Summer mortality of Pacific oyster Crassostrea gigas

Monitoring bivalve mortalities at the national level

A historical analysis of oyster mortalities in France

Mortalities in the Morest study sites

Objectives of chapter 1

Thermal characteristics of the study sites

Thermal dynamics and mortalities

Summary

Pluviometric results at the national scale

Pluviometric results at the Morest study sites

Summary

Relationship between mortality and trophic resources (quantitative aspect)

Relationship between mortality and trophic resources (qualitative aspect)

Summary

The sedimentary risk in the study sites

Studies on the chemistry of the sediment in the study sites

Summary

Spatial and temporal variability of the environmental risks under study

The thermal risk

The pluviometric risk

The trophic risk

The sedimentary risk

Analysis of a combined environmental risk
 

Experiments performed under controlled conditions

Field experiments

Live material

Analytical methods

Evolution in metabolic needs with changes in temperature

Evolution of metabolic needs during gametogenesis

Use of reserves at different temperatures

The use of reserves depending on the intensity of gametogenesis

The effect of age on use of reserves

Annual variation in glycogen enzymes

Reserves and mortality

Conclusions on reserve utilization

Analysis in controlled conditions

Field studies

Modeling energetic fluxes over gametogenesis

Oyster hemocytes: multipurpose cells

Hemocyte parameters and temperature

Hemocyte parameters and reproduction

Effect of hypoxia

Effect of pesticides

Potential sources of toxicity from the sediment

Potential toxicity sources in water and quality of the nutritional environment

Relationships between distance from the sediment and stress in oysters in the ‘bottom-rack’ experimental model

PART I. Study of the genetic basis of summer mortality resistance in juvenile Pacific oyster Crassostrea gigas over four generations of selection

Introduction: context and objectives

First generation: estimation of the genetic basis of spat survival in their first summer in the field

Materials and methods

Results from the first generation

Second generation: divergent selection for high and low survival of spat in their first summer in the field

Materials and methods

Results

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

Production of the G3 batches

Field study results

Fourth generation: repeatability of response to selection

G4 production

Studies on the G batches

Field survival performances in the second summer period

Survival of batches that spent two summers in the field

Survival of batches that spent their first summer in the nursery and their second summer in the field

Laboratory studies of spat survival performance and correlations with field data

Results of the laboratory experiments

Comparisons between mortalities in the field and the laboratory

Discussion and prospects for future research

Genetic basis vs.vertical transmission of a pathogenic agent?

Why is there so much genetic variation for resistance to summer mortalities in natural populations?

Prospects for future research
 

PART II. Towards Gigas+, a selection program to improve summer survival of the Pacific oyster Crassostrea gigas in France

A review of the use of selection methods for shellfish improvement worldwide

Introduction

The French shellfish industry

Genetic improvement methods used in France

Commercial selection programs

Points for the creation of a collaborative selection program to improve oyster summer survival in France: Gigas+