Monitoring freshwater ecosystems by means of environmental DNA methods offers new opportunities for detecting invasive species. An Eawag study has shown that an invasive jellyfish is more widespread in Switzerland than previously thought.
“I would never have thought that this species would be so widespread,” states Rosetta Blackman, a postdoctoral researcher at the aquatic research institute Eawag. She is referring to the peach blossom jellyfish (Craspedacusta sowerbii), a small freshwater jellyfish that is harmless to humans. It originates from the Yangtze River basin in China and is considered an invasive species in Switzerland. Although it is known to occur in Switzerland, it was not known how widespread the species was – despite the fact that invasive species are regularly searched for in Swiss lakes and rivers.
Routine monitoring in water bodies
The reason why the researchers were now able to detect it in many Swiss river catchments is because they used a new method: the determination of what is known as environmental DNA (eDNA). This method extracts DNA from water samples to identify the biodiversity in the water body. This approach could establish itself in the future as a complementary method to the traditional monitoring of invasive species, says Blackman. Invasive, i.e. alien, species pose a problem for ecosystems, as they can replace native species. Therefore, it is important to detect their presence as early as possible so that measures can be taken quickly to prevent them from spreading further. In Switzerland, the Federal Office for the Environment (FOEN) and the cantons carry out regular routine monitoring in water bodies for this purpose. Traditionally, this is done using methods such as electrofishing or kick-net sampling.
The latter is used, for example, for macroinvertebrates: these are small invertebrates visible to the naked eye, such as beetles, snails, crustaceans and larval forms of may-, stone- or caddisflies. Hundreds of species of which live in our water, with around 50 invasive species known to be present in Switzerland. In kick-net sampling, samples are gathered by disturbing the substrate of the river or lake and the species collected as they float downstream into a net. They are then identified in the field or in the laboratory under the microscope.