21st September 2018

Wicken Fen BioBlitz

On 22nd July 2018, we attended the Wicken Fen edition of Chris Packham’s 2018 BioBlitz. This was our first BioBlitz experience and also the first time we had worked with volunteers to collect water samples.

Our CEO, Kat, gave a talk to an audience that ranged from young children to National Trust ecologists, explaining about how we can capture the genetic material of fish from the water and sequence it to identify the species. 

After the talk we headed out with a group of six volunteers to collect some samples from the fenland waterways known as ‘lodes’. The volunteers quickly got the hang of using the kits to filter the water and then added the preservative solution to the samples so that the DNA would be stabilised for transport to the lab. It took about 15 minutes to collect each sample.

Back in the lab, we extracted the DNA from the filters and ran our Fish eDNA Metabarcoding analysis to generate a species-by-sample table. This involves making millions of copies of the fish DNA in a process called PCR, and then sequencing it on a high-throughput DNA sequencer machine.


The first thing we noticed was that the samples were really high quality and contained almost no human DNA – the volunteers had done an excellent job! 
The table below shows how much DNA we found for each species in each of the five samples. The size of the bubble in each cell tells you the proportion of sequences assigned to each species in a given sample (for instance 51% of sequences in Monks Lode Upper came from perch). This can broadly be interpreted as an indication of relative abundance.

We detected 12 species of fish (and a toad). All 12 species were detected in a single sample from the confluence of Wicken Lode and Monks Lode.

  • This is the same amount of diversity as has been detected by Environment Agency fish surveys at Wicken Lode since 1984 – and the EA has never found all of these species in a single survey. This shows just how sensitive and powerful a tool eDNA metabarcoding is, even when samples are collected by non-experts.
  • Two species (Gudgeon and Ruffe) appear in EA records but were not detected in the eDNA survey. However each of these was recorded just once, in 1984 and 1990 respectively, so it is likely that the species are no longer present at the site.
  • Two species were detected by the eDNA survey that do not appear in the EA survey data for Wicken Lode. These are Bullhead (Cottus gobo) and Spined Loach (Cobitis taenia), which is a protected species typical of this East Anglian fenland habitat. These small bottom-dwelling fish are difficult to catch so are often under-represented in conventional survey data.

The species list also includes European eel (Anguilla anguilla), which is listed as Critically Endangered on the IUCN Red List, and bitterling (Rhodeus sericeus), which is very rare in the UK.

Most species were found in all four samples in Wicken Lode and Monks Lode

  • Several species (rudd, bitterling, common bream, silver bream) showed the highest relative concentration in the Wicken Lode upper sample and lowest in the Monks Lode upper sample.
  • Bullhead shows the opposite pattern. It is absent from Wicken Lode, appearing at highest concentration in the Monks Lode upper sample and lowest at the confluence between Monks Lode and Wicken Lode. 
  • Perch, pike and roach are the most dominant species overall, accounting for a high proportion of the DNA sequences obtained from the water samples.

A lot of the fish seem not to travel up into Dragonfly ditch, which is a small, overgrown channel only about 1.5 m across. However, this is the point at which there is the greatest concentration of eel.

With thanks to Jeremy Biggs at Freshwater Habitats Trust for bringing the Environment Agency survey data to our attention