Picture this… it’s a typically cold British summer’s evening, the rain has set in and you have re-discovered that hole you thought you had patched up in your waders. Your traps from last night were empty, you are convinced you have turned every stone and searched every suitable habitat and nothing, not even a moulted exoskeleton. Time to get a coffee and dry your socks near the car heater surely, but to be extra thorough you re-check some habitat patches on your way back downstream. Check the net – nothing, check the net again – nothing and then just as you were about to call it a day that flash of red you were dreading… claws snapping angrily and there is no denying that you have found an invasive signal crayfish.
During my PhD investigating invasive crayfish in the UK this was an all too familiar situation which left me with a general discomfort of how easily I could have missed that solitary invader. What if I hadn’t done a bit extra impromptu stone turning? Does the survey protocol need revising? What might I have missed at other sites?
I am sure many of you reading this who have surveyed for invasive and non-native species (INNS) have had comparable experiences and been kept awake by similar questions (OK, maybe that bit is just me!). Whilst there is no denying the value of manual surveying in monitoring INNS populations, such surveys require substantial effort and even with heavy resource investment low-density populations may still go undetected. Considering the reliance on early detection for minimising the impact of INNS on recipient communities this raises a key global issue in INNS management.
Well, time to breathe a bit of positivity into this blog by introducing the concept of environmental DNA, or as it is more commonly known, eDNA.
eDNA refers to the DNA that can be obtained from an environmental sample such as water, sediment, soil, or snow. Sources of this genetic material can be vast including sloughed cells, hair, urine, faeces and gametes. As such, environmental samples can serve as species catalogues, containing genetic material from animals that have interacted with that environment.
The concept of exploiting eDNA is not new but it is only in recent years with the development of methods to detect eDNA from macro-organisms that the full potential of this technology has begun to be explored. Whilst the use of eDNA in ecology is still in relatively early stages and there are some key challenges that remain to be addressed, robust assays have been developed for the detection of several species. Many of the existing eDNA assays have been developed for INNS, and indeed this is one of the main uses of eDNA in ecology at the current time. This is perhaps unsurprising given that several studies have shown that in the field eDNA methods are more sensitive and able to detect species at lower population densities in comparison to traditional survey techniques.
Use of eDNA therefore offers an exciting avenue for facilitating rapid response to INNS, and species detection is only the tip of the iceberg in terms of its potential applications in invasion ecology. For INNS that are already established, eDNA from sediment samples (in which DNA is known to persist for a prolonged time) could be used to reconstruct historic ecosystems, to determine at what stage INNS were introduced and investigate how the ecosystem responded. This is just one other possible application of eDNA from a list that is too extensive to mention in this blog but watch this space for future updates!
Finally, carry on with the field surveys but consider what the water filling your waders might be able to tell you too!
How APEM can help
Not sure if eDNA is right for you? APEM are experienced in providing clients advice on the potential applications of eDNA and how such technologies could be incorporated into their INNS management programmes.
Decided to give eDNA a go? We have expertise in designing experimental laboratory and field-based trials using eDNA for INNS detection.
To find out more about the INNS services APEM offer including in relation to eDNA please visit our webpage.