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Temporal variability of mesozooplankton in the Saronikos Gulf, the Aegean and NW Levantine Seas

Temporal variability of mesozooplankton in the Saronikos Gulf, the Aegean and NW Levantine Seas . I.Siokou-Frangou, E.Christou & S.Zervoudaki. Institute of Oceanography Hellenic Centre for Marine Research. outfalls. Saronikos Gulf. Differentiation.

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Temporal variability of mesozooplankton in the Saronikos Gulf, the Aegean and NW Levantine Seas

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  1. Temporal variability of mesozooplankton in the Saronikos Gulf, the Aegean and NW Levantine Seas I.Siokou-Frangou, E.Christou & S.Zervoudaki Institute of Oceanography Hellenic Centre for Marine Research

  2. outfalls Saronikos Gulf Differentiation Elefsis Bay: semi-enclosed, shallow-30m, eutrophicated area Inner Saronikos: mesotrophic area, influence by the Athens sewage outfalls Before 1994:untreated, surface outflow. After 1994: primary, deep outflow Dominant circulation: cyclonic Outer Saronikos: oligotrophic area, intense influence by the Aegean Sea water mass

  3. Mesozooplankton sampling Monthly J-D 1987 Apr1989-Mar1990 Ma1998-Ma1999 Ma2000-Jn2004 Seasonally 1988 1992-1997 Vertical hauls: Bottom-surface WP-2 net (200μm mesh size) S2 (Elefsis Bay) S7 (outfalls area-75m) S11 (75m) S13 (85m) S16 (80m) Dry weight biomass estimation on preserved samples

  4. Spring max 2003, 2004 • below 50m • Species and groups composition and diversity similar to those observed in previous years

  5. 1987-2004: no clear trend in temperature and salinity • 1998-2004:Increase of effluents volume • 1987-2004: Increase of PO4, NO3 • 1987-2004: Decrease of Chla • no surface strong maxima after sewage treatment, • probably increased grazing of phytoplankton by mesozooplankton Effluents volume

  6. Zooplankton time-series One station, 15 m 0.6 nm from land From November 1989 – today Frequency: two weeks 1m, 5m, 10m (T, S, chl-a) 200 μm WP2

  7. Zooplankton biomass Chl-a Temperature Increasing trend Salinity Slight decreasing trend

  8. Annual cycle of zooplankton biomass at S11 Maxima in spring and some years in summer Similar in the shallow station

  9. Dominant species variability-S11 (based on seasonal sampling, 0-75m)

  10. Cluster analysis of samples collected in Feb/Mar, May/June, Aug/Sep, Dec 1998-99, 2000-04 No significant differentiation among years.

  11. Frontal area Offshore waters Important hydrological mesoscale features affecting pelagic production: Gyres and fronts Seasonal and interannual variability of fronts and gyres position, size and intensity depend on atmospheric conditions variability The Black Sea surface outflow reaches the Aegean Sea with large dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) (Polat & Tugrul, 1996, Sempere et al., 2002).As a result high phytoplankton and zooplankton biomass and production are detected in the frontal area (NE Aegean Sea) compared to the NW and S Aegean Sea (Siokou-Frangou et al., 2002). Phytoplankton pigments distribution in the Aegean Sea (annual mean of czcs images)

  12. KA7 KA6 KA2 KA9 KA8 KA5 KA4 KA3 KA1 -20 Front ) r a -40 b d ( e r u -60 s s e r P -80 -100 0 20 40 60 80 100 28.5 30.5 32.5 34.5 36.5 38.5 Frontal area in the NE Aegean Sea September 1999 Salinity NO2+NO3 Zervoudaki et al., submitted

  13. September 1999 Chla Mesozooplankton biomass Zervoudaki et al., submitted

  14. Northeast Aegean: particular area within E.Mediterranean. • High mesozooplankton biomass, abundance and productivity, very efficient carbon flow to higher levels, fish and benthos (important fishery area) • Hypothesis • Changes in Black sea water outflow both in terms of salinity and volume could result in: • Decrease of the salinity gradient and therefore plankton productivity (also fish and benthos?)

  15. Influence of cyclonic gyres in the mesozooplankton of E.Mediterranean sea June 1999(MATER, TMC) M4 (Cretan gyre)M2 (Rhodos gyre), higher abundance and biomass Siokou-Frangou et al., 2004

  16. 0-200 ind m-3 200-400 400-600 600-800 800-1000 1000-1300 Rhodos gyre area (NW Levantine Sea) During spring vertical mixing within the gyre results in the enrichment of the upper layers with nutrients, higher chla values and mesozooplankton abundance. Exceptionally in Spring 1992: vertical mixing down to 2000m, significant upwelling of deep waters rich in nutrients, very high values of chla and mesozooplankton in the upper layer (dominated by E.monachus) Distribution of mesozooplankton abundance in the 0-50m layer in Spring 1986 and Spring 1992

  17. Since the variability of atmospheric conditions can affect considerably mesozooplankton communities through their impact on physical processes Hypothesis Temperature increase could reduce the vertical mixing depth within cyclonic gyres Few nutrients in the euphotic layer Low phytoplankton biomass and dominance of picoplankters Low mesozooplankton abundance and biomass (scarcity of large herbivores) Impact on large pelagic fish populations (?) which are by nature very poor!

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