villefranche-sur-mer 26-30 octobre 2005 valérie andersen 1, frédérique carcaillet 2, eric...
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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
Villefranche-sur-Mer26-30 octobre 2005
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
Villefranche-sur-Mer26-30 octobre 2005
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
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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
Villefranche-sur-Mer26-30 octobre 2005
Specific composition
20 main species
0-250 m : 22 to 34 species
Vc = std X / mean X, with X = Log (ind/m²+1)
Villefranche-sur-Mer26-30 octobre 2005
Meganyctiphanes norvegica
adults NW juveniles Tyrrhenian Sea
Tyrrhenian Sea = nursery?
Villefranche-sur-Mer26-30 octobre 2005
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
Villefranche-sur-Mer26-30 octobre 2005
Nematoscelis megalops
adults ubiquitous juveniles Tyrrhenian Sea
Villefranche-sur-Mer26-30 octobre 2005
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
Villefranche-sur-Mer26-30 octobre 2005
Euphausia brevis
Tyrrhenian Sea low densities, irregular
Villefranche-sur-Mer26-30 octobre 2005
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
Villefranche-sur-Mer26-30 octobre 2005
Siphonophores
Chelophyes appendiculata SWLensia conoidea
ubiquitous, irregular
Villefranche-sur-Mer26-30 octobre 2005
Salps
Salpa fusiformis Ligurian
Sea
Pegea confoederata SW (swarms)
Thalia democratica coastal + Tyrrhenian
Sea (swarms)
Villefranche-sur-Mer26-30 octobre 2005
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
Villefranche-sur-Mer26-30 octobre 2005
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)
Villefranche-sur-Mer26-30 octobre 2005
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)
Villefranche-sur-Mer26-30 octobre 2005
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
Villefranche-sur-Mer26-30 octobre 2005
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 +++
Villefranche-sur-Mer26-30 octobre 2005
Groups of macroplankton and micronektonand general surface circulation pattern
Villefranche-sur-Mer26-30 octobre 2005
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