Neocalanus spp. and the Structure of the Pelagic Ecosystem in the Subarctic Pacific Ocean

M. Dagg, Louisiana Universities Marine ConsortiumH. Liu, Hong Kong University of science and TechnologyS. Strom, Western Washington University

Surface

Mixed layer

Thermocline

Permanent halocline

N. plumchrus/flemingeri zone

N. cristatus and E. bungii zone

data from Mackas, D.L., H. Sefton, C. B. Miller and A. Raich. 1993. Vertical habitat partitioning by large calanoid copepods in the oceanic subarctic Pacific during spring. Prog. Oceanogr. 32: 259-294.

0 m

35-45 m

100-120 m

N. plumchrus + N. flemingeri CV

0 50 100 150 200 250 300 350 400 450

0-15 m15-30 m30-50 m

0-15 m15-30 m30-50 m

0-15 m15-30 m30-50 m

0-15 m15-30 m30-50 m

0-15 m15-30 m30-50 m

0-15 m15-30 m30-50 m

0-15 m15-30 m30-50 m

0-15 m15-30 m30-50 m

0-15 m15-30 m30-50 m

0-15 m15-30 m30-50 m

12

34

56

78

91

0number ind/m3

May 1984 - 10 stations: mean abundance = 152 CVs / m3(from Mackas et al. 1993)

N. plumchrus + N. flemingeri CV

0 100 200 300 400 500 600

0-10

10-25 m

25-50

0-10

10-25 m

25-50

0-10

10-25 m

25-50

0-10

10-25 m

25-50

0-10

10-25 m

25-50

0-10

10-25 m

25-50

1a1b

2a2b

3a3b

# ind/m3

June 1987 – mean abundance = 204 ind / m3(from Mackas et al. 1993)

                                                                                                                                 

(from Levitus World Ocean Atlas 1994)

5/18/01

copepods bottle-1

0 1 2 3 4 5

App

aren

t gro

wth

rat

e (

d-1)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

< 5 m5-20 m> 20 m

Chlorophyll concentration: < 5 m = 0.577 g l-1

5-20 m = 0.143 g l-1

> 20 m = 0.051 g l-1

5/18/01

copepods bottle-1

0 1 2 3 4 5

App

aren

t gro

wth

rat

e (

d-1)

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

< 5 m5-20 m> 20 m

Chlorophyll concentration: Clearance rate: < 5 m = 0.577 g l-1 -0.068 L cop-1 d-1

5-20 m = 0.143 g l-1 0.088 L cop-1 d-1

> 20 m = 0.051 g l-1 0.208 L cop-1 d-1

5/18/01N. flemingeri and N. plumchrus CV

chlo

r < 5

chlo

r 5-2

0

chlo

r > 2

0ci

liate

s <

20ci

liate

s 20

-30

cilia

tes

> 30

dino

s <

20di

nos

20-3

0

dino

s >

30

Cle

aran

ce r

ate

(L d

-1)

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

are there enough copepods in situ to structure the nano- and pico-food web in the eastern subarctic Pacific?

For 200 copepods m-3 and 1 L cop-1 d-1 = 200 liters d-1 m-3 (0.2 d-1)

Concentration of N. plumchrus/flemingeri CV = 25 - 500 m-3

Clearance rate on large particles (> 20 m) = 0.2 – 2.0 L cop-1 d-1

• growth rates of large diatoms in this Fe limited system are 0.2 - 0.5 d-1

• growth rates of large ciliates and dinoflagellates??

• other copepodid stages must contribute also

Other considerations: top down effect by N. flemingeri/plumchrus

Conclusions

Neocalanus flemingeri and N. plumchrus exert a strong structuring effect on the food web of the N. Pacific Ocean, driving the food web towards a small-cell dominated system by:

removal of large cells (diatoms and microzooplankton)

cascade effect that stimulates small cells

Conclusions

Neocalanus flemingeri and N. plumchrus exert a strong structuring effect on the food web of the N. Pacific Ocean, driving the food web towards a small-cell dominated system by:

removal of large cells (diatoms and microzooplankton)

cascade effect that stimulates small cells

These effects are strongest:• at low food concentrations when copepod clearance rates are highest, and • under nutrient or food limiting conditions when growth rates of prey are reduced

The END