BREEDING PACIFIC OYSTERS Crassostrea gigas FOR RESILIENCE TO CHANGING OCEAN CONDITIONS

In 1996 the Molluscan Broodstock Program (MBP), a partnership between Oregon State University and industry collaborators on the West Coast United States, began a long-term selective breeding program for the genetic improvement of Pacific oysters, an important West Coast and global aquaculture species. Since 2005, the oyster industry has been threatened by the effects of ocean acidification (OA). Anecdotal evidence from commercial oyster hatcheries suggests that larvae from MBP selected stocks are more tolerant of upwelled acidified seawater than their wild counterparts.  This work compares the genotypic and phenotypic effects of high CO₂ culture environments on larvae spawned from selectively bred MBP broodstock and naturalized "wild" stocks.

Larval pools with broad genetic diversity (95 crosses each) were spawned from top performing MBP families and wild broodstock from Willapa Bay, Washington.  These two pools of fertilized eggs were reared through larval phases to post-metamorphic spat in 2 water types: 1) seawater equilibrated to ambient pCO₂ (~400ppm) and 2) seawater replicating upwelled OA conditions (pCO₂≈1600ppm). Larval samples were taken at 2, 6, 10, 16 and 22 days post fertilization and evaluated for phenotype (survival, size, developmental stage) as well as genetic composition of the surviving larval pool.

Preliminary results indicate that broodstock type and CO₂ concentration had strong interactive effects on larval performance.  Mean initial survival and development to D-larvae (48 hours) was higher in Willapa groups in both ambient and high CO₂ concentrations.  Subsequent growth, development rate and spat production, however, was greater and less variable in MBP groups in both ambient and OA conditions (Figure 1).  High CO₂ seawater appeared to have effects that were distinctly different between broodstock types and across developmental stages.  This suggests a complex interaction of genetics and environmental stressors in the growth and survival of Pacific oyster larvae.