Institute of Oceanography
NATIONAL CENTRE FOR MARINE RESEARCH
PLANKTONIC FOOD WEB IN THE AEGEAN
SEA
I.Siokou-Frangou,
and
G.Assimakopoulou* U.Christaki* E.D.Christou* A.Giannakourou*
O.Gotsis-Skretas* L.Ignatiades** K.Pagou* V.Pitta*** S.Psarra***
S.Zervoudaki* F.Van Wambeke****
*National Centre for Marine Research
**National Centre of Research DEMOKRITOS
***Institute of Marine Biology of Crete
****Universite de Marseille
Aegean Sea workshop
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Institute of Oceanography
NATIONAL CENTRE FOR MARINE RESEARCH
Spatial differentiation in the Aegean Sea
•Coastline morphology:
gulfs, islands,straits
•Bottom topography:
alternation of extended
plateaux and basins
•Rivers outflow in the
North.
•Hydrology and circulation
Great diversity of biotopes
Spatial differentiation of
pelagic communities
Aegean Sea workshop
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Pelagic food web
Aegean Sea workshop
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Phytoplankton pigments distribution in the Aegean Sea
(annual mean of czcs images)
Aegean Sea workshop
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2.4 0
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2.2 0
Chla distribution
in N.Aegean (1998)
2.0 0
1.8 0
1.6 0
1.4 0
1.2 0
upper: plot of
mean integrated
values. Horizontal
variability.
1.0 0
0.8 0
0.6 0
0.4 0
0.2 0
0.0 0
0
lower: vertical
transect of chl-α
concentrations
Influence of Pinios
river (W) and Black
Sea Water (E)
1 .1 0
-50
1 .0 0
Pressure (dbar)
0 .9 0
0 .8 0
-100
0 .7 0
0 .6 0
0 .5 0
-150
0 .4 0
0 .3 0
0 .2 0
-200
0 .1 0
0 .0 0
0
50
100
150
200
Distance from M24 (km)
250
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300
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Distribution of mesozooplankton abundance in March-April
1988
NATIONAL CENTRE FOR MARINE RESEARCH
Higher values
in NE Aegean,
decrease in
S.Aegean and
Levantine
Aegean Sea workshop
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Institute of Oceanography
NATIONAL CENTRE FOR MARINE RESEARCH
NE Aegean Sea frontal area (April 2000)
EU project KEYCOP
Vertical distribution of salinity
KA2
KA3
KA4
Total Zooplankton Abundance-April
KA1
6000
2500
5000
2000
4000
1500
3000
1000
2000
500
1000
0
0
20
40
60
Distance (km)
28.5
30.0
31.5
33.0
34.5
0
KA1 KA2 KA3 KA4 KA5 KA6
F
0-10m
36.0
37.5
10-20m
20-50m
column
50-B
39.0
By Zervakis et al.
Aegean Sea workshop
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ind m -3
KA5
ind m -3
KA6
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Vertical distribution of primary
production (μgC/l/h)
Vertical distribution of chlorophyll-a (μg/l)
KA6
KA5
KA2
KA3
KA4
KA6
KA1
-20
KA5
KA4
KA2
KA3
KA1
P re s su r e ( d b ar )
-20
-40
-60
-40
-60
-80
-80
-100
0
20
40
60
-100
0
20
40
60
Distance (km)
Distance (km)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0
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0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
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N6
EU project MATER
N7
N1 N5
N2
Study on the structure
of the pelagic food web
and the carbon flow
through it.
N4
N3
March and September
1997
Positioning of sampling
stations.
Results are average
values over stations of the
areas NE Aegean (NEA),
N.Aegean (NA),
S.Aegean (SA)
S3
S1
S2
Aegean Sea workshop
S6
S7
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Nitrates distribution in the North and South Aegean Sea
NATIONAL CENTRE FOR MARINE RESEARCH
By Souvermezoglou et al.
March 1997
North Aegean
N3
N2
0
South Aegean
N7
N6
N1
N5
S7
<0.25
-100
Pressure (dbar)
-50
Pressure (dbar)
S6
S1
>1.0
<0.25
>0.75
-100
-200
>3.25
-300
-150
-200
0
S2
N4
50
100
150
200
250
>3.0
-400
0
>2.75
20
40
60
80
100
120
Distance (km)
Distance (km)
•The concentration of nutrients in the surface layer of NEA and NA is of the
same low level as in SA (Souvermezoglou et al.)
•The Black Sea surface outflow reaches the Aegean Sea with large amount
of dissolved organic nitrogen (DON) and dissolved organic carbon (DOC)
(Polat & Tugrul, 1996, Sempere et al., 2002)
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Autotrophs biomass (in mg C m-2)
MARCH 1997
2500
2500
2000
2000
1500
1500
mg C m -2
mg C m -2
0-50m
1000
500
0
0
NA
0.2-3μm
•Gradual decrease of
biomass from NEA to SA
in the upper layer (BSW) in
March and September.
1000
500
NEA
•Small cells dominated in
both layers, their
contribution was lower in
SA.
50-100m
SA
NEA
NA
SA
> 3μm
Aegean Sea workshop
•Difference in groups
composition (March:
Coccolithophorids in NEA,
NA-Diatoms in SA)
•September: Deep
chlorophyll max in SA.
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•Bacteria: Important
contribution. No significant
differences among areas
Biomass of heterotrophs
March 1997
1600
1400
1400
1200
1200
1000
1000
mg C m -2
mg C m -2
1600
0-50m
800
600
600
400
200
200
0
0
NA
BACTERIA
CILIATES
SA
•Mesozooplankton: Gradual
decrease from NEA to SA,
stronger in the upper layer
(BSW).
800
400
NEA
•Ciliates: very low
values=grazing control by
copepods, slight increase from
NEA to SA
50-100m
NEA
NA
SA
HNAN
Mesozooplankton
Aegean Sea workshop
•HNAN (September): no
differences among areas.
•Decrease of total heterotrophic
biomass in the upper layer.
Higher biomass in the upper
layer in NEA, NA (BSW)
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Mesozooplankton species composition
(0-50m) September 1997
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Significant differences
between North and South in
the 0-50m layer-Dominance of
cladocerans in the North
Distinct communities
•North: mixte neritic-pelagic
character (more acute in the
NE-influence of Black Sea)
•South: pelagic character.
Differences decrease for the
layer 50-500m and reappear
below 500m different
biotopes?
Aegean Sea workshop
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Carbon partitioning- March 1997
NATIONAL CENTRE FOR MARINE RESEARCH
NEA
0
500
1000
1500
NA
2000
2500
3000
0
500
1000
1500
2000
2500
3000
SA
0
500
1000
1500
2000
2500
3000
mgC m-2
AUTO
BACT
HNAN
Microheterotrophs’ biomass
overwhelms that of autotrophs
Aegean Sea workshop
CIL
MESO
Microbial food web
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Productions
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Bacterial production
Primary production
150
mg C m -2 d-1
mg C m -2 d-1
2500
2000
1500
1000
500
0
mg C m -2 d-1
50
0
NEA
March
80
100
NA
SA
September
Copepod production
NEA
March
NA
SA
September
•Primary production decreased from NEA
to SA (March). Most of PP was due to cells
<3μm (March+September). Regenerated P.
60
•Bacterial production: no significant
differences among areas
40
20
0
NEA
March
NA
SA
September
•Copepod production significantly higher
in NEA than in NA and SA (better energy
flow to higher trophic levels in NEA than
in NA and SA).
Aegean Sea workshop
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S.Aegean Food web: multivorous (Copepods are
feeding both on protozoa and large phytoplankton)
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North Aegean Food web: Microbial (Copepods are feeding mainly on
protozoa).Especially in summer: Consumption of small autotrophs and heterotrophs
by appendicularians and cladoceransmore efficient energy transfer to fish (less
trophic levels). NE Aegean: particular area. Mainly microbial food web with
even more efficient flow to higher levels (fish and benthos).
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Vertical Flux of organic matter in NEA and NA versus SA
•Greater export of primary
production from euphotic
zone
•Very low grazing pressure of
copepods on phytoplankton
(spring)
•Higher amount of dead
zooplankters reach seabottom
•great availability of small
autotrophs
•Higher mesozooplankton biomass
in the whole water column
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Higher zoobenthic biomass in NEA
and NA than in SA-Increased
biomass values in Limnos and
Athos deep basins (Lykoussis et al.,
2002)
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CONCLUSIONS
NATIONAL CENTRE FOR MARINE RESEARCH
The Aegean Sea
Particular area within the Mediterranean Sea due to its
geographic position and environmental conditions.
Area of low nutrients, plankton biomass and production
(oligotrophic area).
Existence of a North-South gradient regarding plankton
biomass and production (although nutrients do not vary).
The species communities of the epipelagic and bathypelagic
layers are differentiated between North and South-distinction of
the NE part. Those of the mesopelagic layer are more similar.
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The N.Aegean sea presents similarities to the
W.Mediterranean Sea both in terms of plankton quantity and
communities, whereas the S.Aegean is similar to other areas of
the E.Mediterranean.
NATIONAL CENTRE FOR MARINE RESEARCH
The results obtained in March and September 1997 suggest:
 a microbial food web dominated in North and a multivorous
food web in the South.
 a more efficient energy transfer through the pelagic
food web towards higher trophic levels (fish and benthos) in
N.Aegean (especially in NE) than in S.Aegean.
 an increased transport of organic matter towards
the bottom of the deep Limnos and Athos basins.
The NE Aegean is a special environment, perhaps due to the local
nature of the higher production (presence of hydrological fronts).
Aegean Sea workshop
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Aegean Sea workshop
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Autotrophs biomass (in Carbon)
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SEPTEMBER 1997
0-50m
50-100m
2500
Dominance of
small cells
2500
2000
1500
mg C m -2
mg C m -2
2000
1000
500
0-50m:
Decrease from
NEA to SA
1500
1000
500
0
0
NEA NA
SA
NEA NA
0.2-3μm
SA
SA: biomass
higher in 50100m than in 050m Deep
Chlorophyll
maximum
> 3μm
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Institute of Oceanography
NATIONAL CENTRE FOR MARINE RESEARCH
SEPTEMBER 1997
0-50m
1600
1400
1400
1200
1200
1000
1000
mg C m -2
mg C m -2
1600
800
600
50-100m
800
600
400
400
200
200
0
0
NEA
NA
SA
NEA
NA
Aegean Sea workshop
SA
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Institute of Oceanography
NATIONAL CENTRE FOR MARINE RESEARCH
Bacterial community (Christaki et al., 1998)
During March and September 1997 higher bacterial activities (production,
enzymatic activity, aminoacid uptake, respiration) were recorded in the lower
salinity water influenced by the BSW.
The above findings implied different bacterial populations and/or different
state of organic matter (e.g. more or less refractory=more or less easily
hydrolysed by bacteria) in the two types of waters (Aegean-BS influenced).
Microzooplankton-Ciliates (Pitta & Giannakourou, 2000)
Significantly higher abundance in NEA than in SA, but the biomass was
lower in NEA due to the dominance of small size species.
Aegean Sea workshop
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Carbon partitioning in September 1994
NEA
NA
0
500
1000
1500
2000
0
500
1000
1500
2000
SA
0
500
1000
1500
2000
mg C m -2
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MDS plot of samples
(similarity among
samples) collected at 050m (a) and 50-100m
(b)
•Differentiation
between N.Aegean and
S.Aegean sea
•Station N4 (in front of
Dardanelles) is
positioned far from
S.Aegean
stations=strong
differences
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March 1997
Consumption of primary production (large cells) by copepods (0-100m)
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NEA
NA
4 (1%)
34 (6%)
546
SA
32
387
Consumption of PP
(13%)
NEA=6%
NA=1%
231
SA=13%
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MDS plot of samples
collected at 100200m©
200-300m (d)
300-500m (e)
•small differences
between areas
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MDS plot of samples
collected at
500-700m (f)
700-1000m (g)
•differences between
areas=communication
among deep basins
Aegean Sea workshop
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Calanus helgolandicus
ind.m-3
0
25
50
75
Eucalanus monachus
ind.m-3
100 125 150
0
100
0
200
100
300
200
10
20
30
300
400
500
m
m
0
400
500
600
600
700
700
800
800
900
March 97
September 97
March 98 (day)
March 98 (night)
900
March 97
September 97
Vertical distribution of Calanus helgolandicus (station N1)
and of Eucalanus monachus (st S1)
Aegean Sea workshop
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Distribution of
mesozooplankton
biomass in the 020m layer (May
1997)
0-20mg/m3
High values in the
area influenced by
BSW
40-60
60-80
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