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Considerations for incorporating real-time PCR assays into routine marine biosecurity surveillance programmes: a case study targeting the Mediterranean fanworm (Sabella spallanzanii) and club tunicate (Styela clava)

Wood, Susanna A., Pochon, Xavier, Ming, Witold, von Ammon, Ulla, Woods, Chris, Carter, Megan, Smith, Matt, Inglis, Graeme, Zaiko, Anastasija
Genome 2019 v.62 no.3 pp. 137-146
DNA, RNA, Styela clava, biosecurity, case studies, invasive species, models, monitoring, quantitative polymerase chain reaction, risk, surveys, New Zealand
Molecular techniques may provide effective tools to enhance marine biosecurity surveillance. Prior to routine implementation, evidence-based consideration of their benefits and limitations is needed. In this study, we assessed the efficiency and practicality of visual diver surveys and real-time PCR assays (targeting DNA and RNA) for detecting two marine invasive species whose infestation levels varied between species and location: Sabella spallanzanii and Styela clava. Filtered water samples (n = 171) were collected in parallel with dive surveys at two locations as part of the New Zealand Marine High Risk Site Surveillance programme: Nelson Harbour (27 sites) and Waitemata Harbour (30 sites). Diver surveys resulted in a greater number of detections compared to real-time PCR: S. clava – 21 versus 5 sites in Nelson, 6 versus 1 in Auckland; S. spallanzanii – 18 versus 10 in Auckland, no detections in Nelson. Occupancy modelling derived detection probabilities for the real-time PCR for S. clava were low (14%), compared to S. spallanzanii (66%). This could be related to abundances, or species-specific differences in DNA shedding. Only one RNA sample was positive, suggesting that most detections were from extracellular DNA or non-viable fragments. While molecular methods cannot yet replace visual observations, this study shows they provide useful complementary information.