Larval crashes are a recurring and economically significant challenge in bivalve aquaculture, yet their causes remain poorly understood and difficult to predict. These crashes limit productivity, particularly during the vulnerable larval stage, highlighting the need for effective interventions. To address this, we aimed to isolate and characterize bacterial strains from bivalve (eastern oyster, Crassostrea virginica, and quahogs, Mercenaria mercenaria) larvae with diverse probiotic traits and evaluate their safety and efficacy, ultimately developing a multi-strain probiotic formulation capable of improving larval survival.
A total of 168 bacterial strains representing 22 genera were isolated and identified from bivalve larval samples from hatcheries on the Atlantic coast of the USA. The isolates were screened for antimicrobial activity, hemolytic activity, biofilm formation, and quorum quenching potential. Four potential probiotic candidates (Algoriphagus yeomjeoni DEN5, Glutamicibacter soli CLAM16, Pseudooceanicola nitratireducens NEH7, and Marinomonas gallaica CLAM9) were selected for their combined probiotic properties. Safety assessments of these strains showed no pathogenic effects on the larvae, with treated larvae exhibiting comparable or improved survival compared to controls. Individual probiotic treatments improved larval survival when challenged with bacterial pathogens Vibrio coralliilyticus RE22 and Aliiroseovarius crassostreae CV919-312. Multi-strain probiotic formulations significantly increased larval survival compared to controls, with the complete consortium outperforming Phaeobacter inhibens S4 alone. Furthermore, the cocktail improved the survival of larvae challenged with diverse marine pathogens recently isolated from hatchery crashes (Fig. 1).
This study highlights the importance of comprehensive screening to identify probiotic candidates with broad functional traits, thereby providing a basis for practical multi-strain probiotic applications in bivalve hatcheries to enhance larval resilience.