title: Exposure to the toxic dinoflagellate Alexandrium catenella modulates juvenile oyster Crassostrea gigas hemocyte variables subjected to different biotic conditions.
abstract: The Pacific oyster Crassostrea gigas is an important commercial species cultured throughout the world. Oyster production practices often include transfers of animals into new environments that can be stressful, especially at young ages. This study was undertaken to determine if a toxic Alexandrium bloom, occurring repeatedly in French oyster beds, could modulate juvenile oyster cellular immune responses (i.e. hemocyte variables). We simulated planting on commercial beds by conducting a cohabitation exposure of juvenile, "specific pathogen-free" (SPF) oysters (naïve from the environment) with previously field-exposed oysters to induce interactions with new microorganisms. Indeed, toxic Alexandrium spp. exposures have been reported to modulate bivalve interaction with specific pathogens, as well as physiological and immunological variables in bivalves. In summary, SPF oysters were subjected to an artificial bloom of Alexandrium catenella, simultaneously with a cohabitation challenge. Exposure to A. catenella, and thus to the paralytic shellfish toxins (PSTs) and extracellular bioactive compounds produced by this alga, induced higher concentration, size, complexity and reactive oxygen species (ROS) production of circulating hemocytes. Challenge by cohabitation with field-exposed oysters also activated these hemocyte responses, suggesting a defense response to new microorganism exposure. These hemocyte responses to cohabitation challenge, however, were partially inhibited by A. catenella exposure, which enhanced hemocyte mortality, suggesting either detrimental effects of the interaction of both stressors on immune capacity, or the implementation of an alternative immune strategy through apoptosis. Indeed, no infection with specific pathogens (herpesvirus OsHV-1 or Vibrio aesturianus) was detected. Additionally, lower PST accumulation in challenged oysters suggests a physiological impairment through alteration of feeding-related processes. Overall, results of this study show that a short-term exposure to A. catenella combined with an exposure to a modified microbial community inhibited some hemocyte responses, and likely compromised physiological condition of the juvenile oysters.
authors.affiliation: Laboratoire des Sciences de l'Environnement Marin (LEMAR), UMR 6539 CNRS UBO IRD IFREMER - Institut Universitaire Européen de la Mer, Technopôle Brest-Iroise - Rue Dumont d'Urville, 29280 Plouzané, France. Electronic address: Malwenn.Lassudrie@gmail.com.
authors.forename: Malwenn
authors.initials: M
authors.lastname: Lassudrie
authors.affiliation: Laboratoire des Sciences de l'Environnement Marin (LEMAR), UMR 6539 CNRS UBO IRD IFREMER - Institut Universitaire Européen de la Mer, Technopôle Brest-Iroise - Rue Dumont d'Urville, 29280 Plouzané, France. Electronic address: Philippe.Soudant@univ-brest.fr.
authors.forename: Philippe
authors.initials: P
authors.lastname: Soudant
authors.affiliation: Laboratoire des Sciences de l'Environnement Marin (LEMAR), UMR 6539 CNRS UBO IRD IFREMER - Ifremer, Laboratoire de Physiologie des Invertébrés, Technopôle Brest-Iroise BP 70, 29280 Plouzané, France. Electronic address: Jean.Louis.Nicolas@ifremer.fr.
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Nicolas
authors.affiliation: Laboratoire des Sciences de l'Environnement Marin (LEMAR), UMR 6539 CNRS UBO IRD IFREMER - Ifremer, Laboratoire de Physiologie des Invertébrés, Technopôle Brest-Iroise BP 70, 29280 Plouzané, France. Electronic address: Philippe.Miner@ifremer.fr.
authors.forename: Philippe
authors.initials: P
authors.lastname: Miner
authors.affiliation: Laboratoire des Sciences de l'Environnement Marin (LEMAR), UMR 6539 CNRS UBO IRD IFREMER - Ifremer, Laboratoire de Physiologie des Invertébrés, Technopôle Brest-Iroise BP 70, 29280 Plouzané, France. Electronic address: Jacqueline.Le.Grand@ifremer.fr.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Le Grand
authors.affiliation: Laboratoire des Sciences de l'Environnement Marin (LEMAR), UMR 6539 CNRS UBO IRD IFREMER - Institut Universitaire Européen de la Mer, Technopôle Brest-Iroise - Rue Dumont d'Urville, 29280 Plouzané, France. Electronic address: Christophe.Lambert@univ-brest.fr.
authors.forename: Christophe
authors.initials: C
authors.lastname: Lambert
authors.affiliation: Laboratoire des Sciences de l'Environnement Marin (LEMAR), UMR 6539 CNRS UBO IRD IFREMER - Institut Universitaire Européen de la Mer, Technopôle Brest-Iroise - Rue Dumont d'Urville, 29280 Plouzané, France. Electronic address: Nelly.Legoic@univ-brest.fr.
authors.forename: Nelly
authors.initials: N
authors.lastname: Le Goïc
authors.affiliation: Laboratoire des Sciences de l'Environnement Marin (LEMAR), UMR 6539 CNRS UBO IRD IFREMER - Institut Universitaire Européen de la Mer, Technopôle Brest-Iroise - Rue Dumont d'Urville, 29280 Plouzané, France. Electronic address: Helene.Hegaret@univ-brest.fr.
authors.forename: Hélène
authors.initials: H
authors.lastname: Hégaret
authors.affiliation: Laboratoire des Sciences de l'Environnement Marin (LEMAR), UMR 6539 CNRS UBO IRD IFREMER - Institut Universitaire Européen de la Mer, Technopôle Brest-Iroise - Rue Dumont d'Urville, 29280 Plouzané, France. Electronic address: Caroline.Fabioux@univ-brest.fr.
authors.forename: Caroline
authors.initials: C
authors.lastname: Fabioux
mesh_terms: D000818:Animals; D049896:Crassostrea / Q000187:drug effects* / Q000276:immunology* / Q000382:microbiology / Q000821:virology; D004267:DNA Viruses / Q000502:physiology; D004141:Dinoflagellida / Q000737:chemistry / Q000502:physiology*; D006434:Hemocytes / Q000276:immunology / Q000382:microbiology / Q000821:virology; D008387:Marine Toxins / Q000633:toxicity*; D014733:Vibrio / Q000502:physiology
chemical_list: D008387:Marine Toxins
keywords: Alexandrium; Crassostrea gigas; Harmful algal blooms; Hemocyte; Microbial challenge