Patrik Le Gall

Organic UV filter concentrations in marine mussels from French coastal regions.

The accumulation of EHMC, OCT and OD-PABA, three common UV filter compounds, was investigated in marine mussels. Wild Mytilus edulis and Mytilus galloprovincialis were sampled in ten sites along the French Atlantic and Mediterranean coasts from June to November. In mussel tissues, 100% of the samples had quantifiable EHMC concentrations ranging from 3 to 256ngg(-1) dry weight, while 55% of the samples had detectable OCT concentrations ranging from under 2 to 7 112ngg(-1) dry weight. These concentrations significantly increased with the rising air temperature in summer, the recreational pressure and the geomorphological structure of the sampling sites (its lack of openness to the wide). This is the first study to report bioaccumulation of UV filters in marine mussels, thus highlighting the need for further monitoring and assessment.

Growth model of the Pacific oyster, Crassostrea gigas, cultured in Thau Lagoon (Méditerranée, France)

Abstract We developed a growth model for the oyster Crassostrea gigas cultured in Thau Lagoon. The oyster standing stock in the lagoon ranged between 10,000 and 15,000 tons a year. Two culture methods are presently in use in Thau Lagoon which are used in about the same proportions. At seeding, initial size of oysters is different among methods. The model was calibrated on (1) growth data accounted for both culture methods and (2) hydrobiological data (temperature, salinity, suspended particulate matter and chlorophyll a ), both recorded in several sites in the lagoon between March 2000 and October 2001. The lagoon is slightly eutrophic: total chlorophyll a and total particulate matter averaged 1.2 μg l −1 and 2.2 mg l −1 , respectively. Organic content accounted for ca. 40–50% of particulate matter. There was no seasonal trend in seston, whereas temperature and salinity were minimal in winter. Oyster growth varied among sites in response to spatial variations in seston. Growth was maximal in summer and minimal in winter because of temperature seasonality. For each location, we modelled growth as a function of particulate organic matter and temperature. Chlorophyll a was left out of the model because of a weaker fit with growth. Growth was modelled as G = a POM b T c Y d , where G is the growth rate in shell length (mm day −1 ) or in mass (g day −1 ), POM is particulate organic matter (mg l −1 ), T is temperature (°C) and Y is either shell length (mm) or mass (total individual mass or dry flesh mass in g). Allometry ( Y d ) allowed us to use the same model for both culture methods. The model yielded a good fit with actual size, either as measured by shell length ( R 2 =0.96) or total individual mass ( R 2 =0.93).

Spatial and Temporal Dynamics of Mass Mortalities in Oysters Is Influenced by Energetic Reserves and Food Quality

Although spatial studies of diseases on land have a long history, far fewer have been made on aquatic diseases. Here, we present the first large-scale, high-resolution spatial and temporal representation of a mass mortality phenomenon cause by the Ostreid herpesvirus (OsHV-1) that has affected oysters (Crassostrea gigas) every year since 2008, in relation to their energetic reserves and the quality of their food. Disease mortality was investigated in healthy oysters deployed at 106 locations in the Thau Mediterranean lagoon before the start of the epizootic in spring 2011. We found that disease mortality of oysters showed strong spatial dependence clearly reflecting the epizootic process of local transmission. Disease initiated inside oyster farms spread rapidly beyond these areas. Local differences in energetic condition of oysters, partly driven by variation in food quality, played a significant role in the spatial and temporal dynamics of disease mortality. In particular, the relative contribution of diatoms to the diet of oysters was positively correlated with their energetic reserves, which in turn decreased the risk of disease mortality.

Inefficient immune response is associated with microbial permissiveness in juvenile oysters affected by mass mortalities on field

ABSTRACT Since 2008, juvenile Crassostrea gigas oysters have suffered from massive mortalities in European farming areas. This disease of complex etiology is still incompletely understood. Triggered by an elevated seawater temperature, it has been associated to infections by a herpes virus named OsHV‐1 as well as pathogenic vibrios of the Splendidus clade. Ruling out the complexity of the disease, most of our current knowledge has been acquired in controlled experiments. Among the many unsolved questions, it is still ignored what role immunity plays in the capacity oysters have to survive an infectious episode. Here we show that juvenile oysters susceptible to the disease mount an inefficient immune response associated with microbial permissiveness and death. We found that, in contrast to resistant adult oysters having survived an earlier episode of mortality, susceptible juvenile oysters never exposed to infectious episodes died by more than 90% in a field experiment. Susceptible oysters were heavily colonized by OsHV‐1 herpes virus as well as bacteria including vibrios potentially pathogenic for oysters, which proliferated in oyster flesh and body fluids during the mortality event. Nonetheless, susceptible oysters were found to sense microbes as indicated by an overexpression of immune receptors and immune signaling pathways. However, they did not express important immune effectors involved in antimicrobial immunity and apoptosis and showed repressed expression of genes involved in ROS and metal homeostasis. This contrasted with resistant oysters, which expressed those important effectors, controlled bacterial and viral colonization and showed 100% survival to the mortality event. Altogether, our results demonstrate that the immune response mounted by susceptible oysters lacks some important immune functions and fails in controlling microbial proliferation. This study opens the way to more holistic studies on the “mass mortality syndrome”, which are now required to decipher the sequence of events leading to oyster mortalities and determine the relative weight of pathogens, oyster genetics and oyster‐associated microbiota in the disease. HighlightsOysters susceptible to the disease mount an inefficient immune response associated with microbial permissiveness.Susceptible oysters are colonized by OsHV‐1 herpes virus and bacteria including potentially pathogenic vibrios.Resistant oysters to the disease expressed important immune effectors that prevent bacterial and viral colonization.

Marine environmental station database of Thau lagoon

On oyster table in the Thau lagoon, Ifremer measures hydrological parameters (temperature, salinity) at high-frequency .Data loggers (NKE: SMATCH and STPS) measure every 15 minutes. To limit biofouling, there is a localized chlorination at the sensor (SMATCH) and a regular rotation of data loggers (STPS). The brand of sensors is WTW. These devices are calibrated regularly with a connection to ITS90 for temperature and IAPSO standards for salinity. The data are qualified by calibrations in the laboratory. For salinity, calibrations in-situ (since 2015) and comparisons between sensors are also conducted. A maximum permissible deviation (EMT) is calculated with the data, taking into account the error of accuracy and the measurement uncertainty (k=2).