Didymo - Concerns go global
Although there is an acute awareness in New Zealand of the invasive alga didymo (Didymosphenia geminata), the organism is not well known in other countries by either members of the general public or by invasion biologists.
Communicating beyond the borders
Biosecurity New Zealand Didymo Technical Advisory
Group Member Dr Sarah Spaulding (in
waders, back to camera) gives her colleagues from
the US Environmental Protection Agency and BNZ
Didymo Science Lead Dr Christina Vieglais (left of
Dr Spaulding) a first-hand view of didymo in US
waters during a visit to Little Boulder
Creek, Colorado last year.
Didymo has a patchy yet widespread distribution in the Northern Hemisphere, but it took the spread into New Zealand to get didymo officially listed as a global invasive species on the Global Invasive Species Information Network. Didymo investigations by Biosecurity New Zealand (BNZ) have inspired collaborations around the world.
In May 2006, the first international symposium on Didymosphenia was held in the United States in Bozeman, Montana. This special session at an American Fisheries Society meeting was sponsored by the US Federation of Fly Fishers (FFF), Montana Department of Fish, Wildlife and Parks and the US Environmental Protection Agency (EPA).
Dr Sarah Spaulding, a diatomist with the US EPA, and also a member of the BNZ Didymo Technical Advisory Group, was the key organiser of the symposium. New Zealand didymo science featured prominently in the programme. The international audience was startled by photos and video of New Zealand didymo blooms. Apparently the levels of biomass which had passed for nuisance blooms in the Northern Hemisphere wouldn’t make a Southlander blink.
Another important outcome was the realisation that didymo has been spreading within the Northern Hemisphere, too, to warmer places that diatomists would not previously have considered suitable.
Piecing together the evidence
Determining management strategies for didymo requires skills that might be used in solving a crime: we need to account for all of the evidence in a coherent, consistent story. It is not entirely clear why the world is suddenly witnessing rapid global spread of didymo coupled with unprecedented biomass levels. Is it simply a function of increased traffic of international vectors, such as globe-trotting freshwater enthusiasts who can zip from Vancouver to Lumsden in less than a day? Or has didymo mutated in a way that allows it to flourish in environments not previously favourable? Could it be a result of climate change? Perhaps it’s a combination of factors.
The work done by BNZ is stimulating international interest in combining clues from the global expression of didymo phylogeography, genetics, morphology, geographic distribution, environmental tolerance, and invasiveness. There is much still to be learned about this new invasive species.
An international alert
A positive outcome of the Montana symposium was a call to arms to launch an international effort to educate those who need to know how to prevent the spread of didymo to new regions. This requires a comprehensive education and outreach programme to change user behaviour. New Zealand is thus far the only country in the Southern Hemisphere where didymo has been reported, but ecological niche modelling indicates that rivers in Australia, Argentina, Chile and Peru are at risk.
An international alert (see previous page) was recently developed to alert others of the potential invasive abilities of didymo and the importance of using the simple decontamination procedures that have been developed.
For a copy of the international flyer:
- Christina C Vieglais, PhD, Senior Adviser,
Post-clearance Response, Biosecurity New Zealand, phone 04 894 0531,
Page last updated: 30 April 2008