IMPACT OF Alexandrium minutum EXPOSURE ON Crassostrea gigas PHYSIOLOGY: AN INTEGRATIVE APPROACH.

• Main Author: Haberkorn, Hansy
• Other Authors: Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Université européenne de Bretagne - European University of Brittany (UEB), Université de Bretagne occidentale - Brest, Philippe Soudant([e-mail])
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2009
• Subjects: physiology; Alexandrium minutum; Crassostrea gigas; interaction; physiologie; [SDV.EE.IEO]Life Sciences [q-bio]/Ecology; environment/Symbiosis; Pacific; Pacific oyster
• Online Access: https://tel.archives-ouvertes.fr/tel-00471896; https://tel.archives-ouvertes.fr/tel-00471896v2/document; https://tel.archives-ouvertes.fr/tel-00471896v2/file/These_Hansy_Haberkorn.pdf

The effects of the toxin-producing dinoflagellate, Alexandrium minutum, upon the Pacific oyster, Crassostrea gigas, were assessed through an integrative approach including behavior, digestion cellular activities and reproduction. In a first time, physiological status of A. minutum was assessed using flow cytometry, microscopy and fluorescent dyes. This allows us to demonstrate that some experimental conditions can be stressful for this dinoflagellate. Experimental systems were adapted to minimize adverse conditions for harmful micro-algae. In a second time, oysters were exposed under laboratory conditions to A. minutum in several experiments and compared to control oysters fed Isochrysis sp. or Heterocapsa triquetra. The shell-valve behavior of C. gigas responded to A. minutum exposure with increased duration of time open and frequency of incomplete closures. Histological observations revealed myopathy in the adductor muscle (myoatrophy, wavy muscle fibers and hyaline degeneration), which is consistent with observed behavioral modifications. Furthermore, a positive correlation was observed between duration of time shell valves were open and quantity of accumulated toxins. A. minutum exposure resulted in activation of defense mechanisms. Increase in mucus production in gills, as well as an inflammatory response in the digestive gland, were observed in A. minutum-exposed oysters. Hemocyte characteristics and functions were also changed. Significant differences, in terms of phenoloxidase activity (PO) and reactive oxygen species (ROS) production of hemocytes, were observed between A. minutum-exposed and control oysters. Hemocyte responses to in vivo A. minutum exposure depended upon reproductive status and toxin accumulation, but also upon metabolic activity during the experiment. Lipid contents in the digestive gland were also affected upon A. minutum exposure. Significant decreases in monoacylglycerol (MAG) and diacylglycerol (DAG) contents, as well as a drastic decrease in phosphatidylcholine (PC) content in ...