ENVIRONMENTAL EFFECTS ON BREEDING PACIFIC OYSTERS Crassostrea gigas ON THE WEST COAST, USA

The Molluscan Broodstock Program (MBP) has been selecting Pacific oysters (Crassostrea gigas ) on the West coast, USA, since 1996. The initial focus has been improvement in yields though selection for higher growth and survival of families planted at  a wide range of different farm sites .  Selection of  these  traits in oysters, and other species grown in the natural environment with little  farmer  input,  is challenging due to  high  variability in  the culture environment over both spatial and temporal scales. Despite these difficulties,  harvest  yields  of MBP-derived families have been found to be 15 to 30% greater after six generations of selection, compared with those of offspring from  non-selected  "wild" parents.

MBP selects families that perform  well  across as wide range of different culture conditions, including coastal , inland (Puget Sound, Washington) , intertidal and subtidal  sites. Heritability values for growth, survival and yield  at  coastal and Puget Sound  sites  were moderate-to-high, ranging from 0.36 to 0.62, with higher values occurring at Puget Sound sites. G enetic correlations for  harvest  traits between these two  locations ranged from 0.46 to 0.69 for yield and survival, respectively. Surprisingly,  genetic  correlations were higher for families planted at subtidal and intertidal sites , ranging from 0.64 to 0.81 for individual average  harvest weight and survival, respectively .

These results indicate that  Pacific oysters on the West Coast, USA, show  considerable  phenotypic plasticity across a wide range of  farm environments; however, the limited  proportion  of "generalist" families  in cohorts (Fig. 1)  will result  in  long-term loss of genetic diversity  unless compensating strategies  are implemented by the breeding program.