Projet Référentiel Plancton de la Baie de Calvi : II. Diversité de l’écosystème planctonique de la Baie de Calvi

Ce rapport présente la diversité de l’écosystème planctonique de la Baie de Calvi. Le premier chapitre rappelle les principales définitions utilisées en écologie planctonique. La suite du texte présente les grands groupes planctoniques rencontrés en Baie de Calvi, leurs principales caractéristiques morphologiques et les grandes lignes de leur écologie. Le texte est illustré de photographies originales de microphytoplancton et de zooplancton de la Baie réalisées à STARESO par les auteurs

Hydrodynamical and ecosystem processes in ice-covered seas of the Southern and Northern Hemispheres

peer reviewedPreface of the 30th International Liège Colloquium on Ocean Hydrodynamics Liège, Belgium (May 4–8 1998) : Hydrodynamical and ecosystem processes in ice-covered seas of the Southern and Northern Hemispheres. Issue of JMS edited by Anne Goffart and Jean-Henri Hecq

Factors controlling the distribution of diatoms and Phaeocystis in the Ross Sea

The spatial and temporal distributions of phytoplankton pigments were investigated in the western and south central Ross Sea during austral spring 1994 and summer 1990. Large gradients in biomass and phytoplankton community composition were observed both in the east-west and south-north directions, in relation to differences in water column structure and stability, which themselves depend on the processes of ice retreat within the different areas. Important are melting in the western Ross Sea, which induces strong stratification, and ice breakup and wind stress in the south central Ross Sea, which result in deep mixing and weakly stratified waters. In the western Ross Sea, the highest chl a concentrations observed in this study (129 - 358 mg m-2 in the upper 100 m) were tightly coupled to the stratified region of meltwater influence and were dominated by diatoms, as indicated by elevated fucoxanthin concentrations (89 - 239 mg m-2 in the upper 100 m). In the diatom bloom area, high levels of phaeophorbides a (maximum value of 192 mg . m-2 in the upper 100 m) indicated that the dominant grazers, identified as Limacina helecina and copepods (Hecq et al., 1992), transferred a sustained part of the diatom production to the herbivore trophic level. Synthesis of our data with published information suggests that the diatom bloom we observed in the western Ross Sea was dominated by the species Fragilariopsis curta, and occurs annually off the coast of Victoria Land from 72°30'S to 77°S within 100 to 250 km from the coastal ice edge. It is assumed to persist on the order of 2.5 - 3 months during summer. In the south central Ross Sea, which was characterized by a poorly or unstratified water column, moderate chl a concentrations (55 - 186 mg m-2 in the upper 100 m) were found in the polynya and in the ice edge area in early spring. 19'-hexanoyloxyfucoxanthin, a biomarker for Phaeocystis, was the major contributor to the total carotenoid abundance (29 - 132 mg m-2 in the upper 100 m), corroborating the hypothesis that Phaeocystis are well adapted to develop in a relatively mixed water column. At the northern limit of the polynya, a quite narrow (c. a. 30 km) diatom bloom (31 - 67 mg fucoxanthin m-2 in the upper 100 m) overlapped with the Phaeocystis bloom in the slightly stratified marginal ice zone. This was an area of increased grazing pressure by various types of herbivorous zooplankton, among which very large amounts of krill were observed.Antar A4/DD/B2

Problematic of the Pelagia noctiluca outbreaks in the Bay of Calvi (Corsica)

peer reviewedThe interannual variations of the Schyphozoan jellyfish Pelagia noctiluca is estimated by weekly measurements in the Bay of Calvi (Corsica) from 2003. The mean annual abundance reaches a dramatic maximum in 2006. The medusae appear by migration of active swarms on the shelf and at the external limit of the Bay. Degraded individuals drift as passive swarms, throughout inner side of the Bay and embayments

Phenotypic characterization of patient dengue virus isolates in BALB/c mice differentiates dengue fever and dengue hemorrhagic fever from dengue shock syndrome

International audienceBACKGROUND: Dengue virus (DENV) infection is the most common arthropod-borne viral disease in man and there are approximately 100 million infections annually. Despite the global burden of DENV infections many important questions regarding DENV pathogenesis remain unaddressed due to the lack of appropriate animal models of infection and disease. A major problem is the fact that no non-human species naturally develop disease similar to human dengue fever (DF) or dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Apart from other risk factors for severe dengue such as host genetics and secondary infection with a heterologous DENV, virus virulence is a risk factor that is not well characterized. RESULTS: Three clinical DENV-1 isolates from Cambodian patients experiencing the various forms of dengue disease (DF, DHF, and DSS) were inoculated in BALB/c mice at three different concentrations. The DENV-1 isolates had different organ and cell tropism and replication kinetics. The DENV-1 isolate from a DSS patient infected the largest number of mice and was primarily neurotropic. In contrast, the DENV-1 isolates from milder clinical dengue cases infected predominantly lungs and liver, and to a lesser extent brain. In addition, infection with the DENV isolate derived from a DSS patient persisted for more than two weeks in a majority of mice compared to the other DENV-1 isolates that peaked during the first week. CONCLUSIONS: These results confirm the in vitro findings of the same DENV-1 isolates, that showed that the isolate derived from a DSS patient can be distinguished based on phenotypic characteristics that differ from the isolates derived from a DF and DHF case 1. We observed in this study that the DSS virus isolate persist longer in vivo with extensive neuroinvasion in contrast to the other DENV-1 isolates originating in milder human cases. Genomic characterization of the three clinical isolates identified six amino acid substitutions unique for the DSS isolates that were located both in structural genes (M and E) and in non-structural genes (NS1, NS3, and NS5). The characterization of these clinically distinct DENV-1 isolates highlight that DENVs within the same genotype may have different in vivo phenotypes. HIGHLIGHTS: * Clinical DENV-1 isolates have different organ tropism in BALB/c mice.* The isolate from a DSS patient is primarily neurotropic compared to the other isolates.* The DENV-1 isolates have different in vivo replication kinetics.* The isolate from a DSS patient persists longer compared to the other isolates.* These phenotypic differences confirm our earlier in vitro findings with the same DENV-1 isolates. Thus, DENVs within the same serotype and genotype may differ enough to affect clinical conditions in vivo

Nutrient and phytoplankton responses to external forcing in a Mediterranean coastal area unbiased by terrestrial inputs and local activities (Calvi, Corsica)

Despite its relative oligotrophy, the northwestern Mediterranean exhibits rich biodiversity and traditional fishing that are fueled by phytoplankton at the basis of the food web. However, long-term observations of phytoplankton biomass reveal high interannual variability controlled by mechanisms that are still poorly understood, but have implications for the way we study and manage coastal zones in a changing world. Here we present a synthesis of a long-term high-resolution study of nutrient and phytoplankton bloom dynamics performed between 1979 and 2011 at a permanent station in the Bay of Calvi (Corsica, northwestern Mediterranean). The ecosystem of the Bay is known to be very sensitive to climate forcing but preserved from local anthropogenic stressors. As a distinctive feature of the area, the winter-spring phytoplankton bloom of the Bay of Calvi is characterized by a very large interannual variability reaching one order of magnitude from one year to another. In order to understand mechanisms controlling this variability, we defined a winter intensity index (WII) that integrates wind stress intensity and water temperature. WII does not evidence any trend over the 1979-2011 period but is closely correlated to nutrient delivery from deep waters and to phytoplankton production. We synthesize our current understanding of phytoplankton response to the combination of external forcings and discuss the impact of expected environmental changes on the pelagic food web in a region that is predicted to be particularly sensitive to long-term changes driven by human activities

Control of plankton phenology by climate variation in a Mediterranean coastal area : results from a long-term study (1979-2011)

Physical processes are known to play major roles in marine plankton succession. However, few studies have addressed the mechanisms that regulate phyto- and zooplankton phenology in a context of changing climate. Here we used a unique long-term (1979-2011) time series performed in a Mediterranean coastal area unbiased by local anthropogenic pressure (PHYTOCLY station, Bay of Calvi, Corsica) to understand how environmental forcing affects the timing, duration and magnitude of the winter-spring phyto- and zooplankton blooms. We showed that phyto- and zooplankton blooms were bottom-up controlled by the establishment of favourable abiotic conditions, i.e. nutrient replenishment by vertical mixing under specific water temperature and wind conditions, for which thresholds were defined. According to the intensity of winter characteristics, there were strong differences in both the abundance and composition of phyto- and zooplankton during the winter-spring period. Our study is consistent with the recent reports that, when occurring, diatoms peaks were added to the initial phytoplankton groups instead of replacing them. In contrast, zooplankton groups followed a replacement sequence. Based on the results provided by our time series, we show that plankton phenology in the Bay of Calvi is highly controlled by climate variation and exhibits contrasted patterns in response to different scenarios of environmental forcing

Adaptation méthodologique de l’indicateur PH2 - Phytoplancton en Méditerranée - 1ère partie. Synthèse des spécificités de la Méditerranée : paramètres abiotiques et biomasse phytoplanctonique totale (chl a).

L’évaluation DCSMM de l’état écologique des Habitats pélagiques repose sur le seul critère D1C6 dans les 4 sous-régions marines françaises (Manche - Mer du Nord, Mers Celtiques, Golfe de Gascogne et Méditerranée Occidentale). Les 3 indicateurs utilisés (PH1, PH2 et PH3) ont été développés par OSPAR pour l’Atlantique Nord-Est. Ils ciblent les caractéristiques des communautés phyto- et zooplanctoniques dont l’organisation est contrôlée par les facteurs abiotiques et biotiques propres à chaque sous-région marine. Les fortes spécificités du milieu pélagique méditerranéen n’ont pas été prises en compte lors de l’évaluation 2018. Cette note synthétise les principales caractéristiques abiotiques de la Méditerranée et leurs impacts sur le développement de la biomasse phytoplanctonique totale (chl a). Il est rappelé en particulier que : • La Méditerranée est un bassin d’évaporation, où les apports d’eau douce ne compensent pas les pertes dues à l’évaporation. Le déficit en eau (≈ 1 m par an) est comblé par une entrée d’Eau Atlantique qui pénètre en surface en Méditerranée par le détroit de Gibraltar. Le flux entrant d’Eau Atlantique, le stress lié aux vents et la bathymétrie contrôlent la circulation de surface de toute la Méditerranée. • Les forçages hydrodynamiques contraignent les distributions horizontale et verticale de la biomasse phytoplanctonique. La distribution horizontale du phytoplancton est caractérisée par une hétérogénéité spatiale importante. • L’oligotrophie de la Méditerranée augmente d’Ouest en Est. En Méditerranée Occidentale, elle est modulée par une série de processus physiques (gyres, systèmes frontaux, ondes internes, …) qui agissent à différentes échelles spatiales et temporelles et enrichissent la couche de surface en nutriments. • Dans la ZEE française, et à l’exception de la région du delta du Rhône, les eaux du large sont plus riches en nutriments et en phytoplancton que les eaux côtières. • Du printemps à la fin de l’automne, une thermocline saisonnière isole les eaux chaudes de surface des eaux froides présentes en profondeur. Durant cette période, les eaux situées au-dessus de la thermocline sont épuisées en nutriments et en phytoplancton dans toutes les zones du large. • Une caractéristique majeure du phytoplancton méditerranéen est la présence d’un maximum profond de chlorophylle (« Deep Chlorophyll Maximum », DCM) pendant toute la période stratifiée. Le DCM est observé dans toute la Méditerranée. Il est situé sous la thermocline et n’est pas détecté par les satellites. Le DCM est une entité dynamique dont les caractéristiques sont contrôlées par les variables abiotiques du milieu. Il constitue la source de nourriture principale pour le zooplancton 6 à 8 mois par an, et attire une partie de l’ichtyoplancton qui s’y rassemble pour profiter de l’agrégation de nourriture. Le DCM a donc un rôle essentiel dans le fonctionnement du milieu pélagique méditerranéen. Les éléments présentés dans ce travail montrent la nécessité : (i) d’intégrer la dimension verticale de la colonne d’eau dans l’évaluation DCSMM de l’état écologique des Habitats pélagiques méditerranéens, (ii) d’adapter l’indicateur PH2-Phytoplancton en intégrant la dimension verticale afin de tendre vers une évaluation réaliste de l’état des Habitats pélagiques méditerranéens

Automatic activies of the spinal cord concerned with the respiratory movements

1. After spinal transection at the medulla-spinal junction the thoracic respiratory movements no longer appear in the adult animals, nevertheless the sporadic spike discharges can be recorded from the intercostal muscles. 2. Both in the acute and chronic experiments the spinal cord is transected at the two levels of Th7 and Thl1 respectively and all the dorsal rootlets coming into that part of the cord lying between the transections are severed. The sporadic spike discharges with irregular intervals varying about 0.5 to 3.0 sec. can be recorded from intercostal muscles in the 8th to 10th segments of the spinal cord isolated. There can never be found any reflex influence of the skin stimulation upon the discharges, which also disappear provided the intercostal nerves innervating the muscles are severed. 3. From these results it may be concluded that the spinal cord is endowed with an ability to initiate the impulses autochthonously to excite the intercostal muscles, even though it is only poorly developed in the adult animals.</p

Plankton ecosystem response to the decadal variation of winter intensity in the Mediterranean Sea : a long-term study (1979-2014)

In the Mediterranean Sea, several studies with distinct data sets indicate that the pelagic ecosystem underwent periods of change in the late 1980s and in the early 2000s. Here we used a unique long-term time series of data collected in the well-preserved Bay of Calvi (Corsica island, Ligurian Sea, NW Mediterranean) from 1979 and 2014 to explore the synchrony between changes in environmental conditions and phyto- and zooplankton dynamics. We identified an almost decadal, long-term variability in winter intensity, with three distinct periods: the 1980s (1979-1988), the 1990s (1989-1998) and the 2000s (1999-2014), which were characterized by moderate, mild and highly variable winters, respectively. We pointed out how the decadal changes in winter intensity affected (i) the duration and intensity of phyto- and zooplankton blooms, (ii) the mean yearly biomasses, and (iii) the nature of the assemblages. High phyto- and zooplankton biomasses were observed in years characterized by moderate and severe winters, and low phyto- and zooplankton abundances were recorded in years with mild winters. Moderate/severe and mild winters were favorable for diatoms and gelatinous zooplankton, respectively. Focusing on meroplanktonic species, we explored ecological consequences of decadal variations observed in the Bay of Calvi for resource management. We highlighted parallelisms with other European seas