Vector management reduces marine organisms transferred with live saltwater bait

The global transfer of live bait creates a potent vector (mechanism) for invasion of marine species, including associated biota (“hitchhikers”) not intended for shipment. Unlike other vectors of non-native species transfer in coastal marine systems (e.g., ship ballast water), vector management strategies to reduce transport of associated biota with live bait are lacking. In this study, we experimentally tested whether simple, inexpensive treatment methods could reduce hitchhiker abundance and richness with live bait shipments, using the Maine live baitworm trade as a model. The Maine bait industry ships locally-harvested polychaete worms and packing algae to coastal regions of the United States, Europe, and Asia, and may unintentionally transfer associated hitchhikers, including known invaders. We exposed packing algae to three osmotic shock treatments (tap water, hypersaline water, and tap + hypersaline water), and measured abundance and richness of all live and dead macroinvertebrate taxa, as well as the condition of baitworms, after shipment to two locations (Maryland and California). Compared to controls, experimental treatments lowered average abundances by up to 99% and up to 93% for richness, and appeared to have no negative effects on bait or algae quality. The simplest treatment, tap water, was statistically as effective as more complicated treatments in reducing associated biota. We suggest that simple osmotic shock treatments on live packing algae prior to shipping could reduce the prevalence of hitchhikers associated with live trade vectors both nationally and internationally with little impact on the respective industries or their stakeholders.