Thousands of species discovered in Guernsey's freshwater habitats
- First island-wide environmental DNA survey detects 2,630 unique organisms across 36 groups in Guernsey's freshwater habitats
- 2,249 organisms had no previous record in the Guernsey Biological Records Database
- European eel DNA detected in 12 waterbodies, mainly in streams
- Invasive brown rat DNA found in 21 waterbodies; American signal crayfish DNA detected at one location
- Second sampling round scheduled for September to confirm findings
A groundbreaking environmental DNA survey of Guernsey's freshwater habitats has detected 2,630 unique organisms across 36 different groups, with 2,249 of these having no previous record in the island's biological database.
The island-wide survey, a joint venture between Guernsey Water and the Guernsey Nature Commission, represents the first comprehensive analysis of life in Guernsey's ponds, streams and brackish waters using environmental DNA technology.
Environmental DNA, or eDNA, works by detecting genetic traces left behind by organisms in water. Samples were collected from 26 locations across the island, comprising 15 streams, nine ponds and two brackish water habitats. Laboratory analysis identified DNA associated with amphibians, birds, fish, mammals, algae, plants, invertebrates and microorganisms.
Water Quality Scientist Tim Harris said: "This is nothing short of incredible and provides the most accurate record of what's in local waters ever undertaken.
"The results have blown us away and frankly we can't quite believe what they've told us. To have more than 2,000 new detections that no one knew about represents a step-change in our understanding of just what's on Guernsey."
A second round of sampling is scheduled for September to confirm the initial findings.
Among the key discoveries, European eel DNA was detected in 12 waterbodies, with detections occurring mainly in streams. The results may help inform further investigation into whether eels can move successfully through Guernsey's freshwater systems and return to the sea.
The survey also detected DNA associated with the invasive brown rat in 21 waterbodies, whilst American signal crayfish DNA was found at one location where the species was already known to be present.
Initial results suggest that newts were detected more frequently in streams, whilst frogs were detected more frequently in ponds. Dragonflies and damselflies were not identified in the first sampling round, and the project team will investigate whether they are detected during the second round.
The highest number of detections at an individual location was recorded in the Vrangue stream, with 748, whilst Pulias pond had the lowest total, with 196. These figures represent DNA detections and should not be interpreted as counts of individual animals or plants.
Mr Harris added: "This survey gives us an exceptionally detailed baseline from which we can monitor change, support conservation activity and improve our understanding of potential water-quality risks. The findings also demonstrate how much remains to be discovered about the life present in Guernsey's freshwater environment."
Nature Commission Ecologist Charlotte Burgoine said: "It's been great to work with Guernsey Water to understand more about our freshwater species with eDNA sampling. We certainly have a lot more freshwater data after the first sampling round. It will be good to complete the second sampling round, see if anything different pops up, and then analyse the results. We can include the results in our next State of Nature report and contribute records to the biological database, filling a big data gap."
The survey will help Guernsey Water better understand the health of freshwater ecosystems and identify changes which could affect water quality over time.
Q&A
Q: How many new species were discovered in the survey?
A: The survey detected 2,630 unique organisms across 36 different groups, with 2,249 having no previous record in the Guernsey Biological Records Database.
Q: What is environmental DNA and how does it work?
A: Environmental DNA (eDNA) works by detecting genetic traces left behind by organisms in water. If an organism has been in the water, the test can detect it through the DNA it leaves behind.
Q: When will the findings be confirmed?
A: A second round of sampling is scheduled to take place in September 2026 to confirm the initial findings from the first survey.
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