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

Bei Sun,Candice Way,Richard Rivkin,Rebecca Mouland

doi:10.3391/ai.2010.5.1.2

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 (7.5×10 8 to 3.4×10 9 cells L -1 ) was significantly (P < 0.001) higher than those in ballast water (2.5×10 8 to 2.1×10 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.

Highlights

Oceanic transport accounts for more than 80% of total global shipments of commercial cargo
Ballast water age was computed as the number of days between the date of mid-ocean ballast water exchange (MOE) exchange or take-up in the port and the date when the ballast water was collected in a Canadian port
Propagule pressure shows a positive correlation with species establishment success (Lockwood et al 2005) and the abundance of microorganisms in ballast waters is considered a proxy for propagule pressure (Drake and Lodge 2007)

Summary

Introduction

Oceanic transport accounts for more than 80% of total global shipments of commercial cargo. To attenuate the risk of ballast water-mediated invasions, the International Maritime Organization established mid-ocean ballast water exchange (MOE) guidelines in 1997 (International Maritime Organization 1997). The rationale for MOE is that most coastal organisms will be flushed out during exchange (being replaced by oceanic species) and that the different physicochemical characteristics of coastal and oceanic waters will impair the survival of the coastal organisms that are released from ballast water into the open ocean. Oceanic species released into ports with coastal environmental conditions will unlikely survive, or become established (Smith et al 1999). This justification may not apply to resistant and euryhaline microorganisms with wide environmental tolerances

Methods

Results

Conclusion