what is limiting marine heterotrophic microorganisms ? johnny berglund marine ecology department of...
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![Page 1: What is limiting marine heterotrophic microorganisms ? Johnny Berglund Marine ecology Department of Ecology and Environmental Science Umeå University](https://reader036.vdocument.in/reader036/viewer/2022062308/56649d415503460f94a1b964/html5/thumbnails/1.jpg)
What is limiting marine heterotrophic microorganisms ?
Johnny Berglund
Marine ecology
Department of Ecology and Environmental Science
Umeå University
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Aquatic food web
by Kristina Wiklund, UMF
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Some marine protists...
Rhynchomonas nasuta
Parvicorbicula sp.Plagioselmis prolonga
Bodo saliens
Copyright ©, Mats Kuylenstierna & Bengt Karlson
Mesodinium rubrum5m
5m
Heterotrophic nanoflagellates (HNF)
Ciliates
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18E 20E 22E 24E 26E
U m eå
Lu leå
Turku
Vaasa
N orrbyn
Sweden
F in land
A5
A1 3
B3B7
C 1C 3
C 1 4
60N
62N
64N
66N
18E 20E 22E 24E 26E
60N
62N
64N
66N
Study area:Gulf of Bothnia
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Gulf of Bothnia• Low salinity from 3 psu to 7 psu• Mean depth of 40 m in B.Bay and 66 m in B.Sea• Strong seasonality, ice-cover of 120 and 60 days• High river runoff
Annual average, Kuparinen et al. 1996
0
1
2
3
4
5
Bacterial biomass Phytoplankton biomass Zooplankton biomass
mm
ol
C m
-3
Bothnian Bay
Bothnian Sea
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Seasonal pattern in bacterial and HNF abundance
HNF <5 ym
0
500
1000
1500
2000
2500
3000
3500
0 10 20 30 40 50
N m
l-1
Bothnian Bay
Bothnian Sea
Bacteria
0.0E+00
1.0E+06
2.0E+06
3.0E+06
4.0E+06
5.0E+06
0 10 20 30 40 50
N m
l-1Bothnian Bay
Bothnian Sea
week
week
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Question:
What is limiting growth of heterotrophic nanoflagellates (HNF)?- especially small flagellates <5m
Why?Because small flagellates (1-3 m) are most important predators on heterotrophic bacteria (Wikner & Hagström 1988 and others)
Hence, small flagellates are an important link to higher trophical levels
Definition (Osenberg & Mittelbach 1995):
Limitation is the extent to which a population’s, or trophic level’s, per capita growth
rate is depressed by the action of a particular factor, for example resource availability or predator risk.
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Bothnian Sea
0
500
1000
1500
2000
2500
3000
3500
4000
0 10 20 30 40 50
Week
N m
l-1
0.00E+00
5.00E+05
1.00E+06
1.50E+06
2.00E+06
2.50E+06
3.00E+06
3.50E+06
4.00E+06
Bac
t. m
l-1
Bothnian Bay
0
500
1000
1500
2000
2500
3000
3500
4000
0 10 20 30 40 50
N m
l-1
0.00E+00
5.00E+05
1.00E+06
1.50E+06
2.00E+06
2.50E+06
3.00E+06
3.50E+06
4.00E+06
Bac
t. m
l-1
HNF < 5 Bact.
Factor 1:
~1.5*106 ml-1
~2.5*106 ml-1
Natural threshold for HNF growth
Bacteria as resource
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f.w. <90 <10 <5 <0.80.00
0.02
0.04
0.06
0.08
0.00
0.02
0.04
0.06
0.08
Bio
volu
me
(mm
3 l -1)
0.00
0.02
0.04
0.06
0.08
Treatment
f.w. <90 <10 <5 <0.80.0
0.2
0.4
0.6
0.8
0.0
0.2
0.4
0.6
0.8
0.00
0.02
0.04
0.06
0.08
Gro
wth
ra
te (
d-1)
0.0
0.2
0.4
0.6
0.8
0.0
0.2
0.4
0.6
0.8
0.0
0.2
0.4
0.6
0.8
1.0
A. Heterotrophic bacteria
0.0
0.2
0.4
0.6
0.8
1.0
Initial growth rate Maximal biovolume
B. Small flagellates
C. Medium flagellates
D. Large flagellates
E. ChoanoflagellatesSamuelsson, K. & Andersson, A. 2002Predation limitation in the pelagic microbial food web,AME in press
• 0.8 – 5 m flagellates most important predator on bacteriaHeterotrophic
bacteria
HNF
PROBLEM...to distinguish effect of predation and effect of reduced competition for bacteria (resource)
Medium HNF
f.w
.
<90
<10
<5
<0.
8
f.w
.
<90
<10
<5
<0.
8
Factor 2:
• thightly size structured food-chain
Predation by large flagellates and ciliates
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Hence, there are two factors limiting the
heterotrophic nanoflagellates
1. resource
2. predation
Lets setup an experiment to evaluatethe importance of the factors
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•Limitation can be measured by quantifying the increase in a population’s per capita growth rate following the removal of a particular form of limitation, for example after the addition of a surplus resource or removal of predators.
(Osenberg & Mittelbach 1995)
2 after removal of limitation
1 in natural conditions
Timet1t0
lnN2
lnN1
LnN
0
1 = (lnN1 –lnN0) / (t1-t0)
Limitation L = 2 -1
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+ bacteria
no addition
< 90 m < 10 m < 5 m
Experimental setup to determine limiting factors for HNF
Treatment Resource limitation Predator 5-10 m limitation
Predator 10-90 m limitation
< 90 m + + + < 90 m + bakt. - + + < 10 m + + - < 10 m + bakt. - + - < 5 m + - - < 5 m + bakt. - - -
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Dialysis bags incubated in situ at 4 m
depth
Duration: 4 days with sampling every day
Performed in June 2001
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Results
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
+ pred.90 -bakt.
+ pred.90 +bakt.
+ pred.10 -bakt.
+ pred.10+bakt.
- pred.-bakt.
- pred.+bakt.
HN
F g
row
th r
ate
h-1
Highly significant (p<0.001) effect of adding bacteria (resource)
Weak effect of predation (p<0.05) by large protozoans (10-90m)
(No effect of predation by large flagellates (5-10 m))
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Results...
Relativ importance (change in pop. Growth)
resource 62 % and predation 38 %
Ls (h-1) Lp (h
-1)
B2 - B1 0.0092
B4 - B3 0.0110 B5 - B1 0.0062
B6 - B5 0.0084
B6 - B2 0.0054 Mean 0.0095 Mean 0.0058 Stdev. 0.0013 Stdev. 0.0006
To evaluate possible seasonal variations a second experiment was performed in September 2001
-same experimental setup
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Experiment 2
Results...
0
0.005
0.01
0.015
0.02
+ pred.90 -bakt.
+ pred.90 +bakt.
- pred.- bakt. - pred. +bakt.
HN
F gr
owth
rat
e
Again significant (p<0.005) effect of adding bacteria
Relativ importance of resource 81 % and predation 19 %,
though effect of predation not significant
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Conclusions
• HNF growth mostly resource limited
microbial food web bottom-up regulated
Modelling still to come....
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Thank you for your attention!
Acknoledgements:
Agneta Andersson
Kristina Samuelsson
Thomas Kull
Umeå Marine Science Center