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Figure. Seasonally migrating copepods appeared at Station K2. We can identify two groups of the copepods by the life cycle. Red: surface spawning species , Yellow: deep spawning species. C. jashinovi. C. pacificus. N. cristatus. M. pacifica. E. bungii. N. flemingeri. N. plumchrus.

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slide1

Figure. Seasonally migrating copepods appeared at Station K2. We can identify two groups of the copepods by the life cycle.

Red: surface spawning species,Yellow: deep spawning species.

C. jashinovi

C. pacificus

N. cristatus

M. pacifica

E. bungii

N. flemingeri

N. plumchrus

depth distribution of surface spawning copepods
Depth distribution of surface-spawning copepods

Calanus pacificus concentrated their biomass above 50 m, and dominated by adult males and females. They would emerge dormancy and start reproductions.

Depth (m)

Eucalanus bungii showed two abundance peaks at surface and in mid-layers. Over the study period, they decreased younger specimens and they started a downward migration.

Depth (m)

Metridia pacifica was a strong diel migrator, residing at mid-layers in daytime and at the surface in nighttime. Thus, they are active.

Depth (m)

Figure 4. Depth distribution of the surface-spawning species in the layers above 1000 m collected by IONESS. Abundance is mean of four day-night deployments during the study period (n=4). Bars show standard error.

depth distribution of deep spawning copepods
Depth distribution of deep-spawning copepods

Younger specimens of Neocalanus cristatus appeared abundantly in the layers above 100 m and they were developing into overwintering stage toward the end of our study period.

Depth (m)

Overwintering stages were dominated Neocalanus flemingeri and they resided at the mesopelagic layers throughout the study period, showing dormancy.

Depth (m)

Neocalanus plumchrus was most predominant species among zooplankton community and concentrated overwintering stage at the surface.

Depth (m)

Figure 5. Depth distribution of the surface-spawning species in the layers above 1000 m collected by IONESS. Abundance is mean of four day-night deployments during the study period (n=4). Bars show standard error.

slide4

Table 1. Active carbon flux by the dominant diel migrants, Metridia pacifica and its comparison to POC flux. *Data from Ken.

Parameter

1 Aug.

5 Aug.

12 Aug.

16 Aug.

Migrant population

Biomass (mgC m-2)

56.8

60.1

110.5

189.0

Abundance (102 animals m-2)

10.5

31.9

82.4

107.3

Weighted mean depth in daytime (m)

215.5

243.5

214.9

185.9

Ambient temperature in daytime (˚C)

3.2

3.2

3.3

3.3

Active carbon flux (mgC m-2 day-1)

Respiration

1.0

1.3

2.6

4.1

Egestion

0.7

1.0

1.9

3.1

Mortality

0.3

0.3

0.6

0.9

Total

2.0

2.5

5.0

8.2

POC flux (mgC m-2 day-1)*

62.4

-

22.8

-

Ratio of active carbon flux to POC flux (%)

3.2

-

21.9

-

Active carbon flux by Metridia pacifica is estimated to be 2-8 mgC m-2 day-1. Respiratory and egestion fluxes showed a similarly importance, and mortality flux was minor component.

These active carbon flux by the single species was accounted for more than 20% of sinking POC flux.

slide5

Table 2. Respiratory flux (mgC m-2 day-1) by the diel vertical migrants in the world’s oceans modified from Al-Murairi & Landry (2001). ME: Mesozooplankton, MA: Macrozooplankton, MP: M. pacifica. PC: Particulate carbon flux.

Location

Migrant biomass

Flux

Compared to PC

Source

(mgC m-2)

Component

(%)

Depth (m)

Atlantic

NFLUX

29

ME+MA

2

3

150

Longhurst et al. (1990)

BATS

192

ME

12

30

150

Dam et al. (1995)

BATS

49

ME+MA

1

5

150

Steinberg et al. (2000)

Pacific

E. Equator

96

ME

3

15

150

Zang & Dam (1997)

E. Equator

155

ME

6

20

150

Zang & Dam (1997)

E. Equator

53

ME+MA

6

4

150

Le Borgne & Rodier (1997)

W. Equator

47

ME+MA

3

6

150

Le Borgne & Rodier (1997)

ALOHA

158

ME+MA

4

15

150

Al-Murairi & Landry (2001)

ALOHA

-

ME+MA

1-5

7-29

150

Steinberg et al. (in prep.)

K2

-

ME+MA

10-29

16-127

150

Steinberg et al. (in prep.)

K2

57-189

MP

1-4

2-3

150

Kobari et al. (in prep.)

Comparing with the results of the world’s oceans, respiratory flux of K2 zooplankton community showed the largest numbers and was nearly equal to sedimentary flux in the NW Pacific as shown by Debbie.

Although Metridia pacifica was dominant diel migrants, they were accounted for 10% of the zooplankton respiratory flux.

Therefore other zooplankton taxa would more important for respiratory flux.

slide6

Table 4. Active carbon flux (mgC m-2 year-1) by the ontogenetic vertical migrants in the world’s oceans. CF: C. finmarchicus, NT: N. tonsus, NC: N. cristatus, NF: N. flemingeri, NP: N. plumchrus, Note: carbon flux at station K2 is shown as daily basis (mgC m-2 day-1).

Location

Migrant biomass

Flux

Compared to PC

Source

(mgC m-2)

Spp.

(%)

Depth (m)

Atlantic Ocean

OWS I

346

CF

275

<1

200

Longhurst & Williams (1992)

Southern Ocean

ST

-

NT

3400

262

1000

Bradford-Grieve et al. (2001)

STF

-

NT

9300

-

-

Bradford-Grieve et al. (2001)

SAT

-

1700

340

1000

Bradford-Grieve et al. (2001)

NT

Pacific Ocean

OWS P

-

NC+NF+NP

5000

185

1000

Bradford-Grieve et al. (2001)

Oyashio

7300

NC+NF+NP

4300

91

1000

Kobari et al. (2003)

K2

322

NF

3*

9-20

500

Kobari et al. (in prep.)

K2

1757

NC+NP

?

-

-

Kobari et al. (in prep.)

Active carbon flux by ontogenetic migration of N. flemingeri was estimated to be 3 mgC m-2 day-1 and was accounted for 20% of sinking POC at 500 m.

Unfortunately, the active carbon flux by other two Neocalanus could not be estimated because they still resided at surface and were active.

If it depends on migrant biomass, other two Neocalanus species will produce much larger carbon flux than those by N. flemingeri.

This flux could not be negligible and significant carbon pathway to the mesoplagic.

slide7

Table 1. Community feeding rates and faecal pellets production by the ontogenetically migrating copepods in the layer above 150 m. *Data from Phil, **Data from Ken.

Parameter

Source

1 Aug.

5 Aug.

12 Aug.

16 Aug.

Primary production (PP)*

590.1

427.5

300.3

355.2

Ratio of PP

Pico

48.2

47.8

56.8

59.9

Nano

17.7

22.8

21.7

22.5

Micro

34.1

29.4

21.5

17.6

Biomass

2427.1

1246.3

1267.3

1319.5

Respiratory requirement

86.3

48.9

49.4

52.8

Feeding rate

215.7

122.1

123.5

131.9

Ratio grazed

Phytoplankton

2.4

2.5

2.7

3.4

Other POC

97.6

97.5

97.3

96.6

Faecal pellet production

64.7

36.6

37.0

39.6

Units are mgC m-2 d-1, excepted for copepod biomass (mgC m-2) and ratio (%).

Picophytoplankton unedible for the copepods dominated primary production.

We measured pigment concentrations in copepod guts and estimated feeding rate and its composition.

Phytoplankton composed <3% of the ingested carbon and their carbon demands should be relied on POC other than phytoplankton.

Thus, their faecal pellets are also considered to come from non-phytoplankton materials.

These results suggest that some fraction of the exported carbon could be channeled through microbial food web and the copepod community.

contribution of the copepod faecal pellets to sinking poc
Contribution of the copepod faecal pellets to sinking POC

Figure 6. Sinking POC flux and faecal pellet production (FPP) by the ontogenetic migrating copepods. POC flux at each layer was estimated from the formula of Pace et al. (1987) and primary production (Data from Phil).

Since they were actively feeding on non-phytoplankton materials and transform them into faecal pellets, this process is considered to be an important carbon pathway during seasons dominated by small phytoplankton.

Comparing with sinking POC flux estimated from the equation of Pace and others, the copepod community feces composed less than 10% of sinking POC above 150 m, and their contribution to sinking POC is considered to be small.

what we knew from the ontogenetic migrants
What we knew from the ontogenetic migrants?

1. Most of the copepod community resided at surface during our study period and was developing with actively feeding on non-phytoplankton.

2. Carbon budget of the copepod feeding and egestion shows that a large fraction of their ingested carbon is channeled through microbial food web but their faecal pellets are minor component of sinking POC.

3. Active carbon flux by dominant diel migrant composed more than 20% of the sedimentary POC flux at 150 m and can be supplement source for the mesopelagic carbon demand.

4. Active carbon flux by ontogenetic migration of single species was account for 20% of the sedimentary POC flux at 500 m, and could be an important source for the mesopelagic carbon demand considering with the copepods residing at surface.

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