1. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop1 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

2. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop2 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 biotopesSpatial differentiation of pelagic communities

3. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop3 Pelagic food web

4. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop4 Phytoplankton pigments distribution in the Aegean Sea (annual mean of czcs images)

5. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop5 Chla distribution in N.Aegean (1998) upper: plot of mean integrated values. Horizontal variability. lower: vertical transect of chl-α concentrations Influence of Pinios river (W) and Black Sea Water (E)

6. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop6 Distribution of mesozooplankton abundance in March-April 1988 Higher values in NE Aegean, decrease in S.Aegean and Levantine

7. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop7 NE Aegean Sea frontal area (April 2000) EU project KEYCOP 0204060 Distance (km) 28.530.031.533.034.536.037.539.0 KA6KA5 KA4 KA3 KA2 KA1 Vertical distribution of salinity By Zervakis et al.

8. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop8 Vertical distribution of chlorophyll-a (μg/l) Vertical distribution of primary production (μgC/l/h)

9. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop9 EU project MATER Study on the structure of the pelagic food web and the carbon flow through it. 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)

10. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop10 Nitrates distribution in the North and South Aegean Sea By Souvermezoglou et al. 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)

11. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop11 Autotrophs biomass (in mg C m -2 ) Institute of Oceanography MARCH 1997 0.2-3μm > 3μm Small cells dominated in both layers, their contribution was lower in SA. Gradual decrease of biomass from NEA to SA in the upper layer (BSW) in March and September. Difference in groups composition (March: Coccolithophorids in NEA, NA-Diatoms in SA) September: Deep chlorophyll max in SA.

12. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop12 Biomass of heterotrophs BACTERIAHNAN CILIATES Mesozooplankton March 1997 Bacteria: Important contribution. No significant differences among areas Ciliates: very low values=grazing control by copepods, slight increase from NEA to SA Mesozooplankton: Gradual decrease from NEA to SA, stronger in the upper layer (BSW). 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)

13. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop13 Mesozooplankton species composition (0-50m) September 1997 Institute of Oceanography 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?

14. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop14 Carbon partitioning- March 1997 Microbial food web AUTOBACT HNAN CILMESO Microheterotrophs’ biomass overwhelms that of autotrophs

15. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop15 Productions Primary production decreased from NEA to SA (March). Most of PP was due to cells <3μm (March+September). Regenerated P. Bacterial production: no significant differences among areas 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).

16. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop16 S.Aegean Food web: multivorous (Copepods are feeding both on protozoa and large phytoplankton)

17. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop17 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).

18. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop18 Vertical Flux of organic matter in NEA and NA versus SA Very low grazing pressure of copepods on phytoplankton (spring) great availability of small autotrophs Higher mesozooplankton biomass in the whole water column Greater export of primary production from euphotic zone Higher amount of dead zooplankters reach sea- bottom Higher zoobenthic biomass in NEA and NA than in SA-Increased biomass values in Limnos and Athos deep basins (Lykoussis et al., 2002)

19. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop19 CONCLUSIONS 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.

20. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop20  The NE Aegean is a special environment, perhaps due to the local nature of the higher production (presence of hydrological fronts).  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 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.

21. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop21

22. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop22

23. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop23 Autotrophs biomass (in Carbon) Institute of Oceanography SEPTEMBER 1997 0.2-3μm > 3μm Dominance of small cells 0-50m: Decrease from NEA to SA SA: biomass higher in 50- 100m than in 0- 50m Deep Chlorophyll maximum

24. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop24 SEPTEMBER 1997

25. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop25 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.

26. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop26 Carbon partitioning in September 1994

27. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop27 MDS plot of samples (similarity among samples) collected at 0- 50m (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

28. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop28 Consumption of primary production (large cells) by copepods (0-100m) March 1997 Consumption of PP NEA=6% NA=1% SA=13%

29. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop29 MDS plot of samples collected at 100- 200m© 200-300m (d) 300-500m (e) small differences between areas

30. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop30 MDS plot of samples collected at 500-700m (f) 700-1000m (g) differences between areas=communication among deep basins

31. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop31 Vertical distribution of Calanus helgolandicus (station N1) and of Eucalanus monachus (st S1)

32. NATIONAL CENTRE FOR MARINE RESEARCH Institute of Oceanography Aegean Sea workshop32 Distribution of mesozooplankton biomass in the 0- 20m layer (May 1997) High values in the area influenced by BSW