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Mesozooplankton distribution in the North Aegean Sea in relation to the Black Sea water advection during July & September 2003. A. Ramfos, S. Isari, S. Somarakis, C. Koutsikopoulos, A. Kallianiotis and N. Fragopoulu Department of Biology University of Patras, Greece.

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slide1

Mesozooplankton distribution in the North Aegean Sea in relation to the Black Sea water advection during July & September 2003

A. Ramfos, S. Isari, S. Somarakis, C. Koutsikopoulos, A. Kallianiotis and N. Fragopoulu

Department of Biology

University of Patras, Greece

slide2

Description and significance of the area

Oligotrophic trend towards

the South Aegean

(Siokou-Frangou et al. 2002)

Purpose of mesozooplankton study

Investigation of mesozooplankton abundance, species composition and distribution patterns…

…in relation to the main hydrological characteristics of the area.

  • Major fishing ground of
  • anchovy & sardine
  • Extended continental shelf
  • BSW influence
  • Riverine influence
slide3

WP2 net (200μm mesh, mouth area of 0.25 m2)

  • Opening closing mechanism
  • Haul speed 0.8-1.2 m/sec
  • Samples preserved in 4% borax-buffered formaldehyde solution (8<pH<9)
  • Estimation of zooplankton total abundance and biomass
  • Counting of zooplankton taxa
  • Identification of copepods and cladocerans to species level

Zooplankton sampling

Surveys were carried out onboard the oceanographic vessel “Aegaeo”

July 2003

September 2003

slide4

Sampling grid

  • 32 mesozooplankton sampling stations (in a grid of 52 stations)
  • samples were collected in three distinct layers

Layer

July 2003

September 2003

0-50 m

32

32

50-100 m

9

7

100-200 m

3

3

Frontal area

TOTAL

44

42

slide5

Hydrology of the area

More saline and cold water of Levantine origin below 50m

Homogenous temperature and salinity values below 50m

Strong stratification of the water column during all surveys

Seasonal thermocline - Less saline BSW in the surface layer

slide6

Hydrology of the area

Fluorescence at 10m

Salinity at 10m

Temperature at 10m

July 2003

September

2003

slide7

Hydrology of the area

Salinity

Temperature

July 2003

September

2003

slide8

Mean mesozooplankton abundance and biomass

Biomass (mg/m3)

Abundance (ind/m3)

  • Mesozooplankton abundance and biomass values showed strong vertical decrease
  • Generally higher values in the summer period than autumn
slide9

3

3

1076 - 7810 ind/m

1076 - 7810 ind/m

3

542- 4895 ind/m

3

2.8 -14.8 mg/m

3

3.2 - 17 mg/m

Horizontal distribution of total zooplankton abundance and biomass

in the surface layer (0-50 m)

July 2003

September 2003

Abundance

Biomass

slide10

Mean relative abundance (%) of zooplankton groups: Layer 0-50 m

80%

July 2003

3510 ind/m3

September 2003

2071 ind/m3

slide11

Mean relative abundance (%) of zooplankton groups: Layer: 50-100 m

July 2003

1021 ind/m3

September 2003

522 ind/m3

slide12

Mean relative abundance (%) of zooplankton groups: Layer: 100-200 m

July 2003

129 ind/m3

September 2003

78 ind/m3

slide13

Horizontal distribution of zooplankton groups: Layer: 0-50 m

July 2003

Higher abundance values were observed in

the coastal and/or frontal stations

Copepods

Cladocerans

Doliolids

Appendicularians

Chaetognaths

Salinity at 10m

slide14

Horizontal distribution of zooplankton groups: Layer: 0-50 m

September 2003

Lower abundance values when compared to July (except copepods)

More homogenous distribution of the dominant groups

Copepods

Cladocerans

Doliolids

Appendicularians

Chaetognaths

Salinity at 10m

slide15

Species assemblages – July & September 2003

A

Epipelagic

(0-50 m)

B

Intermediate

(50-100 m)

C

Mesopelagic

(100-200 m)

July 2003

Acartia clausi

Pseudoevadne tergestina

Both surveys

Oithona spp.

Clausocalanus spp.

Oncaea spp.

C. vanus

C. pergens

Lucicutia flavicornis

Pleuromamma spp.

Scolecithricella spp.

Both surveys

Penilia avirostris

Oithona spp.

Clausocalanus spp.

Paracalanus parvus

Temora stylifera

September 2003

Clausocalanus furcatus

Evadne spinifera

Oithona spp., Clausocalanus spp., Oncea media

Farranula rostrata,Mesocalanus tenuicornis

Ctenocalanus vanus,Centropages typicus

July: P.avirostris – September: C. pergens

5 groups of samples according to season and sampling layer

58% similarity level – NMDS stress value: 0.13

slide16

Assemblages in the surface layer – July 2003

Coastal area

Penilia avirostris, Oithona spp., Acartia clausi, Paracalanus parvus, Pseudoevadne tegrestina

Gyre area

Penilia avirostris, Oithona spp., Pseudoevadne tegrestina, Acartia clausi

Frontal area

Penilia avirostris, Oithona spp., Acartia clausi, Paracalanus parvus, Pseudoevadne tegrestina

Farranula rostrata, Oncaea media

slide17

Assemblages in the surface layer – September 2003

Coastal area

Acartia clausi, Paracalanus parvus, Penilia avirostris, Evadne spinifera

Central area

Penilia avirostris, Clausocalanus furcatus, Paracalanus parvus, Oithona spp.

Southern area

Low abundance values

Low dominance

High diversity

slide18

BSW

inflow in the

N. Aegean

Hydrological variability

Higher abundance and biomass when the inflow is higher e.g July

Strong mesozooplankton variability

Spatial

Temporal

3 assemblages with respect to depth

mainly cladocerans

3 assemblages in the horizontal plane related to gyres and frontal structures

copepods

Conclusions