Using eDNA to develop a national citizen science-based monitoring programme for the great crested newt (Triturus cristatus)

Highlights

• We evaluated the use of eDNA methods for monitoring great crested newts in the UK.

• eDNA was more effective than standard methods in detecting newt presence or absence.

• Volunteers were able to collect eDNA samples successfully with only limited training.

• A national volunteer eDNA monitoring programme is feasible for great crested newts.

• We suggest that eDNA could be used in volunteer biodiversity surveys more generally.

Abstract

The use of environmental DNA (eDNA) is rapidly emerging as a potentially valuable survey technique for rare or hard to survey freshwater organisms. For the great crested newt (Triturus cristatus) in the UK, the substantial cost and manpower requirements of traditional survey methods have hampered attempts to assess the status of the species. We tested whether eDNA could provide the basis for a national citizen science-based monitoring programme for great crested newts by (i) comparing the effectiveness of eDNA monitoring with torch counts, bottle trapping and egg searches and (ii) assessing the ability of volunteers to collect eDNA samples throughout the newt’s UK range. In 35 ponds visited four times through the breeding season, eDNA detected newts on 139 out of 140 visits, a 99.3% detection rate. Bottle traps, torch counts and egg searches were significantly less effective, detecting newts 76%, 75% and 44% of the time. eDNA was less successful at predicting newt abundance being positively, but weakly, correlated with counts of the number of newts. Volunteers successfully collected eDNA samples across the UK with 219 of 239 sites (91.3%) correctly identified as supporting newts. 8.7% of sites generated false negatives, either because of very small newt populations or practical difficulties in sample collection. There were no false positives. Overall, we conclude that eDNA is a highly effective survey method and could be used as the basis for a national great crested newt monitoring programme.

Introduction

The use of environmental DNA (eDNA), nuclear or mitochondrial DNA that is released from an organism into the environment, is rapidly emerging as a potentially valuable survey technique for detecting cryptic or difficult to survey freshwater organisms (Lodge et al., 2012, Sutherland et al., 2013). Proof of concept studies have shown that eDNA can be used to detect the presence of amphibians, fish, invertebrates (including dragonflies and crustaceans), mammals and water birds (Ficetola et al., 2008, Goldberg et al., 2011, Olson et al., 2012, Thomsen et al., 2012), and to assess fish and amphibian abundance (Takahara et al., 2012, Pilliod et al., 2013a). Depending on the taxonomic group and habitat, results so far indicate that eDNA may be more, equally or slightly less effective at detecting species than traditional methods (respectively, Dejean et al., 2012 for American bullfrog (Lithobates catesbeianus); Pilliod et al., 2013a for two riverine amphibians; Thomsen et al., 2012 for large white-faced darter dragonfly (Leucorrhinia pectoralis)). Thus although eDNA may have a future use as an important survey and monitoring method for freshwater organisms, it is essential to test its effectiveness compared to existing survey methods (Thomsen et al., 2012) to establish the taxa to which it can be validly applied.

A particularly important attribute of eDNA methods is that the water samples needed for analysis are usually quicker and more technically straightforward to collect than are biotic data (Ficetola et al., 2008. Thomsen et al., 2012). This opens a new opportunity for credible monitoring surveys to be undertaken by volunteer surveyors in citizen science programmes as volunteer surveyors often have less time, or more limited taxonomic skills, than professional ecologists. The use of volunteers for water and biodiversity monitoring is growing worldwide (Silvertown, 2009, Schmeller et al., 2009, Roy et al., 2012) reflecting both a need for data which far outstrips the resources available for professional monitoring programmes and a recognition of the benefits of engaging ‘ordinary citizens’ with science and nature. In practice, however, the validity and effectiveness of a volunteer-based eDNA survey programme has yet to be tested.

In this study we compared the use of eDNA with traditional methods for surveying the great crested newt (Triturus cristatus), a protected species listed in Annexes II and IV of the EC Habitats Directive (European Commission, 1992). At present, substantial survey effort is required to assess whether great crested newts are absent from a site, with typically 4-6 annual visits needed, using at least three survey methods on each occasion (Sewell et al., 2010). The survey effort required to collect adequate data has so prevented the establishment of a robust national monitoring programme for the species in the United Kingdom either by professional surveyors, where the cost would be considerable, or by volunteers working on the UK National Amphibian and Reptile Recording Scheme (Wilkinson and Arnell, 2013), for whom the substantial time commitment, combined with lack of funds for professional support to arrange site access permission, has prevented the establishment of a survey programme.

Our study firstly assessed the effectiveness of eDNA methods for the detection of the great crested newt compared to the standard survey techniques used for this species: torch counting, bottle trapping and egg searching, and secondly, investigated the ability of volunteers to collect eDNA samples from the known range of the great crested newt in the United Kingdom, to inform the development of a national surveillance scheme for the species involving the use of volunteer collected data.