Dietary exposure of Pacific oyster (Crassostrea gigas) larvae to compromised microalgae results in impaired fitness and microbiome shift.

The Pacific oyster Crassostrea gigas is the world's most cultivated oyster and seed supply is heavily reliant on hatchery production where recurring mass mortality events are a major constraint. Outbreaks of bacterial infection via microalgal feed are frequently implicated in these mortalities. This study assessed the effects of feeding compromised microalgae to developing oyster larvae. Intentionally stressed (high pH) or non-stressed microalgae were fed to 11 day-old oyster larvae at two feeding rations for 96h, followed by a recovery period. Biological endpoints of larval fitness were measured following the 96h exposure and subsequent recovery. Bacterial communities associated with the microalgae feed , rearing seawater, and the oyster larvae, were characterized and correlated with effects on oyster fitness.