Gene Expression as an Indicator of Environmental Stress in the Pacific Oyster, Crassostrea gigas

Pacific oysters, Crassostrea gigas, are an important aquaculture species worldwide.  Recent mass mortalities of C. gigas larvae in the Pacific Northwest have been linked to upwelling events and acidic water, as well as emerging diseases.  High mortalities have created concern over how stocks of C. gigas will respond to a changing ocean environment.  Concurrently, urbanization in coastal areas affects water quality, which may adversely impact multiple life stages of Pacific oyster.  To understand the current and future effects of environmental stressors on Pacific oyster populations, we exposed C. gigas larvae to different regimes of projected acidified ocean scenarios.  We looked at the expression of genes involved in the stress and immune responses in the larvae to understand how oysters will be affected by future ocean conditions.  Additionally, we monitored the larval phenotype throughout development, noting whether there were individuals that showed resistance to normally detrimental conditions, thus hinting at adaptive potential within the population.  We also used Next-Generation Sequencing to compare gene expression profiles in adult oysters between pristine and urban sites where adult C. gigas are found.  Multivariate statistics were used to compare expression profiles over multiple genes between sites.  End-of-century projections for water quality, including ocean acidification and urbanization, indicate that C. gigas will be exposed to increasingly acidic and polluted waters that could provide a consistent selection pressure necessitating adaptation to a changing environment for population survival.  The plentiful genomic resources available to C. gigas allow for an in-depth look into the interaction between the oyster and its environment, potentially providing insight in the mechanisms of the mortality events.