Effects of age and environment on survival of summer mortality by two selected groups of the Pacific oyster Crassostrea gigas

Type Article
Date 2010-02
Language English
Author(s) Degremont LionelORCID1, Boudry PierreORCID2, Ropert MichelORCID3, Samain Jean-Francois2, Bedier Edouard4, Soletchnik Patrick5
Affiliation(s) 1 : IFREMER, Lab Genet & Pathol, F-17390 La Tremblade, France.
2 : IFREMER, UMR Physiol & Ecophysiol Mollusques Marins M100, F-29280 Plouzane, France.
3 : IFREMER, Lab Environm Ressources Normandie, F-14520 Port En Bessin, France.
4 : IFREMER, Lab Conchylicole Bretagne, F-56470 La Trinite, France.
5 : IFREMER, Lab Environm Ressources Pertuis Charentais, F-17390 La Tremblade, France.
Source Aquaculture (0044-8486) (Elsevier Science Bv), 2010-02 , Vol. 299 , N. 1-4 , P. 44-50
DOI 10.1016/j.aquaculture.2009.12.009
WOS© Times Cited 27
Keyword(s) Summer mortality, Age, Environment, Genetic, Crassostrea gigas
Abstract This study investigated the effects of age (first or second summer of life) and environment (three study sites on French coasts) on summer mortality in Crassostrea gigas, using three generations of oysters produced during the Morest project. For each generation, two groups of oysters, selected either as 'resistant' (R) or 'susceptible' (S) to summer mortality at the age of 6 months in Rivière d'Auray (RA, South Brittany), were evaluated. In Ronce (Marennes-Oléron Bay) and RA, R oysters had low mortality during their first and second summers, while mortality was higher during the second summer in Baie des Veys (BDV, Normandy). In RA, S oysters exhibited higher mortality during their first summer than during their second, while the opposite result was found in BDV, indicating a significant environment by age interaction. Some oysters were also protected from mortality risk factors during their first year by keeping them in a nursery; they were then deployed at the two sites the following spring. Mortality in R oysters during their second year was lower than in S oysters in RA and BDV. Interestingly, mortality of the S oysters deployed in RA during their second year was much lower than the mortality observed in S oysters deployed during their first year, suggesting that S juveniles are more susceptible to summer mortality than S adults. As a consequence, the difference in mortality between the two selected groups in RA decreased from 40-45% to 5-9% when oysters were protected from summer mortality at the juvenile stage. In BDV, the difference in mortality between the two selected groups was similar whether oysters were deployed during their first or second year. The first reproductive event in oysters, combined with genetic differences between the groups interacting with local environmental conditions can go some way to explaining summer mortality events in our study. Cumulative mortality for each generation and site was higher in the S group than in the R group, indicating a positive response to selection in oysters up to 18 months old. Mortality was split into three categories: low background mortality, genetic effects from the selection and unknown mortality on which no investigation has yet concentrated. Finally, culture strategy on oyster farms is discussed with respect to oyster age and environment.
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