Villefranche-sur-Mer 26-30 octobre 2005 Valérie Andersen 1, Frédérique Carcaillet 2, Eric Thiébaut 3, Marc Picheral 1, Marie-Dominique Pizay 1 and Paul

Villefranche-sur-Mer26-30 octobre 2005

Valérie Andersen1, Frédérique Carcaillet2, Eric Thiébaut3, Marc Picheral1, Marie-Dominique Pizay1 and Paul Nival1

1 - Laboratoire d’Océanographie de Villefranche (LOV, UMR 7093), Villefranche-sur-Mer2 – Ecosystèmes lagunaires (EL, UMR 5119), Montpellier

3 - Biologie des Organismes Marins et Ecosystèmes (BOME, UMR 5178), Paris

Macroplankton and micronekton in the Ligurian and Tyrrhenian Seas. Horizontal distribution in

spring

Thanks to Jacques Sardou for his help in taxonomic analyses


Sampling sites

Biomed 1 cruise11-27 April 1994

* 5 transectsdistance between stationsA, B, C, D: 10 nautical milesE: 20 miles

* Hauls - 0-700 m (except coastal stations A1 & B1 and transect E)- midday, midnight(only midnight for B1, D2 & D3)- multiple opening and closing net(Bioness)- 500 µm mesh

* CTD casts, bottle samplingtemperature, salinityChlorophyll a


Vertical distribution

Organisms highly concentrated in the surface layer at night(species living in the surface layers by day and at night both, diel migrants)

below 250 m depth: mainly Cyclothone braueri and C. pygmaea (fish)

19 stations sampled at night (16 stations by day)

Analyses based on numerical density (individuals per m²), night, 0-250 m

Vertical distributions: Andersen et al. 1998 Oceanol. Acta


Macroplankton and micronectonTotal (0-250 m; night)

similar densities of the total community throughout the explored area

excepted in the Tyrrhenian Sea(Thalia democratica, juveniles of Meganyctiphanes norvegica and Nematoscelis megalops)

different patterns according to the species


Specific composition

20 main species

0-250 m : 22 to 34 species

Vc = std X / mean X, with X = Log (ind/m²+1)


Meganyctiphanes norvegica

adults NW juveniles Tyrrhenian Sea

Tyrrhenian Sea = nursery?


Comparison with historical data

Meganyctiphanes norvegicaCasanova, B., 1974. Thèse es Sciences Naturellessampling between 1961 and 1968 (various cruises)essentially in autumn and winteradults (full symbols), larvae (open symbols)

Northern species, north of 40°N particularly abundant in the central zone of the Ligurian Sea Biomed results (in spring) in agreement with Casanova’s data

40° N


Nematoscelis megalops

adults ubiquitous juveniles Tyrrhenian Sea


Nematoscelis megalopsCasanova, B., 1974. Thèse es Sciences Naturellessampling between 1961 and 1968 (various cruises)essentially in autumn and winteradults (black symbols), larvae (white symbols)

ubiquitous species +/- homogeneously distributed in the western Mediterranean Sea Biomed results (in spring) in agreement


Euphausia brevis

Tyrrhenian Sea low densities, irregular


Euphausia brevisCasanova, B., 1974. Thèse es Sciences Naturellessampling between 1961 and 1968 (various cruises)essentially in autumn and winteradults (black symbols), larvae (white symbols)

southern species(tropical and sub-tropical areas) abundant in the Tyrrhenian Sea Biomed results (in spring) in agreement


Siphonophores

Chelophyes appendiculata SWLensia conoidea

ubiquitous, irregular


Salps

Salpa fusiformis Ligurian

Sea

Pegea confoederata SW (swarms)

Thalia democratica coastal + Tyrrhenian

Sea (swarms)


Hydrology

characteristics of- coastal waters- frontal zone- central zone

(no data for D2 and D3)

Transect C : small eddy Tyrrhenian Sea- higher temperature of MAW and LIW- North : running of freshwater from the Italian coast


Chlorophyll a

mg Chl a/m²; 0-200 m

high standing stocksin the frontal and central zones of the Ligurian Sea

Tyrrhenian Sea very poor in phytoplankton(high abundances of phytophagous zooplankton)


Environmental conditions

Ascending Hierarchical Classification(Euclidean distances)temperature, salinity: surface (MAW), 100 m (WIW), 250 m (LIW)Chlorophyll a: surface, 30 and 50 m (sub-superficial peak)


sim

ilari

ty- Ascending HierarchicalClassification- Multi-Dimensionnal Scaling

based on - similarity index of Bray Curtis- Log (species density + 1)

2 groups of Tyrrhenian stations

group of 2 coastal stations

mixed group4 groups

E2

E1

E3

E4

A1

D2

D1

A3

A4

B4

D3

C1

C2

C4

B2

B1

C3

A2

B3100

90

80

70

60

Similarity

sim

ilari

ty

Zooplankton – AHC and MDS


sim

ilari

ty- Ascending HierarchicalClassification- Multi-Dimensionnal Scaling

based on - similarity index of Bray Curtis- Log (species density)

E2

E1

E3

E4

A1

D2

D1

A3

A4

B4

D3

C1

C2

C4

B2

B1

C3

A2

B3100

90

80

70

60

Similarity

sim

ilari

ty

Zooplankton – AHC and MDS

2 groups of Tyrrhenian stationsCavolinia inflexa +++Euphausia hemigibba +++Pegea confoederata: noGennadas elegans: no

group of 2 coastal stationsThalia democratica +++

mixed group4 groups

Chelophyes appendiculata +++

Euphausia krohni +++M. norvegica larvae +++


Groups of macroplankton and micronektonand general surface circulation pattern


Conclusions

Different patterns according to the speciesNematoscelis megalops: ubiquitousEuphausia brevis: Tyrrhenian SeaSalpa fusiformis: Ligurian Sea, …but also irregular distribution of some speciesSwarms of Lensia conoidea, Pegea confoederata, …

Spatial structuringnot entirely related to the hydrological structureshigh infuence of species swarms: scale at which the species aggregates?

Needs for data at smaller horizontal scales(and in the northern part of the Ligurian Sea)

Tyrrhenian Sea = nursery?Abundance of juveniles of M. norvegica and N. megalops

Influence of warmer temperatures?

Trophic conditions in the Tyrrhenian SeaVery low chlorophyll contentHigh densities of phytophagous zooplankton (salps, euphausiid larvae)

top-down control?

Further analyses of these cruise data?Analysis of copepod community (shorter generation time)Analysis of samples collected during a similar cruise in autumn

Documents

Villefranche-sur-Mer 26-30 octobre 2005 Valérie Andersen 1, Frédérique Carcaillet 2, Eric Thiébaut 3, Marc Picheral 1, Marie-Dominique Pizay 1 and Paul