Edition 2, May 2009
Toxic Marine Invaders Under The Microscope
See all stories in this edition
May 20th, 2009
The role global shipping plays in spreading microorganisms (including a toxic algae that causes frequent closures of Tasmanian aquaculture farms) has come under the spotlight of researchers analysing ballast water flowing into the lower Chesapeake Bay in the US.
And although Lisa Drake from the US Coast Guard Academy and her team have not focused on climate change they note that rising sea temperatures are likely to see tropical micro-ogranisms, including pathogens, expand their distribution.
The increase in international shipping over the past century has dramatically increased the volume of ballast water transported around the globe, carrying with it bacteria, viruses and microalgae.
Aquatic microorganisms are highly abundant in marine waters and are the most prevalent organisms transported by ships travelling between international ports.
Drake and colleagues found they were present in large numbers in in ballast water tanks – in ballast water, sediments and biofilm (the microbes, organic matter and other material coating the surface). They estimated that 1020 microorganisms were discharged annually from ballast water tanks into the lower Chesapeake Bay.
They are capable of surviving prolonged periods in unfavourable conditions and their dispersal is facilitated by their small size and simple requirements for survival.
In Tasmania the dinoflagellate (Gymnodinium catenatum) that causes closure of aquaculture farms is thought to have arrived via ships transporting woodchips to Japan and South Korea.
Although the spread of pathogenic or toxic microorganisms can have devastating effects on ecosystems and economic resources, the researchers note that their invasion biology is poorly known.
One often-cited example of the potential for great harm due to microorganisms in ballast water was the cholera epidemic in South America in the early 1990s, which was blamed on ships carrying the cholera bacterium in ballast water from Asia.
References
Drake LA, Doblin MA, Dobbs FC. 2007. Potential microbial bioinvasions via ships’ ballast water, sediment, and biofilm. Marine Pollution Bulletin 55: 333-341.