A longitudinal study of Pacific oyster (Crassostrea gigas) larval development: isotope shifts during early shell formation reveal sub-lethal energetic stress

ABSTRACT: Three cohorts of Pacific oyster (Crassostrea gigas) larvae at Whiskey Creek Shellfish Hatchery (WCH) in Netarts Bay, Oregon, were monitored for stable isotope incorporation and biochemical composition: one in May 2011 and two in August 2011. Along with measures of growth and calcification, we present measurements of stable isotopes of carbon in water, algal food, and the shell and tissue, and nitrogen in food and tissue across larval development and growth. These relatively unique measures through larval ontogeny allow us to document isotopic shifts associated with initiation and rate of feeding, and the catabolism of C-rich (lipid) and N-rich (protein) pools. Similar ontological patterns in growth and bulk composition among the cohorts reinforce prior results, suggesting that the creation of the initial shell is energetically expensive, that the major carbon source is ambient dissolved inorganic carbon, and that the major energetic source during this period is maternally derived egg lipids. The May cohort did not isotopically reflect its food source as rapidly as the August cohorts, indicating slower feeding and/or higher catabolism versus anabolism. Our measurements also document differences in bulk turnover of organic carbon and nitrogen pools within the larvae, showing far greater conservation of nitrogen than carbon. These stable isotope and bulk biochemical measurements appear to be more sensitive indicators of sub-lethal environmental stress than the commonly used metrics of development and growth.