Abstract
Bacterial abundance, population dynamics and related environmental parameters were determined in ballast water during a trans- Pacific voyage from Japan to the west coast of Canada. Water samples were collected from four ballast tanks, two of which underwent mid-ocean exchange (MOE) and two that remained unexchanged (control). Bacterial abundances in the unexchanged tanks increased from ~6.4×10 8 cells/L on Day 0 to 1.8×10 9 cells/L on Day 7, whereas in MOE tanks, abundances increased from
Highlights
The establishment of non-indigenous species in marine and freshwater environments is a worldwide issue and a concern to human and environmental health and aquatic biodiversity (IMO 2008; Transport Canada 2007)
(1) The relationship found between bacterial abundance, temperature and dissolved oxygen concentrations has potential to be used in predicting patterns of bacterial abundance during oceanic transit and propagule pressure
(2) mid-ocean exchange (MOE) does not significantly reduce bacterial numbers but it is necessary to examine changes in community structure to fully determine the efficacy of MOE. (3) The increase in bacterial abundance in the first 7 to 10 days of our voyage and general decline in the voyage of Drake et al (2002) show that the length of the voyage plays a critical role in determining the number of bacteria that will be deballasted
Summary
The establishment of non-indigenous species in marine and freshwater environments is a worldwide issue and a concern to human and environmental health and aquatic biodiversity (IMO 2008; Transport Canada 2007). Invasive aquatic organisms are potentially transported from region-to-region via ballast water that is taken on-board ships at ports and stored in tanks to enhance the ship’s stability and maneuverability during voyage (Transport Canada 2007). The generally accepted method to control the introduction of aquatic invasive species is the mid-ocean exchange (MOE) of ballast water. This requires ships to exchange ballast water at least 200 nautical miles away from shore and where ocean depths are at least 200 m (IMO 2008; Transport Canada 2007), and the justification for this protocol is that coastal organisms are flushed out and replaced with oceanic organisms that are not likely to survive in low salinity or coastal systems. Since there is invariably some residual water left in the tank, this results in the retention of low abundances of coastal organisms in the tanks, some of which may be euryhaline and able to survive the dilution with high salinity water (Wonham et al 2001; Taylor et al 2007; Transport Canada 2007)
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