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Phytoplankton Community Structure in the HNLC Subarctic
Pacific Ocean is determined by Neocalanus flemingeri and N. plumchrus. **
Michael Dagg1, Suzanne Strom2
and Hongbin Liu3
1
Louisiana Universities Marine Consortium Louisiana, USA
2
Shannon Point Marine Laboratory Washington, USA
3
Hong Kong University of Science and Technology Clear Water Bay,
Kowloon, Hong Kong
** submitted DSR, March 2008revised August 2008
(from Levitus: World Ocean Atlas 1994)
-
Low phytoplankton concentrations, -
iron-limited growth (especially large cells)-
Small phytoplankton –
microzooplankton
grazers-
Large grazers consume microzooplankton and large phytoplankton-
Most important large grazers are Neocalanus spp.
The mortality of large phytoplankton remains the least understood component of the lower
trophic-level dynamics in the SPO
Here we re-evaluate the contribution of N. flemingeri and
N. plumchrus to the control of phytoplankton biomass and community structure in
the
subarctic
Pacific Ocean.
Surface
Mixed layer
Thermocline
Permanent halocline
N. plumchrus/flemingeri zone
N. cristatus and E. bungii zone
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
5/18/01
copepods bottle-1
0 1 2 3 4 5
App
aren
t gro
wth
rate
(d-1
)
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
< 5 μm5-20 μm> 20 μm
Chlorophyll concentration:< 5 μm = 0.577 μg l-1
5-20 μm = 0.143 μg l-1> 20 μm = 0.051 μg l-1
5/18/01
copepods bottle-1
0 1 2 3 4 5
App
aren
t gro
wth
rate
(d-1
)
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
< 5 μm5-20 μm> 20 μm
Chlorophyll concentration: Clearance rate:< 5 μm = 0.577 μg l-1 -0.068 L cop-1 d-1
5-20 μm = 0.143 μg l-1 0.088 L cop-1 d-1
> 20 μm = 0.051 μg l-1 0.208 L cop-1 d-1
Exp 1 - 5/18/01
phytoplankton ciliates dinoflagellates
< 5
chl
5-20
chl
> 2
0 ch
l>
20 C
oscin
o>2
0 G
ram
m>
20 P
seud
o 1
> 20
Pse
udo
2
< 20
cil
20-3
0 cil
> 30
cil
< 20
din
o20
-30
dino
Cle
aran
ce ra
te (L
cop
-1 d
-1)
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0N. flemingeri CVN. plumchrus CV
Additional experiments with counts
Chlorophyll concentration (μg l-1)< 5 μm 5-20 μm >20 μm total0.27
0.05
0.05
0.37
1.00
0.24
0.06
1.300.18
0.13
3.41
3.73
Exp 2 - 5/24/01
phytoplankton ciliates dinoflagellates
< 5
chl
5-20
chl
> 2
0 ch
l
< 20
cil
20-3
0 cil
30-4
0 cil
40-5
0 cil
> 50
cil
< 20
din
o20
-30
dino
> 30
din
o
Cle
aran
ce R
ate
(L c
op-1
d-1
)
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
N. flemingeri CVN. plumchrus CV
Exp 3 - 5/13/03
phytoplankton ciliates dinoflagellates
< 5
chl
5-20
chl
> 2
0 ch
l
< 20
cil
20-3
0 cil
> 30
cil
< 20
din
o20
-30
dino
Cle
aran
ce R
ate
(L c
op-1
d-1
)
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0N. flemingeri CVN. plumchrus CV
Exp 4 - 5/27/01
phytoplankton ciliates dinoflagellates
< 5
chl
5-20
chl
> 2
0 ch
l
< 20
cil
20-3
0 cil
30-4
0 cil
40-5
0 cil
> 50
cil
< 20
din
o20
-30
dino
30-4
0 di
no40
-50
dino
50-6
0 di
no60
-70
dino
> 70
din
o
Cle
aran
ce ra
te (L
cop
-1 d
-1)
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
N. flemingeriN. plumchrus
Exp 2 –
0.37 μg l-1Exp 3 –
1.30 μg l-1Exp 4 –
3.73 μg l-1
Clearance rate
Reference
Comments0.12
Frost et al., 1983
high copepod concentrations0.04
Landry and
Lehner-Fournier, 1988
high copepod concentrations0.112
Dagg, 1993
total chlorophyll removal0.04 -
1.08
Dagg
and Wyman, 1983
gut pigment converted to clearance 0.17 -
0.94
Gifford, 1993
cell counts0.24 -
0.96
Tsuda
et al., 2006
total ambient chlorophyll 0.12 -
0.60
Dagg
and
Walser, 1987
small cell (12 mm) and high concs0.32 -
0.38
Landry and
Lehner-Fournier, 1988
mesocosm -
total chlorophyll0.12
Landry et al., 1993a
mesocosm
-
total chlorophyll0.42, 0.45, 0.17
Landry et al., 1993
mesocosm
-
Nitzschia,
centrics, ciliates0.00 -
2.40
this study
Same general pattern observed for N. cristatus CV
< 5 μm> 20 μm
From Liu, Dagg and Strom. 2005. J. Plankton Res. 27: 647-662
Neocalanus cristatus CVChlor < 5 μm = 0.39 μg l-1
Chlor 5-20 μm = 0. 06 μg l-1
Chlor > 20 μm = 0.07 μg l-1
Chlorophyll size FloCAM size (μm ESD) fraction (μm)
< 5 5-20 > 20 11-20 21-30 31-40 41-50 51-60 >60
Cle
aran
ce ra
te (L
cop
-1 d
-1)
-1
0
1
2
3
4
n = 4 replicates
FloCAM showed same general pattern
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
910
number 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
0-1010-25 m
25-500-10
10-25 m25-500-10
10-25 m25-500-10
10-25 m25-500-10
10-25 m25-500-10
10-25 m25-50
1a1b
2a2b
3a3b
# ind/m3
June 1987 –
mean abundance = 204 ind m3(from Mackas
et al. 1993)
Inner Shelf Station29-May-01, 23:53
Number per m30 200 400 600 800
Dep
th (m
)
0
25
50
75
100
Neocalanus cristatusCIV Neocalanus spp. CV
Outer Shelf Station19-May-01, 00:10
Number per m30 200 400 600 800
0
25
50
75
100J. Napp, C. Baier, & J. Lanksbury, unpublished
Vertical Distribution
Middle Shelf Blue Water (GAK4)26-May-01, 23:54
Number per m 3
0 200 400 600 800
Dep
th (m
)
0
25
50
75
100
Neocalanus cristatus CIV Neocalanus spp. CV
Middle Shelf Bloom (4IW)25-May-01, 23:52
Number per m 3
0 200 400 600 8000
25
50
75
100
(J. Napp, C. Baier, & J. Lanksbury, unpublished)
Other abundance data
Miller, 1993; Goldblatt
et al., 1999; Kobari
et al., 2003 report average abundances to depths somewhat greater than the seasonal thermocline
but compressing these populations into the upper 50 or 25 m results in CV concentrations similar to those observed by Mackas
et al. (1993): 60 to 260 m-3
(Miller, 1993); 200 to 400 m-3
(Goldblatt
et al., 1999) and 180 to 510 m-3
(Kobari
et al., 2003).
Underway pumping of surface water by Kawamura (1990) commonly showed surface concentrations between 200-600 CVs m-3, and > 800 m-3
on several occasions
N. flemingeri and
N. plumchrus concentrations in surface waters are typically several hundred m-3, and population distributions are highly patchy, both horizontally and vertically.
Growth rates of phytoplankton
Growth rate (d-1)
reference
comments
0.54, 0.98, 1.33
Noiri
et al., 2005
Grow-out experiments at 5, 8 and 13oC0.1, 0.4
Noiri
et al., 2005
Fe conc
< 0.5 nM, 8 and 13oC0.0 -
0.5
Tsuda
et al., 2005
SEEDS enrichment experiment-early0.5 -
0.9
Tsuda
et al., 2005
SEEDS enrichment experiment-max growth0.2 -
0.5
Tsuda
et al., 2005
SEEDS enrichment experiment-post bloom0.3 -
0.5 Saito et al., 2005
SEEDS -
outside Fe enriched patch0.2 -
0.9
Boyd/Harrison, 1999
eastern SPO -
spring0.3 -
0.8
Boyd/Harrison, 1999
eastern SPO -
summer0.3 -
1.0
Booth et al., 1993
eastern SPO0.1 -
0.7 Landry et al., 1993b
eastern SPO0.2 -
0.6
Rivkin
et al., 1999
eastern SPO0.0 -
0.8
Strom/Welschmeyer, 1991
eastern SPO0.24
Boyd et al., 1999
eastern SPO
Population clearance rate
0.8
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0.2
0.2
Copepod concentration (CV m-3)
0 100 200 300 400 500
Cle
aran
ce ra
te (L
cop
-1 d
-1)
0.0
0.5
1.0
1.5
2.0
population clearance rate (d-1)
• growth rates of large diatoms in this Fe limited system are 0.2 -
0.4 d-1
• growth rates of large ciliates and dinoflagellates??
• other copepodid
stages must contribute also
Other considerations: top down effect by N. flemingeri/plumchrus
Post-ontogenic
descent
Annual phytoplankton max (Yoo
et al., 2008; Clemons and Miller, 1984; Boyd and Harrison, 1999; Parsons and Lalli, 1988)
a higher fraction of phytoplankton growth is consumed by microzooplankton
(Strom and Welschmeyer, 1991)
N. cristatus moves up into the surface layer after the descent of N. flemingeri and N. plumchrus so its contribution to surface layer grazing will increase at this time (Mackas
et al., 1993; Goldblatt
et al., 1999)
Other mesozooplankton, especially Oithona spp. and Pseudocalanus spp., increase in surface water at this time, although their grazing capacity is small (Liu et al., 2008).
Phytoplankton growth may be further reduced by onset of low light (fall/winter) season
Conclusions
Neocalanus spp. exert a strong structuring effect on the nano-and pico-
food webs of the N. Pacific Ocean, tending to drive the food web towards a small-cell dominated system by
a)
selective removal of large cellsb)
cascade effect
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 lowest
The END
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