Reproduction and respiration of a climate change indicator species: effect of temperature and variable food in the copepod Centropages chierchiae

The abundance of the calanoid copepod Centropages chierchiae has increased at the northern limits of its distribution in recent decades, mainly due to oceanic climate forcing, suggesting this as a key species in monitoring climate change. Laboratory experiments were conducted to study the combined effect of temperature, food type and concentration on the egg production rate (EPR) and hatching success (HS) of C. chierchiae. Females were fed on two monoalgal diets (Gymnodinium sp. and Phaeodactylum tricornutum) at two food concentrations and at three different temperatures (13, 19, 24C). Respiration rates of both genders were measured at four different temperatures (8, 13, 19, 24C). EPR was significantly different between temperatures and food concentrations, the maximum EPR being attained when the copepods were exposed to high food levels and at 19C. Prey type significantly influenced EPR; feeding on P. tricornutum resulted in higher egg production than Gymnodinium sp. HS was significantly lower at 13C than at 19 and 24C and higher with Gymnodinium sp. Respiration rates were sex independent and increased exponentially with temperature. To maintain basal metabolism, the minimum food intake of P. tricornutum ranged between 0.4 and 1.8 g C and for Gymnodinium sp. between 0.03 and 0.13 g C. Food intake was always higher than the metabolic demands, except for the highest temperature tested (24C). The present results confirm the sensitivity of C. chierchiae to temperature variations and may help in understanding the successful expansion of its distribution towards northern latitudes.Portuguese Science and Technology Foundation (FCT) [PTDC/MAR/098643/2008, PTDC/MAR/111304/2009, PTDC/MAR/0908066/2008]; FCT [SFRH/BD/28198/2006]; [SFRH/BPD/38332/2007

The severity of pandemic H1N1 influenza in the United States, from April to July 2009: A Bayesian analysis

Background: Accurate measures of the severity of pandemic (H1N1) 2009 influenza (pH1N1) are needed to assess the likely impact of an anticipated resurgence in the autumn in the Northern Hemisphere. Severity has been difficult to measure because jurisdictions with large numbers of deaths and other severe outcomes have had too many cases to assess the total number with confidence. Also, detection of severe cases may be more likely, resulting in overestimation of the severity of an average case. We sought to estimate the probabilities that symptomatic infection would lead to hospitalization, ICU admission, and death by combining data from multiple sources. Methods and Findings: We used complementary data from two US cities: Milwaukee attempted to identify cases of medically attended infection whether or not they required hospitalization, while New York City focused on the identification of hospitalizations, intensive care admission or mechanical ventilation (hereafter, ICU), and deaths. New York data were used to estimate numerators for ICU and death, and two sources of data - medically attended cases in Milwaukee or self-reported influenza-like illness (ILI) in New York - were used to estimate ratios of symptomatic cases to hospitalizations. Combining these data with estimates of the fraction detected for each level of severity, we estimated the proportion of symptomatic patients who died (symptomatic case-fatality ratio, sCFR), required ICU (sCIR), and required hospitalization (sCHR), overall and by age category. Evidence, prior information, and associated uncertainty were analyzed in a Bayesian evidence synthesis framework. Using medically attended cases and estimates of the proportion of symptomatic cases medically attended, we estimated an sCFR of 0.048% (95% credible interval [CI] 0.026%-0.096%), sCIR of 0.239% (0.134%-0.458%), and sCHR of 1.44% (0.83%-2.64%). Using self-reported ILI, we obtained estimates approximately 7-96lower. sCFR and sCIR appear to be highest in persons aged 18 y and older, and lowest in children aged 5-17 y. sCHR appears to be lowest in persons aged 5-17; our data were too sparse to allow us to determine the group in which it was the highest. Conclusions: These estimates suggest that an autumn-winter pandemic wave of pH1N1 with comparable severity per case could lead to a number of deaths in the range from considerably below that associated with seasonal influenza to slightly higher, but with the greatest impact in children aged 0-4 and adults 18-64. These estimates of impact depend on assumptions about total incidence of infection and would be larger if incidence of symptomatic infection were higher or shifted toward adults, if viral virulence increased, or if suboptimal treatment resulted from stress on the health care system; numbers would decrease if the total proportion of the population symptomatically infected were lower than assumed.published_or_final_versio

Modele d'ecosysteme pelagique des eaux cotieres de la Mer Ligure

A simplified model of the pelagic ecosystem of the coastal surface waters (0 to 20 m) of the Ligurian Sea (Mediterranean) is described. Phytoplankton, copepods, salps, chaetognaths, dissolved inorganic nitrogen and particulate organic matter are considered. The system is open (winter input of deep nutrients and sedimentation of particulate organic matter) and is influenced by temperature and irradiance. This model simulates the typical annual variation of the plankton in the considered area. Nevertheless, a simulation during five years shows that, in contrast with the other state variables, salps and chaetognaths have an unstable behaviour. We assume that these organisms migrate in the superficial waters

Model of copepod growth and development: moulting and mortality in relation to physiological processes during an individual moult cycle

International audienceA mathematical model of copepod population dynamics coupling individual growth and development was tested. The results show in detail the effect of applying various hypotheses, particularly concerning the relationship between certain physiological processes (ingestion, egestion, excretion, oogenesis, etc.) and processes controlling the time course of abundance of individuals in each instar (mortality rate, moulting rate, reproduction). The model shows the changes in physiological processes (~ngestion, growth rate, etc.) at the individual level as a function of age within stage, and consequently the probability of moulting and death. If an indiv~dual remains for some time at one stage, its growth rate decreases, weight does not increase, the abil~ty to moult is lost and the probability of death is greater. In addition, the model glves the mean values of processes for the whole population, as could be obtained expenmentally, but it also provides an explanation of the variability of processes related to the population age structure. Finally, the results of this mathematical model led to an experimental test of the validity of the hypotheses put forward. The mathematical model can be used in all conditions, since it simulates values of processes constant in time as long as the external conditions are also constant, while remaining capable of expressing the internal dynamics of a population when the environment is suddenly perturbed

Spatial distribution of the copepod Centropages typicus in Ligurian Sea (NW Mediterranean). Role of surface currents estimated by Topex-Poseidon altimetry

A particle-tracking model was used to simulate the dispersion and development of the planktonic copepod Centropages typicus during spring in Ligurian Sea. We show that mesoscale current structure, with a coastal jet and eddies, plays a key role in the transport and dispersion of C. typicus during its life cycle. Although, in the north, offshore Nice, cohorts can be advected southwestward out of Ligurian basin, more to the south others are retained in the central eddy and may give the start to the spring bloom of this species. However, input of individuals from the south through the Corsican Channel and along the west coast of Corsica may also be important in spring. This study shows that the ambit of C. typicus population is larger than the Ligurian Sea. (C) 2004 Academie des sciences. Published by Elsevier SAS. All rights reserved

Influence of meteorological variability on primary production dynamics in the Ligurian Sea (NW Mediterranean Sea) with a 1D hydrodynamic/biological model

In order to estimate the effects of the meteorological variability on the gross primary production in the Ligurian Sea (NW Mediterranean Sea), a coupling between a hydrodynamic model and a biological one is realized. The one-dimensional version of the GHER hydrodynamic model includes heat and momentum exchanges at the air-sea interface. It is coupled with a simple food-web model from the LEPM. A simulation performed with real meteorological data for the year 1985 reproduces reasonably the seasonal phytoplanktonic dynamics and the distribution between diatoms and flagellates. From this simulation, an annual gross primary production integrated over 200 m of 46.4 g C m-2 year-1 is computed which is representative of an oligotrophic environment. In order to estimate the relative effect on the gross primary production of the meteorological variability on the one hand and of the initial conditions on the other hand, several runs have been performed for the year 1985 with different conditions of light, wind intensity and nitrate initial quantity. The first simulations are performed with daily and monthly mean solar radiation and wind intensity. An averaging of wind intensity yields a decrease in the gross primary production and leads to unrealistic phytoplankton dynamics. It seems then necessary to take into account the 3-hourly variability of the wind intensity in order to simulate the phytoplankton dynamics with relatively good accuracy. On the other hand, an averaging of the solar radiation leads to an increase in the gross primary production. The following simulations are performed with an increase (decrease) in the solar radiation, the wind intensity or the nitrate initial quantity which are representative of the variability observed in a 5-year set of meteorological and hydrobiological data (1984-1988). An increase in the solar radiation is found to reduce the gross primary production, while an increase in the initial nitrate quantity or the wind intensity leads to a higher gross primary production, and the reverse. In the case of variations of the solar radiation (±2%), the simulations give an annual gross primary production integrated over 200 m included between 44.8 and 46.7 g C m-2 year-1, representing a variability of 4%. With the variations of the surface wind intensity (±10%), the runs carry to an annual gross primary production integrated over 200 m from 34.1 to 59.1 g C m-2 year-1, representing a variability of 54%. The variations of the initial nitrate concentration (±50%) lead to an annual gross primary production integrated over 200 m between 20.7 and 69.8 g C m-2 year-1 which represents a variability of 108%. An analysis of the relationship between the total gross primary production and the annual mean depth of the mixed layer has shown that the deeper the mixed layer is, the higher is the total annual gross primary production

Short time-scale analysis of the NW Mediterranean ecosystem during summer-autumn transition: A 1D modelling approach

Modelling was used as a tool to better understand the physical and biological processes observed during the multidisciplinary cruise DYNAPROC 2 (DYNAmic of rapid PROCesses in the water column), which took place in the Ligurian Sea in September-October 2004. The aim of the cruise was to study the short time-scale physical and biological processes that occur when the ecosystem switches from summer oligotrophy to autumnal mesotrophy. In this study, we have tested two 1D physical-biological coupled models. The first was a classical model in which surface layer dynamics were obtained using the turbulent kinetic energy model of Gaspar [Gaspar et al., 1990]. The simulated food-web took into account ten state variables: three nutrients, three classes of phytoplankton, two classes of zooplankton and two types of detritus. The second model (called IDA, Isopycnals Depth Adjustment) was based on the initial one but it took into account the measured variations of isopycnals depths. The results showed that the IDA model most efficiently reproduced the observed ecosystem dynamics. We have therefore used the IDA model to show that physical processes observed during the cruise had a major effect on biological compartment, mainly on nano- and picophytoplankton. (C) 2010 Elsevier B.V. All rights reserved

THE DIEL MIGRATIONS AND VERTICAL DISTRIBUTIONS OF ZOOPLANKTON AND MICRONEKTON IN THE NORTHWESTERN MEDITERRANEAN-SEA .2. SIPHONOPHORES, HYDROMEDUSAE AND PYROSOMIDS

Vertical distributions and diel migrations in the 0- 1000 m water column at a position in the Northwestern Mediterranean Sea are given in detail for the main species of gelatinous macrozooplankton: three siphonophores (Abylopsis tetragona, Chelophyes appendiculata and Lensia conoidea), one hydromedusa (Solmissus albescens) and one pyrosomid (Pyrosoma atlanticum). Extensive diel vertical migration occurred in these five species, particularly in A.tetragona, S.albescens and P.atlanticum for which the bulk of the population migrated as a compact unit. Pyrosoma atlanticum underwent the largest migration, with a mean amplitude of 515 m. The migration pattern of L.conoidea was more complex. Its day-distribution was bimodal and at night part of the population ascended towards the surface, while the other part appeared to undergo a weak reverse migration of approximately 50 m. Timing of the migrations was observed from horizontal hauls at a given depth around sunset and sunrise, and the migratory cycles presented a clear diurnal symmetry