francensis was detected in France in 2001 in moribund oysters since then this bacterium has been regularly detected during oyster mortality events. Studies performed since 2010 has provided strong evidence that OsHV-1 µVar is causally linked to increased oyster spat mortality at sea water temperatures above 16 ☌. Similar outbreaks were reported in 2010-11 from Australia and New Zealand. gigas) was observed in France and other European countries from 2008 onwards. A new pattern of mass mortality of Pacific oysters ( C. aestuarianus and 4) feasibility, availability and effectiveness of the disease prevention and control measures. It also demonstrates that time-series are key elements to further link environmental changes and occurrences of enzootic diseases.This updated scientific opinion on oyster mortality addresses 1) the role of ostreid herpesvirus (OsHV-1) in mortality, 2) evidence for a role of Vibrio aestuarianus in mortality, 3) effectiveness of water treatment in inactivating OsHV-1 and V. Integration of both environmental and physiological markers contribute to the RESCO network specifics, and provide a primary contribution in the research developed to understand oysters mortality events. The RESCO is a network build from field observations, and the data collected are designed for both scientific applications and management assistance for state stakeholders. Geographical location of the RESCO II network workshop sites
RESCO network's actions thus contribute to disentangle the biotic and abiotic parameters involved in mortality phenomena, by implementing a proactive and integrative approach, accounting for the different compartments (environment / host / infectious agents) likely to interact with the evolution of the oysters’ farming performances. Environmental variables (temperature, salinity) are also collected. Growth and mortality are monitored every fifteen days along with data associated with the presence of infectious agents in sentinel oysters. To this end, sentinel batches of oysters corresponding to different origins (wild or hatchery, diploid or triploid) and to two rearing age classes (spats or 18 months-old adults) are deployed simultaneously in 13 sites covering the main shellfish growing regions of the French coastline.
This monitoring allows the acquisition of a nationally-spread dataset on mortality and growth, to investigate and contribute to the understanding of the spatio-temporal dynamics of the breeding performances of this species. Since 2009, the RESCO network has been monitoring sentinel batches of the cupped oyster Crassostrea gigas in different areas selected among the REMORA network. These unique national datasets relative to the mortality and growth of two oyster age classes address important questioning regarding the spatiotemporal evolution of oyster performances. Field studies were carried out by “Laboratoires Environnement Ressources” (LERs) for the sites included in their geographical area of investigation. The REMORA network is a key complementary element in the framework of environmental IFREMER monitoring networks ( REPHY, REMI, ROCCH). Most of the sites were located on the foreshore at a comparable immersion levels. These sites were spread over the main French oyster farming areas and provided a national coverage of the multi-year evolution of oyster culture performances. These sentinel batches were distributed simultaneously every year on the different network sites (in March), and were monitored on a quarterly basis. In order to compare data in time and space for these two age classes, sentinel batches of oyster were selected according to a set of origin and size criteria. From 1995 onward, monitoring of 6 months-old spat oysters farming performances were integrated into the REMORA network. From 1993 to 2009 (creation of the RESCO network from this year on), the REMORA network monitored yearly mortality and growth of standardized batches of 18 months-old oysters. The REMORA network carried out by IFREMER was a national network designed to survey the farming performances of the Pacific oyster Crassostrea gigas. 1 : Ifremer, Laboratoire Physiologie des Invertébrés UMR 6539 LEMAR, ZI de la pointe du Diable, 29280 Plouzané, FranceĢ : Ifremer, Laboratoire Environnement Ressources Normandie, Avenue du Général de Gaulle, 14520 Port-en-Bessinģ : Ifremer, Service Valorisation de l'Information pour la Gestion Intégrée et la Surveillance, Rue de l'Île d'Yeu, 44980 NantesĤ : Ifremer, Laboratoire Environnement Ressources Morbihan Pays de Loire, 12 rue des Résistants, 56470 La Trinité sur merĥ : Ifremer, Laboratoire de Génétique et Pathologie des Mollusques Marins, Station de La Tremblade, 17390 La Tremblade
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