The amount of environmental DNA increases with freshwater crayfish density and over time

Abstract

Over the last years, the analysis of environmental DNA (eDNA) has become an important approach to investigate species communities. Due to its non‐invasive nature and high sensitivity, this method is excellently suited to monitor the occurrence of endangered or invasive species. Native freshwater crayfish are threatened across Europe. Due to their nocturnal activity and hidden lifestyle, crayfish monitoring is difficult and time consuming with conventional methods. Thus, eDNA‐based monitoring of native, as well as invasive crayfish, would be an immense advantage in the conservation of these animals. However, although several assays for the detection of various crayfish species have been published, comparably little is known on the relationship between eDNA concentration and crayfish population densities; a pre‐requisite for estimating population sizes from eDNA measurements. In this study we, therefore, performed a set of laboratory experiments to investigate the relationship between eDNA concentrations and crayfish densities—measured as either crayfish size or biomass. We found a strong correlation between the two measurements and could also show that the amount of eDNA showed a linear increase during the first three days (at least) after crayfish were introduced to aquaria. Additionally, our experiments also suggest that crayfish activity might have a strong influence on the eDNA signal strength. Our findings will help to optimize eDNA‐based monitoring of freshwater crayfish, important for the conservation of these charismatic animals.

Exploring the eDNA dynamics of the host-pathogen pair Pacifastacus leniusculus (Decapoda) and Aphanomyces astaci (Saprolegniales) under experimental conditions

“…The huge increase (> 1000 fold) in eDNA concentrations in the high-density tanks with non-fed crayfish at 10 °C might be explained by injuries from aggressive interactions (Sint et al 2021) combined with the relatively clean water with assumingly low microbiological activity. In a similar tank experiment, Dunn et al (2017) successfully detected eDNA of P. leniusculus, but only established a significant relationship between eDNA concentration and crayfish biomass when female crayfish were ovigerous.…”

“…Contrary to our findings and those of Dunn et al (2017), Harper et al (2018) observed an increase in eDNA concentration when comparing tanks with one and three P. leniusculus. Additionally, Sint et al (2021) 2021) took multiple samples up to 59 hours after the crayfish had been added to the tanks, the sampling in our experiment and that of Dunn et al (2017) was conducted after seven and eleven days, respectively. This could have led to a state of saturation or equilibrium where eDNA is emitted from crayfish at a similar rate to its degradation by microbial activity (Barnes et al 2014;Salter 2018;Saito and Doi 2021), thus obscuring any differences between the tested factors.…”

“…Additionally, presence-absence monitoring of the pathogen and both the susceptible host and the carrier have yielded good results (Agersnap et al 2017;Rusch et al 2020). However, even though some studies show correlation between population density and eDNA quantity for fish species (Takahara et al 2012;Doi et al 2015a;Lacoursière-Roussel et al 2016;Capo et al 2019Capo et al , 2021, no clear correlation has yet been established between the detectable amount of eDNA and crayfish population density (Dougherty et al 2016;Dunn et al 2017;Johnsen et al 2020; but see Chucholl et al 2021 andSint et al 2021). The emission of eDNA seems to be influenced by numerous biotic and abiotic factors (Roussel et al 2015;Stewart 2019), such as ambient water temperature, lifecycle and corresponding behaviour of crayfish (Dunn et al 2017).…”

Environmental DNA: Enhancing Species Detection and Study Comparability with Synthetic DNA Tracers

“…eDNA studies in terrestrial environments have conventionally involved collection of targeted specimens, such as animal residues left on trees, fecal deposits, or samplings from hoof or paw prints in earth or snow 26,27 , hampering widespread application. However, the challenge of sampling terrestrial environments is currently being reassessed by the transformative discovery that the DNA of animal, insect, and non-anemophilous plants can be reliably recovered from filtered air samples [28][29][30][31][32] . In a notable study conducted at the Copenhagen Zoo 28 , Clare et al showed that airborne eDNA could be collected in a localized manner and analyzed to disclose specific species within a defined geographical radius.…”

“…eDNA has been widely applied for both aquatic and terrestrial species detection in a variety of ecological contexts. As discussed below, in aquatic samples from lotic environments, eDNA density increases with species density and biomass, although the relationship is not linear 29,30 . Although data from head-to-head comparisons are limited, several studies suggest that eDNA performs favorably compared with conventional gold-standard methods, and may in some cases produce superior results.…”