Microbial ecology of ballast water during a transoceanic voyage and the effects of open-ocean exchange

The only procedure used frequently to reduce the risk of invasion by ballast-mediated biota is open-ocean exchange of ballast water, a procedure in which vessels release coastal water and replace it with oceanic water. Limited information exists concerning the effects of transport upon the aquatic microbial community throughout transit and following open-ocean exchange, A transoceanic voyage aboard a commercial bulk carrier afforded us the opportunity to sample the microbial community in exchanged and unexchanged ballast-water holds during the journey from Hadera, Israel to Baltimore, USA. Five days following the exchange process, all microbial metrics tested (i.e. bacteria concentration, virus-like particle density, chl a and phaeopigment concentration, and microbial biomass) had decreased 1.6- to 34-fold from initial values, With respect to microbial measures, no significant differences existed between exchanged and unexchanged holds on Day 15, the final day of sampling. We stress that we quantified differences in total microorganism abundance and biomass, not species composition, and more research is necessary to determine the changes that nonindigenous microorganisms, including potential pathogens, may effect in receiving waters.