Threat to fish

Jason South Fairfax Media / Getty

THE Mekong river teems with life as it flows to the South China Sea. But the unique species found here are under threat from plans to build hydropower dams along the river. A new environmental monitoring technique may help limit the damage, by quickly counting all the species upstream using only DNA pulled out of the river. That information could be used to influence dam locations at the planning stage.

Traditional surveying methods would take years to identify ecological hotspots that dams should avoid – time developers don’t want to waste. “There’s no way you’re going to sample that [large an area] with the traditional methods,” says Douglas Yu at the Kunming Institute of Zoology in China.

Yu hopes to speed up surveying by gathering the fragments of DNA littered throughout the environment and identifying the species they belong to with DNA sequencing. He wants to work with Chinese ecologists to carry out “eDNA surveys” in the Mekong, building up a picture of where rare and vulnerable species live.

The idea is based on recent research that suggests every river acts as a conveyor belt for genetic material released from cells shed from the species living there – what’s called environmental DNA (eDNA). Identifying species like this – in much the same way that microbiologists use DNA sequencing to identify bacteria in a sample – could revolutionise wildlife surveys. This would allow biologists to quickly detect many of the species in an ecosystem.


The technique works well for identifying aquatic species. Last year, a team of European ecologists sampled water from streams and ponds in France and the Netherlands for DNA, then cross-referenced their results with extensive traditional surveys. They looked for fish by eye and caught frogs and salamanders in nets. When they compared the results, they found that eDNA showed as many or more fish species at 89 per cent of the sites they visited.

“With the techniques we are using, we obtain all the fish species, including the very rare ones,” says Pierre Taberlet at the Joseph Fourier University in Grenoble, France, who carried out the test.

“The world is permeated with DNA. Collect it and sequence it and you get a much better view of life“

The eDNA survey worked well for amphibians, too: at every survey site, the team found as many or more amphibian species through eDNA as they did through the traditional survey. That’s because many well-hidden species are hard to find by eye.

It’s not just useful for water dwellers: eDNA found in rivers could also give a picture of land-dwelling creatures. A group led by Kristy Deiner at Cornell University in Ithaca, New York, sequenced the eDNA found in samples from eight sites in the Glatt river system in Switzerland. They turned up 296 families of organisms – everything from aquatic worms and shellfish to plants and fungi that lived on the land around the Glatt.

Taberlet isn’t sure that river eDNA sampling is good enough to survey all the land in a river’s watershed. “You’re at risk of missing a lot of species,” he says. In addition, Deiner’s team only identified organisms to the family level, not to species. “What can you do with identification at just the family level for biodiversity research? I think there is some improvement to do,” he says.

The sheer scale of rivers gives them potential as environmental monitoring systems, says Si Creer at Bangor University in the UK. “You could almost use the rivers as an ecological pulse to try to find out how what we’re doing on the land is reflected in the biodiversity of the river,” he says.

He also points out that eDNA surveys overcome the problem in using taxonomists to identify all of an ecosystem’s species: no one’s knowledge is complete. “Even a team of taxonomists can only look at the diversity of a community within the limit of what they’re able to do,” he says.

Yu says eDNA surveys could make wildlife monitoring cheaper, faster and more available to those with fewer resources. “The world is just permeated with DNA,” he says. “You just have to collect it and sequence it in the right way, and then you get a much better view of life.”

This article appeared in print under the headline “Rivers of DNA”

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