O n the US West coast, Pacific oyster larvae often experience severe mass mortality events caused by the bacterial shellfish pathogen Vibrio coralliilyticus (Vcor ). This study evaluated the efficacy of four probiotic bacteria strains to increase the survival of Pacific oyster larvae when exposed to Vcor . Each probiotic strain was chosen due to its ability to inhibit the growth of Vcor on an agar plate or improve the survival of infected larvae. Individually, the probiotics displayed variable improvements in larval survival, but when used in combination, survival of infected larvae significantly improved (Figure 1) . The probiotic cocktail has also been found to improve the overall survival of larvae and increase settlement rates.
An experiment assessing timing of probiotic application showed that larval survival rates improved when receiving the probiotics earlier in their development. Larvae that received the probiotic mixture one-hour post- fertilization had 20% lower mortality compared to the larvae that received the probiotics at 24 hours post- fertilization (Figure 2). This finding suggests that probiotics stimulate the innate immune response, leading to significantly higher larval survival and benefiting hatchery production.