Monitoring a Norwegian freshwater crayfish tragedy: eDNA snapshots of invasion, infection and extinction

Abstract

1. The European noble crayfish Astacus astacus is threatened by crayfish plague caused by the oomycete Aphanomyces astaci, which is spread by the invasive North American crayfish (e.g. signal crayfish Pacifastacus leniusculus). Surveillance of crayfish plague status in Norway has traditionally relied on the monitoring survival of cage-held noble crayfish, a method of ethical concern. Additionally, trapping is used in crayfish population surveillance. Here, we test whether environmental DNA (eDNA) monitoring could provide a suitable alternative to the cage method, and a supplement to trapping.2. We took advantage of an emerging crayfish plague outbreak in a Norwegian watercourse following illegal introduction of disease-carrying signal crayfish, and initiated simultaneous eDNA monitoring and cage-based surveillance, supplemented with trapping. A total of 304 water samples were filtered from several sampling stations over a 4-year period. eDNA data (species-specific quantitative real-time PCR [qPCR]) for the presence of A. astaci, noble and signal crayfish within the water samples were compared to cage mortality and trapping. 3. This is the first study comparing eDNA monitoring and cage surveillance during a natural crayfish plague outbreak. We show that eDNA monitoring corresponds well with the biological status measured in terms of crayfish mortality and trapping results. eDNA analysis also reveals the presence of A. astaci in the water up to 2.5 weeks in advance of the cage method. Estimates of A. astaci and noble crayfish eDNA concentrations increased markedly during mortality and vanished quickly thereafter. eDNA provides a snapshot of the presence, absence or disappearance of crayfish regardless of season, and constitutes a valuable supplement to the trapping method that relies on season and legislation. 4. Synthesis and applications. Simultaneous eDNA monitoring of Aphanomyces astaci (crayfish plague) and relevant native and invasive freshwater crayfish species is well-suited for early warning of invasion or infection, risk assessments, habitat evaluation and surveillance regarding pathogen and invasive/native crayfish 1662 | Journal of Applied Ecology STRAND eT Al.

Detection of an invasive aquatic plant in natural water bodies using environmental DNA

“…Environmental DNA (eDNA), which is shed by all living organisms in the environment, is increasingly used for the detection of elusive or low abundant species and has been shown to be equally or more sensitive than traditional surveying methods [6, 7]. So far, the majority of developed eDNA single species detection methods have primarily focused on aquatic animals including mammalians [8, 9], fish [8, 10–17] Molluscs [18, 19], crustacea [20–22], amphibians [23, 24] reptiles [25–27] and insects [28–30]. Detection of aquatic plant eDNA has been scarce in comparison [31].…”

Experimental evaluation of the potential for crayfish plague transmission through the digestive system of warm‐blooded predators

“…It is thus clear that no massive sporulation occurred in the experimental tanks at or shortly before the time of filtration (24 and 48 hr after the excrement addition). Detection of very low amounts of A. astaci spores would nevertheless require filtering of substantially higher water volumes (as used in recent studies focusing on detection of this pathogen from environmental DNA; e.g., Strand et al, , ; Wittwer et al, ).…”

“…Crayfish plague caused by the oomycete Aphanomyces astaci Schikora is undoubtedly the most serious disease of crayfish (Diéguez‐Uribeondo et al, ), which drastically reduced European populations of these crustaceans in the 19th and early 20th century (Alderman, ). Although latent infections with the crayfish plague pathogen have been recently reported from various populations of several European indigenous crayfish species (see review in Svoboda, Mrugała, Kozubíková‐Balcarová, & Petrusek, ), mass mortalities caused by the pathogen are still widespread across Europe (e.g., Caprioli et al, , ; Filipová, Petrusek, Matasová, Delaunay, & Grandjean, ; Kozubíková‐Balcarová et al, ; Strand et al, ; Viljamaa‐Dirks et al, ), and crayfish plague is considered responsible for recent steep declines of native crayfish in various countries (Holdich, Reynolds, Souty‐Grosset, & Sibley, ). Furthermore, the presence of A. astaci has also been recently reported from crayfish populations introduced to Japan, Brazil, Indonesia and Madagascar (Andriantsoa et al, ; Martín‐Torrijos et al, ; Mrugała, Kawai, Kozubíková‐Balcarová, & Petrusek, ; Peiró et al, ; Putra et al, ), indicating a potential threat to crayfish species native to those regions.…”

Mutational, transcriptional and viral shedding dynamics of the marine turtle fibropapillomatosis tumor epizootic

“…Consequently, accurate, sensitive, non-invasive techniques are required to detect and monitor pathogens and pathogenic vectors outside of host systems 45,86 . eDNA approaches have been shown to detect aquatic pathogens earlier than traditional methods and provide advanced warning of infection and mass mortality events 40,45 . Recently, Ranaviruses, have been detected by eDNA analysis in environmental water samples from susceptible host species habitats, and demonstrated a strong relationship between environmentally-shed viral load and host tissue viral load 45 .…”

“…Environmental DNA is a forensics approach to the extraction and identification of organismal DNA fragments (genetic material) released into the environment and is a rapidly advancing, non-invasive approach capable of improving endangered species detection and early pathogen detection [35][36][37][38][39][40][41][42][43] . Environmental samples can be analyzed for micro-and macro-organisms by several eDNA methods including metabarcoding and species-specific quantitative PCR (qPCR) 38,40,44 . The development of a rapid and high throughput sampling scheme to detect virus shedding into the marine environment would benefit pathogen surveillance efforts, and consequently the performance of wildlife health status monitoring could be improved 31,45 .…”