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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.

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Presentation on theme: "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."— Presentation transcript:

1 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 Nival 1 1 - Laboratoire dOcéanographie de Villefranche (LOV, UMR 7093), Villefranche-sur-Mer 2 – 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

2 Villefranche-sur-Mer 26-30 octobre 2005 Sampling sites Biomed 1 cruise 11-27 April 1994 * 5 transects distance between stations A, B, C, D: 10 nautical miles E: 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 sampling temperature, salinity Chlorophyll a

3 Villefranche-sur-Mer 26-30 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

4 Villefranche-sur-Mer 26-30 octobre 2005 Macroplankton and micronecton Total (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

5 Villefranche-sur-Mer 26-30 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)

6 Villefranche-sur-Mer 26-30 octobre 2005 Meganyctiphanes norvegica adults NWjuveniles Tyrrhenian Sea Tyrrhenian Sea = nursery?

7 Villefranche-sur-Mer 26-30 octobre 2005 Comparison with historical data Meganyctiphanes norvegica Casanova, B., 1974. Thèse es Sciences Naturelles sampling between 1961 and 1968 (various cruises) essentially in autumn and winter adults (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 Casanovas data 40° N

8 Villefranche-sur-Mer 26-30 octobre 2005 Nematoscelis megalops adults ubiquitousjuveniles Tyrrhenian Sea

9 Villefranche-sur-Mer 26-30 octobre 2005 Nematoscelis megalops Casanova, B., 1974. Thèse es Sciences Naturelles sampling between 1961 and 1968 (various cruises) essentially in autumn and winter adults (black symbols), larvae (white symbols) ubiquitous species +/- homogeneously distributed in the western Mediterranean Sea Biomed results (in spring) in agreement

10 Villefranche-sur-Mer 26-30 octobre 2005 Euphausia brevis Tyrrhenian Sea low densities, irregular

11 Villefranche-sur-Mer 26-30 octobre 2005 Euphausia brevis Casanova, B., 1974. Thèse es Sciences Naturelles sampling between 1961 and 1968 (various cruises) essentially in autumn and winter adults (black symbols), larvae (white symbols) southern species (tropical and sub-tropical areas) abundant in the Tyrrhenian Sea Biomed results (in spring) in agreement

12 Villefranche-sur-Mer 26-30 octobre 2005 Siphonophores Chelophyes appendiculata SW Lensia conoidea ubiquitous, irregular

13 Villefranche-sur-Mer 26-30 octobre 2005 Salps Salpa fusiformis Ligurian Sea Pegea confoederata SW (swarms) Thalia democratica coastal + Tyrrhenian Sea (swarms)

14 Villefranche-sur-Mer 26-30 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

15 Villefranche-sur-Mer 26-30 octobre 2005 Chlorophyll a mg Chl a/m²; 0-200 m high standing stocks in the frontal and central zones of the Ligurian Sea Tyrrhenian Sea very poor in phytoplankton (high abundances of phytophagous zooplankton)

16 Villefranche-sur-Mer 26-30 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)

17 Villefranche-sur-Mer 26-30 octobre 2005 similarity - Ascending Hierarchical Classification - 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 group 4 groups similarity Zooplankton – AHC and MDS

18 Villefranche-sur-Mer 26-30 octobre 2005 similarity - Ascending Hierarchical Classification - Multi-Dimensionnal Scaling based on - similarity index of Bray Curtis - Log (species density) similarity Zooplankton – AHC and MDS 2 groups of Tyrrhenian stations Cavolinia inflexa +++ Euphausia hemigibba +++ Pegea confoederata: no Gennadas elegans: no group of 2 coastal stations Thalia democratica +++ mixed group 4 groups Chelophyes appendiculata +++ Euphausia krohni +++ M. norvegica larvae +++

19 Villefranche-sur-Mer 26-30 octobre 2005 Groups of macroplankton and micronekton and general surface circulation pattern

20 Villefranche-sur-Mer 26-30 octobre 2005 Conclusions Different patterns according to the species Nematoscelis megalops: ubiquitous Euphausia brevis: Tyrrhenian Sea Salpa fusiformis: Ligurian Sea, … but also irregular distribution of some species Swarms of Lensia conoidea, Pegea confoederata, … Spatial structuring not entirely related to the hydrological structures high 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 Sea Very low chlorophyll content High 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


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