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Vertical distribution and population structure of large
grazing copepods during spring phytoplankton bloom in
the Oyashio region
Atsushi Yamaguchi, Yuka Onishi, Aya Omata, Mariko Kaneda, Momoka
Kawai and Tsutomu Ikeda (Hokkaido University)
A
0
Large grazing copepods
5 mm
O
ya
sh
io
B
Okhotsk Sea
2000
io
Kurosh
Hokkaido
A-4★
A-5
A-5★
4000
6000
North Pacific
8000
Location of station
(A-line: A5)
Metridia
pacifica
C6F
Eucalanus
bungii
C6F
NeocalanusNeocalanus
flemingeri plumchrus
C5
C6F
Neocalanus
cristatus
C6F
Dominant calanoid copepods
in the Oyashio region
Role of large grazing copepods in the Oyashio region
Bacteria (5.4%)
Total: 31.3 g DM m-2
Phytoplankton (26.6%)
Microzooplankton (6.7%)
Mesozooplankton (51.1%)
0
25
50
75
100
5 mm
Large grazing copepods
Metridia
pacifica
Neocalanus
Neocalanus
plumchrus
flemingeri
Eucalanus
Neocalanus
bungii
cristatus
Chaetognaths (9.0%)
Other copepods (9.1%)
Mesozooplankton
Diapausing copepods (65.4%)
Neocalanus cristatus (31.0%)
Metridia pacifica (6.1%)
Metridia okhotensis (4.4%)
Neocalanus plumchrus (15.0%)
Neocalanus flemingeri (6.2%)
Eucalanus bungii (13.2%)
Reproductive timing of large grazing copepods: varied with species
Eucalanus bungii
Metridia pacifica
Epipelagic
Neocalanus flemingeri
Neocalanus plumchrus
Mesopelagic
Neocalanus cristatus
Suspension feeders/ diapause
Bathypelagic
Spring
bloom
Suspension feeders
S
O
N
D
J
F
M
A
M
0
5000
mg DM m-2
J
J
A
Neocalanus spp. utilize spring phytoplankton bloom as energy to growth, while
Eucalanus bungii and Metridia pacifica utilize them as energy to reproduction.
Studied parameters on copepods
Population structure: Enumerated with copepodid stages on the
samples collected by NORPAC net (0-500 m). For Eucalanus
bungii, gonad maturation of C6F and nauliar abundance were
also enumerated.
Vertical distribution: Stratified VMPS tows (9 strata from 01000 m) were made, and depths of 25%, 50% and 75% of
population resided were calculated with stages.
Gut pigment: Fresh specimens collected from 0-150 m in day
and night were immersed in N,N-Dimethylformamide and
measured with Turner-design fluorometer
Egg production: C6F of Eucalanus bungii, Metridia pacifica, M.
okhotensis were reared in the filtered seawater with bottommesh equipped plastic chamber (to prevent cannibalism) one
night. Hatching rates of eggs were also examined.
Chemical contents: Temporal changes in individual wet mass,
dry mass, ash of Neocalanus cristatus C5 and Metridia pacifica
C6F were evaluated.
Results: satellite image of SST and Chl. a during OECOS
Temperature (˚C)
Chlorophyll a
High
Low
A-4
A-5
A-4
A-5
A-line (A-5: 42˚00’N, 145˚15’E; A-4: 42˚15’N, 145.07’E)
There observed clockwise warm water mass throughout the
study period.
Chlorophyll a was higher in the coastal zone and warm water
eddy, and had peak around 9 April 2007.
200
0
4
3
150
2
100
Composition (%)
250
Day (A-5)
N:D (A-5)
0-150 m
A-5 (Day)
A-5 (Night)
A-4 (Night)
N:D (A-5)
25
75
50
0
0
100
4
0
150-500 m
Night (A-5)
200
3
150
2
100
1
50
0
0
April
Composition (%)
0-500 m
250
March
0-150 m
50
1
N:D (A-5)
Wet mass (g m-2: 0-500 m)
Wet mass (g m-2: 0-150 m)
Temporal changes in whole mesozooplankton wet mass
25
0-150 m
50
75
150-500 m
100
March
April
Distribution depths of mesozooplankton became shallower in April?
Eucalanus bungii
60
75
40
50
20
25
0
0
9-14
Mar.
10
15
20
Apr. 2007
25
30
C1
C2
C3
C4
C5
C6
40
30
20
10
0
9-14
Mar.
Vertical distribution
200
400
600
Copepodid stage
29 Apr.
C1
C2
C3
C4F
C4M
C5F
C5M
C6F
C6M
5 Apr.
C1
C2
C3
C4F
C4M
C5F
C5M
C6F
C6M
1000
8 Mar.
C1
C2
C3
C4F
C4M
C5F
C5M
C6F
C6M
Depth (m)
0
800
Day
Night
50
Pigment content
(ng Chl. ind-1)
100
Composition (%)
Abundance (inds. m-3)
Population structure
80
Gut pigment
(C6F)
Abundance
Nauplii
10
15 20 25
Apr. 2007
30
No DVM and
distributed
around 400 m in 8
March, started to
awake in 5 April,
and recruitment
of new generation
in 29 April.
Eucalanus bungii
Abundance
Nauplii
100
60
75
40
50
20
25
0
10
15
20
Apr. 2007
C3
C4
30
III
75
IV
50
V-1
25
V-2
0
9-14
Mar.
C6
Males
Sex ratio (% females)
Composition (%)
Females
25
C2
II
100
C5
0
9-14
Mar.
C1
I
Gonad maturation (C6F)
Composition (%)
80
Composition (%)
Abundance (inds. m-3)
Population structure
100
10
15
20
25
30
Apr. 2007
VI
VII
Sex ratio
100
C6
75
50
C5
25
C4
0
9-14
Mar.
10
15
20
Apr. 2007
25
30 9-14
Mar.
10
15
20 25
Apr. 2007
30
C6
75
C4
C5
50
25
0
9-14
Mar.
10
15
20
25
30
Apr. 2007
Recruit of adult male observed in March. Sex ratio skewed to females in
C6. Gonad of adult females matured rapidly during 5-10 April.
Reproductive female (V-1 and V-2) dominated during 10-20 April.
Eucalanus bungii
Composition of normal
egg and hatchability
100
Normal egg
50
Abnormal egg
0
100
75
50
Normal egg (%)
25
Hatchability (%)
0
9-14
10
Mar.
Individual recruitment
(inds. female-1 day-1)
Composition (%)
150
15
20 25
30
9-14
10
Mar.
Apr. 2007
Individual recruitment
150
100
50
0
Population recruitment
(inds. m-3 day-1)
Egg production rate
(eggs female-1 day-1)
Egg production
15 20
25
30
Apr. 2007
Population recruitment
500
400
300
200
100
0
9-14
Mar.
10
15
20 25
Apr. 2007
30
9-14
Mar.
10
15
20
25
30
Apr. 2007
Before 10 April, proportion of normal egg and hatchability were both
lower, while increased after 15 April. Estimated population recruitment
was peaked during 15-20 April.
Metridia pacifica
Abundance
60
75
40
50
20
25
0
0
9-14 5
Mar.
10
15
20
Apr. 2007
25
30
C1
C2
C3
C4
C5
C6
10
5
0
9-14
Mar.
Vertical distribution
200
400
600
Copepodid stage
29 Apr.
C1
C2
C3
C4F
C4M
C5F
C5M
C6F
C6M
5 Apr.
C1
C2
C3
C4F
C4M
C5F
C5M
C6F
C6M
1000
8 Mar.
C1
C2
C3
C4F
C4M
C5F
C5M
C6F
C6M
Depth (m)
0
800
Day
Night
15
Pigment content
(ng Chl. ind-1)
100
Composition (%)
Abundance (inds. m-3)
Population structure
80
Gut pigment
(C6F)
10
15 20 25
Apr. 2007
30
In the end of April
(29 April), most of
the stages (except
C6F) ceased DVM
and stayed daytime
depth throughout
the day.
Metridia pacifica C6F
Individual mass
2000
Water
Water
(%WM)
Wet-mass
70
95
100
Ash
20
p=0.21 (ns)
80
Dry-mass
200
AFDM
(%DM)
Individual mass (µg ind.-1)
1000
90
AFDM
90
85
p=0.06 (ns)
80
1
10
100
1
10
20
March
30
10
20
April
30
During March to April, water
content and ash-free dry mass
content were not varied.
AFDM
200
10
20
March
30
10
20
April
30
Metridia pacifica
Composition of normal
egg and hatchability
Normal egg
30
20
10
Abnormal egg
0
100
10
Mar.
15
20 25
25
Individual recruitment
15
10
5
0
Mar.
20 25
Apr. 2007
10
30
15 20
25
30
Apr. 2007
Population recruitment
40
30
20
10
0
15
9-14
Mar.
Apr. 2007
10
Hatchability
50
30
20
9-14
Normal egg
75
0
9-14
Individual recruitment
(inds. female-1 day-1)
Composition (%)
40
Population recruitment
(inds. m-3 day-1)
Egg production rate
(eggs female-1 day-1)
Egg production
9-14
Mar.
10
15
20
25
30
Apr. 2007
Egg production of normal and abnormal eggs fluctuated greatly, and there
were no constant temporal trend detected. Estimated population
recruitment was greater after 20 April.
Metridia okhotensis
Abundance
30
75
50
20
25
10
0
0
9-14
Mar.
10
15
20
Apr. 2007
25
30
C1
C2
C3
C4
C5
C6
150
100
50
0
9-14
Mar.
Vertical distribution
200
400
600
Copepodid stage
29 Apr.
C1
C2
C3
C4F
C4M
C5F
C5M
C6F
C6M
5 Apr.
C1
C2
C3
C4F
C4M
C5F
C5M
C6F
C6M
1000
8 Mar.
C1
C2
C3
C4F
C4M
C5F
C5M
C6F
C6M
Depth (m)
0
800
Day
Night
200
Pigment content
(ng Chl. ind-1)
100
Composition (%)
Abundance (inds. m-3)
Population structure
40
Gut pigment
(C6F)
10
15 20 25
Apr. 2007
30
In March, they
distributed around
400 m both day and
night. In early
April, C5F/M
started DVM, while
ceased DVM
(except C6F) in the
end of April.
Metridia okhotensis
Composition of normal
egg and hatchability
Normal egg
Abnormal egg
100
10
Mar.
15 20 25
Normal egg (%)
75
50
25
Hatchability (%)
0
9-14
Individual recruitment
(inds. female-1 day-1)
Composition (%)
30
25
20
15
10
5
0
30
9-14
10
Mar.
Apr. 2007
Individual recruitment
8
6
4
2
Population recruitment
(inds. m-3 day-1)
Egg production rate
(eggs female-1 day-1)
Egg production
25
15 20 25
30
Apr. 2007
Population recruitment
20
15
10
5
0
0
9-14
Mar.
10
15 20 25
Apr. 2007
30
9-14
Mar.
10
15 20 25
30
Apr. 2007
Egg production of Metridia okhotensis observed after 17 April.
Composition of normal egg was high, while hatchability fluctuated.
Population recruitment reached 20 inds. m-3 day-1.
Neocalanus cristatus
Abundance
9
75
6
50
25
3
0
0
9-14
Mar.
10
15
20
Apr. 2007
25
30
C1
C2
C3
C4
C5
C6
400
300
200
100
0
9-14
Mar.
Vertical distribution
200
400
600
Copepodid stage
29 Apr.
C1
C2
C3
C4
C5-T
C5-I
C5-S
C6F
C6M
5 Apr.
C1
C2
C3
C4
C5-T
C5-I
C5-S
C6F
C6M
1000
8 Mar.
C1
C2
C3
C4
C5-T
C5-I
C5-S
C6F
C6M
Depth (m)
0
800
Day
Night
500
Pigment content
(ng Chl. ind-1)
100
Composition (%)
Abundance (inds. m-3)
Population structure
12
Gut pigment
(C5)
10
15 20 25
Apr. 2007
30
No apparent
DVM for most
of the stages.
Gut pigment
was not varied
between day
and night after
10 April.
Neocalanus cristatus
Abundance
12
100
9
75
6
50
3
25
C2
C3
C4
C5
0
0
9-14
Mar.
Cumulative composition (%)
C1
Composition (%)
Abundance (inds. m-3)
Population structure
10
15
20
Apr. 2007
25
C6
30
100
C5
75
C4
C1
C2
C3
C3
50
C2
C4
25
C5
C1
0
March
April
During March to April,
Neocalanus cristatus
developed from
C2 (-17 March)
C3 (17 March-11 Apri)
C4 (11 April-)
Stage duration of C3 was
estimated to be 24 days.
Neocalanus cristatus C5
Individual mass
30
Wet-mass
Water
(%WM)
10
80
100
5
0
0.4
Ash
0.3
r2=0.54, p<0.001
60
Dry-mass
AFDM
(%DM)
Individual mass (mg ind.-1)
20
10
Water
100
AFDM
90
80
70
60
r2=0.65, p<0.0001
1
0.2
10
20
March
30
10
20
April
30
0.1
Through March to April, water
contents decreased, while ashfree dry mass (=organic mass)
increased.
AFDM
10
5
0
1
10
20
March
30
10
20
April
30
Neocalanus flemingeri
Abundance
30
75
20
50
25
10
0
0
0 9-14 5
Mar.
10
15
20
Apr. 2007
25
30
C1
C2
C3
C4
C5
C6
40
30
20
10
0
9-14
Mar.
200
400
600
29 Apr.
C1
C2
C3
C3
C4
C5
C6F
C6M
C4
C5
C6F
C6M
C1
C2
Copepodid stage
C4
C5
C6F
C6M
5 Apr.
1000
C1
C2
C3
Depth (m)
0
8 Mar.
10
15 20 25
Apr. 2007
30
No DVM was
observed. Gut
pigment was
also not varied
between day
and night.
Vertical distribution
800
Day
Night
50
Pigment content
(ng Chl. ind-1)
100
Composition (%)
Abundance (inds. m-3)
Population structure
40
Gut pigment
(C5)
Neocalanus flemingeri
Abundance
40
100
30
75
20
50
10
25
C2
C3
C4
C5
0
0
0 9-14 5
Mar.
Composition (%)
C1
Composition (%)
Abundance (inds. m-3)
Population structure
10
15
20
Apr. 2007
25
C6
30
80
C1
60
C2
C3
40
C4
20
C5
0
C6
March
April
Through March to April,
Neocalanus flemingeri
developed from
C1 (9 April- 18 April),
C2 (18 April- 25 April)
to
C3 (25 April-)
Duration time of C1 was
estimated to be 9 days,
and that of C2 to be 7
days.
Neocalanus plumchrus
Abundance
100
15
75
10
50
5
25
Composition (%)
Abundance (inds. m-3)
Population structure
0
0
9-14
Mar.
10
15
20
Apr. 2007
25
30
C1
C2
C3
C4
C5
After 8 April,
Neocalanus plumchrus
occurred near surface
layer.
C6
Vertical distribution
200
400
600
8 Mar.
5 Apr.
29 Apr.
Copepodid stage
C1
C2
C3
C3
C4
C5
C6F
C6M
C1
C2
C4
C5
C6F
C6M
1000
C4
C5
C6F
C6M
800
C1
C2
C3
Depth (m)
0
Summary
Reproductive and developmental timing of large copepods during
spring phytoplankton bloom was evaluated.
March
E. bungii
M. pacifica
April
Gonad maturation Peak of nauplii
Peak of reproduction
C3-C6M dominated
Greater abundance (C6)
M. okhotensis
N. cristatus
No DVM (diapause)
C2
Low recruitment to population Cease DVM
DVM (C5F/M)
Reproduction Cease DVM
C4
C3
N. flemingeri
C1
N. plumchrus
Recruitment started
C2
C3