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International audience; Biological variability is no longer considered as statistical noise, but rather as an adaptive benefit. This variability comes from consistent differences in behavioral and physiological responses among individuals to a changing/challenging environment, named “coping style”, “temperament” or “personality”. Many studies have described how to characterize personality traits and how to assess their consistency over time and between different contexts; however, little is known about the environmental factors shaping personality development. Because contrasting personalities are maintained with evolution, this lead to the widespread assumption that genes play a predominant role in personality. In many cases, personality traits are however also likely to be determined by individual experience, which is probably at least as important as genetics in shaping personality. The aim of this study was to assess how environmental variability (herein food predictability) impacts behavioral responses, particularly the shyness-boldness axis, one of the most widely shared animal personality trait. Here, we reared juvenile seabass (95 days old) from two divergent strains selected for feed deprivation tolerance under standard conditions for 40 days. Thereafter, we submitted them to two feeding treatments (Predictable versus Unpredictable) starting at 135 dph and lasting 60 days. Seabass reared under a predictable food supply (PFS) grew faster and were shyer than fish reared under an unpredictable food supply (UFS) (i.e. they took more time to exit the refuge zone of a Z-maze; UFS: 132.47 ± 34.63 s; PFS: 336.79 ± 56.97 s) but their exploration tendency was similar. We also examined the behavioral responses of these fish facing a hypoxic challenge. Hypoxia tolerance results were consistent before and after the two feeding treatments. Our findings show the importance of early environmental experience as a driving force shaping boldness. In addition, we provide further evidence that predictable feeding time should be respected in studies assessing essential functions such as growth and behavior. Although personality traits are partially heritable, this study demonstrates the important influence of environmental conditions and life history on behavior.

International audience

International audience; Polycyclic aromatic hydrocarbons (PAH) emission in the environment is constantly increasing with human activity. The goal of this study was to assess long term consequences of fish early exposure to PAH on behaviour. Eggs were collected from AB zebrafish strain and were placed at 4 hours post fertilization (hpf) until 96 hpf in a 3 cm diameter Petri dish containing 3 g reference sediment either plain (control) or spiked with a mixture of Benzo[a]pyrene, Pyrene and Phenanthrene at environmental concentrations based on values measured in the Seine Estuary (France), a highly polluted site. Thereafter, larvae were transferred in clean water and raised until adulthood. Behavioural tests such as locomotion during 24-hrs, sudden dark change challenge and T-maze exploration were performed at adults’ stage (F0) and sudden dark change on larvae produced by F0 adults. In adults, during night or dark period, contaminated fish were significantly less active than control fish. A similar observation was made for contaminated F0 in T-maze safe area. Contaminated F1 larvae were more active when light was on than control and less active when the light was off. This study indicates that contamination of zebrafish using environmentally relevant concentration during the very first stage of development with a PAH mixture of 3 molecules induced late behavioural effects measured at the adult stage. Further, effect was transmitted to the next generation and behavioural responses of F1 larvae were different to that of F1 control larvae. Consequences on fish abilities (e.g. predator escape, food search, courtship) will be discussed.

International audience

Spatial and interannual variations of phytoplankton diversity were characterized along the French Atlantic Coast in relation to physical factors and large-scale climatic indices using phytoplankton surveys conducted from 1993 to 2010 in four geographical areas. This study relates phytoplankton diversity to oyster recruitment success by comparing a 'specific' versus a 'functional' diversity approach. Functional diversity was represented by functional groups of different phytoplanktonic functional traits (size, shape, toxicity), relevant for oyster feeding during growth, reproduction and larval development. Phytoplankton diversity patterns along the French Atlantic coast corresponded to a geographical distribution mainly driven by a latitudinal gradient and hydrodynamic features as confirmed by the functional characteristics of the indicator species recorded for each geographical area (C-S-R strategies of Reynolds, specific habitat). This geographical typology was less clear for functional diversity. Only few functional groups were explained by physical factors: the non-toxic small and solitary cells were in particular related to temperature, with high densities observed in the southern areas. Even if temporal variation was less important in explaining the phytoplankton diversity patterns, the main drivers explaining the interannual pattern were the large-scale climatic indices, mainly the Atlantic Multidecennal Oscillation. Functional groups were readily explained by climatic indices than species even if the relationships cannot be applied generally because of the non-linearity of the correlations (local and temporal variations). However, the potentially toxic, small and linear phytoplankton were anticorrelated to NAO. The functional approach thus brings constructive elements concerning the relationships between the prey assemblage of oysters and their physical drivers. Redundancy and co-inertia analyses appeared as complementary analyses in investigating phytoplankton pattern of variation, being particularly useful in analyzing geographical and temporal diversity fluctuation, respectively. (C) 2012 Published by Elsevier Ltd.

International audience; Along the French coast of the Bay of Biscay, the seasonal progression of phytoplankton presents specific hydrographic conditions compared to other temperate areas due to the influence of two large river plumes (Loire and Gironde). However, in spite of the occurrence of a microphy-toplankton bloom during winter and phosphate limitation in spring, the dynamics of the planktonic food web on the continental shelf of the Bay seem to correspond with the characteristics typical of temperate oceans with the dominance of herbivory during spring and the development of the microbial food web under the stable post-bloom environment. Existing plankton data from recent scientific cruises were combined with inverse and network analyses to construct five model ecosystems between late winter and late spring and to investigate the structure and the function of the food web. The analysis of those models confirmed that the absolute amount of biogenic carbon export from the planktonic food web follows a continuum from high carbon export to depth when the microphytoplankton winter bloom is not consumed by grazers to carbon recycling within the microbial food web after the spring bloom when the water column is strongly stratified. Therefore, the winterespring period corresponds to a situation of high export. The particular hydrological conditions of the Bay of Biscay are not altering the capacity of the planktonic food web to export the greatest absolute amount of carbon during spring to plankton predators such as small pelagic fishes. However, this study showed that, in proportion to the primary production, the relative amount of biogenic carbon export to higher trophic levels does not vary considerably among the three types of planktonic food web function. Bacterial activity seems to have a higher control on relative export than phytoplankton size structure.

Les baies du golfe de Gascogne (France) hébergent des habitats où la sole, Solea solea, est le plus abondant des poissons plats. Cette étude vise à évaluer le fonctionnement des habitats pour leur rôle de nourriceries, en analysant la croissance et la condition des juvéniles de sole pendant leur première année. Les données de deux séries, 1999 et 2000, de chalutages mensuels sont comparées à celles acquises lors d'une expérience de 6 mois en mésocosme impliquant l'élevage de poissons originaires de la même nourricerie. La croissance observée est comparée à la croissance potentielle, en utilisant un modèle expérimental décrivant la croissance en fonction de la température. Les soles du groupe d'âge 0 capturées dans la nourricerie atteignent une taille moyenne de 130 mm en septembre. Le taux de croissance est de 0,7-0,9 mmjour-1 en été et, Tidal embayments in the Bay of Biscay (France) host nursery grounds where common sole, Solea solea, is the most abundant flatfish species. This study aimed to appraise the way those habitats function as nurseries through juvenile sole's responses in somatic growth and condition (Fulton's K) during their first year of occupancy. Field data, two yearly trawling series, taken monthly, were compared with a 6-month-long mesocosm experiment involving reared fish of the same wild origin. Growth rates were compared with predicted maximum growth according to an experimentally established model in relation to temperature. In the field, 0-group sole total length (TL) averaged 130 mm from September onwards in 1999 and 2000. Mean growth rates were 0.7-0.9 mmday-1 in summer and

International audience; The structure and summertime production of planktonic communities and the role of nondiatom planktonic cells were studied in coastal ponds, which are areas traditionally used for fattening and greening table-sized oysters. The abundance and biomass of nano–microplanktonic protists were determined at weekly intervals between February 1998 and February 1999 in a coastal pond without oysters in the French Atlantic coast near La Rochelle. The production of these microbiotas was determined in the summer period. The structure of plankton communities revealed the following observations: (1) microphytoplanktonic cells were mostly diatoms and dinoflagellates, (2) microzooplank-tonic cells were mainly ciliates, and (3) nanoplanktonic cells were represented by pigmented (80–90% of the nanoplankton biomass) and colorless nanoflagellates. Diatoms were dominated by Naviculiineae. Dinoflagellates were dominated by Peridiniales. Oligotrichida were predominant in the ciliate community. Protist biomass levels were nine times higher from April to August (summer period 1033 mg C L _ 1) than from September to March (winter period 114 mg C L _ 1). Whatever the season, nanoflagellates were dominant in the water column (66 and 53% of the entire protist biomass in the summer and winter periods, respectively). Nanoflagellates represented the highest production of nano–microplanktonic communities (76% of carbon protist production) in the coastal pond in summer and showed the shortest generation time (7.1 h). Dinoflagellates came after nanoflagellates in production (19.5% of carbon protist production). Diatoms represented only a supplementary carbon resource available for higher trophic levels, whereas, until now, they were considered as the principal food of oysters in coastal ponds. Ciliates were a small source of carbon, but their growth rate was high. We suggest, first, that nanoflagellates represented the primary resource available in the pond and could constitute an important food resource for higher trophic levels, such as oysters, farmed in this type of pond. Overall, the system appeared to be more autotrophic than hetero-trophic. Because inorganic nutrients are quickly exhausted in a semiclosed pond, pigmented flagellates dominated the carbon biomass, production and biomass of bacteria were high (thus, the microbial food web appeared to be active in this pond), and mixotrophy seemed to be an important trophic mode there.

Long-term changes of the taxonomic composition of the phytoplankton communities of two French littoral ecosystems (Marennes-Oleron Bay and Aiguillon Bay) were investigated in order to estimate the benthic contribution in terms of biomass. A long-term phytoplankton survey (REPHY - IFREMER) provided phytoplankton densities at different taxonomic levels of identification from 1995 to 1999. The database was homogenised at the taxonomic level of the genus and the log 10 -density was used as an indicator of the biomass. At all stations investigated, a strong seasonality governed the changes in the number of genera and the log 10 -density. No significant differences were found between the stations. Factorial Correspondence Analyses were performed to provide a typology of sampling dates and corresponding functional groups of genera. Pennate diatoms were dominant in winter periods, while centric diatoms and dinoflagellates characterised summer and fall periods. Moreover, the log 10 -density of pennate diatoms did not follow a seasonal pattern. The relative contribution of this group, which appeared to be the most representative of the benthic microalgal communities, had a maximum variation range of 1 to 84% and was well correlated with the turbidity recorded at the same time. This study was a first step to provide a frame for further studies about the coupling between benthic and pelagic microalgal biomasses in semi-enclosed European-type littoral ecosystems.

Pearl oysters are farmed in oligotrophic tropical atoll lagoons where planktonic communities are dominated by production from cyanobacteria smaller than 2 pm. Paradoxically, the pearl oyster Pinctada margaritifera only retains particles larger than 2 Pm. In this study, we assess the relative contribution of hetero/mixotrophic microbiota to the available planktonic resource. In Takapoto Atoll, picocyanobacteria are the dominant biomass (20 mug C l(-1)). The carbon biomass of ciliates and dinoflagellates ranges from 1 to 24 and 0.5 to 5 mug C l(-1) respectively, with a mean of 6 mug C l(-1) for ciliates and 2 mug C l(-1) for dinoflagellates. The possible retention by P. margaritifera on a natural protist suspension was investigated. Due to its high clearance rates (ca 20 l h(-1) g(-1)) the pearl oyster retained 85 mug C h(-1) g(-1) from ciliates and 55 mug C h(-1) g(-1) from dinoflagellates. Conversely, cyanobacteria were not efficiently retained by the bivalve and did not efficiently contribute to its diet. From our experiments, we concluded that hetero/mixotrophic protists rapidly and efficiently process the picoplanktonic resource towards filter-feeders, particularly pearl oysters.

Under conditions of natural irradiance, the development and decline of a flagellate-dominated phytoplankton population was followed in a coastal North Atlantic pond over a 3 d period in summer 1986. Irradiance negatively affected phytoplankton biomass estimated as chlorophyll a, which decreased during the day at photosynthetically available radiation (PAR) levels above 600 to 1000 μmol m-2s-1; chlorophyll a increased at PAR values below this threshold. In addition, an inverse relationship was found between changes in chlorophyll a and changes in dissolved inorganic nitrogen, indicating synthesis of nitrogenous biomass mainly at night and degradation mainly during the day, with intense exchanges of material between the particulate and dissolved nitrogen fractions. The natural abundance of 13C in particulate matter increased initially, and then remained constant, and was controlled mainly by the ratio β-carboxylases activity: ribulose biphosphate carboxylase activity. The hypothesis that the latter enzyme is broken down under high irradiance and is partly responsible for increases in external dissolved nitrogen was rejected.

International audience; In French Atlantic coastal ponds of Charente, oysters can grow under conditions where phytoplankton production is limited by nutrients exhaustion. Such ponds typically show a high concentration of ciliates and flagellates during the growing season (1 x 104 to 3 x 105 cells l-1 in June 1997). In order to evaluate the importance of the "protozoan trophic link " for energy transfer from the " microbial food web" to large benthic suspension feeders, we offered a coastal pond community of ciliates and flagellates as potential prey to the oyster, Crassostrea gigas. Clearance rate, filtered particles and relative retention efficiency were evaluated. In the grazing experiment, 94 % of ciliates and 86 % of flagellates (size between 4 and 72 μm), were retained by the oyster. Whatever their size, protists were similarly retained by the oyster gills. In terms of carbon, oyster retain on average 126 μg carbon (C) h-1 g-1 dry weight, a value over 4 times higher than reported for phytoplankton. These results indicate that a field community of protists can contribute in coastal oyster rearing ponds to the energy requirements of the oyster Crassostrea gigas. We report here the first experimental evidence of a significant retention of a protist community by oysters, supporting the role of protists as a trophic link between picoplankton and benthic filter-feeding bivalves.