) (Robison et al., 2010; Uttal and Buck, 1996); thisspecies also has a low metabolic rate and engages in little
swimming activity, which may be considered adaptations
to the low oxygen concentration in the deep layer, i.e.
the OML (Childress and Thuesen, 1993; Thuesen andChildress, 1993). In the subarctic and subtropical regions,
OML, which is a prominent environmental parameterfor vertical changes, is observed below 200 m (Fig. 2).
From the viewpoint of adaptation to the OML, the low
metabolic rates of P. meseres (Childress and Thuesen, 1993;
Thuesen and Childress, 1993) may facilitate its distribution in the OML. Notably, P. meseres occurs only in the
deep layer of the subarctic region (Amei et al., 2021).
Because the vertical ﬂux of fecal pellets is reported to bemuch higher in the subarctic region than in the subtropical region (Kobari et al., 2016), the increased food availability may also support the distribution of P. meseres in thesubarctic region. In the pelagic polychaete community,
carnivorous pelagic polychaetes dominated the surface ofboth the subarctic and subtropical regions. However, thecompositions of deep-sea communities varied regionally.
The scarcity of sinking particles and the low availabilityof fecal pellet ﬂux in the subtropical region (Kobari et al.,2016) may prevent the distribution of particle feeders in
the deep layer of the subtropical region. In the deep layer

NUMBER 4

K. AMEI ET AL.

DIEL, SEASONAL AND VERTICAL CHANGESDATA AVAILABILITY

Honda, M. C., Wakita, M., Matsumoto, K., Fujiki, T., Siswanto, E.,
Sasaoka, K., Kawakami, H., Mino, Y. et al. (2017) Comparison ofcarbon cycle between the western Paciﬁc subarctic and subtropical
time-series stations: highlights of the K2S1 project. J. Oceanogr., 73,
647–667.

Data will be provided by the corresponding author on request.

REFERENCES

Amei, K., Jimi, N., Kitamura, M., Yokoi, N. and Yamaguchi, A. (2020)
Community structure and seasonal changes in population structureof pelagic polychaetes collected by sediment traps moored in thesubarctic and subtropical western North Paciﬁc Ocean. Zoosymposia,
19, 41–50.
Boyd, P. W., Gall, M. P., Silver, M. W., Coale, S. L., Bidigare, R. R. andBishop, J. (2008) Quantifying the surface-subsurface biogeochemical
coupling during the VERTIGO ALOHA and K2 studies. Deep-Sea
Res. II , 55, 1578–1593.
Bray, J. R. and Curtis, J. T. (1957) An ordination of the upland forest
communities of southern Wisconsin. Ecol. Monogr., 27, 325–349.

Hopkins, T. L. and Torres, J. J. (1989) Midwater food web in the vicinityof a marginal ice zone in the western Weddell Sea. Deep-Sea Res., 36A,
543–560.
Joost, D., Aoki, N., Havassy, J., Katija, K. and Osborn, K. J. (2021)
Metachronal swimming with ﬂexible legs: a kinematics analysisof the midwater polychaete Tomopteris. Integr. Comp. Biol., 61,
1658–1673.
Kaneko, R., Nagata, T., Suzuki, S. and Hamasaki, K. (2016) Depthdependent and seasonal variability in archaeal community structurein the subarctic and subtropical western North Paciﬁc. J. Oceanogr., 72,
427–438.
Kitamura, M., Kobari, T., Honda, M. C., Matsumoto, K., Sasaoka,
K., Nakamura, R. and Tanabe, K. (2016) Seasonal changes in themesozooplankton biomass and community structure in subarctic
and subtropical time-series stations in the western North Paciﬁc. J.
Oceanogr., 72, 387–402.

Buesseler, K. O., Lamborg, C. H., Boyd, P. W., Lam, P. J., Trull, T.
W., Bidigare, R. R., Bishop, J. K. B., Casciotti, K. L. et al. (2007)
Revisiting carbon ﬂux through the ocean’s twilight zone. Science, 316,
567–570.

Kobari, T., Nakamura, R., Unno, K., Kitamura, M., Tanabe, K., Nagafuku, H., Niibo, A., Kawakami, H. et al. (2016) Seasonal variability
in carbon demand and ﬂux by mesozooplankton communities atsubarctic and subtropical sites in the western North Paciﬁc Ocean.
J. Oceanogr., 72, 403–418.

Childress, J. J. and Thuesen, E. V. (1993) Effects of hydrostatic pressure
on metabolic rates of six species of deep-sea gelatinous zooplankton.
Limnol. Oceanogr., 38, 665–670.

Kolbasova, G. and Neretina, T. (2021) A new species of Pelagobia(Lopadorrhynchidae, Annelida), with some notes on literature records
of Pelagobia longicirrata Greeff, 1879. Zootaxa, 5023, 77–92.

Christiansen, S., Hoving, H., Schütte, F., Hauss, H., Karstensen, J.,
Körtzinger, A., Schröder, S., Stemmann, L. et al. (2018) Particulatematter ﬂux interception in oceanic mesoscale eddies by the polychaete
Poeobius sp. Limnol. Oceanogr., 63, 2093–2109.

Lebour, M. V. (1922) The food of plankton organisms. J. Mar. Biol. Ass.
U.K., 12, 644–677.

Dales, K. P. (1957) Pelagic Polychaetes of the Paciﬁc Ocean, Vol. 7, Universityof California Press, Berkeley and Los Angeles, pp. 99–168.
Day, J. H. (1967) A monograph on the Polychaeta of southern Africa. Trustees Br.
Museum, London, 656, 1–878.
Elskens, M., Brion, N., Buesseler, K., Van Mooy, B. A. S., Boyd, P.,
Dehairs, F., Savoye, N. and Baeyens, W. (2008) Primary, new andexport production in the NW paciﬁc subarctic gyre during the vertigo
K2 experiments. Deep-Sea Res. II , 55, 1594–1604.
Feigenbaum, D. (1979) Predation on chaetognaths by Typhloscolecid
polychaetes: one explanation for headless specimens. J. Mar. Biol. Ass.
U.K., 59, 631–633.
Fernández-Álamo, M. A., Sanvicente-Añorve, L. and AlatorreMendieta, M. A. (2003) Changes in pelagic polychaete assemblages
along the California current system. Hydrobiologia, 496, 329–336.
Fujiki, T., Matsumoto, K., Mino, Y., Sasaoka, K., Wakita, M.,
Kawakami, H., Honda, M. C., Watanabe, S. et al. (2014) Seasonal
cycle of phytoplankton community structure and photophysiologicalstate in the western subarctic gyre of the North Paciﬁc. Limnol.
Oceanogr., 59, 887–900.
Halanych, K. M., Cox, L. N. and Struck, T. H. (2007) A brief review ofholopelagic annelids. Integr. Comp. Biol., 47, 872–879.
Honda, M. C., Kawakami, H., Matsumoto, K., Wakita, M., Fujiki,T., Mino, Y., Sukigara, C., Kobari, T. et al. (2016) Comparison ofsinking particles in the upper 200 m between subarctic station K2 andsubtropical station S1 based on drifting sediment trap experiments. J.
Oceanogr., 72, 373–386.

Masuzawa, J. (1969) Subtropical mode water. Deep-Sea Res., 16A,
463–472.
Matsumoto, K., Abe, O., Fujiki, T., Sukigara, C. and Mino, Y. (2016)
Primary productivity at the time-series stations in the northwestern
Paciﬁc Ocean: is the subtropical station unproductive? J. Oceanogr., 72,
359–371.
Matsumoto, K., Honda, M. C., Sasaoka, K., Wakita, M., Kawakami, H.
and Watanabe, S. (2014) Seasonal variability of primary production
and phytoplankton biomass in the western Paciﬁc subarctic gyre:
control by light availability within the mixed layer. J. Geophys. Res.,
119, 6523–6534.
Mileykovskiy, S. A. (1969) Vertical distribution, reproduction, andabundance of mass pelagic polychaetes in the north-western Paciﬁc.
Oceanology, 9, 549–557.
Minchin, P. R. (1987) An evaluation of the relative robustness oftechniques for ecological ordination. Vegetatio, 69, 89–107.
Rakusa-Suszczewski, S. (1968) Predation of Chaetognatha by Tomopteris
helgolandica Greef . J. Cons. Int. Explor. Mer, 32, 226–231.
Robison, B. H., Sherlock, R. E. and Reisenbichler, K. R. (2010) The
bathypelagic community of Monterey canyon. Deep-Sea Res. II , 57,
1551–1556.
Shannon, C. E. and Weaver, W. (1949) The Mathematical Theory ofCommunications, University of Illinois Press, Urbana, pp. 1–146.
Steinberg, D. K., Cope, J. S., Wilson, S. E. and Kobari, T. (2008) A
comparison of mesopelagic mesozooplankton community structurein the subtropical and subarctic North Paciﬁc Ocean. Deep-Sea Res.
II , 55, 1615–1635.

675

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

Amei, K., Dobashi, R., Jimi, N., Kitamura, M. and Yamaguchi, A.
(2021) Vertical changes in abundance, biomass and community structure of pelagic polychaetes down to 1000 m depths at station K2 inthe western subarctic Paciﬁc Ocean covering the four seasons andday-night. J. Plankton Res., 43, 442–457.

JOURNAL OF PLANKTON RESEARCH

VOLUME 45

Sun, D. and Wang, C. (2017) Latitudinal distribution of zooplankton
communities in the western Paciﬁc along 160 E during summer 2014.
J. Mar. Syst., 169, 52–60.
Tebble, N. (1962) The distribution of pelagic polychaetes across theNorth Paciﬁc. Bull. British Mus. Nat. History Zool., 7, 371–492.

NUMBER 4

PAGES 661–676

2023

Wakita, M., Honda, M. C., Matsumoto, K., Fujiki, T., Kawakami, H.,
Yasunaka, S., Sasai, Y., Sukigara, C. et al. (2016) Biological organiccarbon export estimated from the annual carbon budget. observedin the surface waters of the western subarctic and subtropical North
Paciﬁc Ocean from 2004 to 2013. J. Oceanogr., 72, 665–685

Thuesen, E. V. and Childress, J. J. (1993) Metabolic rates, enzyme
activities and chemical compositions of some deep-sea pelagic worms,
particularly Nectonemertes mirabilis (Nemertea; Hoplonemertinea) andPoeobius meseres (Annelida; Polychaeta). Deep-Sea Res. I , 40, 937–951.

Wald, G. and Rayport, S. (1977) Vision in annelid worms. Science, 196,
1434–1439.

Tittensor, D. P., Mora, C., Jetz, W., Lotze, H. K., Richard, D., Berghe,
E. V. and Worm, B. (2010) Global patterns and predictors of marine
biodiversity across taxa. Nature, 466, 1098–1101.

Yasuda, I., Hiroe, Y., Komatsu, K., Kawasaki, K., Joyce, T. M., Bahr,F. and Kawasaki, Y. (2001) Hydrographic structure and transport of
the Oyashio south of Hokkaido and the formation of North Paciﬁcintermediate water. J. Geophys. Res., 106, 6931–6942.

Uttal, L. and Buck, K. R. (1996) Dietary study of the midwater polychaete Poeobius meseres in Monterey Bay. California. Mar. Biol., 125,
333–343.

Yokoi, N., Abe, Y., Kitamura, M., Honda, M. C. and Yamaguchi, A.
(2018) Comparisons between POC and zooplankton swimmerﬂux
from sedimenttraps in the subarctic and subtropical North Paciﬁc.
Deep-Sea Res. I , 133, 19–26.

676

Downloaded from https://academic.oup.com/plankt/article/45/4/661/7197098 by Hokkaido University user on 04 August 2023

Ushakov, P. V. (1974) Fauna of the USSR: Polychaetes, Israel Program for
Scientiﬁc Translations, Jerusalem.

Yasuda, I. (2003) Hydrographic structure and variability in the
Kuroshio-Oyashio transition area. J. Oceanogr., 59, 389–402.