Redistribution of heterotrophic prokaryotes through ballast water: A case study from the west coast of Canada

Abstract

Oceangoing ships contribute to the introduction of invasive, benign and pathogenic bacteria via ballast water discharge. Here we report the bacterial abundance and cell size in ballast and receiving port waters in Vancouver, British Columbia (Canada) ports during 2007 and 2008. Bacterial abundance in port water (7.5x10(8) to 3.4x10(9) cells L-1) was significantly (P < 0.001) higher than those in ballast water (2.5x10(8) to 2.1x10(9) cells L-1) and was higher in unexchanged than ballast water that was exchanged at-sea. There was no significant difference in bacterial abundances between 2007 and 2008 for each sample type. Bacterial cell volume showed a different pattern, with no significant difference among sample types and a two-fold larger average cell volume during 2007 than 2008. Bacterial abundance and cell volume in ballast water were not correlated with ballast water age, end-of-voyage temperature, salinity or pH. The absence of predictive relationships between measured physiochemical and bacterial variables in ballast water highlights the difficulty of predicting bacterial abundance or cell volume from the physiochemical factors alone. Future studies should focus on the bacterial community structure in ballast and port waters, the fate of bacteria in the new environment, and regional susceptibility to invasion by the introduced bacteria.