Introduction
Management and conservation of rare or at-risk species requires knowledge of species distribution via the detection of populations which could be at low densities. Traditionally, population monitoring is carried out by visual detection, identification, and counting. However, for the last decade environmental DNA (eDNA) has been used as a non-invasive sampling technique as it is reliable, cost effective, less harmful to the ecosystem and correlates well with conventional survey results (Biggs et al., 2015; Darling 2019).
eDNA describes the DNA that is present within an environmental sample for example water, soil, sediment, or air. The eDNA present in an environment includes DNA that originates from sloughed cellular material (e.g. skin cells) or that is excreted (e.g. faeces and urine) or secreted (e.g. saliva) by organisms occupying the environment in question (Rees et al., 2014). Similarly, the DNA of organisms that visit the environment can also be present, for example birds or mammals drinking from a water body. The presence of an organism’s DNA within a water body is short lived as DNA has been shown to be degraded to undetectable levels within days to weeks and is affected by UV light, pH and microbial activity (Shogren et al., 2017; Seymour et al., 2018; Zulkefi et al, 2019). This suggests that the detection of an organism’s DNA is a demonstration of its presence or very recent presence and is a suitable surrogate for the detection/capture of the organism itself (Pilliod et al., 2013; Strickler et al., 2015;). The analysis of eDNA by sensitive PCR-based approaches, therefore, has become an important tool for measuring species presence/absence and has been successfully used to detect many aquatic species including the highly invasivePotamopyrgus antipodarum New Zealand mud snail within rivers (Goldberg et al, 2013; Clusa et al. 2016).
The Shining ram’s-horn snail Segmentina nitida (Muller, 1774) is a small (4-6 mm diameter) rare European freshwater snail (Figure 1) which is highly sensitive to changes in management of ditches and is found only in good quality, well vegetated ditches (Rowson et al, 2021). Although once common in UK, and widespread across lowland England and south Wales, the range of this species has substantially declined since the 1840s (Kerney, 1999). Its presence has been verified at only a few locations in southeast England where it is mainly confined to marshes and shallow drainage ditches with dense emergent vegetation (Watson and Ormerod, 2003). S. nitida is listed as a rare and declining Section 41 species and also a Ramsar criteria feature of Stodmarsh National Nature Reserve (NNR). In order to provide sensitive management of ditches at this site, there is a requirement to know where theS. nitida occurs. Here, we describe a qPCR assay for the detection of S. nitida and demonstrate the detection of this species within ditch water samples from Stodmarsh NNR with known presence/absence status.