summer mortality of pacific oyster crassostrea gigas
TRANSCRIPT
Summer mortalityof Pacific oysterCrassostrea gigasThe Morest Project
Jean-François Samain, Helen McCombie, editors
Summer mortality
of Pacific oyster
Crassostrea gigas
The Morest Project
This sample, taken in early September 2002 on theAuray study site, shows the first phenotypic differen-tiation observed between resistant oysters (above),which had spawned in July, and susceptible oysters(below), which had developed gonads but did notspawn this year.
Summer mortality
of Pacific oyster
Crassostrea gigas
The Morest Project
Jean-François Samain, Helen McCombieEditors
Éditions Quæc/o Inra, RD 10, 78026 Versailles Cedex
Collection Synthèses
Summer Mortality of Pacific Oyster
Crassostrea gigas
The Morest ProjectJean-François Samain, Helen McCombie2007, 400 p.
Bioclimatologie. Concepts et applicationsSané de Parcevaux, Laurent Huber2007, 336 p.
Plantes transgéniques : faits et enjeux André Gallais, Agnès Ricroch2006, 304 p.
L’agronomie d’aujourd’huiMichel Sebillotte, Thierry Doré, Marianne Le Bail, Philippe Martin, Bertrand Ney,Jean Roger-Estrade2006, 368 p.
Reproduction sexuée des conifères et production de semences en vergers àgrainesGwenaël Philippe, Patrick Baldet, Bernard Héois, Christian Ginisty2006, 572 p.
La photosynthèseProcessus physiques, moléculaires et physiologiquesJack Farineau, Jean-François Morot-Gaudry2006, 412 p.
L’armillaire et le pourridié-agaric des végétaux ligneuxJean-Jacques Guillaumin2005, 504 p.
© Éditions Quæ, 2008 ISBN 978-2-7592-0055-9 ISSN 1777-4624
The intellectual Property Code of July 1st 1992 prohibits the photocopying for collective use without theauthorisation of those having such rights. Failure to respect this injunction puts the edition at risk, particularlyif it is scientific. All reproductions, partial or complete, of the present work are prohibited without theauthorisation of the Editor or of the French Centre for Exploitation of Copyrights (CFC), 20, rue desGrands-Augustins, 75006 Paris.
V
Acknowledgements
This work could not have been completed without the support of the regions of Basse-Normandie, Bretagne, Pays de la Loire and Poitou-Charentes; the Conseil généraldu Calvados and European funding from the IFOP via the CNC (Comité nationalde la conchyliculture). We thank them for their concerted effort that was decisivefor the success of our activities.
This support completed our funding needs by adding to those allocated to us byIfremer, who we also thank for the decision to put this project into action, bringingtogether numerous teams and laboratories, and for providing financial support untilthe end of the project. In particular, we thank Jean-François Minster, managing direc-tor of Ifremer at the time of the project and Maurice Héral, the scientific director.
Apart from the skills and facilities available at the different Ifremer laboratories, wethank the directors of the other institutes in France where we found complementaryexpertise. This meant that several specialists from the CNRS, universities at Nantes,Montpellier and Brest, Muséum national d’histoire naturelle at Concarneau andInstitut Pasteur in Paris were largely involved in the project.
The Morest collaboration also allowed close working contact with regional and depart-mental structures for the transfer of research to the industry. We particularly thankSmel, Smidap, Creaa and Sysaaf for their efficient contributions to the fieldworkand the interaction they maintained with the industry.
We also thank the Comité national de la conchyliculture (CNC) who followed thiswork closely throughout the project and who raised many relevant questions aboutthe research, generating fruitful scientific and technical debate. The Sections régio-nales conchylicoles (SRC), and their presidents and secretaries also played an essen-tial role by establishing exchanges with the industry at the regional level. We trulyappreciated their initiatives in encouraging this dialogue for which we are very grate-ful. We, therefore, thank the whole of the shellfish industry for their actions andsupport in the fieldwork, and their reflection and help with obtaining funding.
As coordinator, I warmly thank all of the scientific and technical participants whoagreed to involve themselves in this challenge, to have continued throughout theduration of the project and to have participated actively in the pluridisciplinary
VI
construction of the programs and their realization. They can be congratulated forhaving been part of this scientific and technical challenge that was also a great humanexperience. Thank you for the pleasure of working together.
On behalf of all the Morest partners,
J.-F. Samain,Coordinator
VII
Coordinator
Samain J.-F.
Expert review panel
Pr. Ford S.Haskin Shellfish Research LaboratoryRutgers UniversityNew Jersey, USA
Pr. Tremblay R.Institut des Sciences de la MerUniversité du Québec à Rimouski, Québec
Pr. Bonhomme F.Université de Montpellier, Francereprésentant le Conseil scientifique de l’Ifremer
Dr Héral M.Directeur scientifique de l’Ifremer Paris, France
Reading committee
Bédier E., Boudry P., Boulo V., Burgeot T., Huvet A., Knoery J., Lambert C., Le Coz F.,McCombie H., Martin A.-G., Mazurié J., Moal J., Nicolas J.-L., Pouvreau S.,Quiniou F., Ropert M., Samain J.-F., Van Wormhoudt A.
Editing committee
Bédier E., Boudry P., Burgeot T., Courtay N., Howe V., Huvet A., Lambert C.,Mazurié J., Moal J., McCombie H., Nicolas J.-L., Pouvreau S., Ropert M.,Samain J.-F., Soletchnik P.
Translation
McCombie H.
Internet site
http://www.ifremer.fr/morest-gigas/
Martin A.-G., Masson J.-C., Bonnet C., Chécinski G. Laponche A.
VIII
Contributors
We would particularly like to thank the staff of the laboratories and partner institu-tions in the Morest project for their active contribution to its realization.
Laboratory addresses and contributors
1. Unité mixte de recherche (UMR 100), Physiologie et écophysiologie des mol-lusques marins, Ifremer, centre de Brest (PE2M), BP 70, 29280 Plouzané, France
Bacca H., Bourles Y., Cahu C., Cochard J.-C., Conan J.-P., Daniel J.-Y., Dela-porte M., Dubrunfault T., Dupé F., Enriquez-Diaz M., Fleury E., Garnier M.,Huvet A., Labreuche Y., Le Coz J.-R., Le Moullac G., Le Roux A., Le Souchu P.,Loiseau V., Marrec F., Mingant C., Misko P., Moal J., Nicolas J.-L., Pouvreau S.,Queau I., Quéré C., Robert R., Samain J.-F., Séguineau C.
2. Laboratoire de Génétique et Pathologie (LGP), Ifremer, Ronce-les-Bains, 17390La Tremblade, France
Arzul I., Barbosa-Solomieu V., Billy J.-C., Boudry P., Bouilly K., Breugnot M.,Brizard R., Byrnes N., Chollet B., Cornette F., Dégremont L., Fortin A.,Gagnaire B., Garcia C., Gay M., Goubet A., Grouhel S., Heurtebise S., Joly J.-P.,Kerdudou N., Lapègue S., Ledu C., Miossec L., Pépin J.-F., Phélipot P.,Renault T., Reynaud Y., Robert M., Saulnier D., Thébaud A.
3. Laboratoire Environnement-Ressources des pertuis Charentais (LERPC),Ifremer, 17390 La Tremblade, France
Blouin F., Couty A., David D., De Ambrogi C., Doner D., Faury N., Geairon P.,Goulletquer P., Guilpain P., Le Moine O., Madec P., Malestroit P., Meissner A.,Prou J., Razet D., Robert S., Seugnet J.-L., Soletchnik P., Stanisieres J.-Y.
4. Station Ifremer, Polder des champs, 85230 Bouin, France
Dupuy B., Haure J., Martin J.-L., Nourry M., Palvadeau H., Papin M., Penisson C.
5. Laboratoire Environnement-Ressources Morbihan-Pays de la Loire (LERPDL),Ifremer, 56470 La Trinité, France
Abily E., Bédier E., Bouget J.-F., Claude S., Fleury P-.G., Langlade A., Le Coz F.,Le Mouroux G., Martin A.-G., Mazurié J.
6. Laboratoire Environnement-Ressources de Normandie (LERN), Ifremer, BP 32,14520 Port-en-Bessin, France
Boisseaux A., Daniel A., Ernande B., Gangnery A., Grangeré K., Hugonnet V.,Jacqueline F., Justome V., Le Gagneur E., Lesaulnier N., Mary C., Rauflet F.,Riou P., Ropert M.
7. Unité mixte de recherche (UMR 5119), Écosystèmes lagunaires (Écolag), placeE. Bataillon, université de Montpellier, CC 80, 34095 Montpellier Cedex 5, France
Avarre J.-C., Avazeri J., Bachère E., Boulo V., Escoubas J.-M., Gonzales M.,Guéguen Y., Janeth M., Zattara B.
8. Laboratoire d’Écotoxicologie (LBEX Nantes), Ifremer, BP 21105, 44311 NantesCedex 03, France et LBEX Brest, Ifremer, BP 70, 29280 Plouzané, France
IX
Arzul G., Burgeot T., Caisey X., Cozic A., Géret F., Grouhel A., Klein B.,Ménard D., Quiniou F., Rousseau S.
9. Unité mixte de recherche (UMR 100), Physiologie et écophysiologie des mol-lusques marins, université de Caen (PE2M), Esplanade de la Paix, 14032 CaenCedex, France
Costil K., Dufour C., Favrel P., Frouel S., Hanquet A.-C., Henry J., Heude C.,Kellner K., Laisney J., Lefèbvre S., Lelong C., Mathieu M., Mathieu J., Royer J.
10. Unité mixte de recherche (UMR 5178), Station de Biologie marine du Muséumnational d'Histoire naturelle (MNHN Concarneau), BP 225, 29900 Concarneau,France
Buzin F., Delarche A.-S., Farcy E., Hillion M., Lanthoene V., Mahe A., MavicA.-S., Rochex A., Van Wormhoudt A., Wache Y.
11. Laboratoire Environnement marin (Lemar), équipe Interaction Hôte Pathogène(IHP) et Résistance aux Stress Anthropiques (RSA), Institut universitaire euro-péen de la mer, université de Brest, place Nicolas Copernic, 29280 Plouzané,France
Boutet I., Choquet G., David E., Gonçalves M., Hégaret H., Jegaden M., Lam-bert C., Le Goic N., Marhic A., Moraga D., Paillard C., Soudant P., Tanguy A.
12. Centre de recherche sur les Écosystèmes Littoraux Anthropisés (Créla), UMR6217, CNRS-Ifremer-ULR (université de la Rochelle), place du Séminaire, BP 5,17137 L’Houmeau, France
Alunno-Bruscia M., Bouchet V., Brêret M., Guillou G., Imbert N., Leguay D.,Malet N., Mornet F., Sauriau P.-G., Struski C., Thomas H.
13. Laboratoire de Biogéochimie des Contaminants Métalliques (LBCM), Ifremer,rue de l’Ile d’Yeu, BP 21105, 44311 Nantes Cedex 03, France
Knoery J.
14. Département Dynamiques de l’environnement côtier (Dyneco), Ifremer,
centrede Brest, BP 70, 29280 Plouzané, France
Bacher C., Dumas F., Gohin F., Grangeré K., Grouhel A., Masson J.-C.,Menesguen A., Struski C.
15. Département Informatique et données marines (IDM), Ifremer, centre de Brest,BP 70, 29280 Plouzané, France
Bonnet C., Chécinski G., Maros E., and other members the IDM/ISI and IDM/RIC services, Delauney L., Le Bihan C., Salvetat F.
16. Département Technologie des Systèmes Instrumentaux (TSI), Ifremer, centrede Brest, BP 70, 29280 Plouzané, France
Aoustin Y., Barbot S., Dorval P., Hamon M., Le Piver D., Podeur C., QuéménerL., Repécaud M., Woerther P.
17. Département Essais et Recherche Technologiques (ERT/IC), Ifremer, centre deBrest, BP 70, 29280 Plouzané, France
Delauney L., Le Bihan C., Maros E., Salvetat F.
X
18. Institut Pasteur, 25 rue du docteur Roux, 75015 Paris, France
Binesse J., Chakroun N., Le Roux F., Mazek D., Zouine M.
19. Laboratoire Environnement-Ressources d’Arcachon (LERA) Ifremer, quai duCommandant Silhouette, 33120 Arcachon, France
Auby I., D'Amico F., Maurer D.
20. Laboratoire Environnement-Ressources Languedoc-Roussillon (LERLR), Ifremer,avenue Jean Monet, BP 71, 34203 Sète Cedex, France
Barret J., Munaron D.
21. Groupe d’Étude des Milieux Estuariens et Littoraux (Gemel), Centre régionald’étude côtières, 54 rue du docteur Charcot, 14530 Luc-sur-Mer, France
Sylvand B.
22. Girpa, Angers Technopôle, 8 rue Becquerel, 49070 Beaucouze, France
Communal P.-Y., Jadas Hecart A., Royer A., Violeau D.
23. Institut Maurice Lamontagne, ministère des Pêches et des Océans, CP 1000,Mont-Joli, Québec, Canada G5H 3Z4
Fréchette M.
Development and advisory bodies to the industry
24. Syndicat des Sélectionneurs Avicoles et Aquacoles Français (Sysaaf), Stationde recherche avicole, centre INRA de Tours, 37380 Nouzilly, France
Coudurier B., Haffray P., Rault P.
25. Syndicat Mixte d’Équipement du Littoral (Smel), Conseil général, Maisondu département, 98 route de Candol, 50008 Saint-Lô Cedex, France
Blin J.-L., Bouchaud B., Pacary S., Richard O.
26. Centre Régional d’Expérimentation et d’Applications Aquacoles (Creaa),Prise de Terdoux, 17480 Le Château d’Oléron, France
Mille D., Phillipe B.
27. Syndicat Mixte de Développement de l’Aquaculture en Pays de Loire (Smidap),3 rue Célestin Freinet, 44200 Nantes, France
Glize P., Pajot R., Trintignac P.
Associations representing the shellfish industry
Le Comité national de la conchyliculture (CNC), 12 rue de Javel, 75015 Paris,and its local representatives,
Section régionale de Normandie-mer du NordSection régionale de Bretagne NordSection régionale de Bretagne SudSection régionale des Pays de la LoireSection régionale du Poitou-Charentes
XI
Section régionale d'Arcachon AquitaineSection régionale de Méditerranée
With notable contributions by Brest G., Chantereau S., Guillaumie B., Monnier M.,Jansens A., Savary M., Jenot H., Dreano A.
Le Syndicat des Écloseurs et Nurseurs de Coquillages (Senc), Mairie de Bouin,place de l’église, 85230 Bouin, France
With the contribution of:Société Atlantique de Mariculture (Satmar): Diss B., Le Borgne Y., Toulorges J.-F.Vendée naissain, polder des Champs, 85230 Bouin, France: Angeri S.SCEA Sodabo, polder des Champs, 85230 Bouin, France: Le Goff J.-Y
All the professionals in the industry who allowed us to use their
parcs
, in baie des Veys,rivière d’Auray, baie de Quiberon, bassin de Marennes-Oléron, notably:
M. Daniel.,M. Frish, M. Le Meitour, M. Pourtier, M. Roger, M. Cadoret (Sobaie).
Personnel of environmental authorities
Direction régionale de l’Environnement de Basse-Normandie (Diren), CitisLe Pentacle, avenue de Tsukaba, 14209 Hérouville-Saint-Clair Cedex, France
Forray N., directeur de la Diren de Basse-Normandie.
Agence de l’eau Seine-Normandie, Délégation au littoral et à la mer, 21 rue l’Hommede Bois, 14600 Honfleur, France
Bruchon F.
Météo France, allée des Tamaris, 17000 La Rochelle, France
Teams who hosted our seminars and meetings
Conseil régional de Normandie
École de la mer, Aquarium de La Rochelle
Ifremer, centre de Brest
Ifremer, centre de Nantes
Ifremer programs and strategy management
La direction des Programmes et de la Stratégie (DPS), centre de Nantes, rue del’Ile d’Yeu, BP 21105, 44311 Nantes Cedex 03, France
Baud J.-P., Conche N., Gérard A., Goulletquer P., Héral M., Lassalle E.
Administrative and financial management
Borgetto M., Brélivet M., Dulot F., Gourmelen L., Guézennec D., Hihn C., Morvan M.
Ifremer communications department
Fournier L., Millet B., Youénou G.
…and all those that we may have forgotten…
XIII
Contents
Acknowledgements
................................................................................................. V
Preface
..................................................................................................................... XIX
1. Evaluation of summer mortality risk factors in shellfish farming ecosystems
............................................................................ 1
Introduction ..................................................................................................... 1Monitoring bivalve mortalities at the national level ............................. 2A historical analysis of oyster mortalities in France.............................. 2Mortalities in the Morest study sites....................................................... 5Objectives of chapter 1............................................................................. 9
The thermal risk factor ................................................................................... 9Thermal characteristics of the study sites............................................... 9Thermal dynamics and mortalities.......................................................... 11Summary.................................................................................................... 15
The pluviometric risk factor ........................................................................... 15Pluviometric results at the national scale ............................................... 16Pluviometric results at the Morest study sites........................................ 18Summary.................................................................................................... 26
The trophic risk factor .................................................................................... 26Relationship between mortality and trophic resources (quantitative aspect)................................................................................. 27Relationship between mortality and trophic resources (qualitative aspect) ................................................................................... 36Summary.................................................................................................... 40
The sediment risk factor ................................................................................. 41The sedimentary risk in the study sites................................................... 42Studies on the chemistry of the sediment in the study sites ................. 46Summary.................................................................................................... 49
Discussion–conclusion .................................................................................... 50Spatial and temporal variability of the environmental risks under study 50The thermal risk........................................................................................ 51The pluviometric risk ............................................................................... 52
Summer mortality of Pacific oyster
Crassostrea gigas
XIV
The trophic risk ......................................................................................... 55The sedimentary risk ................................................................................ 57Analysis of a combined environmental risk............................................ 59
2. Mortality risks associated with physiological traits of oysters during reproduction
............................................................................................... 63
Introduction ..................................................................................................... 63Materials and methods.................................................................................... 64
Experiments performed under controlled conditions ............................. 64Field experiments...................................................................................... 66Live material.............................................................................................. 66Analytical methods ................................................................................... 68
Gametogenesis, nutrition and mortalities ..................................................... 68Metabolic needs in summer............................................................................ 71
Evolution in metabolic needs with changes in temperature ................... 71Evolution of metabolic needs during gametogenesis ............................ 71
The use of reserves over the summer period ................................................ 74Use of reserves at different temperatures .............................................. 74The use of reserves depending on the intensity of gametogenesis ..... 76The effect of age on use of reserves ........................................................ 78Annual variation in glycogen enzymes.................................................... 79Reserves and mortality ............................................................................. 80Conclusions on reserve utilization .......................................................... 81
Nutrition and energy balance during summer .............................................. 82Analysis in controlled conditions ............................................................ 83Field studies............................................................................................... 85Modeling energetic fluxes over gametogenesis...................................... 87
Immune deficiency in summer ....................................................................... 94Oyster hemocytes: multipurpose cells ...................................................... 94Hemocyte parameters and temperature................................................. 95Hemocyte parameters and reproduction................................................ 97
General conclusion.......................................................................................... 105
3. Oyster summer mortality risks associated with environmental stress
........ 107
Introduction ..................................................................................................... 107Experimental stress studies............................................................................. 109
Effect of hypoxia........................................................................................ 109Effect of pesticides.................................................................................... 117
Sources of disturbance and environmental stress examined with the ‘bottom-rack’ comparison model..................................................... 120
Potential sources of toxicity from the sediment ..................................... 121Potential toxicity sources in water and quality of the nutritional environment ................................................................ 127Relationships between distance from the sediment and stress in oysters in the ‘bottom-rack’ experimental model .............................. 138
Conclusion........................................................................................................ 150
Contents
XV
4. The genetic basis of summer mortality in Pacific oyster spat and potential for improving survival by selective breeding in France
...................................... 153
PART I. Study of the genetic basis of summer mortality resistance in juvenile Pacific oyster
Crassostrea gigas
over four generations of selection
....................................................................................................... 153Introduction: context and objectives ............................................................. 153First generation: estimation of the genetic basis of spat survival in their first summer in the field..................................................................... 155
Materials and methods ............................................................................. 155Results from the first generation............................................................. 158
Second generation: divergent selection for high and low survival of spat in their first summer in the field ......................................................... 160
Materials and methods ............................................................................. 160Results ....................................................................................................... 162
Third generation: repeatability of the response to divergent selection for high or low spat survival in the first summer and expression of the character in triploids ............................................................................ 164
Production of the G3 batches.................................................................. 164Field study results ..................................................................................... 165
Fourth generation: repeatability of response to selection........................... 167G4 production........................................................................................... 167Studies on the G4 batches ....................................................................... 169
Field survival performances in the second summer period........................ 170Survival of batches that spent two summers in the field ....................... 171Survival of batches that spent their first summer in the nursery and their second summer in the field ............................. 172
Laboratory studies of spat survival performance and correlations with field data .................................................................................................. 172
Results of the laboratory experiments .................................................... 172Comparisons between mortalities in the field and the laboratory ....... 174
Discussion and prospects for future research............................................... 175Genetic basis
vs.
vertical transmission of a pathogenic agent?............... 178Why is there so much genetic variation for resistance to summer mortalities in natural populations?...................................... 178Prospects for future research................................................................... 179
PART II. Towards Gigas+, a selection program to improve summer survival of the Pacific oyster
Crassostrea gigas
in France
............. 179A review of the use of selection methods for shellfish improvement worldwide ............................................................ 179
Introduction............................................................................................... 179The French shellfish industry .................................................................. 180Genetic improvement methods used in France..................................... 181Commercial selection programs.............................................................. 182
Points for the creation of a collaborative selection program to improve oyster summer survival in France: Gigas+................................ 190
Objectives of Gigas+ ................................................................................ 190
Summer mortality of Pacific oyster
Crassostrea gigas
XVI
Advantages and limiting factors of the Gigas+ selection program ......... 192Conclusions ............................................................................................... 193
Appendix: Summary list of Morest generations and batches studied......... 194
5. Phenotypic characteristics of ‘R’ and ‘S’ oyster lines, selected for resistance or susceptibility to summer mortality
........................... 197
Introduction ..................................................................................................... 197Differences in gametogenesis and reproductive effort between R and S oysters ................................................................................. 198
Gametogenesis at the spat stage.............................................................. 198Gametogenesis at 18 months ................................................................... 199
Comparative energy balance of R and S oysters .......................................... 204Energy supply within the animal: energy components .......................... 205Comparative measurements of carbohydrate pathways during the critical period preceding mortalities..................................... 207
Defense capacities of R and S oysters ........................................................... 209Materials and methods ............................................................................. 209The genetic basis of hemocyte parameters............................................. 210Hemocyte parameters in R and S oysters............................................... 210
Stress responses of R and S oysters ............................................................... 221Experimental study of the adaptation mechanisms of R and S oysters in conditions of hypoxia and pesticide exposure...................................... 221Effect of pesticide exposure on the use of energy ................................. 224Environmental stress associated with gametogenic effort in R and S oysters ..................................................................................... 227
Aneuploidy levels of R and S oysters............................................................. 228R and S oyster responses to pathogenic agents ............................................ 230
Bacterial infections ................................................................................... 230Herpes virus status of R and S stocks ..................................................... 232Conclusion on the role of pathogens in the mortality of R and S stocks....................................................................................... 233
Differential gene expression between R and S oysters and the identification of physiological functions conferring resistance to summer mortality......................................................................................... 234
Differential gene expression in natural conditions before a mortality episode ....................................................................... 234Differential gene expression under experimental conditions and the study of risk factors ..................................................................... 236
General discussion and conclusion ................................................................ 239
6. Oyster summer mortality risks associated with pathogens
.......................... 243
Introduction ..................................................................................................... 243Finding and identifying potential candidate pathogens............................... 245
Repamo-Morest: abnormal
Crassostrea gigas
mortalities declared between 2001 and 2005............................................................. 245
Contents
XVII
Vibrio
bacteria found in oysters during mortality episodes (2001–2004) in hatcheries and oyster parcs ................................................................. 252Taxonomic characterization of bacterial isolates................................... 255Development of specific diagnosis tools................................................. 258
Pathogenicity and conditions of expression of infection.............................. 260Bacteria and reproduction of mortalities in the laboratory.................... 260OsHV-1 virus, infection and transmission.............................................. 270
The search for bacterial virulence genes....................................................... 272Strains of
Vibrio aestuarianus
.................................................................... 272Virulence factors in strains of the
Vibrio splendidus
group................... 275Pathogenic agents and risk definition............................................................ 278
Temporal variation of
Vibrionaceae
flora in oysters and the marine environment .................................................................... 278Ecology of
Vibrio aestuarianus
................................................................. 282Conclusion ....................................................................................................... 285
7. Temperature as a risk factor in oyster summer mortality
............................ 289
Introduction ..................................................................................................... 289Oyster physiology ............................................................................................ 290
Gametogenic stages and 19˚C.................................................................. 290Spawning and 19˚C .................................................................................. 292Energy balance and 19˚C ........................................................................ 292Respiration................................................................................................ 295Hemocyte parameters and temperature ................................................ 297
The sediment and 19˚C .................................................................................. 298Sediment remineralization and 19˚C....................................................... 298Diffusion and temperature ...................................................................... 300Sediment effects and partial spawning ................................................... 302
Genetics and temperature .............................................................................. 302Pathogens and temperature............................................................................ 303
What influence does temperature have on bacteria?............................ 303What influence does temperature have on herpes virus OsHV-1?...... 304
General conclusion.......................................................................................... 305
8. A synthesis of the Morest project and recommendations for forecasting and managing oyster summer mortalities
................................. 307
Introduction ..................................................................................................... 307
PART I. Analysis of summer mortality using an interaction model
......... 308Seawater temperature..................................................................................... 309Reproduction ................................................................................................... 309
The stage of reproductive development ................................................. 309Reproductive effort .................................................................................. 309Food level .................................................................................................. 309Oyster age.................................................................................................. 310
Oyster genetics................................................................................................. 310Stress................................................................................................................. 310
Summer mortality of Pacific oyster
Crassostrea gigas
XVIII
Distance from the sediment..................................................................... 310Freshwater releases in full summer......................................................... 311Annual freshwater inputs ......................................................................... 311Other stresses ............................................................................................ 311
Conclusion on the risk factors of the interaction model.............................. 311
PART II. Risk management
........................................................................... 312Temperature risk.............................................................................................. 312
Risks associated with the 19˚C temperature threshold .......................... 312Thermal dynamics and mortality risks in the first and second years.... 315
Reduction of mortality risks in the first year (first summer) ....................... 316Rearing on sites where the temperature is lower than 19˚C .................. 316Trophic limitation at the spat stage ......................................................... 316Risk reduction by increasing the distance from the sediment .............. 319Discussion and conclusion ....................................................................... 324
Reduction of mortality risks in the second year (second summer)............. 325Rich trophic environments: reducing reproductive effort by livestock transfers ................................................................................. 325Discussion and conclusion ....................................................................... 331Less rich environments............................................................................. 332
Exploitation of genetic variability .................................................................. 332Purging of naturally collected spat .......................................................... 332Selection of resistant oysters.................................................................... 334Triploid oysters .......................................................................................... 335
Discussion and conclusion .............................................................................. 336
PART III. Risk forecasting methods
............................................................. 336Forecasting risk timing .................................................................................... 336Forecasting the scale of mortality risk ........................................................... 336
The pluviometric effect ............................................................................. 336The development of forecasting methods .............................................. 341Models ....................................................................................................... 341New instruments: real-time monitoring probes ..................................... 346
Discussion and conclusion .............................................................................. 348
References
............................................................................................................... 349