Limitations of eDNA analysis for Carcinus maenas abundance estimations

Abstract

Background Environmental DNA (eDNA) is an effective tool for the detection and monitoring of presence or absence of rare and invasive species. These techniques have been extended to quantify biomass in vertebrates, particularly in fish species. However, the efficacy of eDNA techniques to quantify biomass in invertebrate species has rarely been examined. This study tested whether eDNA could be used to determine the biomass of the world-wide invasive green crab, Carcinus maenas. In a controlled laboratory study, the relationship between biomass and C. maenas eDNA concentration was examined in the context of different biotic (activity) and abiotic (temperature) parameters. Results When incubating different numbers of crabs in sterile saltwater for up to 7 days, a relationship between eDNA concentration and biomass was observed at temperatures of 6.7 ℃ and 18.7 ℃, but not at 12.8 ℃. Additionally, motor activity, aggression level, time of sampling, and features of organismal decay had significant impact on the concentration of C. maenas eDNA collected. Conclusions We show that eDNA concentration did not correlate with biomass, and that biomass, temperature, organismal characteristics, and potentially many more parameters affect shedding and degradation rates for eDNA in this species, thus, impacting the recoverable eDNA concentration. Therefore, eDNA techniques are not likely to provide a reliable signal of biomass in the invasive invertebrate species C. maenas.

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

“…This is supported by our field data with no clear correlation between eDNA detectability and crayfish population density (as estimated by CPUE). A study on another crustacean, the green crab (Carcinus maenas), recently concluded that eDNA cannot be used to rigorously predict the biomass of the target species under controlled conditions (Danziger et al 2022). The conclusion that eDNA is seemingly not a well-suited tool for the quantification of biomass and population density of P. leniusculus is also in concordance with the recently-published study by Johnsen et al (2020).…”

“…At 10 °C and in the absence of food, we observed an over 1000-fold increase in P. leniusculus eDNA and 50-fold increase in A. astaci eDNA from a 10-fold increase of crayfish density. While planning the experiment, we expected the availability of food to increase the eDNA concentrations through an increased activity level (Danziger et al 2022) and faeces production (Ghosal et al 2018). However, when crayfish were fed, we detected less P. leniusculus eDNA in tanks with high crayfish density than in low-density tanks.…”

Challenges in eDNA detection of the invasive European green crab, Carcinus maenas

“…It was questioned earlier whether crustaceans leave a detectable eDNA signal in the water, due to their exoskeleton and subsequent potentially reduced eDNA release (Dougherty et al 2016;Tréguier et al 2014), another study showed significantly lower eDNA shedding rates in crustaceans compared to invertebrates without an exoskeleton (Andruszkiewicz et al 2020). Our laboratory studies demonstrate that our primers and probe can detect eDNA C. maenas in small volumes of water from holding tanks in laboratory setting (Danziger et al 2022). Furthermore, our field data show that despite the low concentration of eDNA release by crabs, green crab eDNA (potentially, but unlikely aided by the presence of larvae) can indeed be detected not only in small volume laboratory samples, but in water samples from the field at various depths, despite the highly dynamic water mixing in this estuary system.…”

Interrogating 1000 insect genomes for NUMTs: A risk assessment for estimates of species richness

“…After its release into the environment, DNA is rapidly degraded [ 53 , 54 ]. As a result, most eDNA studies employ primer sets which amplify short (e.g.…”