An eDNA Breakaway in Marseille

Published: 19th May 2022

What happens when you invite the NatureMetrics team to meet with the world’s conservationist community in Marseille, France for the annual IUCN World Conservation Congress? A field trip, of course, along the beautiful Calanques coastline- a series of rocky cliffs and bays found along the jagged coast between the city of Marseille and the town of Cassis.

An opportunity to get hands-on with new technology

Despite huge interest in environmental DNA (eDNA), few conservationists have had the opportunity to gain directexperience of working with it.

In fact, a recent WILDLABS survey of conservationists, technologists, engineers, data scientists, entrepreneurs and change makers found that while 94% of respondents rated eDNA/genomics as ‘very helpful’ or a ‘game changer’ for advancing conservation, only 11% had actually used it.

The IUCN conference was the perfect time to help change that, with several thousand decision-makers coming together from government, civil society, business, and academia to further the agenda of nature conservation.

Sampling under the Marseille Sun

We gathered a select but diverse crew of curious conference attendees – from the CEO of The Wildlife Trusts in the UK to a Canadian primatologist, an NGO founder from Lebanon and project officers, conservationists and IUCN Congress members from around the world. Grateful for a chance to break out of the conference halls, we headed for the beautiful coastline of the Calanques National Park and found a spot where

we could congregate on the rocks with easy and safe access to the seawater for a demo of the sampling process. Collecting an eDNA sample is as simple as drawing water up in a large syringe and pressing it through a small disk that contains a filter membrane. DNA is trapped on the filter, which is then sent to the laboratory for analysis. A single filter can reveal the presence of tens or hundreds of species, unearthing a world that would otherwise remain hidden to the casual observer. Following the demo, the group split into three teams, each of which collected a sample from the shoreline. In addition, one particularly dedicated participant (operating entirely at his own risk) employed his expert free-diving skills to collect water from 30 metres below the surface.

When the sun’s shining, there are worse things to do than sit by the seashore filtering water; the group experimented with different filtering stances – some undeniably more elegant than others – and a certain amount of competitive spirit was in evidence!

Gorse-covered white cliffs led down to clear, clean water, making the Calanques popular with swimmers – as well as a multitude of fish species, our samples revealed.

In just 5 water samples, we detected the DNA of 47 different fish, 40 of which could be identified to species level. All of these were typical for Mediterranean waters – particularly for the shallow rocky habitat found at Calanques, and there was a clear difference between the shore samples and the deeper sample collected by the freediver.

Although the deeper water sample had the lowest overall diversity (16 species) it was the only one where Conger eel (Conger conger) and two Picarel (Spicara) species were detected. The Picarels are commonly associated with seagrass beds, such as the Posidonia that is found in the Calanques National Park. By contrast, there were several species found in all four shoreline samples that were absent from the deeper sample, including the striking-looking red black triplefin (Tripterygion tripteronotum). These are species that hide in the diverse shallow algal communities growing on the rocky coast.

Several common fisheries species were detected, including European seabass (Dicentrarchus labrax), Big-scale sand smelt (Atherina boyeri) and Whiting (Merlangius merlangius), but there was one fish you wouldn’t want on the table – the Salema porgy (Sarpa salpa) can be ichthyoallyeinotoxic (i.e. cause hallucinations in humans if eaten).

A duck was also detected in one sample – occasionally we do pick up something other than fish with a fish assay!

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