Impact of copepod grazing on developmental dynamics of an iron-induced phytoplankton bloom (EisenEx)
J. Henjes, P. Assmy, C. Klaas and V. Smetacek J.
Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
Size
Phytoplankton µm
M E S O
M I C R O
N A N O 200
20
2 2000
modified after Klaas (1997)
Zooplankton
Food web dynamics
Internationale Kooperation
• Food source for many large pelagic predators
• Intensive grazing pressure on phytoplankton, protozoa, detritus and faecal pellets in the euphotic zone
+
turnover rate of organic material → regeneration of macronutrients – vertical particle fluxes(Dubischar et al. 2002)
• Small copepods (e.g. Oithona, Ctenocalanus, Oncaea) show high abundances and account for a significant amount of the zooplankton biomass
Potential role of small pelagic copepods in the ecosystem of
the Southern Ocean
EisenEx (2000)
Africa
Antarctica
Provided by SeaWIFS Project, NASA/Goddard Space Flight Center and ORBIMAGE
Day 21 (IN-PATCH) Day 21 (OUT-PATCH) Chl a[mg m-3]
SeaWIFS satellite image of the Fe- induced phytoplankton bloom
Cruise track and area of fertilization
•200 ml water samples (microprotozoa)
10 µm gauze
•concentrated water samples (metazooplankton)
Statistical data analysis:
Differences between IN- and OUT-STATIONS:
UNPAIRED T-TEST
Correlation between vertical distribution of individual parameters:
PARTIAL CORRELATION ANALYSIS
•7 discrete depth between 10 and 150 m
(temporal trend: 80 m depth-integrated abundance and biomass)
Methods
▪ How does grazing impact of copepods affect the temporal development of the microprotozoan groups?
▪ How does this affect microprotozoan grazing on the phytoplankton bloom?
▪ What is the response of the small copepod community during the experiment?
Objectives
0 10 20 30 40 50 60 70 80
0 2 4 6 8 10 12 14 16 18 20 22 Days since first Fe-release
Copepod nauplii (103 Ind. m -3 ) IN-PATCH
OUT-PATCH
Copepod nauplii
N.S.
70%
0 10 20 30 40 50 60 70 80
0 2 4 6 8 10 12 14 16 18 20 22 Days since first Fe-release
Small copepods (103 ind. m -3 ) IN-PATCH
OUT-PATCH
Copepodites and adults of small species (<1.5 mm)
P < 0.01
N.S. = not significant
26%
Temporal development of small copepods
0 10 20 30 40 50 60 70 80
Day-2 Day 7 Day 17
% of standing stock grazed d-1
Hdinos Ciliates
Grazing impact of metazoa
Calculated from clearance rates of Schultes et al. (in prep.)
Large copepods (>2 mm)
IN OUT
Small copepods (<1.5 mm)
IN OUT
Initial Initial
0 10 20 30 40 50 60 70 80
Day-2 Day 7 Day 17
% of standing stock grazed d-1
Hdinos Ciliates
(integrated over 80 m depth)
Temporal development of microprotozoa
N.S. = not significant
Heterotrophic dinoflagellates
0 200 400 600 800 1.000 1.200 1.400
0 2 4 6 8 10 12 14 16 18 20 22 Days since first Fe-release
Standing stock in mg C m -2 IN-PATCH
OUT-PATCH
Aloricate + tintinnid ciliates
0 100 200 300 400 500 600 700 800
0 2 4 6 8 10 12 14 16 18 20 22 Days since first Fe-release
Standing stock in mg C m -2
IN-PATCH
OUT-PATCH P < 0.01 P < 0.01
N.S.
10 µm
Vertical distribution: Tintinnid ciliates vs. small copepods (<1.5 mm)
-1 -0,8 -0,6 -0,4 -0,2 0 0,2 0,4 0,6 0,8 1
0 2 4 6 8 10 12 14 16 18 20 22
Days since first Fe-release
Correlation coefficient
IN-PATCH OUT-PATCH
Empty tintinnidloricae (x10 6 Ind. m -2 )
Empty tintinnid loricae
(integrated over 150 m depth)
0 20 40 60 80 100 120 140 160
0 2 4 6 8 10 12 14 16 18 20 22 Days since first Fe-release
IN-PATCH
OUT-PATCH P < 0.05 N.S.
Other indicators for grazing on microprotozoa
N.S. = not significant
Other indicators for grazing on microprotozoa
0 20 40 60 80 100 120
Day 0 Day 21 Day 21
Emptytintinnidloricae(106 Ind. m -2 ) Cymatocylis spp.
Codonellopsis pusilla Other tintinnid ciliates
50 µm
70 µm
IN OUT
Diatoms
Grazing impact of microprotozoa on the bloom
Calculated from clearance rates of dark incubation experiments
IN OUT
Other phytoplankton
0 5 10 15 20 25 30
Day 0 Day 8 Day 21 Day 21
% of standingstock grazedd-1
20-40µm 40-60µm >60µm
IN OUT
0 5 10 15 20 25 30
Day 0 Day 8 Day 21 Day 21
% of standing stock grazed d-1
20-40µm 40-60µm >60µm
Heterotrophic dinoflagellates and aplastidic ciliates stocks are mainly controlled by small copepods
Interactions between copepods and microprotozoa facilitated population growth of diatoms within an iron-induced bloom
Conclusions
Vertical net hauls seriously undersample small copepods in contrast to Niskin bottle sampling
Small copepods show a clear increase in the iron-induced bloom indicating that they were food limited
Acknowledgements
Many thanks to
the crew of R.V Polarstern and participants
of EisenEx
Metazoan faecal pellet carbon
(integrated over 150 m depth)
Grazing impact of metazoa
0 50 100 150 200 250 300
0 2 4 6 8 10 12 14 16 18 20 22
Days since first Fe-release Metazoan faecal pellet carbon in mg C m -2
IN-PATCH
OUT-PATCH P < 0.01
.
Krägefsky et al. (in prep.)
. .mean over 80 m depth mean over 160 m depth
.
Mechanism for congragation of small copepods
Grazing impact on microprotozoa
Small copepods (<2.0 mm)
Large copepods (>2 mm)
Calculated from clearance rates of Schultes et al. (in prep.)
0 10 20 30 40 50 60 70 80
Day-2 IN-PATCH
(day 7)
OUT-PATCH (day 17)
% of standing stock grazed d-1
Hdinos Ciliates Diatoms
0 10 20 30 40 50 60 70 80
Day-2 IN-PATCH
(day 8)
OUT-PATCH (day 9)
% of standing stock grazed d-1
Hdinos Ciliates Diatoms
