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Volunteers conducted a survey of residents in the sea around Denmark

Biologists from Aarhus University and the University of Copenhagen have studied the environmental DNA in water samples collected simultaneously by 370 volunteers on two occasions from almost 100 sites along the Danish coast. The combination of citizen science and environmental DNA has provided an effective overview of biodiversity in Danish coastal waters.

2021.07.22 | Peter F. Gammelby

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Niels-Ole Hørlyk took water samples in Bønnerup Marina as one of 200 volunteers in the HavBlitz citizen science project on 29 September 2019. Photo: Private.

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A map of the sites from where the volunteers twice collected water samples. Graphic: AU

Together, the water samples collected by 370 volunteers from the Danish Society for Nature Conservation contained DNA from 59 fish species, which corresponds to almost 90 per cent of the fish living close to Danish coasts. Some of the samples also contained DNA from porpoise and harbour seal.

Sequencing DNA from water or soil samples, for example, is gradually becoming a common method for studying biodiversity in specific areas. But this is the first time that researchers have combined the technique with citizen science at national scale in Denmark.

The HavBlitz project began in 2019 as a collaboration between the Department of Biology at Aarhus University, the Museum of Natural History at the University of Copenhagen and the Danish Society for Nature Conservation, with support from the Velux Foundation.

200 samples simultaneously

On 29 September 2019 and 10 May 2020, approx. 200 volunteers also took samples at the same time from the same selected locations. 94 per cent of the samples reached the researchers safely, which according to Associate Professor Philip Francis Thomsen from the Department of Biology at AU was rather impressive.

"By taking the samples at exactly the same time from all 100 sites, this method provides a snapshot of the biological diversity of fish – a snapshot that is virtually unaffected by short-term variations in the DNA of the aquatic environment. And researchers can't do this by themselves by taking the samples in a conventional way," says Philip Francis Thomsen.

Three interesting conclusions

PhD student Sune Agersnap from the Department of Biology points to the three most interesting conclusions from the DNA material:

"We documented existing knowledge about the spread of the round goby. This is an invasive species which we have to keep an eye on. We received DNA from species such as tadpole fish, five-beard rockling, common topknot and Montagu's sea-snail, which are otherwise difficult to find and which rarely show up in ordinary fish surveys. And the environmental DNA gave us an overview of the large geographical distribution of the other members of the goby family. These are otherwise rather difficult to determine."

The most important conclusion from HavBlitz, however, is that the combination of citizen science and environmental DNA works, and, according to the researchers, it could easily be scaled to other countries – or even to continental and global projects.

The research team is putting the finishing touches to a scientific article about their results, but you can already get an overview from the HavBlitz project website, www.havblitz.dk, where the data is freely available (in Danish). 


Associate Professor Philip Francis Thomsen
Department of Biology - Genetics, Ecology and Evolution,
Aarhus University
Email: pfthomsen@bio.au.dk
Mobile: +45 2714 2046

Sune Agersnap, PhD student
Department of Biology - Genetics, Ecology and Evolution,
Aarhus University
Email: sagersnap@bio.au.dk
Mobile: +45 6170 0647

Department of Biology