Investigating passive eDNA samplers and submergence times for marine surveillance

Passive environmental DNA (eDNA) samplers offer a cost-effective and scalable approach to marine biodiversity monitoring, potentially aiding detections of non-indigenous species. This study explored the efficiency of passive eDNA samplers to detect a variety of globally problematic marine invasive species in field conditions: <i>Sabella spallanzanii</i>, <i>Styela clava</i>, <i>Bugula neritina</i> and <i>Undaria pinnatifida</i>. Four passive sampler substrates, nylon filters, positively charged nylon discs, nylon mesh, and artificial sponges, were tested across six submergence times, ranging from 10 to 720 min, against standard filtration-based approaches. Our results demonstrated that passive samplers could achieve comparable or even higher eDNA yields than traditional active filtration methods, indicating their potential for biosecurity surveillance. Species-specific droplet-digital PCR (ddPCR) assays provided sensitive and quantifiable eDNA signals, though assay validation remains crucial to avoid false negatives. Significant variation in eDNA signal detection highlighted the importance of considering both material selection and submersion time, depending on the targeted organisms. Furthermore, 18S rRNA metabarcoding was undertaken to assess how the overall detected biodiversity might interfere with species-specific detections. Certain sessile organisms, such as ascidians and polychaetes, dominated early representation on the passive filters but did not interfere with species-specific detection. By optimizing material selection, submersion time, and assay validation, passive eDNA sampling can enhance the sensitivity and reliability of eDNA-based monitoring, contributing to improved marine biosecurity and conservation efforts.