The Atlantic sea scallop (Placopecten magellanicus) supports one of the most economically important fisheries in the northeastern United States. Scallop farmers rely on the acquisition of juvenile sea scallops, known as spat, to continue production, but wild spat collection is inconsistent and limited to a short season. Hatcheries in the state of Maine could reliably produce spat year-round, but struggle with mortality events, presumably induced by pathogenic bacteria. Probiotics have decreased mortality amongst infected bivalve larvae in other industries and could be implemented to decrease larval sea scallop mortality.
Seven probiotic bacteria were identified from literature and screened in vitro for potential benefits to sea scallop larvae. Bacterial competition assays were used to examine the inhibition of a model pathogen, Vibrio pectenicida, by probiotic candidates. Challenge trials involving larval sea scallops and V. pectenicida (10⁵ CFU/mL) were also conducted to test the effectiveness of applied probiotics on challenged and non-challenged larvae. Two probiotic candidates displayed beneficial impacts to Atlantic sea scallop larvae. Alteromonas macleodii (10⁵ CFU/mL) increased survival amongst challenged larvae (RPS 46% ± 11) and Pseudoalteromonas espejiana (10⁴ CFU/mL) amongst non-challenged larvae (RPS 46%). The effect of both promising probiotic treatments on larval sea scallops were tested at a hatchery scale with in vivo challenge trials. A. macleodii had a negative impact on larvae growth and survival. P. espejiana improved the rate of larval sea scallop growth and development during the late straight hinge to early pediveliger stage, where larvae mortality typically occurs.
This study can improve hatchery protocols through the implementation of the probiotic P. espejiana. Further investigation into potentially problematic Pseudomonas and Vibrio species is underway in tandem with the isolation of lytic bacteriophages to explore phage therapy in the hatchery. The use of P. espejiana in conjunction with bacteriophages may prove critical to the success of Atlantic sea scallop hatcheries in Maine.