Dr. Judith van Bleijswijk Tierens Verhagen

Molecular ecologist Judith van Bleijswijk searches for genetic traces that all conceivable types of organisms leave behind in the environment, the so-called eDNA. ‘Fish, mammals, … all organisms leave DNA behind in the environment via the release of slime or skin cells, for example. In 2020, we were able to describe in the scientific literature that those traces form a useful reflection of the life present. Of course, those traces are strongly diluted in the sea. Nevertheless, in a single coffee mug filled with water from the Marsdiep, I can easily find the genetic traces of 15 different fish species. And that allows research on fish without catching a single one.’

Genetics versus the fishing net

‘The database of genetic information of organisms in the Wadden Sea is already quite complete. That means that we can recognise the majority of organisms using DNA methods. Obviously, that is far more difficult for areas such as the Atlantic Ocean. There are many species that we do not even know about, let alone that we could identify their DNA in a water sample.’

‘Searching for traces of DNA is far more sustainable and animal-friendly than capturing animals for research. Yet at the same time, we cannot use this technique for everything that could be achieved with a fishing vessel. For example, we obtain information about the relative mass abundance of species, but we cannot say anything about the number or the size classes of the fish found. On the other hand, we can probably better detect species that hide in complex environments such as coral reefs than our fellow researcher using a net.’

Bird faeces and marine fungi

‘The analysis of DNA traces can be applied to many more samples. For example, we are also helping our colleagues from the red knot research with the analysis of bird faeces, as we can identify the insects that these birds have eaten. That subsequently allows them to learn more about the effects of the changing climate on the breeding success of these birds. Furthermore, we are investigating the role of fungi in seas and oceans. This is still such a young area that we recently added more than 300 new marine fungal cultures to the collection of the Westerdijk Institute of Fungal Biodiversity.’